Do metrics of sexual selection conform to Bateman's principles in a wind-pollinated plant?

Abstract

Bateman's principles posit that male fitness varies more, and relies more on mate acquisition, than female fitness. While Bateman's principles should apply to any organism producing gametes of variable sizes, their application to plants is potentially complicated by the high levels of polyandry suspected for plants, and by variation in the spatial distribution of prospective mates. Here we quantify the intensity of sexual selection by classical Bateman metrics using two common gardens of the wind-pollinated dioecious plant Mercurialis annua . Consistent with Bateman's principles, males displayed significantly positive Bateman gradients (a regression of fitness on mate number), whereas the reproductive success of females was independent of their ability to access mates. A large part of male fitness was explained by their mate number, which in turn was associated with males' abilities to disperse pollen. Our results suggest that sexual selection can act in plant species in much the same way as in many animals, increasing the number of mates through traits that promote pollen dispersal.

Digest: Sexual conflict as a novel hypothesis for the evolution of gynodioecy*

“…Besides confirming a novel hypothesis for the evolution of gynodioecy, this study adds to the growing body of work suggesting that concepts from sexual selection and sexual conflicts may apply to plants (Tonnabel et al. 2019). It opens the way for future investigations on whether the duration of the male phase fosters the number of sexual partners, being thus subject to sexual selection.…”

Rapid divergence in vegetative morphology of a wind-pollinated plant between populations at contrasting densities

“…We predicted that higher density, by increasing the degree of polygamy compared to low density, would place more relative weight on male-male competition for mates. Accordingly, we estimated that the male opportunity for sexual selection (i.e., variance in the number of sexual partners) was elevated by 65% (0.43 versus 0.26) in one high-density population compared to another at low-density, while this metric remained unaffected by the change in density for females (0.11 versus 0.12), thereby suggesting that our high-density condition indeed exacerbated malemale competition (Tonnabel et al, 2019a). We reasoned that male-male competition for accessing ovules in populations at high density would ultimately favor increased pollen production and male morphologies that promote effective pollen dispersal.…”

Illuminating the incredible journey of pollen

“…With so many pollen grains and so few ovules, the battle for mating success on the male side is much fiercer. The domination of these few ovules by a small number of individuals make male fitness more variable than female fitness (Bateman, 1948; Tonnabel et al, 2019) where some individuals have high male success and others have much lower male success (Fig. 2H).…”