The lion's mane: sexual and natural selection on pollen morphology in Taraxacum

Premise of the study: Spiny pollen has evolved independently in multiple entomophilous lineages. Sexual selection may act on exine traits that facilitate male mating success by influencing the transfer of pollen from the anther to the body of the pollinator, while natural selection acts to increase pollen survival. We postulated that relative to sexual congeners, apomictic dandelions undergo relaxed selection on traits associated with male mating success.

Methods: We explored sexual selection on exine traits by measuring the propensity for Taraxacum spp. pollen to attach to hairs of flower-visiting bumblebees (Bombus spp.) or flies (Diptera: Syrphidae and Muscoidea), and assessed natural selection by testing whether pollen traits defend against consumption.

Key Results: Pollen picked up by bumblebees exhibited a narrower subset of spine spacing phenotypes, consistent with stabilizing selection. Flies picked up larger pollen from flowers than expected at random. Surveys of corbicul...