Ovule Discounting in an Outcrossing, Cryptically Dioecious Tree

Abstract

Abstract. Ovule discounting denotes the reduction in the number of ovules available for cross-fertilization due to the interference of inferior pollen. Traditionally, ovule discounting has been discussed solely from the perspective of compromised outcrossing opportunities as a result of selfing, but the principle is more general. Here, we extend its applicability beyond the simple contrast between selfing and outcrossing by showing that, in the cryptically dioecious tree species Fraxinus ornus, ovule discounting through frequent outcrossing with inferior fathers also constitutes a substantial cost of mating. In F. ornus, hermaphrodites produce pollen capable of siring offspring, but these offspring are less viable than those sired by males and are inferred to produce few, if any, surviving progeny. In this paper, we used microsatellite markers to analyze the mating system and paternity in a wild population of F. ornus. We found that the effective number of sires per mother was low (N ep ϭ 2.93 to 4.95), and that paternity was correlated among progeny sampled from the same mother, but not among progeny sampled from neighboring mothers. Despite the existence of a local spatial genetic structure (up to 30 m), we found no evidence of biparental inbreeding. There was negligible selfing by hermaphrodites, but they sired approximately one fourth of the seeds produced by other hermaphrodites. Given that these progeny are not inferred to reach reproductive maturity, this constitutes a substantial cost of ovule discounting in the broad sense. We discuss the possible reasons for why hermaphrodites invest resources into inferior pollen.

Spatiotemporal mating pattern variation in a wind‐pollinated Mediterranean shrub

“…This method provides more accurate estimates of correlated paternity than Ritland’s estimator, which has been reported to provide downward biased estimates (Hardy et al. 2004; Verdú et al. 2006; de‐Lucas et al.…”

“…the proportion of full‐sibs within maternal progeny arrays or the proportion of paternal half‐sibs among maternal progeny arrays, and its inverse, the effective number of pollen donors ( N ep ), are parameters of pivotal importance in the study of plant mating systems, allowing a better understanding of the pollination biology of plant species (Hardy et al. 2004; Verdú et al. 2006).…”

DISASSORTATIVE MATING, SEXUAL SPECIALIZATION, AND THE EVOLUTION OF GENDER DIMORPHISM IN HETERODICHOGAMOUSACER OPALUS

“…Finally, as the distance between mates can also be an important determinant of male fertility, a second indirect method based on a mating model that includes distance between candidate fathers and mothers was applied using the PatQuest version 4.0 program (Thomas R. Meagher and collaborators, University of St Andrews, U.K). In this method, male fertility is estimated from a log‐linear regression model as follows (Smouse et al 1999; Elle and Meagher 2000; Vassiliadis et al 2002; Verdú et al 2006): where λ jk is the male fertility of the k th father over the j th mother, δ jk is the distance between them, z k is an indicator variable that represents the sexual group to which the k th father belongs, and γ d and β are the estimated regression coefficients. The siring success of one sexual morph over any other morph is obtained by calculating exp(β), and the significance of the estimated parameters is assessed by pedigree‐based bootstrap permutations using 1000 iterations (Morgan and Conner 2001).…”

Do inbreeding depression and relative male fitness explain the maintenance of androdioecy in white mangrove, Laguncularia racemosa (Combretaceae)?

“…In Phillyrea angustifolia , pollen tube growth was nearly 1.5 times more likely in male pollen vs hermaphroditic pollen (Vassiliadis et al ., 2000), and in several populations, fruit set from crosses made with male pollen was significantly higher (1.9–3.9 times higher) relative to fruit set from crosses made with hermaphroditic pollen (Lepart & Dommee, 1 992; Traveset, 1 994; Vassiliadis et al ., 2000). Male pollination success was also significantly higher than hermaphroditic success in Fraxinus ornus (Dommee et al ., 1999), leading Verdu et al . (2006) to suggest that F. ornus is functionally cryptically dioecious.…”