Comparative phylogeography of a bathymetrically segregated pair of sister taxa of rockfishes (genus Sebastes): black rockfish, Sebastes melanops, and yellowtail rockfish, Sebastes flavidus

Abstract

Twelve pairs of sister taxa in the speciose rock sh genus, Sebastes, overlap coastal distributions but are bathymetrically segregated. These pairs are ideal for comparative studies to understand how life-history traits, historical events, and environment interact to produce population genetic structure. Black rock sh, Sebastes melanops, forms one such pair. Its sister species, yellowtail rock sh (Sebastes avidus), shows a genetic cline likely in uenced by a dispersal barrier at Cape Mendocino, CA and northward range expansion. Due to geographic overlap and close systematic relationship, we predicted black rock sh was in uenced by similar evolutionary processes and thus would show genetic pattern concordance with yellowtail rock sh. We analyzed ~ 1000 black rock sh from 22 sites spanning the species' range to test the null hypothesis of no structure, using the same markers that characterized yellowtail rock sh (i.e., 812 bp of the mitochondrial cytochrome b gene and six microsatellite loci). We reject the null hypothesis based on existence of at least three populations and microsatellite genetic divergence that separates the Alaskan and Continental U.S. populations (F CT =0.021, p < < 0.001), and a mitochondrial genetic cline near Cape Mendocino (F CT = 0.132, p < 0.01). We also found single collections genetically divergent from neighboring collections. Like yellowtail rock sh, oceanographic dispersal barriers and northern range expansion were inferred to in uence black rock sh, however, unlike yellowtail rock sh, Cape Mendocino did not split the range into two stocks and was therefore inferred to be a less severe barrier. We hypothesize a higher frequency of extinction/recolonization events in black rock sh populations may have led to more complex genetic structure.