The population ecology of male gametophytes: the link between pollination and seed production

Abstract

The fate of male gametophytes after pollen reaches stigmas links pollination to ovule fertilisation, governing subsequent siring success and seed production. Although male gametophyte performance primarily involves cellular processes, an ecological analogy may expose insights into the nature and implications of male gametophyte success. We elaborate this analogy theoretically and present empirical examples that illustrate associated insights. Specifically, we consider pollen loads on stigmas as localised populations subject to density-independent mortality and density-dependent processes as they traverse complex stylar environments. Different combinations of the timing of pollen-tube access to limiting stylar resources (simultaneous or sequential), the tube distribution among resources (repulsed or random) and the timing of density-independent mortality relative to competition (before or after) create signature relations of mean pollen-tube success and its variation among pistils to pollen receipt. Using novel nonlinear regression analyses (two-moment regression), we illustrate contrasting relations for two species, demonstrating that variety in these relations is a feature of reproductive diversity among angiosperms, rather than merely a theoretical curiosity. Thus, the details of male gametophyte ecology should shape sporophyte reproductive success and hence the dynamics and structure of angiosperm populations.

Flower traits, habitat, and phylogeny as predictors of pollinator service: a plant community perspective

“…, Aizen and Harder , Burd , Harder et al. ). Thanks to this vast amount of work, the ecological and evolutionary consequences of variable pollinator service at different scales are now reasonably well understood.…”

Quantitative and qualitative consequences of reduced pollen loads in a mixed‐mating plant

“…Furthermore, in the present study, we tested pollen competition within a single paternal individual from a single pollination event, whereas pollination by multiple pollen donors, with variation in the timing of pollen deposition, may be more likely in nature. In this case, poor‐quality pollen grains could exclude late arriving high‐quality pollen grains from ovule fertilization, thus diminishing the rate of increase in seed set with increasing pollen numbers in natural populations, compared with our experimental population (Harder, Aizen, & Richards, ). Finally, we constrained blossom seed set to a maximum of three seeds, possibly increasing the chances of these seeds to mature compared to the possible nine seeds produced in natural populations.…”

“…Although three pollen grains per stigma should be sufficient to achieve a full seed set (three seeds) in D. scandens, we observed that 19 pollen grains were required on average. This might be due to a minimum pollen load necessary to initiate pollen-tube germination (Brewbaker & Kwack, 1963), and positive density-dependent effects facilitating pollen germination at moderate densities (Harder et al, 2016). Furthermore, pollen mortality due to physiological causes or poor genetic quality may eliminate pollen grains before the onset of pollen-tube competition (Harder et al, 2016).…”

The costs and benefits of pollinator dependence: empirically based simulations predict raspberry fruit quality

“…We assumed that ovule fertilization required germination of at least five pollen grains, whereas the probability that a particular pollen tube reaches the ovary generally declines with increasing stigmatic pollen receipt owing to pollen‐tube competition (Harder et al. , b). Such density‐dependent pollen‐tube success has two consequences.…”