Abstract
Understanding the mating system and reproductive success of a species provides evidence for sexual selection. We examined the mating system and the reproductive success of captive adult black sea bream (Acanthopagrus schlegelii), using parentage assignment based on two microsatellites multiplex PCR systems, with 91.5% accuracy in a mixed family (29 sires, 25 dams, and 200 offspring). Based on the parentage result, we found that 93.1% of males and 100% of females participated in reproduction. A total of 79% of males and 92% of females mated with multiple partners (only 1 sire and 1 dam were monogamous), indicating that polygynandry best described the genetic mating system of black sea bream. For males, maximizing the reproductive success by multiple mating was accorded with the sexual selection theory while the material benefits hypothesis may contribute to explain the multiple mating for females. For both sexes, there was a significant correlation between mating success and reproductive success and the variance in reproductive success of males was higher than females. Variation in mating success is the greatest determinant to variation in reproductive success when the relationship is strongly positive. The opportunity for sexual selection of males was twice that of females, as well as the higher slope of the Bateman curve in males suggested that the intensity of intrasexual selection of males was higher than females. Thus, male–male competition would lead to the greater variation of mating success for males, which caused greater variation in reproductive success in males. The effective population number of breeders (N b) was 33, and the N b/N ratio was 0.61, slightly higher than the general ratio in polygynandrous fish populations which possibly because most individuals mated and had offspring with a low variance. The relatively high N b contributes to the maintenance of genetic diversity in farmed black sea bream populations.
Highlights
Mating systems, mainly determined by the frequency of mating in each of the sexes and influenced by environment factors, describe the way in which animal societies are structured in relation to their sex-specific sexual behavior, mating, and reproductive success (Andersson, 1994; Emlen & Oring, 1977)
This study provides a demonstration of a genetic approach to analyze the mating system and quantify the variance in individual mating and reproductive success of black sea bream
The genetic evidence uncovered that polygynandry appeared to be a predominant mating strategy in black sea bream
Summary
Mainly determined by the frequency of mating in each of the sexes and influenced by environment factors, describe the way in which animal societies are structured in relation to their sex-specific sexual behavior, mating, and reproductive success (Andersson, 1994; Emlen & Oring, 1977). Mating systems with the evenness of mate number and lower variance in reproductive success among multiple mating broodstock increase the effective population size, resulting in a greater genetic variation (Sugg & Chesser, 1994). Among Sparidae fish species (commonly known as sea bream or porgy), various studies have been carried out (Alós, CabanellasReboredo, & March, 2012; Broadhurst, Butcher, & Millar, 2019; Gardner, Deeming, Wellby, Soulsbury, & Eady, 2015; La Mesa et al, 2011); the mating system, variance in reproductive success of males and females, and the fidelity of genetic diversity transmission from parents to offspring remain unknown. Based on Bateman's principles (Bateman, 1948), we show how the variation in mating success within and between the sexes can affect reproductive success in males and females, and influence the strength and direction of sexual selection. The effective population size of breeders was calculated to assess the risk for inbreeding in our captive black sea bream population
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