Fine-scale genetic structure arises during range expansion of an invasive gecko.

Kristen Harfmann Short,Kenneth Petren,Robert C Fleischer

doi:10.1371/journal.pone.0026258

Abstract

Processes of range expansion are increasingly important in light of current concerns about invasive species and range shifts due to climate change. Theoretical studies suggest that genetic structuring may occur during range expansion. Ephemeral genetic structure can have important evolutionary implications, such as propagating genetic changes along the wave front of expansion, yet few studies have shown evidence of such structure. We tested the hypothesis that genetic structure arises during range expansion in Hemidactylus mabouia, a nocturnal African gecko recently introduced to Florida, USA. Twelve highly variable microsatellite loci were used to screen 418 individuals collected from 43 locations from four sampling sites across Florida, representing a gradient from earlier (∼1990s) to very recent colonization. We found earlier colonized locations had little detectable genetic structure and higher allelic richness than more recently colonized locations. Genetic structuring was pronounced among locations at spatial scales of tens to hundreds of meters near the leading edge of range expansion. Despite the rapid pace of range expansion in this introduced gecko, dispersal is limited among many suitable habitat patches. Fine-scale genetic structure is likely the result of founder effects during colonization of suitable habitat patches. It may be obscured over time and by scale-dependent modes of dispersal. Further studies are needed to determine if such genetic structure affects adaptation and trait evolution in range expansions and range shifts.

Highlights

Genetic structure often arises as the result of restricted gene flow and genetic drift among populations over relatively long periods of time [1]
There was no evidence for isolation by distance (IBD) at any of the four sites according to Mantel tests, most likely because populations are not at equilibrium
Genetic processes of range expansion may be important for understanding natural range expansions, biological invasions, and tracking of habitat shifts due to climate change [51,52]

Summary

Introduction

Genetic structure often arises as the result of restricted gene flow and genetic drift among populations over relatively long periods of time [1]. At first this may seem counterintuitive because expanding populations are typically large, but structure arises primarily at the leading edge of the expansion where population sizes can be quite small [2,3]. When dispersal is limited in a patchy environment, colonization of new populations at the leading edge of range expansion can create genetic structure reflecting small founding populations that carry only a subset of genetic diversity and are isolated from other sources of migrants [2,3]. Gene flow among populations may erode structure [4,5], but even temporary genetic structure at the leading edge can have lasting effects on the evolutionary trajectory of an expanding population. Understanding the dynamics at the leading edge of range expansion is critically important, because range expansions associated with biological invasions are increasing, and because range shifts, which require expansion in at least one direction, are expected to occur broadly due to climate change [10,11]

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Discussion

Conclusion