Life-history traits and ontogenetic colour change in an arboreal tropical python, Morelia viridis D. Wilson 1 , R. Heinsohn 1 & J. Wood 2 1 Centre for Resource and Environmental Studies, Australian National University, Canberra, Australia 2 Statistical Consulting Unit, Australian National University, Canberra, Australia Keywords green python; Pythonidae; growth; sexual dimorphism; sex ratio. Correspondence David Wilson, Centre for Resource and Environmental Studies, Australian National University, Canberra 0200, Australia. Tel: +61 2 61256777; Fax: +61 2 61250757 Email: davidw@cres.anu.edu.au Received 17 October 2005; accepted 25 April 2006 doi:10.1111/j.1469-7998.2006.00190.x Abstract The Pythonidae are a widely distributed group of snakes that fill a variety of niches in Africa, Asia and Australasia. We used mark–recapture techniques to describe the life-history traits and colour change in the green python Morelia viridis,a species that is popular in the captive pet industry but poorly known in the wild. Modelling of growth rates revealed that males and females reach sexual maturity after 2.4 and 3.6 years, respectively, and are predicted to live for at least 15 years. Extrapolation from small individuals revealed a highly seasonal breeding period with hatching in late November. However, few hatchlings were recorded in any one year, suggesting that adults do not breed every year. The adult sex ratio did not differ from parity, but immature females outnumbered immature males. Approxi- mately 50% of all snakes captured were adult sized. Sexual dimorphism was not detected in the adults, but juvenile females have larger heads than males. Ontogenetic colour change (OCC) from yellow to green occurred between 53 and 59 cm and, based on growth rates, occurs at c. 1 year of age. This change took place rapidly without an associated shedding of skin. Green pythons have a slow life history, and populations may be vulnerable to removal of individuals for the captive pet trade. They also provide excellent opportunities for examining the evolutionary significance of OCC. Introduction The pythons (Pythonidae) are a widely distributed family of c. 24 species occurring in tropical, sub-tropical and tempe- rate areas of Africa, Asia and Australasia (Greer, 1997). Pythons have radiated extensively, with species filling ecolo- gically diverse niches from the desert to the tropical rain- forest and aquatic ecosystems (Barker & Barker, 1994). They range in size from the diminutive pygmy python Antaresia perthensis, which reaches 47 cm (Shine & Slip, 1990), to the giant reticulated python Python reticulatus of South East Asia, which has been recorded close to 9 m in length (Murphy & Henderson, 1997). Adult pythons are predominantly ambush predators of mammals, but some have specialized to feed on reptiles, birds, fish, frogs or invertebrates, and many show ontogenetic changes in diet (Slip & Shine, 1988; Greer, 1997; Shine et al., 1998). In some areas pythons are an important ecosystem predator and can maintain very high densities (Groombridge & Luxmoore, 1991; Shine & Madsen, 1997; Shine et al., 1998). Pythons show remarkable variation in both body coloration and patterns between species, resulting in high demand from the captive pet trade and for skins for the leather industry. Some species may be threatened by the skin and captive pet trades (Groombridge & Luxmoore, 1991; Jenkins & Broad, 1994), although the true extent of the problem is rarely known. Green pythons Morelia viridis are one of the smaller pythons and occur throughout New Guinea and far north- ern Australia (Barker & Barker, 1994; O’Shea, 1996). They inhabit lowland and low montane rainforests, secondary forests and regrowth areas, ranging from sea level to low– mid-montane forest (O’Shea, 1996). There are several fea- tures that make the green python interesting for study. It is the most arboreal python and is almost exclusively noctur- nal (Greer, 1997), rarely being observed on the ground or during the day. Females are known to maintain a defined home range but males adopt a roaming mate-searching strategy (Wilson, Heinsohn & Legge, in press), and both the roaming strategy and sexual dichotomy are rare among snakes (Macartney, Gregory & Larsen, 1988). The most striking feature of green pythons, however, and one that sets them apart from almost all other snake species is their extreme juvenile dichromatism and subsequent ontogenetic colour change (OCC). Individuals hatch as one of two colour morphs, bright yellow or ‘brick’ red, and both morphs may exist in a single clutch. Only the yellow neonate morph has thus far been recorded in Australia (Barker & Barker, 1994). The distribution of red morph juveniles is poorly known, but includes the Baliem Valley and the island of Biak in Papua, Indonesia and areas in the Sepik basin of Papua New Guinea (G. Maxwell, pers. comm.; Rawlings & Donnellan, 2003). Both colour morphs subsequently Journal of Zoology 270 (2006) 399–407 c  2006 The Authors. Journal compilation c  2006 The Zoological Society of London 399 Journal of Zoology. Print ISSN 0952-8369