No evidence that seed predators constrain pollinator-mediated trait evolution in a tropical vine

Premise of The Study - Turnover in biotic communities across heterogeneous landscapes is expected to lead to variation in interactions among plants, their mutualists, and their antagonists. Across a fragmented landscape in northern Costa Rica, populations of the euphorb vine Dalechampia scandens vary widely in mating systems and associated blossom traits. Previous work suggests that populations are well adapted to the local reliability of pollination by apid and megachilid bees. Here, we test whether variation in the intensity of predispersal seed predation by Nanobaris seed weevils also contributes to the observed variation in blossom traits.

Methods - We studied spatio-temporal variation in the relationships between floral advertisement and the probability of seed predation within three focal populations. Then, we assessed among-population covariation of predation rate, pollination reliability, mating system, and blossom traits across 20 populations.

Key Results - The probability of seed predation was largely unrelated to variation in floral advertisement both within focal populations, and among the larger sample of populations. The rate of seed predation was only weakly associated with the rate of cross-pollination in each population but tended to be proportionally greater in populations experiencing less reliable pollination.

Conclusions - These results suggest that, while solitary bees and seed weevils differ in their responses to landscape-scale environmental heterogeneity, geographic variation in the relative intensities of mutualistic and antagonistic interactions have not affected the evolutionary trajectories of floral advertisement in plant populations in this system. Thus, pollinator-driven floral trait evolution in Dalechampia scandens in our study area appears not to be constrained by conflicting seed-predator-mediated selection.