Paternal effects on functional gender account for cryptic dioecy in a perennial plant

Abstract

Natural selection operates on the mating strategies of hermaphrodites through their functional gender, i.e. their relative success as male versus female parents. Because functional gender will tend to be strongly influenced by sex allocation, it is often estimated in plants by counting seeds and pollen grains. However, a plant's functional gender must also depend on the fate of the seeds and pollen grains it produces. We provide clear evidence of a paternal effect on the functional gender of a plant that is independent of the resources invested in pollen. In the Mediterranean tree Fraxinus ornus, males coexist with hermaphrodites that disperse viable pollen and that sire seeds; the population would thus appear to be functionally androdioecious. However, we found that seedlings sired by hermaphrodites grew significantly less well than those sired by males, suggesting that hermaphrodites may be functionally less male than they seem. The observed 1 : 1 sex ratios in F. ornus, which have hitherto been difficult to explain in the light of the seed-siring ability of hermaphrodites, support our interpretation that this species is cryptically dioecious. Our results underscore the importance of considering progeny quality when estimating gender, and caution against inferring androdioecy on the basis of a siring ability of hermaphrodites alone.

Adaptive evolution of reproductive and vegetative traits driven by breeding systems

“…Despite the slight overlap in the 95% CI, the trend, which is consistent in all the models, suggests biologically important information. Unisexual forms are usually super-specialized in one of the sexual functions, outcompeting the same function of the monoecious individuals (Verdú, 2004;Verdú et al ., 2004a). According to this, the sexual specialization of males in some Acer species studied allows them to hoard most of the male function in the population, relegating the fitness gain of monoecious individuals to the female function (Sato, 2002;Verdú et al ., 2004b; G.G., M.V.…”

Ovule Discounting in an Outcrossing, Cryptically Dioecious Tree

“…To determine the extent of pollen competition, we compared seed set obtained in open-pollinated inflorescences with that obtained in inflorescences in which pollen from males was experimentally supplied. Pollinations were performed on 10 hermaphrodites, with four replicates per treatment (for experimental details, see Verdú et al 2004). The proportions of seeds sired as a result of supplementary pollination and open-pollination were compared using a generalized linear mixed model via penalized quasi-likelihood (glmmPQL; the MASS library on the R ststistical package; Ihaka and Gentleman 1966), with a Poisson distribution of errors and a canonical link.…”

“…Fraxinus ornus (Oleaceae) is an insect-pollinated tree in which males cooccur with individuals that produce both seeds and pollen (Dommée et al 1999;Verdú 2004;Verdú et al 2004). The species has previously been described as androdioecious (Dommée et al 1999), but the fact that males typically occur at a frequency of 0.5 indicates that F. ornus is functionally dioecious and that hermaphrodites are thus func- , and see Discussion).…”

Ovule Discounting in an Outcrossing, Cryptically Dioecious Tree

“…Five nuclear microsatellite loci were used in the analysis: FEMSATL4, FEMSATL16, FR39, FR41 (Lefort et al 1999;Verdú et al 2004), and FR16. FR16 is a new marker developed by the company Bionostra S.L.…”

“…Fraxinus ornus (Oleaceae) is an insect-pollinated tree in which males cooccur with individuals that produce both seeds and pollen (Dommée et al 1999;Verdú 2004;Verdú et al 2004). The species has previously been described as androdioecious (Dommée et al 1999), but the fact that males typically occur at a frequency of 0.5 indicates that F. ornus is functionally dioecious and that hermaphrodites are thus func- tionally female (Verdú et al 2004, and see Discussion).…”