Abstract
For many species in nature, a sire's progeny may be distributed among a few or many dams. This poses logistical challenges--typically much greater across males than across females--for assessing means and variances in mating success (number of mates) and reproductive success (number of progeny). Here we overcome these difficulties by exhaustively analyzing a population of green swordtail fish (Xiphophorus helleri) for genetic paternity (and maternity) using a suite of highly polymorphic microsatellite loci. Genetic analyses of 1476 progeny from 69 pregnant females and 158 candidate sires revealed pronounced skews in male reproductive success both within and among broods. These skews were statistically significant, greater than in females, and correlated in males but not in females with mating success. We also compare the standardized variances in swordtail reproductive success to the few such available estimates for other taxa, notably several mammal species with varied mating systems and degrees of sexual dimorphism. The comparison showed that the opportunity for selection on male X. helleri is among the highest yet reported in fishes, and it is intermediate compared to estimates available for mammals. This study is one of a few exhaustive genetic assessments of joint-sex parentage in a natural fish population, and results are relevant to the operation of sexual selection in this sexually dimorphic, high-fecundity species.
Highlights
Darwin (1871) introduced the concept of sexual selection in response to the conundrum posed by extravagant, typically gender-restricted, phenotypic features that seem to be of no adaptive value in their bearers
Knowledge about genetic mating systems in nature is important for studies in population dynamics and behavioural ecology
Our study is among the few available attempts to estimate male mating success and reproductive success jointly in a natural population of fish
Summary
Darwin (1871) introduced the concept of sexual selection in response to the conundrum posed by extravagant, typically gender-restricted, phenotypic features that seem to be of no adaptive value (and may lower viability) in their bearers. Genetic appraisals of male mating success and reproductive success have been limited mostly to species with reliable pedigree or long-term census data, such as several mammals (Say et al 2003; Hayes et al 2006; Rossiter et al 2006; Vanpé et al 2008), birds (Alatalo et al 1996; Reynolds et al 2007), and lizards (Lebas 2001; Morrison et al 2002) Even in such favourable logistical circumstances, substantial numbers of progeny often cannot be ascribed to known sires. Successful attempts at complete paternity assessment in other animal groups are few (Jones et al 2002; Gopurenko et al 2007)
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