Associate Professor Jardin Botanique de Montréal Montréal, Quebec, Canada
Background/Question/Methods
Pollination can be regarded as a significant part of the ecological niche of plants, as the majority of plants rely on pollinators as a resource to ensure their reproduction and may compete for them. Plants also adapt to their pollinator environment, promoting evolutionary divergence of floral traits. It has long been recognized that pollinators have an impact on the strength and directionality of floral evolution and floral phenotypic variation, but the width of the pollination niche can also impact morphological variation. Indeed, floral traits of pollination specialists are expected to be under relatively constant selection pressure and thus exhibit less phenotypic variation than species with more generalist pollination strategies. It is therefore predicted that generalists will demonstrate greater intraspecific variation than specialists in their floral shapes, as a result of multiple conflicting selective pressures imposed by different functional types of acting visitors.
We test this hypothesis using 24 species of Antillean Gesneriaceae for which two main pollination strategies evolved repeatedly. We quantified corolla shapes from 233 individuals using geometric morphometrics. Using the first 3 principal components of the floral morphospace and ancestral reconstructions of the pollination strategies, we analyzed the evolution of the intraspecific variation in a hierarchical Bayesian framework.
Results/Conclusions
We found that in most aspects of the corolla morphology, generalist species evolved independently towards greater optimal intraspecific variation than specialists. This result is in line with the hypothesis of more variable generalists at an intraspecific level as opposed to specialists. It also highlights the importance of considering the evolution of variation itself, which is rarely examined at the macro-evolutionary scale. Generalists may be visited homogeneously by pollinators of different functional types or, conversely, individuals within generalist populations may be pollinated by heterogeneous guilds of pollinators, which may be the source of significant intraspecific variation. Whether the greater intraspecific variation of pollination generalists is the result of greater variation overall or the presence of many diversified specialized phenotypes within species still needs further exploration.
