Darwin's ‘mystery of mysteries’: the role of sexual selection in plant speciation

Abstract

Sexual selection is considered one of the key processes that contribute to the emergence of new species. While the connection between sexual selection and speciation has been supported by comparative studies, the mechanisms that mediate this connection remain unresolved, especially in plants. Similarly, it is not clear how speciation processes within plant populations translate into large‐scale speciation dynamics. Here, we review the mechanisms through which sexual selection, pollination, and mate choice unfold and interact, and how they may ultimately produce reproductive isolation in plants. We also overview reproductive strategies that might influence sexual selection in plants and illustrate how functional traits might connect speciation at the population level (population differentiation, evolution of reproductive barriers; i.e. microevolution) with evolution above the species level (macroevolution). We also identify outstanding questions in the field, and suitable data and tools for their resolution. Altogether, this effort motivates further research focused on plants, which might potentially broaden our general understanding of speciation by sexual selection, a major concept in evolutionary biology.

How Important Is Sexual Isolation to Speciation?

“…In plants, sexual isolation might arise from differences in (1) flowering phenology, (2) pollinator specialization, and (3) PMPZ barriers (e.g., pollen-stigma interactions and pollen competition; Baack et al 2015;Garlovsky et al 2023;Haghighatnia et al 2023). The relative rate (as opposed to strength, see below) of floral-related divergence during speciation compared to other sources of reproductive isolation can be difficult to disentangle, especially when there may be interacting effects, for example, pollination-related phenotypes and ecogeographic components.…”