The cost of self‐promotion: ecological and demographic implications of the mentor effect in natural plant populations

Abstract

Under the mentor effect, compatible heterospecific pollen transfer induces self-pollen germination in otherwise self-incompatible plants. The mentor effect could be considered a novel mode of reproductive interference if it negatively impacts fitness. Yet to date, this phenomenon has predominately been investigated under experimental conditions rather than in situ. We address this gap in natural populations of the self-incompatible native dandelion, Taraxacum ceratophorum, where selfing only occurs in association with hybridization from exotic Taraxacum officinale.We tested whether self-fertilization rate increases in the hybrid zone, as predicted due to the mentor effect. Using results from these investigations, we created an exponential growth model to estimate the potential demographic impacts of the mentor effect on T. ceratophorum population growth.Our results demonstrate that the strength of the mentor effect in Taraxacum depends on the prevalence of pollinator-mediated outcross pollen deposition rather than self-pollination. Demographic models suggest that reduced outcrossing in T. ceratophorum under exotic invasion could negatively impact population growth through inbreeding depression.We demonstrate the mentor effect is rare in natural populations of T. ceratophorum due to masking by early life cycle inbreeding depression, prevalent outcrossing, and ovule usurpation by heterospecific pollen.

Pollen interference between rare and common species

“…For our species, self-incompatible species showed an overall lower seed set, while breeding system did not affect seed number or HPI in any way. Self-compatibility might play a role especially in a natural community, where HP can act through the mentor effect (de Nettancourt, 1997), and allowing for self-fertilization even in self-incompatible flowers, with consequent ovule abortion (Lynn, Sullivan, & Galen, 2022). In our study we showed how self-incompatible species are less likely to produce seeds even when enough pollen is present.…”