Presentation Title

Sex and aggression among males: does mating system influence the evolution of competitive behavior in the pollen of flowering plants?

Start Date

November 2016

End Date

November 2016

Location

HUB 302-124

Type of Presentation

Poster

Abstract

Few studies have evaluated the effects of plant mating system on the evolution of pollen performance in angiosperms, despite predicted differences between self-fertilizing (i.e., selfing) and outcrossing species in the intensity of competition among genetically distinct pollen grains. In this study, we test two predictions concerning how pollen performance should evolve in selfing vs. outcrossing species. These predictions follow from the observation that the intensity of competition among genetically distinct pollen grains is likely to be much stronger in outcrossing than in selfing taxa because the stigmas of outcrossers receive multiple pollen genotypes that must compete for access to unfertilized eggs, while those of selfers receive only a single genotype. As a result, natural selection on pollen performance traits should be much stronger in outcrossers than in selfers. First, we tested the prediction that, due to sustained selection favoring aggressive and competitive pollen grains in outcrossing taxa, they should evolve pollen grains that germinate faster and/or produce faster-growing pollen tubes than self-fertilizing taxa. Second, we tested the prediction that, given stronger selection among pollen genotypes on the stigmas of outcrossed relative to selfing species, genetic variation in pollen performance traits in outcrossers should be eliminated more readily than in selfing species, resulting in lower genetic variation in pollen performance traits in outcrossing populations. Previous studies on pollen performance in closely related selfing vs. outcrossing species have not controlled for temperature, soil nutrients, and precipitation, all of which may affect pollen germination and pollen tube growth rates within the style. Our experimental study aimed to minimize environmentally-induced variation in pollen performance by growing two sister species with contrasting mating systems in the native wildflower genus, Clarkia, under controlled conditions to understand the evolutionary relationship between mating system and pollen competition.

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Sex and aggression among males: does mating system influence the evolution of competitive behavior in the pollen of flowering plants?

HUB 302-124

Few studies have evaluated the effects of plant mating system on the evolution of pollen performance in angiosperms, despite predicted differences between self-fertilizing (i.e., selfing) and outcrossing species in the intensity of competition among genetically distinct pollen grains. In this study, we test two predictions concerning how pollen performance should evolve in selfing vs. outcrossing species. These predictions follow from the observation that the intensity of competition among genetically distinct pollen grains is likely to be much stronger in outcrossing than in selfing taxa because the stigmas of outcrossers receive multiple pollen genotypes that must compete for access to unfertilized eggs, while those of selfers receive only a single genotype. As a result, natural selection on pollen performance traits should be much stronger in outcrossers than in selfers. First, we tested the prediction that, due to sustained selection favoring aggressive and competitive pollen grains in outcrossing taxa, they should evolve pollen grains that germinate faster and/or produce faster-growing pollen tubes than self-fertilizing taxa. Second, we tested the prediction that, given stronger selection among pollen genotypes on the stigmas of outcrossed relative to selfing species, genetic variation in pollen performance traits in outcrossers should be eliminated more readily than in selfing species, resulting in lower genetic variation in pollen performance traits in outcrossing populations. Previous studies on pollen performance in closely related selfing vs. outcrossing species have not controlled for temperature, soil nutrients, and precipitation, all of which may affect pollen germination and pollen tube growth rates within the style. Our experimental study aimed to minimize environmentally-induced variation in pollen performance by growing two sister species with contrasting mating systems in the native wildflower genus, Clarkia, under controlled conditions to understand the evolutionary relationship between mating system and pollen competition.