Taxonomic Revision of the Obligate Plant-Ants of the Genus Crematogaster Lund ( Hymenoptera : Formicidae : Myrmicinae ) , Associated with Macaranga Thouars ( Euphorbiaceae ) on Borneo and the Malay Peninsula

The cosmopolitan myrmicine genus Crematogaster Lund, 1831 is among the largest genera of ants, with the highest diversity of species found in tropical regions (Bolton, 1995; Longino, 2003; Blaimer, 2012a; Bolton, 2014). Species of this genus often show an arboreal lifestyle, nesting in cavities of woody plants or in carton nests that are usually attached to plant parts (Blaimer, 2010). Aside from extensive associations with trophobionts (Dejean et al., 1996; Seufert & Fiedler, 1999; Blaimer, 2010), numerous species of Crematogaster Abstract The taxonomy and natural history of ants of the genus Crematogaster Lund, 1831 (Crematogaster borneensis-group of the former subgenus Decacrema) obligately associated with myrmecophytic host-plants of the euphorb genus Macaranga are reviewed. Within this group of ants Crematogaster borneensis André, 1896 (with five subspecies and four varieties), Crematogaster captiosa Forel, 1910 as well as Crematogaster decamera Forel, 1910 have previously been described from SE Asia. Here we synonymise C. borneensis subsp. capax Forel, 1911, C. borneensis subsp. hosei Forel, 1911, C. borneensis subsp. sembilana Forel, 1911, and C. borneensis var. macarangae Viehmeyer, 1916 with C. borneensis André, 1896. Crematogaster borneensis var. harpyia Forel, 1911, C. borneensis var. insulsa Forel, 1911, C. borneensis subsp. symbia Forel, 1911, and C. borneensis subsp. novem Forel, 1911 are synonymised with C. captiosa Forel, 1910. In addition we describe five new species: C. claudiae sp. nov., C. hullettii sp. nov., C. linsenmairi sp. nov., C. maryatii sp. nov., and C. roslihashimi sp. nov.. Seven of these eight species are placed into two informal species subgroups based on queen morphology, life-history characters and a formerly published molecular phylogeny. Keys are provided for the identification of queens and workers, as well as natural history information on the eight ant species. The morphology of these Macarangaassociated Crematogaster (formerly Decacrema) species is compared to the only other three species described for this former subgenus in SE Asia, i.e. C. angulosa André, 1896, C. biformis André, 1892 and C. cephalotes Smith, 1857. Sociobiology An international journal on social insects

in return for nesting space in hollow stems as well as food in the form of food-bodies and extrafloral nectar (Fiala et al., 1989).With one exception (see below), all species belong to one group (formerly subgenus Decacrema) that was recently placed into the Crematogaster borneensis-group within the subgenus Crematogaster sensu stricto after subgeneric revision (Blaimer, 2012a;Blaimer, 2012b).
When the ecology and evolution of this ant-plant symbiosis was initially studied in a few myrmecophytic Macaranga species on Peninsula Malaysia, they appeared to be inhabited by a single Crematogaster species only, namely Crematogaster borneensis André, 1896 (Baker, 1934;Ong, 1978;Tho, 1978).However, it soon became obvious that ants associated with different Macaranga species comprised a species complex (Fiala & Maschwitz, 1990).Within the last decade, several research groups have independently classified the Macaranga-associated Crematogaster species into a total of nine morphospecies (Fiala et al., 1999;Feldhaar et al., 2003a;Feldhaar et al., 2010) or five morphospecies from one site in Sarawak (Itino et al., 2001).However, a key to the morphospecies has not been published to date, preventing a comparison of the results obtained by the different research groups.Quek and her coworkers circumvented the problem by using phylotypes based on mitochondrial DNA sequences in order to uncover the evolutionary history of the Crematogaster ants involved in this symbiosis (Quek et al., 2004;Quek et al., 2007).Some lineages are, however, congruent with at least four of our delimited morphospecies (unpubl. results, and Quek et al., 2007).Ueda et al. (2015) identified six distinct lineages in a small region in Sarawak using mitochondrial and nuclear DNA markers.These six lineages were, however, assigned to three morphospecies only, which were formerly published by Itino et al. (2001).A comparison with the morphospecies used in Fiala et al. (1999) and Feldhaar et al. (2003a) was again not possible due to a lack of formal description in all studies.Therefore, the comparability of most ecological studies would be highly facilitated by a taxonomic revision of this group of obligate plant-ants.In addition, a full understanding of evolutionary processes such as speciation or ongoing hybridization among lineages of the involved Crematogaster species can only be attained by a combination of morphological and genetic data.Our first molecular phylogenetic analyses over a broad distribution area mostly confirmed the morphospecies; however, some mismatches, possibly due to introgression, were observed particularly in the mtDNA data, whereas the microsatellite data separated most of the species (Feldhaar et al., 2003a;Feldhaar et al., 2008;Feldhaar et al., 2010).
Here we provide a taxonomic revision of the species of the Crematogaster borneensis-group obligately associated with Macaranga.The Macaranga-associated Crematogaster are compared with the type material of the three other described former Decacrema -species from Peninsula Malaysia and Borneo (C.angulosa André, 1896, C. cephalotes Smith, 1857, andC. biformis André, 1892) that are presumably not associated with Macaranga.To facilitate ecological studies on this Macaranga-ant-system we provide keys for queens and workers.This study is based mainly on material from Peninsula Malaysia, Sabah, Sarawak and East Kalimantan and may therefore not allow secure identification of ants from a few other parts of Sundaland (such as Sumatra and West Kalimantan) where Macaranga-ant associations also occur but have not been widely sampled.In these regions, however, no ecological studies on the system have been conducted thus far; such studies have been mainly concentrated in Peninsular Malaysia, Sabah and eastern Sarawak.
A short overview of the natural history of the Macarangaassociated Crematogaster (Crematogaster borneensis-group) species is given to allow comparison of former ecological studies conducted by different research groups.
The diagnostic character for the subgenus Decacrema (Forel, 1910) was the normally 10-segmented (sometimes 9-segmented, (Emery, 1922)) antenna of workers and females (Santschi, 1918).Males have 12 antennal segments in African species but only 10 or 11 in the Indo-Malayan region (Emery, 1922).Due to its discontinuous distribution (comprising Africa, Madagascar and the Indo-Malay region including New Guinea), as well as the differing number of antennal segments in males among regions, Emery (1922;p. 137) had already suggested that the subgenus Decacrema may not be monophyletic.Blaimer recognizes three monophyletic clades based on molecular data (Blaimer, 2012a), and recommends grouping the species of this hyperdiverse genus into two subgenera only, since most formerly recognized subgenera are not retrieved as monophyletic groups (Blaimer, 2012a;Blaimer 2012b).
As only three species obligately associated with Macaranga host-plants (C.borneensis, C. decamera and C. captiosa) have been included into the molecular phylogeny, monophyly is only clarified for those species, while the affiliation of the other former Decacrema species to this clade remains unknown to date (Blaimer, 2012a;Blaimer, 2012b).Blaimer suggests the name Crematogaster borneensis-group for this clade (Blaimer, 2012b).In accordance with Blaimer´s suggestions we will refer to the Macaranga-associated Crematogaster species formerly belonging to the subgenus Decacrema as Crematogaster (Crematogaster-borneensis-group).
The earlier taxonomic literature on Macaranga-inhabiting Crematogaster (Crematogaster-borneensis-group) species contains only very short and rather anecdotal descriptions of various species, subspecies and 'varieties', based only on a few individuals (mainly workers but also several queens).Forel (1911) and Viehmeyer (1916Viehmeyer ( (1915))) both already suggested that Crematogaster borneensis may be very variable or a species complex, which is also reflected in the large number of subspecies and varieties described.For C. borneensis var.macarangae Viehmeyer, 1916 as well as two varieties and two subspecies of Crematogaster borneensis collected by Haviland and determined by Forel (1911) it is mentioned that the ants were collected "from a tree called Macaranga" (Forel, 1911).

