Hermaphroditism promotes mate diversity in flowering plants

Abstract

PremiseGenetically diverse sibships are thought to increase parental fitness through a reduction in the intensity of sib competition, and through increased opportunities for seedling establishment in spatially or temporally heterogeneous environments. Nearly all research on mate diversity in flowering plants has focused on the number of fathers siring seeds within a fruit or on a maternal plant. Yet as hermaphrodites, plants can also accrue mate diversity by siring offspring on several pollen recipients in a population. Here we explore whether mate composition overlaps between the dual sex functions, and discuss the implications for plant reproductive success.MethodsWe established an experimental population of 49 Mimulus ringens (monkeyflower) plants, each trimmed to a single flower. Following pollination by wild bees, we quantified mate composition for each flower through both paternal and maternal function. Parentage was successfully assigned to 240 progeny, 98% of the sampled seeds.ResultsComparison of mate composition between male and female function revealed high mate diversity, with almost no outcross mates shared between the two sexual functions of the same flower.ConclusionsDual sex roles contribute to a near doubling of mate diversity in our experimental population of Mimulus ringens. This finding may help explain the maintenance of hermaphroditism under conditions that would otherwise favor the evolution of separate sexes.

Edge effects and mating patterns in a bumblebee-pollinated plant

“…Thus, edge plants were not pollen-limited, so seed production was not lower than for interior plants (which received nearly seven visits). However, this raises the possibility that interior plants might have more scope for mate choice (since a smaller fraction of pollen on stigmas could be successful in fertilization; Christopher et al 2019 ). Our data do not allow us to test this possibility.…”

“…To assess paternity, we genotyped 5 seedlings per fruit (965 seedlings total) with eight microsatellite loci following the methods of Nunziata et al (2012) . Genotypes of all maternal plants were known ( Christopher et al 2019 ). The multilocus exclusion probability given known maternal genotypes was 0.98.…”

Selfing rates vary with floral display, pollinator visitation and plant density in natural populations of Mimulusringens

“…Previous work has demonstrated that M. ringens exhibits biparental inbreeding and correlated matings (flowers that receive one pollinator visit have approximately three sires per fruit; Christopher et al., 2019; Karron et al., 2006). Although these factors may bias the estimate of the outcrossing rate, MLTR accounts for them by using a correlated‐matings model that takes a progeny pair as the unit of observation (Ritland, 2002).…”

Plant sexual reproduction: perhaps the current plant two-sex model should be replaced with three- and four-sex models?

“…The parent sporophyte in this case acts to nurture its female gametophytic progeny, and also nurtures the male gametophytes which may be its direct progeny or this pollen may be the offspring of some other sporophytic individuals. These nurturing and other interactions are clearly important (Crawford and Yanofsky 2008), and subject to selection, but are not here considered to be mating. Thus under the four-sex model mating occurs between gametophytic males and females, but not between one generation and another in the plant life cycle; females and males mate with one another, but male gametophytes do not mate with the sporophytic parents of female gametophytes.…”