Selection of floral traits by pollinators and seed predators during sequential life history stages

Organismal traits often influence fitness via interactions with multiple species. That selection is not necessarily predictable from pairwise interactions, such as when interactions occur during different lifecycle stages. Theoretically, directional selection during two sequential episodes, e.g., pollination and seed survival, can generate quadratic or correlational selection for a set of traits that passes both selective filters. We compared strength of selection during pollination versus seed predation in the field and tested whether interactions with multiple species give rise to non-linear selection on floral traits. We planted common gardens with seeds of two species of Ipomopsis and hybrids in sites where pollination was primarily by hummingbirds or also included hawkmoths. We examined selection on six floral traits, including corolla width, sepal width, color, nectar, and two scent compounds.  Female fitness (seeds) was broken down into fitness during (1) pollination (seeds initiated) and (2) seed predation (proportion seeds escaping fly predation). All traits showed evidence of selection. Directional and quadratic selection were stronger during seed initiation than seed predation. Correlational selection occurred mostly during seed initiation rather than arising from combining species interactions at two points in the lifecycle.  These results underscore how multispecies interations can combine to exert selection on trait combinations.

Methods
Data were collected on plants in the field.