Natural history of the Macaranga-associated Crematogaster (Crematogaster borneensis-group) ants
As extensive work on this ant-plant symbiotic system has been conducted over the last decades, we here summarize only some important aspects (for a detailed compilation see e.g.Feldhaar et al., 2010 and references therein).All associations between Crematogaster (Crematogaster borneensis-group) and Macaranga begin by newly mated foundress queens swarming and searching for a suitable host for colonization.Mating flights are presumably nocturnal and occur all year round (personal observation, B. Fiala and H. Feldhaar).After localization of a host-plant, probably by chemical cues (Inui et al., 2001;Jürgens et al., 2006), single queens enter the plant by chewing an entrance hole into an internode.The hole is sealed from the inside and colony founding is claustral.The first emerging workers open up the internode from inside and start foraging for food provided by the plant, i.e. food bodies (Beccarian bodies) and extrafloral nectar as well on honeydew from specific coccids living in the interior of the stem (Fiala & Maschwitz, 1991;Fiala & Maschwitz, 1992).Whereas several colonies may be founded simultaneously on a seedling, only a single colony dominates each host due to competitive replacement.Ant colonies grow as available nesting space and food provisioning increases with the growth of the host-plant.Workers are never found leaving their host for foraging.
The eight species of Crematogaster (Crematogaster borneensis-group) associated with Macaranga can be subdivided into two subgroups based on the morphology of queens and life history characters, which are largely supported in phylogenetic analyses (Feldhaar et al., 2003a;Quek et al. 2004, Quek et al. 2007).They were named C. decamerasubgroup and C. captiosa-subgroup after one member of the respective subgroup corresponding to an already described species (Feldhaar et al., 2003a).Ants belonging to the decamerasubgroup, as well as C. maryatii which, based on mitochondrial DNA sequences, does not cluster with either subgroup (Feldhaar et al., 2003a), have distinctly smaller queens than ants of the captiosa-subgroup and share life-history characters such as an earlier onset of reproduction than the latter (Feldhaar et al., 2003b).This late onset of reproduction may preclude species of the captiosa-subgroup from reproducing on slow-growing Macaranga hosts specialized to grow in primary forest habitats (e.g.M. angulata or M. havilandii).
All obligately Macaranga-associated Crematogaster (Crematogaster borneensis-group) colonize host species belonging to the sections Pachystemon and Pruinosae within the genus Macaranga (Blattner et al., 2001;Davies et al., 2001).The section Winklerianae that is endemic to Borneo is exclusively colonized by a species that we had named Crematogaster morphospecies 8 in former publications by our group (Fiala et al., 1999).This species belongs to a different subclade of the genus Crematogaster and was never found on Macaranga species of sections Pachystemon or Pruinosae.Since its placement within the genus Crematogaster is still unclear we have not included this species in the present study.Three Macaranga species (M.puncticulata, and, in part of their range, M. lamellata and M. griffithiana) were found to be specifically inhabited by different species of the genus Camponotus, subfamily Formicinae (Maschwitz et al., 1996;Federle et al., 1998a;Federle et al., 1998b;Maschwitz et al., 2004).
The associations of ants and plants are not strictly species-specific, as each of the eight species of Crematogaster (Crematogaster borneensis-group) inhabits between two to seven different Macaranga hosts over their whole distributional range.From the plants´ point of view, each species of Macaranga is obligately associated with up to three different Crematogaster (Crematogaster borneensis-group) species (with exception of M. winkleri and M. winkleriella that are always colonized only by C. msp.8) (Fiala et al., 1999;Feldhaar et al., 2003a;Feldhaar et al., 2003b).Nonetheless, non-random recurring association patterns between the two groups are stable over a wide geographic range (Fiala et al., 1999;Feldhaar et al., 2003a;Feldhaar et al., 2003b;Quek et al., 2004;Quek et al., 2007).Macaranga hosts generally show a smaller geographic distribution in comparison to the ants, and a higher degree of endemism.In contrast, four out of the eight species of Crematogaster (Crematogaster borneensisgroup) occur over the whole distributional range of this ant-plant association comprising Malaya, Sumatra and Borneo and some smaller islands in the Sunda-region (Fiala et al., 1999;Quek et al., 2007).These widespread species of Crematogaster (Crematogaster borneensis-group) often inhabit different Macaranga species in different regions and may also colonize more than one host plant species within a region (Fiala et al., 1999;Feldhaar et al., 2003a;Feldhaar et al., 2003b;Quek et al., 2004;Quek et al., 2007).However, at most three Macaranga species per site are inhabited by a particular ant species.The Crematogaster (Crematogaster borneensis-group) each colonize a nonrandom subset of Macaranga-species that shares specific morphological traits (Fiala et al., 1999;Quek et al., 2004;Feldhaar et al., 2010).Macaranga-hosts form two distinct groups with host plants whose stems are covered with an epicuticular wax-bloom and non-waxy hosts lacking such coating, with the exception of a few hosts that have only a slight wax-cover (M.glandibracteolata) or produce waxblooms only as large trees (M.indistincta) (Blattner et al., 2001).Only "wax-runners" are able to walk on the slippery, waxy plant surfaces, whereas workers of the other species will either drop off the plant or can only move very slowly on such host stems (Federle & Brüning, 2005;Federle et al., 1997).Wax-running ability is a species-specific trait facilitated by a combination of morphological, locomotory and behavioural adaptations (Federle & Brüning, 2005).A second trait influencing ant colonization involves stems that need to be actively excavated, versus naturally hollow stems (Feldhaar et al., 2010).In the former, energy expenditure during colonization may be higher for the ant partner.Thus, host species with stems that need to be actively excavated tend to be colonized by species of the captiosa-subgroup with larger queens.As a consequence, hosts of the solidstemmed section Pruinosae are solely colonized by queens of the captiosa-subgroup.These hosts can only be colonized when seedlings are taller than approximately 50 cm.Hosts are then more strongly lignified in comparison to the small and relatively thin-tissued seedlings Macaranga species of the section Pachystemon that develop swollen internodes for ant colonization.The larger size of queens, their presumably stronger mandibles and their greater energy reserves enable queens of the captiosa-subgroup to also found colonies in tips of branches of large, abandoned Macaranga hosts.This behaviour was never observed for queens of the decamerasubgroup and C. maryatii (Feldhaar et al., 2003b).

Materials and Methods
All measurements were taken at 6.5x to 40x magnification with a stereomicroscope (Leica M3C).Measurements (Fig 1 ) were made with a micrometer stage with digital output in increments of 0.001mm.All measurements are presented in mm.Additional material not included in the measurements has been collected and identified according to our keys from many more sites in all regions and has supported our species concept.

