Tuberaria guttata

Reproductive assurance weakens pollinator-mediated selection on flower size

The consequences of delayed selfing by reproductive assurance for selection on flower size in mixed-mating species is relevant to understand the evolution of plant breeding systems.

In animal-pollinated plants, direct and indirect selection for large and small flowers in predominantly outcrossing and selfing species, respectively, is a common consequence of pollen limitation (PL). However, many hermaphroditic species show a mixed-mating system known as delayed selfing, which provides reproductive assurance (RA) only when outcrossing is not realized. Although RA is expected to reduce pollinator-mediated selection towards larger flowers, the consequences of delayed selfing for selection on flower size in mixed-mating species remain overlooked. Teixido and Aizen investigated whether RA weakens selection on flower size in Tuberaria guttata, a mixed-mating annual herb.

Tuberaria guttata

Pollinator visitation increased and RA decreased with flower size in all populations. Increasing RA diminished but did not fully alleviate PL, because of early-acting inbreeding depression. In the least-visited and most pollen-limited population, RA increased seed production by >200 %, intensely counteracting the strong pollinator-mediated selection for larger corollas. In the most-visited population, however, RA increased seed production by an average of only 9 %. This population exhibited the largest fraction of individuals that showed a decrease in seed production due to selfing and the weakest pollinator-mediated selection on flower size.

The results suggest that the balance between the extent of RA and outcrossing contributes to determine flower size in mixed-mating systems. Pollinator-mediated selection favours larger flowers by increasing outcrossed seeds, but the benefits of RA greatly lessen this effect, especially under severe conditions of pollen limitation. Their findings also indicate that a mixed-mating system can represent an β€˜evolutionary trap’ under an adequate pollinator supply.

Alex Assiry

Alex Assiry is an editorial assistant in the Annals of Botany Office. When not working, Alex listens for the opportunity to help.

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