Variation in self-compatibility among genotypes and across ontogeny in a self-fertilizing vertebrate, <i>Kryptolebias marmoratus</i>

Mixed-mating strategies can maximize the benefits and limit the costs of both self-fertilization and outcrossing. In addition to ecological conditions and population dynamics, the economics of mixed mating are determined by individual self-compatibility, i.e. the proportion of self-fertilization events that result in viable offspring. In gynodioecious (hermaphrodites and females) and androdioecious (hermaphrodites and males) species, self-compatibility of hermaphrodites dictates the reproductive potential of the other sex and can exert strong selection on maintenance of the non-hermaphroditic sex. Mangrove rivulus fish populations are androdioecious, and males result from hermaphrodites changing sex. Hermaphrodites overwhelmingly reproduce through internal self-fertilization, but occasionally oviposit unfertilized eggs, which males can fertilize externally. We tested the hypotheses that self-compatibility and fecundity would vary with age and as a function of genotypic variation in propensities for sex change. We reveal that fecundity and self-compatibility vary within individuals across ontogeny and among genotypes with different propensities to change sex. Hermaphrodites from genotypes that frequently change sex were significantly less fecund and self-compatible than hermaphrodites from genotypes that rarely change sex. These differences in self-compatibility and fecundity have the potential to drive mating strategy evolution in mangrove rivulus, specifically the fitness of males and associated spatiotemporal variation in sex ratios within and among populations.