C. hullettii 4b
Legs in comparison to alitrunk relatively longer (RLEG between 0.61 and 0.69).Propodeal spines always prominent and acute, with the tip of the spine distinctly exceeding the posterior margin of the propodeal spiracle (LPS/WL ranging from 0.12 to 0.17).Head always longer than wide (CI < 0.98) (Fig S1.4C and S1.4D)  ).Petiole nodiform in dorsal view and as wide as or slightly wider than postpetiole, PI ranging from 0.98 to 1.07, PI rarely < 1.0.RLEG ranging from 0.67 to 0.72, in most workers RLEG < 0.7.Endemic to host species found on Borneo (Sabah, Sarawak, East Kalimantan), mostly on waxy host plants of the section Pachystemon (see queen key above)

Synonymic list of Crematogaster (Crematogaster borneensisgroup) species from Borneo and the Malay Peninsula obligately associated with Macaranga
In this study eight species of Crematogaster (Crematogaster borneensis-group) are recognized (including five new species), belonging to three species subgroups.Species subgroups were designated based on morphological characters of the queen caste, i.e. queens of the decamera-subgroup are smaller (WL ranging from 1.7 to 2.3 mm) and have relatively smaller compound eyes (EL<0.5 mm) than queens of the captiosa-subgroup (WL ranging from 2.2 to 2.9 mm and EL > 0.5 mm) (Feldhaar et al., 2003a;Feldhaar et al., 2010) (see Table S.1 for comparison of morphospecies designations used by our group and synonymized or new species names).
All workers of Crematogaster (Crematogaster borneensisgroup) workers including those associated with Macaranga have ten antennal segments.The workers of the Macarangaassociated Crematogaster species are all monomorphic.This is in contrast to the other three described species belonging to the former Decacrema from SE-Asia (C.angulosa, C. biformis and C. cephalotes) that all have dimorphic workers (see Supplementary Fig S2 .1A to S2.3B).Body size may vary strongly within species although this is dependent on colony size (e.g.TL ranges from ~ 2.1 mm to 3.3 mm in Crematogaster captiosa workers).Thus, especially in workers relative measures (e.g.SI or RLEG) are more important characters than absolute measurements (e.g.SL or LHT) (see overview of most important distinguishing characters of workers in Table 1).Workers collected from small colonies are also lighter in colour.In queens shade of body coloration is a useful character, as are absolute measures.If possible, queens should be used for determination as worker characteristics are sometimes less distinctive (see overview of most important characters distinguishing queens in Table 1).
Most of the diversity of the species is apportioned between the decamera-subgroup and the captiosa-subgroup.The placement of C. maryatii is unclear.In the molecular phylogeny based on mitochondrial DNA this species does not cluster with either group and came out most basal.Based on nuclear DNA (elongation factor 1α) (Feldhaar et al., 2010) this species is not separated from species of the captiosa-group.However, queen morphology and life-history characters resemble that of the decamera-group.Small size of queens and workers and early onset of reproduction may be a convergent trait though as this seems to enable usage of less productive and slow growing host plants (Feldhaar et al. 2010).Therefore, we currently do not place C. maryatii in either group.

Worker description
Colour medium to dark brown with head and gaster a slightly darker shade than alitrunk.Workers monomorphic in size.Total body length of workers ranges from 2.3 mm to 3.0 mm.Head and gaster shiny with smooth surface, alitrunk slightly less shiny and faintly shagreened.All body parts bear appressed pubescent hairs.Long flexuous setae present on head gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites.Only few setae on alitrunk and one pair each on petiole and postpetiole.Head subquadratic but slightly elongated, usually longer than wide and only slightly rounded on sides.Anterior clypeal margin slightly convex and with a row of long erect setae projecting anteriorly.Occipital margin slightly concavely rounded, occipital lobes rounded.Mandibles relatively short and with four denticles, capable of closing tightly against the clypeus.Denticles increasing continuously in size from most proximate to most distal denticle.Surface of mandibles smooth, covered with short pubescent hairs.Antennae relatively long in comparison to head width (SI 0.65-0.79;usually > 0.7) and covered in short pubescent hair.Terminal three funicular segments form a club, sometimes only the terminal two segments.
Compound eyes elliptically shaped and not protruding over margin of head in full-face view.Pronotum and mesonotum form a convex dome in profile that is flattened dorsally.Anterodorsal surface of pronotum sloping downwards as steep as posterodorsal surface of mesonotum.Metanotal groove slightly notched and clearly developed; promesonotal suture is visible but not prominent (Fig S1 .6Cand S1.6D).
Propodeal spines very short or nearly absent, but dorsum of the propodeal spiracle with a nodiform elevation.Slope of posterior face of propodeum similar to posterior slope of mesonotum and approximately 45°.

Queen description
Queens small, from 5.4 to 6.6 mm in total body length and uniformly dark brown in colour.Surface of head and gaster smooth and shiny, alitrunk slightly less shiny and faintly shagreened.All body parts bear appressed pubescent hairs.Long flexuous setae present on head gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites.A row of long erect setae pointing anterior present on the clypeus.Mandibles relatively short, capable of closing tightly against the clypeus.
Head usually longer than wide (CI: 0.90-1.04;mean 0.97).Sides of the head straight and head narrower anterior than posterior.Occipital margin of the head straight.Occipital lobes rounded.Anterior clypeal margin slightly convex.Terminal 3 segments of funiculus forming a distinct antennal club.Antennal scrobes strongly developed, with an acute and marked dorsal margin; the frontal carinae short.
Compound eyes only slightly oval-shaped from lateral view and maximum head width with compound eyes slightly wider than HW (see Fig 3.7,Fig S1.6A and S1.6D).Compound eyes small relative to head length spanning one third or less of HL.Maximum diameter of compound eyes from 0.34 to 0.38 mm.Ocelli relatively small in diameter.The two lateral ocelli widely spaced and the median ocellus always smaller in diameter than the distance between the two lateral ocelli.
Mesoscutum convexly rounded anterodorsally.Mesoscutellum nearly in horizontal plane in lateral view.Propodeum flattened dorsally and drops off steeply posterior of the propodeal spiracle.Mesoscutum relatively short, stretching out over approximately a third of the alitrunk in lateral view.In dorsal view, posterior margin of the propodeum forms a straight line and mesonotum is broadly triangular.Propodeum not armed with spines.
Petiole in dorsal view rounded and node approximately as wide as long.Petiole approximately as wide as postpetiolar node (PI 0.97-1.12).In lateral view the petiole anterodorsally flattened and sloping downwards, and slightly longer than the postpetiole.Postpetiole rounded in lateral view without distinct nodes and subquadratic in dorsal view.(See Table 1 for comparative overview of queen characters.)

Distribution and biology
Crematogaster maryatii is endemic to Borneo and is associated with hosts of the section Pachystemon only (M.havilandii, M. hypoleuca, M. motleyana, locally M. angulata, rarely M. indistincta).The species colonizes waxy as well as non-waxy hosts, but the latter mostly in primary forest habitats, such as M. indistincta (Danum Valley) or M. angulata (Poring Hot Spring at higher elevation).Due to the small-sized queen, small workers and early onset of reproduction (when colonies comprise approximately 500 workers) such hosts in relatively dark primary forest habitats may still sustain colonies of C. maryatii and enable them to reach the reproductive phase.In secondary forest the small queens may be able to colonize small saplings earlier than the larger queens of the captiosagroup (e.g. in M. hypoleuca).Thus, the queens are usually found in the very first internodes developed by saplings (Feldhaar, pers. obs.).In previous publications by our group this species was referred to as Crematogaster msp.7 (Fiala et al., 1999;Feldhaar et al., 2003b;Feldhaar et al., 2010).

Diagnosis
Species of the Crematogaster decamera-group typically have relatively small workers and queens that are dark brown in colour.The compound eyes are smaller than 0.5 mm in diameter (EL) and eye length usually comprises less than one third of head length (REL < 0.35).Diameter of the median ocellus of queens always smaller than the distance between the two lateral ocelli (OW < OD1).Propodeal spines of workers are absent in C. decamera and C. roslihashimi and only very short in C. hullettii.Species only colonize Macaranga hosts of the section Pachystemon.

Lectotype
Queen

Worker description
Colour medium to dark brown with head and gaster a slightly darker shade than the alitrunk.Workers monomorphic in size.Total body length of workers 2.4 mm to 3.6 mm.Head and gaster shiny with smooth surface, alitrunk slightly less shiny and faintly shagreened.All body parts bear appressed pubescent hairs.Long flexuous setae present on head, gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites.Only few setae on alitrunk and one pair each on petiole and postpetiole.Head subquadratic but slightly elongated (CI ≤1.0), usually longer than wide and only slightly rounded on sides.Anterior clypeal margin slightly convex and with a row of long erect setae projecting anteriorly.Occipital margin straight, occipital lobes rounded.Mandibles relatively short and with four denticles, capable of closing tightly against the clypeus.Denticles increasing continuously in size from most proximate to most distal denticle.Surface of mandibles smooth, covered with short pubescent hairs.Antennae are relatively long in comparison with head width (SI 0.68-0.78;mean 0.72) and covered in short, pubescent hair.Terminal two funicular segments form a club, sometimes the terminal three segments are clubbed.
Compound eyes elliptically shaped and not protruding over margin of head in full-face view.Pronotum and mesonotum form a convex dome in profile.Anterodorsal surface of pronotum sloping downwards less steep than posterodorsal surface of mesonotum.Metanotal groove slightly notched and clearly developed, whereas promesonotal suture visible but not prominent.

