Male diet, female experience, and female size influence maternal investment in swordtails

Correlations between male phenotype and female investment in offspring size or number may result from either male influences or female responses to male phenotype. Theory has predicted that females may invest differentially in response to mate attractiveness either to take advantage of her partner’s attractiveness or to compensate for it. The outcome can depend on the female’s expected future fitness. Empirical evidence also suggests that females adjust offspring size or fecundity according to the genetic or phenotypic traits of the male. Though the role of future fitness in empirical results is often difficult to assess, female experience has been shown to influence reproductive investment. This result could indicate that experience informs the female’s assessment of current and future mating opportunities (i.e., expected future fitness). Here, we tested whether female experience and mate attractiveness affected offspring size and number in sheepshead swordtails. We manipulated mate attractiveness by feeding males different diets, as females have been shown to prefer well-fed males. We found that females exposed to well-fed males, and then mated to poorly fed males, produced the largest offspring. Clutch size increased more rapidly with female size for females with mates on a poor diet, independent of female experience. Our results suggest that swordtail females elevate their investment in offspring size and number when mated to poorly fed males. These results demonstrate that maternal investment can be influenced by female social environment and experience, with underappreciated consequences for offspring fitness.