MORPHOLOGICAL VARIATION OF MOUNTAIN BLACKEYE POPULATIONS IN MALAYSIAN BORNEO 1 Malays. Appl. Biol. (2012) 41(1): 1–10 * To whom correspondence should be addressed. MORPHOLOGICAL VARIATION OF MOUNTAIN BLACKEYE (Chlorocharis emiliae) POPULATIONS IN MALAYSIAN BORNEO RAMJI, M.F.S. 1* , RAHMAN, M.A. 1 and TUEN, A.A. 2 1 Department of Zoology, Faculty of Resource Science and Technology 2 Institute of Biodiversity and Environmental Conservation Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia. * Email: f_sidq@yahoo.com ABSTRACT The mountain blackeye (Chlorocharis emiliae) is one of the few Bornean endemic birds which presents an excellent model species to illustrate evolution and speciation. Here, we use discriminant function analysis to elucidate the morphological variation on 40 specimens of mountain blackeye from four populations namely Mount Kinabalu, Mount Trus Madi, Mount Murud and Mount Mulu. The test successfully distinguished all four populations accordingly by respective nominated subspecies. Tarsus length and bill length were identified as the best predictors from nine character loadings observed which also included bill depth, bill width, head bill, wing length, wing span, tail length and total length. Along with this, the morphological patterns also revealed that solid skeletal characters such as bill length, bill depth, bill width and tarsus are genuine predictors of morphological variation and body size within species as compared to feather-based characters. The evolution of such morphological traits is more pronounced due to different ecological adaptation of the mountain blackeye populations. Several factors such as phenotypic plasticity, foraging behaviours and food availability may have influenced the morphological variation between the subspecies. Key words: character loading, evolution, foraging behaviours, morphological variation, phenotypic plasticity, subspecies INTRODUCTION The study of speciation is habitually postulated from morphological evolution of populations (Larson, 1989). Since the birth of avian taxonomy, species recognition and geographical variation of Bornean birds had been exhaustively analysed based on raw external features (e.g. Banks, 1952; Mees 1955; Harrison 1955, 1956). With regards to the species studied, taxonomic subdivisions of mountain blackeye into four separate subspecies (C. e. emiliae of Mount Kinabalu, C. e. trinitae of Mount Trus Madi, C. e. moultoni of Mount Murud, Mount Mulu, Mount Pueh and Tama Abo Range, C. e. fusciceps of Mount Maga) were largely influenced by their comparative external features, although they were most heavily emphasized through plumage variation as discussed by previous authors (Mees, 1955; Harrison, 1956). Generally, the mountain blackeye is relatively small in size (11-14 cm of total length) but comparatively bigger than their relatives of white- eyes (9-10 cm) (Smythies 1999, Myers 2009). However, previous literatures inferred that the average tail length measurement of mountain blackeye were comparatively similar to that of majority of Zosterops (Mees, 1955; Harrison, 1956). Among the subspecies, the true emiliae of Mount Kinabalu is slightly larger by size and relative proportions as compared to the moultoni populations occurring in Sarawak (Harrison, 1956). Based on the average tail-index, Mees (1955) discovered that the tail-ratio for emiliae is relatively larger than moultoni of Mount Murud and Mount Pueh, thus concluded that tail length was very pronounced in discriminating the morphological variation between both subspecies. By comparing to Gawin (2006), the discriminant function analysis (DFA) results revealed six significant characters measured from three mountain blackeye populations which are bill length, tarsus length, total length, wing span, head bill and bill width. These findings did not coincide with Mees (1955) tail-index analysis, therefore