Queen description
Queens relatively small with total body length from a 6.5 to 7.8 mm and uniformly dark brown in colour.Surface of head and gaster smooth and shiny, alitrunk slightly less shiny and faintly shagreened.All body parts bear appressed pubescent hairs.Long flexuous setae present on head gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites.A row of long erect setae pointing anterior present on the clypeus.Mandibles relatively short, capable of closing tightly against the clypeus.
Head subquadratic, usually approximately as wide as long (CI: 0.96-1.05;mean 1.01).Sides of the head only very slightly convex, occipital margin of the head slightly concave.Occipital lobes rounded.Anterior clypeal margin slightly convex.Terminal four segments of funiculus continuously increasing in size forming an indistinct antennal club.Antennal scrobes strongly developed, with an acute and marked dorsal margin; the frontal carinae short.
Compound eyes small (ranging from 0.39-0.45mm) and usually span less than one third of HL (REL 0.29-0.35).Compound eyes round to oval-shaped from lateral view and convex from dorsal view (see Fig 3.6;Fig S1.5A and S1.5B) with margins of compound eyes protruding over margin of head.Ocelli relatively small in diameter.Diameter of the median ocellus smaller than the distance between the lateral ocelli.
Mesoscutum convexly rounded anterodorsally.Mesoscutellum nearly in horizontal plane in lateral view.Propodeum flattened dorsally and then drops off at an angle of approximately 45° posterior of the propodeal spiracle.Mesoscutum stretches out over less than half of the alitrunk in lateral view.In dorsal view, the posterior margin of the propodeum forms a straight line and the mesonotum is broadly triangular.Propodeum not armed with spines.
Petiole in dorsal view elongate and not concavely rounded on sides and always less wide than postpetiole (PI: 0.88-1.0).Petiole anterodorsally flattened in lateral view and sloping downwards and distinctly longer than the postpetiole.Postpetiole round in dorsal view.(See Table 1 for comparative overview of queen characters.)

Distribution and biology
Crematogaster decamera Forel has a large distributional range and occurs in all geographic regions of the Macaranga-Crematogaster association (Peninsula Malaysia, Sumatra, Borneo).Queens of Crematogaster decamera only colonize saplings, and colonies have an early onset of reproduction.On Peninsula Malaysia several colonies were found that had turned secondarily polygynous or at least contained several mated queens.
This species colonizes glaucous hosts of the section Pachystemon only (M.beccariana, M. constricta, M. havilandii, M. hypoleuca, M. motleyana).It can be distinguished from all other species based on workers only by the complete lack of propodeal spines.Queens from Peninsula Malaysia tend to be smaller than from Borneo, with the largest individuals observed in Sarawak (e.g.mean HW: 1.22 in Peninsula Malaysia (n=6) and 1.35 in Sarawak (n=4)).In earlier publications by our group this species was referred to as Crematogaster morphospecies 6 (Fiala et al., 1999).

Worker description
Colour medium to dark brown with head and gaster being a slightly darker shade than the alitrunk.Workers monomorphic in size.Total body length of workers 2.4 mm to 3.0 mm.Head, alitrunk and gaster shiny with smooth surface, only mesonotum slightly less shiny.All body parts bear appressed pubescent hairs.Long flexuous setae present on head, gaster and abdomen: on head only few in frons, on gaster more on the posterior margins of tergites and sternites.Only few setae on alitrunk and one pair each on petiole and postpetiole.Head subquadratic and approximately as wide as long (CI 0.96-1.03)usually being only slightly rounded on sides.Anterior clypeal margin slightly convex and with a row of long erect setae projecting anteriorly.Occipital margin slightly concave, occipital lobes rounded.Mandibles relatively short and with four denticles, capable of closing tightly against the clypeus.Denticles increasing continuously in size from most proximate to most distal denticle.Surface of mandibles smooth, covered with short pubescent hairs.Antennae relatively short in comparison to head width (SI 0.57-0.62;mean SI: 0.6) and covered in short pubescent hair.Segments of the funiculus continuously increasing in size, with the terminal three funicular segments forming a club.
Compound eyes elliptically-shaped and not protruding over margin of head in full-face view.Pronotum and mesonotum form a convex dome in profile.Anterodorsal surface of pronotum sloping downwards less steep than posterodorsal surface of mesonotum.Metanotal groove slightly notched and clearly developed, whereas the promesonotal suture is visible but not prominent.
Propodeal spines are present but short.The tip of the spine protrudes only slightly over the posterior margin of the propodeal spiracle (Fig S1 .3Cand S1.3D).Slope of the posterior face of the propodeum similar to posterior slope of mesonotum and approximately 45°.Legs relatively short in comparison to alitrunk length (RLEG: 0.58-0.62).Node of petiole and postpetiole in dorsal view rounded.Petiole only slightly longer and always as wide as or wider than postpetiole (PI 1.0-1.15).Subpetiolar process usually absent.(See Table 1 for comparative overview of worker characters.)

Queen description
Queens relatively small with total body length 6.2 to 7.0 mm and uniformly dark brown in colour.Surface of head and gaster smooth and shiny, alitrunk slightly less shiny and faintly shagreened.All body parts bear appressed pubescent hairs.Long, flexuous setae present on head gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites.A row of long erect setae pointing anterior are present on the clypeus.Mandibles relatively short, capable of closing tightly against the clypeus.
Head usually approximately as wide as or wider than long (CI: 0.96-1.07;mean 1.01).Head wider behind the compound eyes than anterior closer to the clypeus.Sides of the head straight, occipital margin of the head slightly concave.Occipital lobes rounded.Anterior clypeal margin slightly convex.Terminal four segments of funiculus continuously increasing in size forming an antennal club.Antennal scrobes strongly developed, with an acute and marked dorsal margin; the frontal carinae short.
Compound eyes small (0.39-0.47 mm) and usually span approximately one third of HL (REL 0.32-0.4).Compound eyes oval in shape from lateral view and convex from dorsal view (see Fig 3.5;Fig S1.3A and S1.3B) with margins of compound eyes protruding over margin of head.Ocelli relatively small in diameter.Diameter of the median ocellus smaller than the distance between the lateral ocelli.
Mesoscutum convexly rounded anterodorsally.Mesoscutellum nearly in horizontal plane in lateral view.Propodeum flattened dorsally and then drops off at an angle of approximately 45° posterior of the propodeal spiracle.Mesoscutum stretches out over less than half of the alitrunk in lateral view.In dorsal view, the posterior margin of the propodeum forms a straight line and the mesonotum is broadly triangular.Propodeum not armed with spines.
Petiole in dorsal view broadly rounded on sides and approximately as wide as postpetiole (PI: 0.95-1.03).In lateral view the petiole anterodorsally flattened and sloping downwards and slightly longer than the postpetiole.Postpetiole round in dorsal view.(See Table 1 for comparative overview of queen characters.)

