Genetic patterns of demography and diversity in eastern North Pacific rockfishes (genus Sebastes).

摘要

The 100 North Pacific rockfish species in the genus Sebastes are highly diverse. Rockfishes fertilize their eggs internally and release swimming larvae. Complex courting behaviors may allow female rockfish to be selective about their mates and may promote and maintain speciation. In this study, I applied genetic techniques to survey the factors that structure rockfish populations and have potential to affect speciation. First, I used microsatellites to test the hypothesis that the rangewide signal of isolation-by-distance previously identified in copper rockfish is the result of localized habitat or oceanographic breaks. I found significant population divergence at both the whole-coast and Oregon-coast scales. I also identified a weak but significant barrier to larval migration south of Newport, Oregon. Second, I used a candidate gene approach to assess the possibility that olfactory receptor related to class A, type 2 (Ora2) genes could differentiate species at mating. I characterized sequence variation in Ora2 genes between five distantly-related rockfishes and tested for evidence of positive selection. My results suggest that rockfishes possess a single, highly conserved Ora2 gene. Although evidence of positive selection was found for nine amino acids, shared alleles were found across all five study species. This suggests that the Ora2 gene in isolation could not differentiate species during mating season. Finally, I tested the hypothesis that rockfishes mate non-randomly based on major histocompatibility complex (MHC) genotype, as has been seen in other fishes. I characterized MHC genotypes of copper and quillback rockfish in a captive-mating population, identified parents of fourteen broods, and drew inferences about mate choice based on known parentage. I found a significant proportion of multiple-fathered broods, a high degree of hybridization, and that these two species possess multiple, highly-variable MHC genes. I did not find strong evidence that females selected males based on MHC. This may be because larval survival is stochastic, which promotes a bet-hedging strategy, rather than a high degree of selectivity. This work complements our understanding of the population genetics of nearshore rockfishes, and offers a first look at two gene families that may function in mate choice to avoid hybridization and improve larval quality.