Siring success and paternal effects in heterodichogamous Acer opalus
Gleiser, G.; Segarra-Moragues, J.G.; Pannell, J.R.; Verdú M.. Siring success and paternal effects in heterodichogamous Acer opalus. Annals of Botany . 2008, Vol. 101, p. 1017-2008.
Heterodichogamy (a dimorphic breeding system comprising protandrous and protogynous
individuals) is a potential starting point in the evolution of dioecy from hermaphroditism. In the genus Acer, previous
work 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-exist
with 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 recorded
across one flowering period. Pollen viability was compared among morphs through hand pollinations both with
pollen 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 relatedness
between pollen donors and recipients could influence the siring success. Finally, paternal effects occurring
beyond the fertilization process were tested for by measuring the height reached by seedlings with different sires
over three consecutive growing seasons.
† Key Results The males and protandrous morphs had higher pollination rates than the protogynous morph, and the
seedlings 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 were
also ruled out.
†Conclusions Males and protandrous individuals are probably better sires than protogynous individuals, as shown
by the higher pollination rates and the differential growth of the seedlings sired by these morphs. In contrast, the
fertility of males was not higher than the male fertility of the protandrous morph. While the appearance of males
in 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.
Heterodichogamy (a dimorphic breeding system comprising protandrous and protogynous
individuals) is a potential starting point in the evolution of dioecy from hermaphroditism. In the genus Acer, previous
work 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-exist
with 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 recorded
across one flowering period. Pollen viability was compared among morphs through hand pollinations both with
pollen 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 relatedness
between pollen donors and recipients could influence the siring success. Finally, paternal effects occurring
beyond the fertilization process were tested for by measuring the height reached by seedlings with different sires
over three consecutive growing seasons.
† Key Results The males and protandrous morphs had higher pollination rates than the protogynous morph, and the
seedlings 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 were
also ruled out.
†Conclusions Males and protandrous individuals are probably better sires than protogynous individuals, as shown
by the higher pollination rates and the differential growth of the seedlings sired by these morphs. In contrast, the
fertility of males was not higher than the male fertility of the protandrous morph. While the appearance of males
in 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.