Distribution and biology
Crematogaster hullettii occurs on Peninsula Malaysia and in Sarawak.On Peninsula Malaysia the species seems to be restricted to higher elevation sites, e.g.Genting Highlands or Fraser's Hill above approximately 500m where it mainly inhabits M. hullettii as well as M. bancana, which ceases to occur with increasing elevation.In Sarawak (Borneo) it was mainly found in lowland sites (but higher elevational regions were little sampled there).Queens on Borneo also colonize only seedlings of nonwaxy host species of the section Pachystemon (M.angulata, M. bancana, M. hullettii, M. petanostyla, M. umbrosa).In Quek et al. (2007) the lineages from the two regions are sister groups, i.e. monophyletic but with some genetic differentiation.Two samples contained in the phylogeny based on mitochondrial DNA and collected in eastern Sarawak cluster with samples of C. claudiae from Sabah and thus surprisingly with the Crematogaster captiosa-subgroup (Feldhaar et al., 2010).However, based on morphological measurements these samples clearly fall within C. hullettii.As hybridization events or introgression of mitochondrial DNA seem to occur in this species complex (2.5% hybrid individuals were found among two species of the C. captiosasubgroup in one area; Feldhaar et al. 2008), we place a stronger emphasis on the morphological data.In former publications by our group this species was referred to as Crematogaster msp. 3 (Fiala et al., 1999;Feldhaar et al., 2003a;Feldhaar et al., 2010).

Description of worker
Colour uniformly light to medium brown.Workers monomorphic in size.Total body length of workers 2.8 mm to 2.9 mm, but this is a measurement from a single mature colony only.Workers from incipient colonies are expected to be smaller.Head and gaster shiny with smooth surface, alitrunk slightly less shiny and faintly shagreened.All body parts bear appressed pubescent hairs.Long flexuous setae present on head gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites.Only few setae on alitrunk and one pair each on petiole and postpetiole.Head distinctly longer than wide and only slightly rounded on sides (CI: 0.90-0.91).Anterior clypeal margin slightly convex and with a row of long erect setae projecting anteriorly.Clypeus with a small median node.Occipital margin slightly concavely rounded, occipital lobes rounded.Mandibles relatively short and with four denticles, capable of closing tightly against the clypeus.Denticles increasing continuously in size from most proximate to most distal denticle.Surface of mandibles smooth, covered with short pubescent hairs.Antennae relatively long in comparison to head width (SI 0.69-0.74)and densely covered in short pubescent hair.Terminal two funicular segments forming a club.
Compound eyes elliptically-shaped and not protruding over margin of head in full-face view.Pronotum and mesonotum form a convex dome in profile.Anterodorsal surface of pronotum sloping downwards as steep as posterodorsal surface of mesonotum.Metanotal groove slightly notched and clearly developed, whereas the promesonotal suture barely visible and not prominent.
Propodeal spines always absent.A nodiform elevation may be present above the propodeal spiracle, albeit not very prominent.Slope of the posterior face of the propodeum similar to posterior slope of mesonotum and approximately 45°.
In dorsal view petiole and postpetiole approximately the same width or petiole slightly broader.Anterodorsal surface of petiole broadly flattened.Both petiole and postpetiole round in dorsal view.Subpetiolar process usually absent.Petiole and postpetiole wide in comparison to MTW (MTW/DPW: <1.8; in all other species >1.8 and usually larger than 1.9).(See Table 1 for comparative overview of worker characters.)

Description of queen
Queens small, 5.8 to 6.1 mm in total body length and uniformly medium to dark brown in colour.Surface of head, gaster and alitrunk not structured but densely covered in pubescent hairs.Long flexuous setae present on head gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites.A row of long erect setae pointing anterior present on the clypeus.Mandibles relatively short, capable of closing tightly against the clypeus.
Head distinctly longer than wide (CI: 0.84-0.89).Sides of the head straight and not becoming narrow towards the clypeus.Occipital margin of the head convex.Occipital lobes rounded.Anterior clypeal margin slightly convex.Terminal four segments of funiculus forming a distinct antennal club.Funiculus covered densely in pubescent hair so that borders between antennal segments barely visible.Antennal scrobes strongly developed, with an acute and marked dorsal margin; the frontal carinae short.
Compound eyes only slightly oval-shaped from lateral view and maximum head width with compound eyes only slightly wider than HW (see Compound eyes small relative to head length spanning one third or less of HL .Maximum diameter of compound eyes 0.3 to 0.32 mm.Ocelli relatively small in diameter.The two lateral ocelli widely spaced and the median ocellus always smaller in diameter than the distance between the two lateral ocelli.
Mesoscutum convexly rounded anterodorsally.Mesoscutellum nearly in horizontal plane in lateral view.Propodeum flattened dorsally and then drops off steeply posterior of the propodeal spiracle.Mesoscutum relatively short, stretching out over approximately a third of the alitrunk in lateral view.In dorsal view, the posterior margin of the propodeum forms a straight line and the mesonotum is broadly triangular.Propodeum not armed with spines.
Petiole in dorsal view rounded and node approximately as wide as long.Petiole slightly less wide than postpetiole (PI≤1.0).In lateral view the petiole and postpetiole nodiform.Petiole and postpetiole broad in relation to MTW (MTW/DPW 1.69-1.78; in all other Macaranga-associated Decacrema MTW/DPW rarely <2.0).(See Table 1 for comparative overview of queen characters.)

Distribution and biology
Crematogaster roslihashimi is a very rare species endemic to a small region on the East coast of Peninsula Malaysia (near Kuantan) and is was found on only two waxcovered hosts of the section Pachystemon (M.constricta, M. hypoleuca).The species is closely related to Crematogaster decamera based on mitochondrial DNA as well as nuclear DNA (EF-1a) (Feldhaar et al., 2003b;Feldhaar et al., 2010).The species was formerly called Crematogaster msp. 9 in publications by our group (Fiala et al., 1999).Crematogaster claudiae has an intermediate morphology of species belonging to the captiosa and the decamera-group.Queens are intermediate in size (HW, HL, WL and EL) and workers possess none or only very short propodeal spines in contrast to the long and acute propodeal spines of workers of the other three species in the captiosa-group.As it clusters with species of the captiosa group in molecular phylogenies based on mitochondrial DNA (Feldhaar et al., 2003a, Feldhaar et al., 2010) and is known to hybridize with C. captiosa locally (Feldhaar et al., 2010, we

Description of worker
Colour light to reddish brown (large workers) with head and gaster being a slightly darker shade than the alitrunk.Workers monomorphic in size.Total body length of workers 2.5 mm to 3.2 mm.Head and gaster shiny with smooth surface, alitrunk slightly less shiny and faintly shagreened.All body parts bear appressed pubescent hairs.Long flexuous setae present on head gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites.Only few setae on alitrunk and one pair each on petiole and postpetiole.
Head subquadratic but slightly elongated, always being longer than wide (CI<0.97)and only slightly rounded on sides.Anterior clypeal margin slightly convex and with a row of long erect setae projecting anteriorly.Occipital margin slightly concavely rounded, occipital lobes rounded.Mandibles relatively short and with four denticles, capable of closing tightly against the clypeus.Denticles increasing continuously in size from most proximate to most distal denticle.Surface of mandibles smooth, covered with short pubescent hairs.
Antennae relatively long in comparison to head width (SI 0.64-0.74;mean 0.68) and covered in short pubescent hair.Terminal three funicular segments form a club, sometimes only the terminal two segments.
Compound eyes elliptically shaped and not protruding over margin of head in full-face view.Pronotum and mesonotum form a convex dome in profile, sometimes slightly flattened dorsally.Anterodorsal surface of pronotum sloping downwards slightly steeper than or as steep as posterodorsal surface of mesonotum.Metanotal groove slightly notched and clearly developed, whereas the promesonotal suture visible but not prominent.
Propodeal spines in lateral view strong and acute.Tip of the spines always protruding over posterior margin of the propodeal spiracle and diverging very slightly.Dorsal face of the propodeum confluent with the horizontal spines or spines bent slightly upwards.Slope of the posterior face of the propodeum similar to posterior slope of mesonotum (Fig S1 .1Cand S1.1D).
In dorsal view petiole always wider than postpetiole (PI: 1.01-1.14).Node of petiole in dorsal view longer than wide and considerably rounded, dorsal surface flat.In profile the anterior face of the petiolar node shorter than the posterior so that the dorsal surface slopes downwards anteriorly.Dorsal surface of the postpetiolar node in profile rounded.Subpetiolar process usually absent.(See Table 1 for comparative overview of worker characters.) In the original description of the worker of C. borneensis by André (1896) he described the worker as having propodeal spines twice as long as their base.Forel (1911) writes that he has had personal contact with M. André and has been told that this was indeed an error made in the original description as spines are shorter (see above).

