Contributions of biogeographical functions to species accumulation may change over time in refugial regions

Arthur F Sands,Thomas Wilke,Sergej V Sereda,Christian Albrecht,Thomas A Neubauer,Sergei Lazarev,Björn Stelbrink

doi:10.1111/jbi.13590

Arthur F Sands, Thomas Wilke + Show 5 more

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https://doi.org/10.1111/jbi.13590

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Abstract

AbstractAimElevated biodiversity is the result of the cradle, museum or sink functions. The contributions of these three functions to species accumulation and their changes through time remain unknown for glacial refugia. Additionally, our understanding of the role these functions played during pre‐glacial periods is limited. We test for changes in contributions of functions through time leading to the current diversity patterns using a model refugium and taxon.LocationAnatolia, Western Palaearctic.TaxonFreshwater neritid snails (genus Theodoxus).MethodsAssessments were made to define molecular operational taxonomic units (MOTUs) for Theodoxus and reaffirm the genus as a suitable model taxon with elevated interspecific diversity in noted glacial refugia. Thereafter, we constructed a time‐calibrated multilocus Bayesian phylogeny of mtDNA and nDNA by using both fossil data and published substitution rates. Ancestral area estimation was performed on the phylogeny to define the contribution of the functions through time.ResultsAccumulation of Theodoxus diversity in Anatolia over the Miocene–Pliocene transition is attributed to the museum function, but its contribution was small as only few divergence events occurred. The cradle function dominated during the Pliocene and Early Pleistocene, when most interspecific diversity built up and extant lineages in Anatolia were established. The sink function acted from the Middle Pleistocene to present‐day, but with only a small contribution to the total extant Anatolian interspecific diversity.Main conclusionOur results do not entirely mitigate the role glacial cycles played in species accumulation, but highlight Ice Ages may have been less effective in forcing temperate aquatic interspecific diversity into more opportune areas. The elevated diversity in refugia may rather be the result of earlier in situ diversification. Elevated interspecific diversity attributed to the legacy of glacially forced retreats may need to be re‐evaluated in cases where refugia have long and complex geological histories such as Anatolia. These results highlight the importance of considering species accumulation through a temporal perspective to adequately explain present‐day biodiversity patterns.

Highlights

Glacial refugia are of particular interest to biogeographers, evolu‐ tionary biologists and ecologists who are trying to understand the heterogeneous distribution of species
Their often high species rich‐ ness can be the result of three possible biogeographical functions: (a) high in situ speciation rates – the “cradle function”, (b) high immi‐ gration rates – the “sink function” and (c) range contraction resulting in relict species – the “museum function” (Pulliam, 1988; Stebbins, 1974; Stenseth, 1984; Figure 1)
The cradle and museum functions alternately acted during pre‐glacial times where most interspecific diversity was accumulated, while during the glacial period only the sink function acted and contributed comparably little to diversity build‐up

Summary

Introduction

Glacial refugia are of particular interest to biogeographers, evolu‐ tionary biologists and ecologists who are trying to understand the heterogeneous distribution of species Their often high species rich‐ ness can be the result of three possible biogeographical functions: (a) high in situ speciation rates – the “cradle function”, (b) high immi‐ gration rates – the “sink function” and (c) range contraction resulting in relict species – the “museum function” (Pulliam, 1988; Stebbins, 1974; Stenseth, 1984; Figure 1). The elevated species richness in these refugia has largely been attributed to the oscillations of pronounced polar ice sheets during the Pleistocene, which forced biota mainly to the south (i.e. sink function). Many refugial regions might be sufficiently old enough to support in situ speciation (i.e. cradle function) (Neubauer, Harzhauser, Kroh, Georgopoulou, & Mandic, 2015; Popov et al, 2006)

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