Alpine Crossroads or Origin of Genetic Diversity? Comparative Phylogeography of Two Sympatric Microgastropod Species

Alexander M Weigand,Markus Pfenninger,Annette Klussmann-Kolb,Adrienne Jochum

doi:10.1371/journal.pone.0037089

Abstract

The Alpine Region, constituting the Alps and the Dinaric Alps, has played a major role in the formation of current patterns of biodiversity either as a contact zone of postglacial expanding lineages or as the origin of genetic diversity. In our study, we tested these hypotheses for two widespread, sympatric microgastropod taxa – Carychium minimum O.F. Müller, 1774 and Carychium tridentatum (Risso, 1826) (Gastropoda, Eupulmonata, Carychiidae) – by using COI sequence data and species potential distribution models analyzed in a statistical phylogeographical framework. Additionally, we examined disjunct transatlantic populations of those taxa from the Azores and North America. In general, both Carychium taxa demonstrate a genetic structure composed of several differentiated haplotype lineages most likely resulting from allopatric diversification in isolated refugial areas during the Pleistocene glacial periods. However, the genetic structure of Carychium minimum is more pronounced, which can be attributed to ecological constraints relating to habitat proximity to permanent bodies of water. For most of the Carychium lineages, the broader Alpine Region was identified as the likely origin of genetic diversity. Several lineages are endemic to the broader Alpine Region whereas a single lineage per species underwent a postglacial expansion to (re)colonize previously unsuitable habitats, e.g. in Northern Europe. The source populations of those expanding lineages can be traced back to the Eastern and Western Alps. Consequently, we identify the Alpine Region as a significant ‘hot-spot’ for the formation of genetic diversity within European Carychium lineages. Passive dispersal via anthropogenic means best explains the presence of transatlantic European Carychium populations on the Azores and in North America. We conclude that passive (anthropogenic) transport could mislead the interpretation of observed phylogeographical patterns in general.

Highlights

Alternations of glacial and interglacial periods as results of climatic fluctuations of the Pliocene and Pleistocene periods most likely triggered the formation of current patterns of biodiversity
We focused on the taxon Carychium (Gastropoda, Pulmonata, Carychiidae), which comprises a group of Holarctic microgastropods inhabiting superficial subterranean habitats [23,24]
Genetic and haplotype diversity The c oxidase subunit I (COI) datasets have a length of 590 homologous base pairs

Summary

Introduction

Alternations of glacial and interglacial periods as results of climatic fluctuations of the Pliocene and Pleistocene periods most likely triggered the formation of current patterns of biodiversity. A frequent observation is the decrease in genetic diversity from the European south to north [10], which led to the ‘southern richness’ versus ‘northern poverty’ hypothesis. This condition can be ascribed to more frequently inhabited (or permanent) southern refugia, possessing a higher population size and genetic diversity than more northern areas, which are only occupied during favorable conditions after bottleneck events of range expansions. Because phylogeographical patterns are highly individualistic and depend upon historical contingency as well as the characteristics specific to the taxa under study (e.g. climatic tolerance, mode of dispersal), it is important to test these hypotheses for a wide range and large number of taxa [8,12,13]

Objectives

Methods

Results

Conclusion