Description of queen
Queens large, 7.0 to 8.5 mm in total body length and uniformly light to medium brown in colour.Surface of head and gaster smooth and shiny, alitrunk slightly less shiny and faintly shagreened.All body parts bear appressed pubescent hairs.Long flexuous setae present on head gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites.A row of long erect setae pointing anterior present on the clypeus.Mandibles relatively short, capable of closing tightly against the clypeus.
Head elongate, always longer than wide (CI: 0.88-0.96;mean 0.91).Sides of the head only very slightly convex, occipital margin of the head straight to slightly convex.Occipital lobes strongly rounded.Anterior clypeal margin slightly convex.Terminal three segments of funiculus continuously increasing in size forming an antennal club that is not very distinct.Antennal scrobes strongly developed, with an acute and marked dorsal margin; the frontal carinae short.
Compound eyes oval-shaped from lateral view and only slightly convex from dorsal view (see Fig 3.1;Fig S1.1A and S1.1B).Compound eyes large relative to head length spanning more than one third of HL.Maximum diameter of compound eyes 0.5 to 0.6 mm.Maximum width of head including compound eyes maximally 10% wider than HW.Ocelli relatively small in diameter.The two lateral ocelli widely spaced and the median ocellus always smaller in diameter than the distance between the two lateral ocelli.
Mesoscutum convexly rounded anterodorsally.Mesoscutellum nearly in horizontal plane in lateral view.Propodeum flattened dorsally and then drops off steeply posterior of the propodeal spiracle.Mesoscutum long, stretching out over approximately half of the alitrunk in lateral view.In dorsal view, the posterior margin of the propodeum forms a straight line and the mesonotum broadly triangular.Propodeum not armed with spines.
Node of petiole in dorsal view roughly rectangular, anterior side broader than posterior one.Petiolar node quadrangular in shape in dorsal view and not as wide as postpetiolar node (PI<1.0).In lateral view the petiole is anterodorsally flattened and sloping downwards and is slightly longer than the postpetiole.Postpetiole round in dorsal and lateral view without distinct nodes.(See Table 1 for comparative overview of queen characters.)

Distribution and biology
Crematogaster borneensis André has a large range and occurs in all geographic regions of the Macaranga-Crematogaster association (Malay Peninsula, Sumatra, and Borneo).It is the most generalised species with respect to host plant use.Queens colonize mostly waxy hosts.However, hosts that develop a slight wax-coating only as mature trees will also be colonized secondarily by this species after having been abandoned due to death of the original colony (e.g.M. indistincta).In this case queens of C. borneensis are found in the tip of branches of abandoned mature hosts.
Crematogaster borneensis is frequently found on hosts of the section Pachystemon (M.aetheadenia, M. glandibracteolata, M. griffithiana, M. lamellata, M. motleyana, M. hypoleuca, M. indistincta, (in the latter two mainly in larger trees, rarely in saplings) as well as the section Pruinosae (M.hosei, M. pearsonii, M. puberula, M. pruinosa).Virgin alate queens have been found to be parasitized by the phorid fly Trucidophora feldhaarae while still inside the nest within the hollow stem of their host plant on Peninsula Malaysia (Maschwitz et al., 2006).
In former publications we have referred to this species as Crematogaster msp. 1 (Fiala et al. 1999).

Description of worker
Workers brown in colour (large workers) with head and gaster a slightly darker shade than the alitrunk.Workers monomorphic in size.Total body length of workers 2.7 to 3.8 mm.Head and gaster shiny with smooth surface, alitrunk slightly less shiny and faintly shagreened.All body parts bear appressed pubescent hairs.Long flexuous setae present on head gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites.Only few setae on alitrunk and one pair each on petiole and postpetiole.
Head subquadratic but slightly elongated, usually being longer than wide (mean CI: 0.97) and only slightly convex on sides.Anterior clypeal margin slightly convex and with a row of long erect setae projecting anteriorly.Occipital margin slightly concavely rounded, occipital lobes rounded.Mandibles relatively short and with four denticles, capable of closing tightly against the clypeus.Denticles increasing continuously in size from most proximate to most distal denticle.Surface of mandibles smooth, covered with short pubescent hairs.
Antennae are relatively long in comparison to head width (SI 0.68-0.76;mean 0.72) and covered in short pubescent hair.Terminal three funicular segments form a club, sometimes only the terminal two segments.
Compound eyes elliptically shaped and not protruding over margin of head in full-face view.Pronotum and mesonotum form a convex dome in profile, sometimes slightly flattened dorsally.Anterodorsal surface of pronotum sloping downwards slightly steeper than or as steep as posterodorsal surface of mesonotum.The metanotal groove is slightly notched and clearly developed, whereas the promesonotal suture is visible but not prominent.
Propodeal spines in lateral view strong and acute.Tip of the spines always protruding over posterior margin of the propodeal spiracle and are diverging very slightly.Dorsal face of the propodeum confluent with the horizontal spines or spines bent slightly upwards.Slope of the posterior face of the propodeum similar to posterior slope of mesonotum (Fig S1.2c and S1.2D).
In dorsal view petiole approximately as wide as postpetiole (PI: 0.96-1.08).Node of petiole in dorsal view longer than wide and considerably rounded, dorsal surface flat.In profile the anterior face of the petiolar node shorter than the posterior so that the dorsal surface slopes downwards anteriorly.Dorsal surface of the postpetiolar node in profile rounded.Subpetiolar process usually absent.(See Table 1 for comparative overview of worker characters.)

Description of queen
Queens are the largest of all Macaranga-associated Crematogaster (Crematogaster borneensis-group); with total body length ranging from approximately 6.8 to 9.3 mm and uniformly medium brown in colour.Surface of head and gaster smooth and shiny, alitrunk is slightly less shiny and faintly shagreened.All body parts bear appressed pubescent hairs.
Long flexuous setae present on head gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites.A row of long erect setae pointing anterior are present on the clypeus.Mandibles relatively short, capable of closing tightly against the clypeus.
Head subquadratic, being usually approximately as wide as long (CI: 0.93-1.04;mean 0.99).Sides of the head only very slightly convex, occipital margin of the head slightly concave.Occipital lobes rounded.Anterior clypeal margin slightly convex.Terminal 3 segments of funiculus continuously increasing in size forming an indistinct antennal club.Antennal scrobes strongly developed, with an acute and marked dorsal margin; the frontal carinae short.
Compound eyes large (rarely below 0.6 mm) and span more than one third of HL.Compound eyes oval-shaped from lateral view and convex from dorsal view (see Fig 3 .2;Fig S1 .2Aand S1.2B) with margins of compound eyes protruding distinctly over margin of head.Maximum width of head including compound eyes between 8 to 16% wider than HW.Ocelli relatively large in diameter.Diameter of median ocellus larger than distance between the lateral ocelli.
Mesoscutum convexly rounded anterodorsally.Mesoscutellum nearly in horizontal plane in lateral view.Propodeum flattened dorsally and then drops off at an angle of approximately 45° posterior of the propodeal spiracle.Mesoscutum long, stretching out over approximately half of the alitrunk in lateral view.In dorsal view, the posterior margin of the propodeum forms a straight line and the mesonotum is broadly triangular.Propodeum not armed with spines.
Node of petiole in dorsal view roughly rectangular, anterior side broader than posterior one.Petiolar node round in shape in dorsal view and often, but not always not as wide as postpetiolar node.In lateral view the petiole anterodorsally flattened and sloping downwards and slightly longer than the postpetiole.Postpetiole trapezoid-shaped in dorsal view and broader anterior than posterior.Petiole and postpetiole do not have distinct nodes.(See Table 1 for comparative overview of queen characters.)

