Siring success and paternal effects in heterodichogamous Acer opalus

GLEISER, G.; SEGARRA-MORAGUES, J. G.; PANNELL, J. R.; VERDÚ, M.

ANNALS OF BOTANY

OXFORD UNIV PRESS

Año: 2008 vol. 101 p. 1017 - 1026

0305-7364

Background and Aims: Heterodichogamy (a dimorphic breeding system comprising protandrous and protogynousindividuals) is a potential starting point in the evolution of dioecy from hermaphroditism. In the genus Acer, previouswork suggests that dioecy evolved from heterodichogamy through an initial spread of unisexual males.Here, the question is asked as to whether the different morphs in Acer opalus, a species in which males co-existwith heterodichogamous hermaphrodites, differ in various components of male in fitness. Methods: Several components of male fertility were analysed. Pollination rates in the male phase were recordedacross one flowering period. Pollen viability was compared among morphs through hand pollinations both withpollen from a single sexual morph and also simulating a situation of pollen competition; in the latter experiment,paternity was assessed with microsatellite markers. It was also determined whether effects of genetic relatednessbetween pollen donors and recipients could influence the siring success. Finally, paternal effects occurringbeyond the fertilization process were tested for by measuring the height reached by seedlings with different siresover three consecutive growing seasons. Key Results: The males and protandrous morphs had higher pollination rates than the protogynous morph, and theseedlings they sired grew taller. No differences in male fertility were found between males and protandrous individuals. Departures from random mating due to effects of genetic relatedness among sires and pollen recipients werealso ruled out. Conclusions: Males and protandrous individuals are probably better sires than protogynous individuals, as shownby the higher pollination rates and the differential growth of the seedlings sired by these morphs. In contrast, thefertility of males was not higher than the male fertility of the protandrous morph. While the appearance of malesin sexually specialized heterodichogamous populations is possible, even in the absence of a fitness advantage, it is not clear that males can be maintained at an evolutionary equilibrium with two classes of heterodichogamous hermaphrodites.