Caves as microrefugia: Pleistocene phylogeography of the troglophilic North American scorpion Pseudouroctonus reddelli.

Robert W Bryson,Warren E Savary,Lorenzo Prendini,Peter B Pearman

doi:10.1186/1471-2148-14-9

Abstract

BackgroundSurvival in microrefugia represents an important paradigm in phylogeography for explaining rapid postglacial re-colonization by species in temperate regions. Microrefugia may allow populations to persist in areas where the climatic conditions on the surface have become unfavourable. Caves generally contain stable microclimates and may represent microrefugia for species capable of exploiting both cave and surface habitats (troglophiles). We examine the phylogeography of the troglophilic North American vaejovid scorpion Pseudouroctonus reddelli using 1,993 base pairs of mitochondrial and nuclear DNA sequence data generated from 12 populations. We use (i) descriptive measures of genetic diversity and population genetics statistics, (ii) reconstructions of phylogeographical structure, spatial diffusion during diversification, and population sizes through time, and (iii) species distribution modelling to test predictions of the hypothesis that caves serve as microrefugia. We compare phylogeographical patterns in P. reddelli with other troglophilic species across the Edwards Plateau karst region of Texas.ResultsResults revealed high haplotype and nucleotide diversity and substantial phylogeographical structure, probably generated during the Pleistocene. Spatial diffusion occurred along the southern edge of the Edwards Plateau from multiple refugia along the Balcones Escarpment. There was little evidence for population and geographical expansion. Species distribution models predicted substantial reductions in suitable epigean habitat for P. reddelli at the Last Glacial Maximum (LGM).ConclusionsHigh genetic diversity, strong phylogeographical structure, diffusion from multiple refugia, and unfavourable climatic conditions at the LGM collectively support the hypothesis that caves served as microrefugia for P. reddelli. Similar patterns of genetic structure in P. reddelli and other troglophilic species across the Edwards Plateau karst region of Texas suggest that caves serving as microrefugia are important for the formation, maintenance, and future survival of troglophilic species in temperate karst regions.

Highlights

Survival in microrefugia represents an important paradigm in phylogeography for explaining rapid postglacial re-colonization by species in temperate regions
We examine the phylogeography of P. reddelli using mitochondrial and nuclear DNA sequence data generated from 12 populations
The observed high genetic diversity, strong phylogeographical structure, spatial diffusion from multiple refugia, and unfavourable climatic conditions at the Last Glacial Maximum (LGM) collectively support the hypothesis that caves served as microrefugia for P. reddelli

Summary

Introduction

Survival in microrefugia represents an important paradigm in phylogeography for explaining rapid postglacial re-colonization by species in temperate regions. Microrefugia may allow populations to persist in areas where the climatic conditions on the surface have become unfavourable. The dramatic climatic oscillations of the Pleistocene profoundly impacted the geographical distribution and genetic structure of species in North America [1,2,3]. Microrefugia are small areas “with local favourable environmental features, in which small populations can survive outside their main distribution area, protected from the unfavourable regional environmental conditions” [14]) to explain discordant genetic structure and predicted paleo-distributions, species may have persisted in scattered microrefugia that supported isolated, low-density populations beyond their inferred distributional boundaries during the Pleistocene [12] Rather than invoking unrealistic long-distance dispersal (e.g. [13]) or ecological niche shifts (e.g. [14]) to explain discordant genetic structure and predicted paleo-distributions, species may have persisted in scattered microrefugia that supported isolated, low-density populations beyond their inferred distributional boundaries during the Pleistocene [12]

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Discussion

Conclusion