Parentage Analysis, Mating System Determinants, and Selection Theory Support Non-Territorial Polygamy in the Black Rockfish, Sebastes melanops

Characterizing the mating systems of exploited species is crucial for their conservation, due to the relationships of mating systems with sexual selection, fitness, and life history traits. Although obtaining some mating system measures on wild Pacific rockfishes (genus Sebastes) is unlikely, integrating observations with selection theory to draw inferences about unsampled parents and the mating system is achievable. We conducted microsatellite parentage analysis of 17 viviparous Sebastes melanops females and over 1200 offspring, exposing one to four sires per brood and multiple paternity in 11 broods (65%), a mean of 2 sires and variance ≈ 1. Multiply sired broods were similar in mean heterozygosity to single sired broods but exhibited greater allele richness (Mann-Whitney U-test: U_s = 66, P < .001). Polyandrous females may compensate for genetic incompatibility of their mates by reallocating maternal resources from defective to viable offspring. Our evaluation of Sebastes mating system determinants indicates a small opportunity for directional sexual selection on males in schooling, non-territorial S. melanops; most determinants allow more mating males. Male evolutionary responses to female spatiotemporal distributions, including an estimated mean of 2.4 mates for unsampled sires and inconspicuous sexual dimorphism, supports male polygamy and a non-territorial polygamy (polygynandry) mating system classification for S. melanops.