Reconciling paleodistribution models and comparative phylogeography in the Wet Tropics rainforest land snailGnarosophia bellendenkerensis(Brazier 1875)

Abstract

Comparative phylogeography has proved useful for investigating biological responses to past climate change and is strongest when combined with extrinsic hypotheses derived from the fossil record or geology. However, the rarity of species with sufficient, spatially explicit fossil evidence restricts the application of this method. Here, we develop an alternative approach in which spatial models of predicted species distributions under serial paleoclimates are compared with a molecular phylogeography, in this case for a snail endemic to the rainforests of North Queensland, Australia. We also compare the phylogeography of the snail to those from several endemic vertebrates and use consilience across all of these approaches to enhance biogeographical inference for this rainforest fauna. The snail mtDNA phylogeography is consistent with predictions from paleoclimate modeling in relation to the location and size of climatic refugia through the late Pleistocene-Holocene and broad patterns of extinction and recolonization. There is general agreement between quantitative estimates of population expansion from sequence data (using likelihood and coalescent methods) vs. distributional modeling. The snail phylogeography represents a composite of both common and idiosyncratic patterns seen among vertebrates, reflecting the geographically finer scale of persistence and subdivision in the snail. In general, this multifaceted approach, combining spatially explicit paleoclimatological models and comparative phylogeography, provides a powerful approach to locating historical refugia and understanding species' responses to them. P hylogeography seeks to reveal biogeographical history of species and the habitats they occupy via (i) qualitative spatial association of divisions between monophyletic clusters of alleles with biogeographic barriers, and (ii) quantitative estimates of historical population size (1-4). Much of this work has focused on mitochondrial DNA; however, stochastic variance limits our confidence in reconstructions of history from a single gene. One approach solving this limitation is to sample more genes (5). A more common approach is comparative phylogeography (6) in which sequence variation is surveyed at a single gene for multiple species across the same landscape. A limitation here is that histories of local extinction and recolonization may vary among species despite a common history of habitat fluctuation.To improve inference of historical biogeography, we need to incorporate spatially explicit evidence from paleoecology into interpretation of species' phylogeography. Some recent studies have promoted the use of fossil evidence along with phylogeography to estimate historical distributions (7) or have examined sequence variation in the fossils themselves (e.g., refs. 8 and 9) However, appropriate fossils are sparse or nonexistent for most taxa. We explore a novel and more widely applicable approach that uses paleoclimatological models of species' distributions in conjunction with phylogeography.

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