Population-level plant pollination mode is influenced by Quaternary climate and pollinators

Patterns in ecology are the products of current factors interacting with history. Nevertheless, few studies have attempted to disentangle the contribution of historical and current factors, such as climate change and pollinator identity and behavior, on plant reproduction. Here, we attempted to separate the relative importance of current and historical processes on geographical patterns of the mating system of the tree species Curatella americana (Dilleniaceae). Specifically, we asked the following: (a) How do Quaternary and current climate affect plant mating system? (b) How does current pollinator abundance and diversity relate to plant mating system? (c) How does mating system relate to fruit/seed quantity and quality in C. americana? We recorded pollinators (richness, frequency, and body size) and performed pollination tests in ten populations of C. americana spread over 3,000 km in the Brazilian savannah. The frequency of self-pollination in the absence of pollinators was strongly influenced by historical climatic instability and not by present-day pollinators. In contrast, seed set from hand-cross and natural pollination were affected by pollinators (especially large bees) and temperature, indicating the importance of current factors on out-cross pollination. Two populations at the Southern edge of the species' distribution showed high level of hand-cross-pollination and high flower visitation by large bees, but also a high level of autogamy resulting from recent colonization. Our results indicate that historical instability in climate has favored autogamy, most likely as a reproductive insurance strategy facilitating colonization and population maintenance over time, while pollinators are currently modulating the level of cross-pollination.