Pollinator abundance shifts where sexual selection acts in a flowering plant

Sexual selection in flowering plants unfolds across multiple sequential episodes, and the balance between them depends on how many pollinators are around, according to a new study of the hermaphroditic plant Brassica rapa published in PLOS Biology.

Although sexual selection is well established in animals, tests in plants remain limited. Theory based on anisogamy predicts that the two sex functions differ in the fitness benefits of gaining additional mates, a pattern repeatedly confirmed in animals. Plant studies, however, have relied solely on genetic parentage analyses to estimate mate numbers, which conflates success in accessing mates with success in fertilizing gametes.

To separate these stages, the researchers combined direct observations of buff-tailed bumblebee (Bombus terrestris) movements with genetic paternity analyses in experimental populations. This design provided independent estimates of the observational number of mates acquired and of realized fertilization success, allowing the team to disentangle consecutive episodes of sexual selection within the same populations.

The results identified pollen competition for ovules as the primary arena for sexual selection in B. rapa. Competition for access to mates constituted a secondary force, and it was stronger in the male than in the female sex function, matching the prediction of classic sexual selection theory.

The ecological context mattered as well. When the researchers experimentally reduced pollinator abundance, the balance between pre- and post-pollination sexual selection shifted, increasing the opportunity for selection on mate acquisition. The authors also found that ignoring pollinator movements led to biased estimates of pre-pollination sexual selection, underscoring the value of pairing behavioral observations with paternity data.

Overall, the study demonstrates that sexual selection in plants is not a single process but a sequence of episodes, shaped by the behavior and abundance of pollinators, with competition among gametes emerging as the dominant stage in this species.

Subject of Research: How pollinator abundance shapes the episodes of sexual selection in the hermaphroditic plant Brassica rapa

Article Title: Pollinator abundance shapes sexual selection in an angiosperm

Article References: Barbot, E., Dufaÿ, M., Janicke, T., Lapeyre, B., Orcel, D., Rousset, F., & Tonnabel, J. (2026). Pollinator abundance shapes sexual selection in an angiosperm. PLOS Biology, 24(10), e3003579. https://doi.org/10.1371/journal.pbio.3003579

Image Credits: AI Generated

DOI: 10.1371/journal.pbio.3003579

Keywords: sexual selection, pollinators, Brassica rapa, Bombus terrestris, paternity analysis, anisogamy, pollen competition, mate acquisition, plant reproduction, PLOS Biology, Pollinator, abundance