Journal
MOLECULAR ECOLOGY
Volume 31, Issue 16, Pages 4242-4253Publisher
WILEY
DOI: 10.1111/mec.16589
Keywords
Australia; central-marginal hypothesis; ddRAD; genetic variation; historical demography; lizards
Funding
- CSUDH Graduate Writing Institute for Excellence Fellowship
- CSUDH Research, Scholarship and Creative Activity Grant
- National Science Foundation [DEB-1754398]
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For many species, local abundance and regional occupancy are highest near the center of their geographic distributions, which supports the central-marginal hypothesis. This hypothesis suggests that niche suitability declines as distance from the geographic center increases, resulting in reduced density and increased patchiness in edge populations. Using genomic data from Australian scincid lizards, we found that a majority of the taxa tested showed patterns of genetic variation consistent with the central-marginal hypothesis. Additionally, taxa with evidence of range expansion were less likely to follow the predictions of the hypothesis.
For many species, both local abundance and regional occupancy are highest near the centre of their geographic distributions. One hypothesis for this pattern is that niche suitability declines with increasing distance from a species geographic centre, such that populations near range margins are characterized by reduced density and increased patchiness. In these smaller edge populations, genetic drift is more powerful, leading to the loss of genetic diversity. This simple verbal model has been formalized as the central-marginal hypothesis, which predicts that core populations should have greater genetic diversity than edge populations. Here, we tested the central-marginal hypothesis using a genomic data set of 25 species-level taxa of Australian scincid lizards in the genera Ctenotus and Lerista. A majority of taxa in our data set showed range-wide patterns of genetic variation consistent with central-marginal hypothesis, and eight of 25 taxa showed significantly greater genetic diversity in the centre of their range. We then explored biological, historical, and methodological factors that might predict which taxa support the central-marginal hypothesis. We found that taxa with the strongest evidence for range expansion were the least likely to follow predictions of the central-marginal hypothesis. The majority of these taxa had range expansions that originated at the range edge, which led to a gradient of decreasing genetic diversity from the range edge to the core, contrary to the central-marginal hypothesis.
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