Contributions to Zoology, 78 (1) - 2009Sara Rocha; Ivan Ineich; D. James Harris: Cryptic variation and recent bipolar range expansion within the Stumped-Toed Gecko Gehyra mutilata across Indian and Pacific Ocean islands

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Introduction

Geckos of the genus Gehyra (Gray, 1834) are some of the most prominent and widespread geckos within the Australasian and Pacific regions. Gehyra mutilata (Wiegmann, 1834) is widespread throughout the Pacific basin, large regions of Southeast Asia, Indonesia and the Indian Ocean. It also occurs in Mexico and it is known to have been introduced in California (USA) and in the French Guiana (Ineich and de Massary, 1997). It occurs in both natural forests and disturbed garden or urban areas and it is the least studied widespread gecko in the world, with little information available on genetic or morphological variation across its distribution.

Fisher (1997) examined allozyme variation within this species across some Southeast Asian (Thailand, Philippines) and Pacific (from Belau to Hawaii) localities and found that 1) samples across the Pacific showed no genetic variation for the loci surveyed, and 2) there were fixed differences at three loci between a group consisting of the Pacific and two southern Asian populations (the ‘southern mainland type’, sensu Fisher, 1997) and a second group of four southern Asian populations (the ‘northern mainland type’, sensu Fisher, 1997). Both groups were present in the Philippines and in Thailand, although sympatry was not found. Fisher (1997) interpreted his results as indicating that the source of the Pacific populations was probably southern Asia and pointed to a recent, possibly human-mediated, range expansion, but the lack of variation at these markers prevented assessment of alternative dispersal hypotheses. Indian Ocean populations were not studied, despite the fact that they are considered to have been introduced throughout this region (Cheke, 1984). It has been assumed (de Massary, 1992; I. Ineich quoted in Glaw and Vences, 1994) that Gehyra populations of Indonesia and from the western Indian Ocean islands are distinct from those of Oceania, and that G. insulensis should be resurrected and used as the proper designation for some or all Pacific populations. Faster evolving mtDNA data could provide increased resolution regarding genetic variation of G. mutilata across the Pacific and could help in assessing the source and mechanisms related to the origin of Indian Ocean islands populations.

FIG2

Fig. 2. ME tree for the 517bp data matrix (complete gap deletion option) with bootstrap values shown alongside the branches. The two haplotypes from the Pacific Ocean clade and the two main clades are separated by two and 53 mutational steps, respectively.

It is important to assess the mechanisms explaining the presence of this species in oceanic islands; introduced reptiles can have varied negative impacts on native species, including predation, competition for food, basking sites and other resources, hybridisation and spread of diseases and parasites, and they may alter the habitat of native species or disrupt ecosystem dynamics. All these processes are especially dangerous when they occur on islands, where the number of endemic species is generally higher and ecosystems are more vulnerable to introductions (Shine et al., 2000). Furthermore, it is on islands that introductions are more frequent and that invasive species have a higher probability of successful establishment (Kraus, 2003). Indeed, several examples exist of strong negative impact of introduced reptiles in island systems (Cogger et al., 1983; Powell et al., 1990; Petren and Case, 1996; Cole et al., 2005).

Our main goal was to assess the origins and genetic variation of Indian Ocean populations of Gehyra mutilata. By comparing them to other southern Asian and Pacific populations, we could assess their putative distinctiveness and better understand previously hypothesised dispersal mechanisms (Fisher, 1997).