Disassortative mating, sexual specialization and the evolution of gender dimorphism in heterodichogamous Acer opalus

GLEISER, G.; VERDÚ, M.; SEGARRA-MORAGUES, J. G.; GONZÁLEZ-MARTÍNEZ, S. C.; PANNELL, J. R.

EVOLUTION

WILEY-BLACKWELL PUBLISHING, INC

Año: 2008 vol. 62 p. 1676 - 1688

0014-3820

In sexually polymorphic species, the morphs are maintained by frequency-dependent selection through disassortative mating.In heterodichogamous populations in which disassortative mating occurs between the protandrous and protogynous morphs, adecrease in female fitness in one morph is hypothesized to drive sexual specialization in the other morph, resulting in dimorphicpopulations. We test these ideas in a population of the heterodichogamous species, Acer opalus. We assessed both prospectivegender of individuals in terms of their allocations and actual parentage using microsatellites; we found that most matings in A.opalus occur disassortatively. We demonstrate that the protogynous morph is maintained by frequency-dependent selection, butthat maintenance of males versus protandrous individuals depends on their relative siring success, which changes yearly. Seedsproduced later in the reproductive season were smaller than those produced earlier; this should compromise reproduction throughovules in protandrous individuals, rendering them male biased in gender. Time-dependent gender and paternity analyses indicatethat the sexual morphs are specialized in their earlier sexual functions, mediated by the seasonal decrease in seed size. Our resultsconfirm that mating patterns are context-dependent and change seasonally, suggesting that sexual specialization can be drivenby seasonal effects on fitness gained through one of the two sexual functions.