Genetic variation in age-dependent attractiveness in a fish with a mixed mating system

Reproductive senescence is common in many taxa and females often show a predictable decline in fecundity after maturity. Attending to these age-dependent cues in female fecundity could help males make optimal mate choice decisions. In this study, we examined reproductive senescence and male mate choice in the androdioecious mangrove rivulus (Kryptolebias marmoratus) where self-fertilizing hermaphrodites exist with rare males and where generations of self-fertilization result in genetically distinct lineages. Hermaphrodites showed a strong decline in fecundity as they aged and genetic lineages varied in their fecundity both at young and old ages. Surprisingly, when given a simultaneous choice between genetically identical old and young hermaphrodites, and with access to both visual and olfactory cues, males did not simply prefer younger hermaphrodites. Instead, male preference for younger vs older partners depended on the genetic lineage of the partners, resulting in a strong genotype x age interaction. For some genetic lineages, hermaphrodites were more attractive to males when younger, but for other genetic lineages, hermaphrodites were more attractive when older. Our results suggest that genetic identity of the partner is key to how males weigh age-dependent changes in fecundity, and that males are able to assess genetic variation in attractiveness over a partner’s reproductive lifespan. Exploring how gamete viability and outcrossing is affected by age across genetic lineages could help us further understand these flexible male preferences.