DISPERSAL AND EVOLUTION OF THE PACIFIC BASIN GEKKONID LIZARDS GEHYRA OCEANICA AND GEHYRA MUTILATA.

Abstract

The Pacific island geckos Gehyra mutilata and Gehyra oceanica were studied on several Pacific Basin archipelagos to determine the degree that their distributions have been modified by humans (as commensals), through the analysis of protein variation using starch gel electrophoresis. Gehyra mutilata is an anthropophilic species that is widespread in the Pacific Basin and Southeast Asia. No protein variation was found in the Pacific Basin and southern Asia, although there were fixed allelic differences between populations of southern Asia and those further north. These results suggest possible recent human-aided transport across the Pacific from a population that experienced a genetic bottleneck in southern Asia. Gehyra oceanica, based on protein variation, consists of two natural groups in the Pacific, a northern (Micronesian) form and a southern (Melanesian and Polynesian) form. The northern form has very similar gene frequencies across its range in Micronesia. The southern form has its greatest allelic diversity in the south-central Pacific. F-statistics for G. oceanica in the south fall within the range of values in the literature for mainland Australian species of Gehyra that are not human commensals and for other island lizards that have been considered as natural dispersers. These values are consistent with the hypothesis that G. oceanica was naturally dispersed across the Pacific, prior to the arrival of humans and that the equatorial currents are a barrier to natural, north-south gene flow/dispersal in Pacific Basin lizards. However, human-aided dispersal within the northern and southern regions cannot be ruled out. By comparing the ecology of these two species, G. oceanica has the adaptations necessary for natural oversea dispersal, whereas G. mutilata has an ecology consistent with human-mediated dispersal, in support of the conclusions from the genetic data.