Abstract
AimMayr's central‐peripheral population model (CCPM) describes the marked differences between central and peripheral populations in genetic diversity, gene flow, and census size. When isolation leads to genetic divergence, these peripheral populations have high evolutionary value and can influence biogeographic patterns. In tropical marine species with pelagic larvae, powerful western‐boundary currents have great potential to shape the genetic characteristics of peripheral populations at latitudinal extremes. We tested for the genetic patterns expected by the CCPM in peripheral populations that are located within the Kuroshio Current for the Indo‐Pacific reef fish, Caesio cuning.MethodsWe used a panel of 2,677 SNPs generated from restriction site‐associated DNA (RAD) sequencing to investigate genetic diversity, relatedness, effective population size, and spatial patterns of population connectivity from central to peripheral populations of C. cuning along the Kuroshio Current.ResultsPrincipal component and cluster analyses indicated a genetically distinct lineage at the periphery of the C. cuning species range and examination of SNPs putatively under divergent selection suggested potential for local adaptation in this region. We found signatures of isolation‐by‐distance and significant genetic differences between nearly all sites. Sites closest to the periphery exhibited increased within‐population relatedness and decreased effective population size.Main ConclusionsDespite the potential for homogenizing gene flow along the Kuroshio Current, peripheral populations in C. cuning conform to the predictions of the CCPM. While oceanography, habitat availability, and dispersal ability are all likely to shape the patterns found in C. cuning across this central‐peripheral junction, the impacts of genetic drift and natural selection in increasing smaller peripheral populations appear to be probable influences on the lineage divergence found in the Ryukyu Islands.
Highlights
Within the spatial distribution of a species, peripheral popula‐ tions can be prone to edge effects that significantly alter their genetic characteristics relative to central counterparts
These 36 outlier loci were removed, and all analyses were performed on a neutral panel of 2,677 single nucleotide polymorphisms (SNPs) with the exception of the principal component analysis, which was run with both panels
STRUCTURE results were consistent with those from the principal components analysis (PCA), with all but one fish from the peripheral population of Okinawa be‐ longing to an exclusive genetic cluster (Figure 3)
Summary
Within the spatial distribution of a species, peripheral popula‐ tions can be prone to edge effects that significantly alter their genetic characteristics relative to central counterparts. It flows past nearly 1,000 km of contiguous shoreline habitat and crosses a large expanse of deep water to the disjunct, sub‐trop‐ ical island reef systems that make up the Ryukyu Islands before turning east off the coast of Honshu, Japan to form the North Pacific Current It can take as little as one ef‐ fective migrant per generation to nullify disruptive genetic drift between two populations (Spieth, 1974), and since the Kuroshio Current can reach mean maximum surface velocities of ~1.2 m/s (~104 km/day) (Yang et al, 2015) there is great potential for ge‐ netic continuity via the dispersive larvae characteristic of most marine organisms.
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