Abstract
Unravelling the history of range shifts is key for understanding past, current and future species distributions. Anthropogenic transport of species alters natural dispersal patterns and directly affects population connectivity. Studies have suggested that high levels of anthropogenic transport homogenize patterns of genetic differentiation and blur colonization pathways. However, empirical evidence of these effects remains elusive. We compared two range-shifting species (Microcosmus squamiger and Ciona robusta) to examine how anthropogenic transport affects our ability to reconstruct colonization pathways using genomic data. We first investigated shipping networks from the 18th century onwards, cross-referencing these with regions where the species have records to infer how each species has potentially been affected by different levels of anthropogenic transport. We then genotyped thousands of single-nucleotide polymorphisms from 280 M. squamiger and 190 C. robusta individuals collected across their extensive species' ranges and reconstructed colonization pathways. Differing levels of anthropogenic transport did not preclude the elucidation of population structure, though specific inferences of colonization pathways were difficult to discern in some of the considered scenario sets. We conclude that genomic data in combination with information of underlying introduction drivers provide key insights into the historic spread of range-shifting species.This article is part of the theme issue ‘Species’ ranges in the face of changing environments (part I)’.
Highlights
The ever-increasing rate of globalization of trade is intensifying the anthropogenic transport of species [1,2], leading to introductions of many species to regions away from their native ranges
Our results provide evidence that putatively varying levels of anthropogenic transport do not preclude our ability to recover patterns of population structure across species ranges that have undergone complex introduction histories
The results supported our initial assumption that the two studied species have been affected by different levels of anthropogenic transport
Summary
The ever-increasing rate of globalization of trade is intensifying the anthropogenic transport of species [1,2], leading to introductions of many species to regions away from their native ranges. Studies of neutral loci have analysed population genomic patterns of NIS in both introduced and native ranges [30,31], identified secondary contacts [32] and detected genetic bottlenecks [33]. Ciona robusta is putatively native to the northwest Pacific [41] and has been recorded in the Mediterranean Sea from the nineteenth century [42], followed by records in South Africa [43], northeast Pacific [44], Australia [45,46], New Zealand [47] and Hong Kong [48] throughout the twentieth century, and the south coast of England [49] since the early twenty-first century Both species’ population genetics have previously been studied using a relatively small number of genetic markers [31,41,42], and no study to date has reconstructed the invasion routes of these NIS using genome-wide tools. We identified the most likely scenario of each set using the ‘RF analysis’ module of DIYABC-RF (see full details in the electronic supplementary material)
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