Distribution and biology
Crematogaster linsenmairi is the largest species of the Macaranga-associated Crematogaster (Crematogaster captiosasubgroup) species and is found over the whole distributional range of the association.It colonizes mainly hosts of the section Pruinosae whose stems need to be actively excavated and have a waxy cover (M.hosei, M. pearsonii, M. pruinosa but also on non-waxy M. puberula).It is also found very rarely on hosts of the section Pachystemon (e.g., M. aetheadenia, M. kingii, M. lamellata, and M. motleyana) in areas where the usual host species are absent (Fiala et al., 1999).

Crematogaster captiosa
Queens colonize seedlings as well as the tips of mature hosts that have been abandoned due to the loss of the original colony.On Peninsula Malaysia secondarily polygynous colonies that contained several queens have been found locally in the Gombak area.

Description of worker
Colour uniformly medium brown.Workers monomorphic in size.Total body length of workers from 2.5 to 3.4 mm.Head, gaster and alitrunk shiny with smooth surface.All body parts bear appressed pubescent hairs.Long flexuous setae present on head, gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites.Only few setae on alitrunk and one pair each on petiole and postpetiole.
Head subquadratic but slightly elongated, always being longer than wide or as long as wide (CI ≤1.0) and only slightly convex on sides.Anterior clypeal margin slightly convex and with a row of long erect setae projecting anteriorly.Occipital margin slightly convexly rounded, occipital lobes rounded.Mandibles relatively short and with four denticles, capable of closing tightly against the clypeus.Denticles increasing continuously in size from posterior (close to clypeus) to anterior.Surface of mandibles smooth, covered with short pubescent hairs.
Antennae relatively short in comparison to head width (SI 0.61-0.65;mean 0.63) and covered in short pubescent hair.Terminal three funicular segments form a club.
Compound eyes elliptically shaped and not protruding over margin of head in full-face view.Pronotum and mesonotum form a convex dome in profile.Anterodorsal surface of pronotum sloping downwards less steep than posterodorsal surface of mesonotum.Metanotal groove slightly notched.Promesonotal suture visible and dorsally slightly notched.
Propodeal spines very short or nearly absent, but then dorsally of the propodeal spiracle nodiform elevation.When short spines are present, the tip of the spines protrudes only slightly over posterior margin of the propodeal spiracle (Fig S1 .7Cand S1.7D).Slope of the posterior face of the propodeum similar to posterior slope of mesonotum and approximately 45°.
In dorsal view petiole and postpetiole round in shape.Petiole always distinctly wider than the postpetiole (PI: 1.13-1.29).In lateral view the anterior face of the petiolar node flattened and sloping downwards anteriorly and petiole longer than postpetiole.Dorsal surface of the postpetiolar node in profile rounded, lateral nodes visible.Subpetiolar process usually absent.(See Table 1 for comparative overview of worker characters.)

Description of queen
Queens medium in size, from 6.5 to 7.2 mm in total body length and uniformly medium brown in colour.Surface of head and gaster smooth and shiny alitrunk slightly less shiny and faintly shagreened.All body parts bear appressed pubescent hairs.Long flexuous setae present on head gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites.A row of long erect setae pointing anterior present on the clypeus.Mandibles relatively short, capable of closing tightly against the clypeus.
Head approximately as wide as long (CI: 0.99-1.05;mean 1.01).Sides of the head straight and head narrowing slightly from posterior towards clypeus.Occipital margin of the head slightly concave.Occipital lobes strongly rounded.Anterior clypeal margin slightly convex.Terminal four segments of funiculus continuously increasing in size forming an indistinct antennal club.Antennal scrobes strongly developed, with an acute and marked dorsal margin; the frontal carinae short.
Compound eyes oval-shaped from lateral view and convex from dorsal view, with the margin of the compound eyes protruding from the sides of the head (see Fig 3.4;Fig S1.7A and S1.7B).Diameter of the compound eyes spans slightly over one third of HL (REL 0.36-0.39).Maximum diameter of compound eyes ranges from 0.45 to 0.5 mm.Ocelli relatively small in diameter.Diameter of median ocellus (OW) always smaller than distance between lateral ocelli (OD1).
Mesoscutum convexly rounded anterodorsally.Mesoscutellum nearly in horizontal plane in lateral view.Propodeum flattened dorsally and then drops off at angle of approximately 45° posterior of the propodeal spiracle.Mesoscutum relatively short, stretching out over less than half of the alitrunk in lateral view.In dorsal view, the posterior margin of the propodeum slightly convexly rounded and the mesonotum broadly triangular.Propodeum not armed with spines.
Node of petiole and postpetiole in dorsal view rounded.Petiole as wide as or wider than the postpetiole (mean PI: 1.05).In lateral view petiole anterodorsally flattened and sloping downwards and slightly longer than the postpetiole.Postpetiole round in dorsal and lateral view without distinct nodes.(See Table 1 for comparative overview of queen characters.)

Distribution and biology
Crematogaster claudiae is endemic to Borneo, possibly even to Sabah (see below).The species had mainly been found on two different species of the section Pachystemon (M.glandibracteolata and M. indistincta).We have evidence that this species may hybridize (at least locally) with Crematogaster captiosa (in Poring Hot Spring) and presumably fertile offspring (queens) can be produced by rare hybrid queens (Feldhaar et al., 2008;Feldhaar et al., 2010).
In comparison to all other species of the captiosasubgroup the queens have relatively small compound eyes (smaller than 0.5 mm) and an earlier onset of reproduction, when colonies comprise approximately 500 workers.Unlike the queens of other captiosa-subgroup species, queens of C. claudiae only colonize saplings.. Two samples contained in the phylogeny based on mitochondrial DNA (Feldhaar et al., 2010) collected in Sarawak cluster with samples of C. claudiae from Sabah (see above in distribution and biology of C. hullettii).Thus, we can currently not exclude that C. claudiae has a wider distributional range than Sabah only.In former publications by our group this species was referred to as Crematogaster msp. 10 (Feldhaar et al., 2008;Feldhaar et al., 2010).

Non-Macaranga associated Crematogaster (formerly Decacrema) from Borneo and Peninsula Malaysia
Three further species of the former subgenus Decacrema have been collected and described from the distributional range of the Crematogaster-Macaranga association: C. angulosa André, C. biformis André and C. cephalotes Smith.As only geographic regions of sampling locality were given but no other information we examined the type material (see supplementary material).We found no match with our specimens from Macaranga.Propodeal spines of Crematogaster angulosa and C. cephalotes are considerably stronger and also longer in proportion to the thorax in comparison to obligately Macaranga-associated Crematogaster species, which may be an adaptation to the life-style in the latter group (Fiala & Maschwitz, 1990).In contrast to the Macaranga-associated Crematogaster borneensis-group species all three species are dimorphic and possess a pronounced metanotal groove.

