Seed paternity in flowering plants: an evolutionary perspective

Abstract

the male function. Also, paternity can be the end result of competition for fertilization among pollen from one or several donors, selection processes occurring between pollen deposition and fertilization, and post-zygotic events such as seed abortion.Pre-zygotic competition and selection processes in flowering plants are relevant under several aspects (e.g. Snow & Lewis 1993;Delph & Havens 1998 AbstractThe ultimate importance of paternal contributions to fitness and of post-pollination selection in flowering plants have remained elusive, largely because of the technical difficulty of assigning paternity. I review empirical studies that use heritable markers to investigate per-fruit seed paternity in natural populations and after experimental multiple-donor pollination. Thirty-one studies covering 23 species from 16 plant families document that in natural populations seeds from a single fruit are often fathered by multiple pollen donors (5 species from 5 families), that donors can differ significantly in seed-siring success (8 species from 6 families), that variation in pollen tube growth rates can be heritable (n = 1 out of 4 studies), that donor and recipient genotypes can simultaneously affect paternity (n = 2), and that temporal order of pollen deposition (n = 1) and environmental effects (n = 2) affect the outcome of pollen competition. These studies also investigate the role of post-pollination selection in the avoidance of inbreeding and for species boundaries. Most studies of male reproductive success in plants to date base on isozyme electrophoresis. The availability in the last decade of highly polymorphic molecular markers such as microsatellite DNA has been expected to open new possibilities to investigate competition and selection during the gametophytic phase. Yet, to date, there is still need for greater data wealth on seed paternity to test theories of sex allocation and to gain deeper understanding of floral trait evolution and of the evolutionary consequences of post-pollination selection in flowering plants.

The effects of inbreeding, genetic dissimilarity and phenotype on male reproductive success in a dioecious plant

“…However, to our knowledge there is no study that has assessed whether male reproductive success in plants is directly affected by the levels of inbreeding, in particular, under conditions of natural interaction with pollinators and mixed pollen loads [1]. In animals with multiple mating, sometimes the effects of inbreeding depression on siring success are only revealed under competition for fertilization [30,31], and few studies have investigated whether inbreeding directly affects male fitness (e.g.…”

“…During pollination, stigmas may receive pollen from multiple individuals [1][2][3] such that pollen tubes compete to fertilize ovules. This promotes the evolution of mechanisms for pollen selection in females that allow the sorting of compatible pollen and increase offspring number or quality, and for selection of male traits that increase attractiveness towards pollinators and pollencompetitive abilities [4][5][6].…”

Balance between inbreeding and outcrossing in a nannandrous species, the moss Homalothecium lutescens

“…Individuals that shared alleles in all loci except for loci with missing data were treated as the same haplotype. In addition, we calculated the effective number of fathers (K E , Bernasconi, 2003) on each female shoot using the following equation K E = 1/Σ(p i ) 2 , where p i is the proportion of the sporophytes fertilized by each distinct father haplotype. When the distinct fathers each sire an equal number of sporophytes on a female shoot, the effective number of fathers (K E ) will be the same as the number of distinct fathers (K).…”

Evidence for inbreeding depression and post-pollination selection against inbreeding in the dioecious plant Silene latifolia

“…Although differential embryo abortion may favour outbred progeny, the widespread existence of prezygotic self-incompatibility mechanisms in plants (Nasrallah, 2002) and the general finding that self-pollen achieves less paternity success than outcross pollen (reviewed by Bernasconi, 2003) indicate that differential pollen success with a simple genetic basis is indeed possible, and may be less costly to the female plant than embryo abortion.…”

“…Most of these studies applied singledonor pollination. However, natural pollen loads may commonly contain pollen from multiple pollen donors (reviewed by Bernasconi, 2003;Mitchell et al, 2005), a condition that provides the opportunity for post-pollination inbreeding avoidance.…”