Range expansions in the evolutionary history of western palaeartic aquatic coleoptera

Resumen

A basic question in geographic range issues is to understand why some species are widespread while others closely related are very restricted geographically. In this work I want to contribute to the understanding of the factors that lead some species to expand their original geographic range and suggest some hypothesis to explain the extreme differences in range size among closely related species. For this aim I reconstruct the evolutionary history of various lineages of aquatic beetles distributed in the Western Palearctic area, in the context of the complex geological and climatical history of this area, in order to shed light about the factors that have contributed to the current distribution of species in these groups. All these lineages are typical of running waters (i.e. with poor dispersal abilities), and include both narrowly distributed endemics and widespread species, showing their potential for range expansions. The different biogeographical reconstructions performed suggests the occurrence of several events of range expansions between the eastern and western sides of the Mediterranean Basin under favourable conditions, followed by fragmentation when conditions deteriorate. Range expansions were mainly across the north shore of the Mediterranean as in the south there is virtual absence in the studied groups of species eastern of Tunisia. Despite that it is not possible to establish a common temporal origin for all studied groups, the Miocene, with its various connections and subsequent isolation among the eastern and western sides of the Mediterranean basin, seems to be involved in the origin and east-west disjunction of some groups. However most of the current species were estimated to have originated during the Pleistocene, including those with widespread distributions, being therefore the epoch with a stronger influence in the present-day distribution. The successive rounds of range expansion and fragmentation resulted mainly in the accumulation of narrow range species in the Mediterranean area, especially the Iberian and Anatolian peninsulas. Despite evidence in some cases of speciation with range stasis within the southern Mediterranean area, some species were able to expand their original range reaching widespread distributions in northern areas, likely as a consequence of a privileged geographical position during a narrow window of favourable conditions. However, differences in physiological or ecological tolerances could also have favoured range expansions in some species and limited them in others although further experimental research in the differences in physiological tolerances in these lineages would be necessary to test this hypothesis.