Abstract Detail

Sexual selection in flowering plants: traits, processes, and estimation

Lynn, Austin [1], Piotter, Emelyn [2], Galen, Candace [3].

The Lion’s Mane: Is the evolution of dandelion pollen sculpturing driven by natural or sexual selection?

Pollen size and sculpture traits vary widely between taxa and are thought to relate to function. Sexual selection may alter the pollen exine through traits that facilitate male-male competition by altering transfer to animal pollinators or from pollinators to the stigma. In contrast, natural selection mediates traits involved in survival of the pollen grain until pollination. Many entomophilous lineages possess echinate or spiny pollen, such as groups within the Asteraceae and Malvaceae. Our preliminary observations of co-occurring sexual and apomictic dandelion species Taraxacum ceratophorum and T. officinale show that sexual species have exaggerated spine traits compared to apomict ones. We designed field experiments to test whether sexual or natural selection acts on pollen sculpture traits. We explored sexual selection on exine traits via propensity for pollen to adhere to hairs of bumblebee (Bombus spp.) or syrphid fly (Diptera: Syrphidae) pollinators and germinate on compatible stigmas. We assessed natural selection by testing for defensive action of spines against consumption by pollinators. Greater distance between spines significantly predicts the capacity of pollen to adhere to a bee, while longer spines characterize pollen that germinates on the stigma compared to pollen washed off the stigma. Syrphid flies pick up dandelion pollen of significantly larger diameter than the pool of pollen produced by the donor flower. Pollen contained in corbiculae (pollen baskets) of foraging bumblebees and in feces of syrphid flies exhibits similar spine and size characteristics as pollen produced by donor flowers, suggesting that natural selection from pollen predation has little influence on pollen morphology. Our results suggest that during bumblebee pollination, sexual selection acts on functionally related aspects of pollen morphology during sequential stages of pollination. Conversely, pollination by syrphid flies suggests natural selection for defense, with foragers selecting pollen sources based on size or nutritional value. For pollination generalists, the composition of floral visitors may influence the balance between sexual and natural selection on pollen traits.

1 - 1301 Old Hwy 63 South , Apt 805, Columbia, MO, 65201, United States
2 - University of Missouri, Division of Biological Sciences, 202 Tucker Hall, Apt 805, Columbia, MO, 65202, United States
3 - 505 S GLENWOOD AVE, 505 S Glenwood Ave, Columbia, MO, 65203, United States

Keywords:
Sexual selection
pollen
evolution
Pollination
mutualism
pollinator-mediated selection.

Presentation Type: Colloquium Presentations
Session: CO08, Sexual Selection in Flowering Plants: Traits, Processes, and Estimation
Location: Tucson H/Starr Pass
Date: Tuesday, July 30th, 2019
Time: 2:15 PM
Number: CO08004
Abstract ID:359
Candidate for Awards:Katherine Esau Award,Ecological Section Best Graduate Student Paper