15 DOES SEXUAL DIMORPHISM EXIST IN SQUIRRELS? A CASE OF FIVE SPECIES OF GENUS CALLOSCIURUS (CALLOSCIURINAE) OF PENINSULAR THAILAND WITH KEYS TO SPECIES Ngagyel Tenzin, 1* Chutamus Satasook, 1, 2 Sara Bumrungsri 1 & Paul J. J. Bates 3 ABSTRACT Sexual dimorphism of four species of Genus Callosciurus (Callosciurus prevostii, Callosciurus notatus, Callosciurus caniceps and Callosciurus erythraeus) in Peninsular Thailand was examined. Callosciurus nigrovittatus was excluded owing to lack of data. A series of Mann Whitney test performed showed no significant difference between the sexes (no sexual dimorphism) in the external measurements, although males are slightly larger than most other species. However, Breadth of rostrum and Height of brain case for Callosciurus erythraeus of the male skull was significantly larger than female. In contrast to others, female Callosciurus prevostii is larger than male, but the sample size was too small to make a meaningful conclusion. Dichotomous keys to species are also constructed based on external and cranial characters. Key words: Callosciurus, dichotomous keys, sexual dimorphism, squirrel. 1Department of Biology, Faculty of Science, Prince of Songkla University, Hatyai 90112, Thailand E- mail : [email protected] 2Princess Maha Chakri Sirindhorn Natural History Museum, Faculty of Science, Prince of Songkla University, Hatyai 90112, Thailand 3Harrison Institute, Centre for Systematics and Biodiversity Research, Bowerwood House, St. Botolph’s Road, Sevenoaks, Kent, TN13 3AQ, Great Britian. u ~ (JPMI<GJA5DG?GDA@DI2C<DG<I?4JG ,J 16 INTRODUCTION Sexual dimorphism is a term used to describe any variation between the two sexes within the same species, a pattern shaped due to sexual selection over space and time. Generally both males and females in case of squirrels are same in size and colouration and may be difficult to identify externally (Gorrell et al., 2012). The information on sexual dimorphism is vital for taxonomical and ecological research. For morphometric-based species classification, in the early stage, taxonomists have to examine whether the sexual variation is present in species or not. In terms of ecology, sexual dimorphism can indicate that the food habits of male and female squirrels are different at least during certain times of the year (Koprowski & Corse 2001). This tells us about the intensity of squirrels as pests in different sexes. Understanding this kind of feeding ecology could greatly enhance the understanding of wildlife conservationists and agriculturalists. It would also help understand the nature of dispersal and their significance to ecosystem. For example natal dispersal is believed to be common in birds and mammals, but the pattern is different for males and females (Holekamp & Sherman 1989). It means that the seed dispersed or the pollen carried by these animals is different for males and females. In addition, it is also useful in field of paleontogy and zoonoses. Thus, as a primary gateway to any kind of researches in squirrels, identifying dimorphism is inevitable. Of the large diversity in Southeast Asia, 17 species in 8 genera occur in Thailand which accounts for slightly more than 60 % of the SE Asian squirrels (Lekagul & McNeely 1988; Corbet & Hill 1992; Wilson & Reeder 2005; Francis 2008; Thorington et al. 2012). However, the natural history of most species is poorly known as some of the squirrels are highly variable or taxonomically complex (example: Callosciurus finlaysonii, C. erythraeus and species of genus Tamiops). Koprowski (2008) remarked about the very few scientific publications of squirrels from this region, inspite of the fact that SE Asia is u ~ (JPMI<GJA5DG?GDA@DI2C<DG<I?4JG ,J 17 harbouring maximum squirrel diversity. Squirrels are the indicators of forest health (Koprowski 2008), but with rapid economical development, and population growth, lowland tropical rain forests defragmentation has triggered the significant loss of these rich biodiversity (Tex, 2011). Thus, it has now become a subject of conservation concern and increased effort should be made towards understanding their occurrence, biology and taxonomy in particular. MATERIALS AND METHODS Study site: All of the specimens examined were the voucher specimen from Thailand’s Natural History Museum (THNHM), Pathumthani. A total of 53 skulls and skins [35 ♂♂, 18 ♀♀] were evaluated from 2010 to 2012. To provide insight into further study of these squirrels, localities and list of specimens are provided in the appendix. The geographic coordinates are centered on the locality, when original description was not clear. u ~ (JPMI<GJA5DG?GDA@DI2C<DG<I?4JG ,J 18 Figure 1: Distribution map of Specimens of four species of genus Callosciurus in Thailand. Block squares [1-5] = Localities of specimens of Callosciurus prevostii. Open circles [6-15) = Localities of specimens of Callosciurus notatus. Open squares [16-31] = Localities of specimens of Callosciurus caniceps. Block circles [32-53] = Localities of specimens of Callosciurus erythraeus. Refer appendix for details. u ~ (JPMI<GJA5DG?GDA@DI2C<DG<I?4JG ,J 19 DATA COLLECTION Measurements: The external measurements and the localities mentioned in the voucher specimens were carefully noted. Skull characters mentioned below were measured up to maximum of 20 adult specimens for one species including males and females (When available). External measurements followed Francis (2008), and cranial measurements followed Lunde & Son (2001). All the measurements were taken using digital caliper. External characters included are: Head and body length (HB): tip of nose to dorsal inflection point of tail, Tail length (T): dorsal inflection point of tail to tip of the last vertebra, Ear length (E): inside of ear from lower notch to outermost margin of pinna, Hind foot length (HF): heel to tip of foot (Excluding claws), Weight (Wt.): body weight. Cranial characters included are: Occipitonasal Length (ONL): The distance from the tip of the nasal to the posterior margin of the occipital, Zygomatic Breadth (ZB): The greatest breadth across the zygomatic arches, Interorbital Breadth (IB): The least distance, as viewed dorsally, across the frontal bones between the orbital fossae, Length of Rostrum (LR): The distance from the tip of the nasal bones to the posterior margin of the zygomatic notch (the anterior edge of the dorsal maxillary root of the zygomatic plate), Height of Braincase (HBC): The distance from the top of the braincase to the ventral surface of the basisphenoid bone, Length of Nasals (LN): The distance from the anterior tip of the nasal bones to the most posterior suture between the nasal and frontal bones, measured parallel to the surface of the nasals, Length of Diastema (LD): The distance from the posterior alveolar margins of the upper incisor to the anterior to the anterior alveolar margins of the first upper molars, Post Palatal Length (PPL): The distance from the posterior margins of the palatal bridge to the posterior edge of the basioccipital bone (the ventral lip of the foramen magnum), Palatal Length (PL): The distance from the anterior u ~ (JPMI<GJA5DG?GDA@DI2C<DG<I?4JG ,J 20 alveolar margins of the incisors to the posterior edge of the palatal bridge, Mandible length (ML): The greatest distance from the most posterior part of the condyle to the most anterior part of the mandible, excluding the lower incisors. Photography: Photographs of voucher specimens of 5 species of the genus were taken to record pelage colour. Photos of skulls were also taken. Data analysis: To determine whether there was sexual dimorphism within the taxa and the significant differences in metric characters (external characters and cranial characters) between taxa, a series of Mann Whitney-test were run at a confidence level of 95%. In addition skull characters were evaluated comparatively to score the diagnostic characters. Principal Component Analysis (PCA) performed on correlation matrix was used for multivariate comparisons for both males and females. RESULT External measurements suggested that females of species Callosciurus caniceps, Callosciurus erythraeus and Callosciurus notatus are slightly smaller than males (Table 1). Similarly 10 cranial characters measured also showed that males are slightly larger than females. However, statistical tests inferred that there is no significant variation between sexes for any of the external measurement. Of 10 cranial characters measured, two were found significant in one species C. erythraeus (Table 2). Breadth of rostrum (BR) and Height of brain Case (HBC) were found significant in Callosciurus erythraeus (Table 2), suggesting BR and HBC in males were larger than females. Also a multivariate analysis (PCA) performed based on 23 cranial characters for both males and females in this species formed discrete grouping indicating sexual dimorphism (Fig. 2). Both external and cranial measurements suggested that females in Callosciurus prevostii have larger skulls, but the sample size (n = 2 ♂♂, n = 2 ♀♀) is too small to make any u ~ (JPMI<GJA5DG?GDA@DI2C<DG<I?4JG ,J 21 meaningful conclusions (Table 2). Externally females posses 2-3 pairs of mammae (teats), while males have large scrotal sacs. Unlike some birds, there is no difference in pelage colour between males and females (Moore & Tate 1965). Figure 2: PCA between the first and the second principal components based on 23 cranial characters for both male and female specimens of genus Callosciurus. CEM = ♂ C. erythraeus, CEF=♀ C. erythraeus,