Enhanced leaky sex expression in response to pollen limitation in the dioecious plant Mercurialis annua

AbstractPhenotypic plasticity is almost ubiquitous across the tree of life, but clear demonstrations that it is adaptive are rare. In dioecious plants, males and females frequently show ‘leaky’ sex expression, with individuals occasionally producing flowers of the opposite sex. Here, we demonstrate that leaky sex expression in the wind-pollinated dioecious herb Mercurialis annua is plastically responsive to its mating context. We compared experimental populations of females growing either with or without males. Females growing in the absence of males were leakier in their sex expression than controls with males, producing more than twice as many male flowers. Moreover, because greater leakiness was more highly represented in the population’s progeny, we conclude that enhanced leakiness in sex expression is adaptive in M. annua. We discuss differences in the degree of plasticity between ploidal races of Mercurialis annua in terms of likely differences in the reliability of the signal plants may perceive for the presence of males in their populations. Our results provide a striking instance of adaptive plasticity in the reproductive behavior of plants and draw attention to possible constraints on plasticity when the environmental signals that individuals receive are unreliable.

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

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2019.0532 ◽

2019 ◽

Vol 286 (1905) ◽

pp. 20190532 ◽

Cited By ~ 6

Author(s):

Jeanne Tonnabel ◽

Patrice David ◽

John R. Pannell

Keyword(s):

Spatial Distribution ◽

Sexual Selection ◽

Reproductive Success ◽

Pollen Dispersal ◽

Male Fitness ◽

Female Fitness ◽

Dioecious Plant ◽

Common Gardens ◽

Mate Acquisition ◽

Mercurialis Annua

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.

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