Concluding remarks
More species may be present in other regions within the distribution range of this ant-plant symbiosis that were not extensively sampled by us (such as Sumatra), which is due to the fact that we (as well as other research groups) conducted most of our ecological studies in the regions treated here.Quek et al. (2007) have sampled over the entire distributional range of the association, and have found 19 distinct lineages of Macarangaassociated Crematogaster (Crematogaster borneensis-group) based on mitochondrial DNA.Lineages between Peninsula Malaysia and Sumatra overlapped greatly (with only one endemic haplotype in Sumatra), and our limited material from Sumatra suggest that species between these two land masses may also overlap in morphology and colonize the same host plants (see also Fiala et al., 1999).Crematogaster roslihashimi, and C. maryatii do not occur on Sumatra.The number of lineages found in Borneo was considerably greater, with ten lineages found exclusively there (Quek et al., 2007).The number of lineages based on mitochondrial DNA may overestimate the number of species present in a given area though, as we have found that within-species sequence divergence can be very high (e.g. up to 14% within C. maryatii, formerly C. msp.7 among samples collected only 50 km apart (Feldhaar et al., 2010)).Similarly high intraspecific divergence of mitochondrial DNA lineages has also been described within Crematogaster kelleri Forel, 1891(Blaimer & Fisher, 2013).In contrast, the morphologically distinct species C. decamera and C. roslihashimi show only very little genetic differentiation on Peninsula Malaysia (Feldhaar et al., 2003a;Feldhaar et al., 2010).In spite of large intraspecific variation of mitochondrial DNA, nuclear markers have underscored our species concept based on morphology.Microsatellite markers of five of the seven species analysed (Feldhaar et al., 2004;Feldhaar et al., 2010;Türke et al., 2010, unpubl. results) show species-specific patterns that are congruent with the species described here.Based on nuclear DNA only these would thus be considered the same lineage.In contrast to Ueda et al. (2015) we found no complete congruence of mtDNA and microsatellite markers.They excluded geographical variability by using samples collected from a single site.Nonetheless they also found admixture and thus evidence for hybridization in 3% of their samples.In conclusion, our data suggests that the number of species described here may be close to the number of species found even with geographically more extensive sampling.For the time being, the present classification will in any case allow to apply species names in future studies instead of morphospecies numbers varying among different authors that cannot be assigned without reference material.
In general, queens as well as workers of all species are quite variable in morphometric measurements.We have found consistent geographic variability among species, e.g. with queens of C. decamera collected from Peninsula Malaysia having generally smaller heads than those collected from Borneo.Nonetheless absolute measurements of queens will generally allow species identification.As workers vary considerably in size in dependence of colony size only relative measurements allow specification (e.g.SI or PI).The total body length of workers by up to one third in workers from small to those from large and older colonies.Likewise, workers of all species described above tend to be darker in colour with increasing colony size.
In former publications we had included Crematogaster morphospecies 5 (Fiala et al., 1999) based on its seeming endemism, as it was found in Sarawak (Lambir Hills) only with a strong host plant preference.In addition, those queens grouped into C. msp. 5 possessed slightly darker longitudinal stripes on the upper surface of the thorax.However, when later comparing a larger number of queens of all species of the captiosa-group, comparatively lightly coloured individuals often also bore these stripes.Here, we have neither described it as a new species nor could we attribute it to a formerly described species.Individuals formerly subsumed under this morphospecies could not be grouped into a species distinctly different from other species described here.Likewise, individuals of this morphospecies did not form a distinct clade in a molecular phylogeny (Feldhaar et al., 2003b;Feldhaar et al., 2010).Based on their morphological characters the few individuals (queens) ever assigned to C. msp. 5 show a combination of characters that would group them with either C. borneensis, C. linsenmairi or C. captiosa, but usually with one character contradicting the others and hampering a distinct placement into either species.However, as we have found individuals of different species of the captiosa-group (C.claudiae and C. captiosa) to hybridize locally (Feldhaar et al., 2008;Feldhaar et al., 2010) individual queens with phenotypes intermediate between two species of the captiosa-group may be the result of such hybridization events.We found a hybridization level of 2.5% (Feldhaar et al. 2008), which is nearly congruent with that published by Ueda et al. (2015).Hybridization events may tend to be more common in areas with relatively small population sizes of potentially hybridizing species such as small islands or isolated patches containing few Macaranga hosts only.
Species identification of Macaranga-associated Crematogaster (Crematogaster borneensis-group) is easier and more conclusive based on queens as they possess more distinct characters than workers (i.e.length of compound eyes and the ocelli; see Table 1 for overview of distinct characters).Female sexuals can often be collected easily and should be collected together with workers.Queens tend to be in the lower part of the stem in small host plants recently colonized.Once Macaranga hosts grow larger the queen remains in the lower part of the lignified tree trunks and then becomes almost inaccessible (Feldhaar et al., 2003b).Nonetheless, virgin queens can often be collected together with workers by cutting off a larger branch of the host.After the reproductive stage has been reached by the colony, female as well as male sexuals are often present and can often be found in the proximal part of the branches close to tree trunks.In this way sexuals can be collected without destroying the whole colony.Crematogaster (Crematogaster borneensis-group) associated with Macaranga have never been observed away from their hosts, with the exception of queens and males during mating flights.Colonies never extend over more than one host tree.Identity of the host-plant can help to confirm species identification; a myrmecologist with limited knowledge of Macaranga species should at least pay attention to whether the host plant´s stem is covered by a glaucous waxcover or not as most Macaranga-associated Decacrema species will either colonize waxy or non-waxy hosts.a decade of support of our work.We acknowledge the help of members of Sabah Parks, namely Jamili Nais, and Maklarin bin Lakim.We are very thankful to K. Eduard Linsenmair who provided logistic and financial support and help in many other ways -but especially years of fruitful discussions on the Crematogaster -Macaranga symbiosis.Phil Ward was very helpful as he kindly introduced HF to the task of describing species.The opportunity to visit Phil Ward at UC Davis was enabled by Jürgen Gadau, providing money for the trip (funding from the SFB 554 Arthropod behaviour by the German Research Foundation (DFG)) as well as a grant to HF within the DFG Priority programm SPP 1127 "Adaptive radiations" (grant FE631/1-2).The DFG also supported UM and BF in earlier stages of our studies.BF also thanks DAAD (Deutscher Akademischer Austauschdienst) for several travel grants.Bonnie Blaimer, Mark-Oliver Rödel, Penny Gullan, Dirk Mezger and Harald Zettel provided helpful comments on an earlier version of this manuscript.We are also grateful to Brian Heterick and an anonymous referee for very helpful comments that greatly improved the manuscript.Special thanks are due to Jack Longino who very much helped us with our first efforts to sort Crematogaster ants at the beginning of our studies.Permissions to conduct research in Malaysia were kindly granted by the Economic Planning Unit (EPU) of the Prime Minister´s Office, Kuala Lumpur, the EPU in Kota Kinabalu, Sabah as well as by the Danum Valley Management Committee and the Forest Department, Sarawak.We are grateful to colleagues collecting and providing ant samples, namely Daniela Guicking, Hans-Peter Heckroth, Armin Jakob, Rainer Kern, Annika Meenken, Ute Moog and Ferry Slik.

Fig 1 .
Fig 1.Standard measurements of Crematogaster workers and queens.See text for definitions.

6 6a
Eye length (EL) between 0.34 to 0.38 mm.HL < 1.22, HW 1.01 -1.2 mm.Compound eyes relatively small in relation to head length in lateral view (REL 0.28 -0.34; Fig 3.7; Fig S1.6A and S1.6B).The first three segments (distal) of the flagellum of the antenna form a distinct club.Species found on Borneo (Sabah, Sarawak, East Kalimantan), mostly on waxy host plants of the section Pachystemon (M.havilandii, M. hypoleuca, M. motleyana) and rarely on the non-waxy M. angulata and M. indistincta (in primary forest or at higher elevation).
André, 1896 C. linsenmairi sp.nov.C. captiosa Forel, 1911 C. claudiae sp.nov.Diagnosis Species of the Crematogaster (Decacrema) captiosasubgroup have relatively large queens with large compound eyes with EL > 0.5 mm (except for C. claudiae (EL 0.45 -0.5 mm) whose queens are generally smaller than the queens of the other species within this group).Queens are medium to light brown in colour.Workers of C. borneensis, C. linsenmairi and C. captiosa possess long and acute propodeal spines.

Table 1 .
Overview of most distinct morphological characters of the Macaranga-associated Crematogaster (borneensis-group) species.