Predicting contemporary range‐wide genomic variation using climatic, phylogeographic and morphological knowledge in an ancient, unglaciated landscape

Abstract

Aim Understanding the spatial distribution of genetic variation across a species’ range is a central tenet in evolutionary biology and the ability to predict such patterns is valuable to conservation management. Genetic diversity and differentiation may be explained by present‐day niche centrality, historical processes, or morphological variation across a species’ range, yet few studies evaluate these factors concurrently. Moreover, there is a particular lack of knowledge of the influence of these factors in ancient, unglaciated landscapes of the Southern Hemisphere. We investigate these concepts for their influence upon spatial patterns of genetic variation in a widespread plant species in a southern biodiversity hotspot. Location South‐western Australia. Taxon Calothamnus quadrifidus . Methods We use genotyping‐by‐sequencing to assess genome‐wide diversity and differentiation across the range of Calothamnus quadrifidus , a morphologically variable species that occurs over a wide geographic range in an ancient, unglaciated landscape. We correlated the patterns of genetic diversity and differentiation with those predicted under four hypotheses regarding effects of geographic centrality, climatic centrality, historical phylogeography and morphological subspecies. Results We found spatial variation in genetic diversity and strong population structuring, and while each hypothesis was consistent with some of these patterns, no hypothesis predicted the full extent of genetic diversity or structure in C. quadrifidus . Main conclusions Our results are indicative of a complex evolutionary history, with multiple factors shaping contemporary genetic variation in C. quadrifidus over time, rather than any one major driving factor. This is enabled by the greater capacity to build complex evolutionary signals in ancient, more stable landscapes like the southwest of Western Australia that are not as predictable as those within the younger, post‐glacial landscapes of the Northern Hemisphere. Finally, our study demonstrates the importance of using an interdisciplinary approach to understanding the spatial patterns of genetic variation across species’ ranges and the influence of ecological, geographical and historical factors.

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