Abstract
Estimating population sizes and genetic diversity are key factors to understand and predict population dynamics. Marine species have been a difficult challenge in that respect, due to the difficulty in assessing population sizes and the open nature of such populations. Small, isolated islands with endemic species offer an opportunity to groundtruth population size estimates with empirical data and investigate the genetic consequences of such small populations. Here we focus on two endemic species of reef fish, the Clipperton damselfish, Stegastes baldwini, and the Clipperton angelfish, Holacanthus limbaughi, on Clipperton Atoll, tropical eastern Pacific. Visual surveys, performed over almost two decades and four expeditions, and genetic surveys based on genomic RAD sequences, allowed us to estimate kinship and genetic diversity, as well as to compare population size estimates based on visual surveys with effective population sizes based on genetics. We found that genetic and visual estimates of population numbers were remarkably similar. S. baldwini and H. limbaughi had population sizes of approximately 800,000 and 60,000, respectively. Relatively small population sizes resulted in low genetic diversity and the presence of apparent kinship. This study emphasizes the importance of small isolated islands as models to study population dynamics of marine organisms.
Highlights
Populations of marine organisms typically are very large, with population sizes (N) of 106 to 109 individuals being common [1]
When looking at polymorphic loci in stacks, we found that more loci were polymorphic in H. limbaughi compared to S. baldwini (6.66% of the loci, compared to 3.55%, respectively), suggesting that the distribution of polymorphisms differs in the two species, but does so in a reverse manner to heterozygosity
We confirmed that there is no evidence of gene flow between H. limbaughi and its sister species, nor between S. baldwini and its sister species, and that the system is effectively closed from a genetic standpoint, validating endemism in these two species
Summary
Populations of marine organisms typically are very large, with population sizes (N) of 106 to 109 individuals being common [1]. Large populations in an open environment are predicted to show high levels of gene flow, resulting in low genetic population structure and speciation rates. An early paradox arose from the observation of elevated speciation rates and strong. Genomics of Clipperton Atoll fishes was financed by the National Geographic Society Pristine Seas program
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