Reproductive assurance weakens pollinator-mediated selection on flower size in an annual mixed-mating species

TEIXIDO, ALBERTO L; AIZEN, MARCELO A

ANNALS OF BOTANY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2019 vol. 123 p. 195 - 209

0305-7364

? Background and Aims In animal-pollinated plants, direct and indirect selection for large and small flowersin 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 reducepollinator-mediated selection towards larger flowers, the consequences of delayed selfing for selection on flowersize in mixed-mating species remain overlooked. We investigated whether RA weakens selection on flower size inTuberaria guttata, a mixed-mating annual herb.? Methods We related pollinator visitation rates to flower size and measured seed production in emasculated,hand cross-pollinated and intact (control) flowers in three natural populations. For each population, we estimatedvariation in PL and RA across individuals differing in flower size and phenotypic selection on this trait.? Key Results Pollinator visitation increased and RA decreased with flower size in all populations. IncreasingRA diminished but did not fully alleviate PL, because of early-acting inbreeding depression. In the least-visitedand most pollen-limited population, RA increased seed production by >200 %, intensely counteracting the strongpollinator-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 adecrease in seed production due to selfing and the weakest pollinator-mediated selection on flower size.? Conclusions The results suggest that the balance between the extent of RA and outcrossing contributes todetermine flower size in mixed-mating systems. Pollinator-mediated selection favours larger flowers by increasingoutcrossed seeds, but the benefits of RA greatly lessen this effect, especially under severe conditions of pollenlimitation. Our findings also indicate that a mixed-mating system can represent an ?evolutionary trap? under anadequate pollinator supply.