Evolutionary game in an androdioecious population: Coupling of outcrossing and male production

Androdioecy, the coexistence of hermaphrodites and males, is very rare in vertebrates but occurs in mangrove killifish living in ephemeral or unstable habitats. Hermaphrodites reproduce both by outcrossing with males and by selling. Outbreeding is advantageous because of inbreeding depression, but it requires encounters with males. The advantages of a propensity for outcrossing among hermaphrodites and the production of males affect each other very strongly. To study the evolutionary coupling of these two aspects, we here analyze a simple evolutionary game for a population composed of three phenotypes: outcrossing-oriented hermaphrodites, selling-oriented hermaphrodites, and males. Outcrossing-oriented hermaphrodites first attempt to search for males and perform outcrossing if they encounter males. If they fail to encounter males, they reproduce via selling. Selling-oriented hermaphrodites simply reproduce by selling. The replicator dynamics may show bistability, in which both the androdioecious population (with outcrossing-oriented hermaphrodites and males) and the pure hermaphroditic population are locally stable. The model shows the fraction of males is either zero or relatively high (more than 25%), which is not consistent with the observed low fraction of males (less than 5%). To explain this discrepancy, we studied several models including immigration and enforced copulation. We concluded that the observed pattern can be most likely explained by a population dominated by selling-oriented hermaphrodites receiving immigration of males. (C) 2021 The Author(s). Published by Elsevier Ltd.

Automated summary

Androdioecy, the coexistence of hermaphrodites and males, is rare in vertebrates, but occurs in mangrove killifish. The advantages of outcrossing-oriented hermaphrodites and the production of males strongly affect each other. Different models are studied to explain the discrepancy between the predicted high male fraction and the observed low male fraction.