Evolution of intraspecific floral variation in a generalist-specialist pollination system

Intraspecific processes impact macroevolutionary patterns through individual variation, selection, and ecological specialisation. According to the niche variation hypothesis, the broader ecological niche of generalist species has been proposed to increase in variation among individuals, either because they are constituted of diversified specialised individuals each exploiting a fraction of the species’ niche, or because they are constituted of true generalist individuals that experience relaxed selection. To test this hypothesis, we surveyed the individual floral morphology of species of Antillean Gesneriaceae, a group that has transitioned between specialisation for hummingbird pollination and generalisation multiple times throughout its evolutionary history. We characterised the profiles of corollas using geometric morphometrics and compared the intraspecific shape variance of specialists and generalists in a phylogenetic context. We used three approaches that differently accounted for the high dimensionality of morphological traits, the ancestral reconstruction of pollination syndromes over time, and the error associated with the estimation of the intraspecific variance. Our findings provide partial support for the niche variation hypothesis. If considering the whole shape in the analysis corroborated this idea, decomposing the shape into principal components indicated that not all aspects of the corolla exhibit the same pattern of variation. Specifically, pollination generalists tend to display greater intraspecific variation than specialists in terms of tubularity, but not of curvature. Accounting for the error in the estimation of the variance also reduced the support for the hypothesis, suggesting that larger sample sizes may be required to reach stronger conclusions. This study emphasises the reciprocal influence between plants and their pollinators on floral morphology at different biodiversity scales, by affecting intraspecific floral variation that can result in macroevolutionary patterns.

Methods
We quantified the corolla shape of species from the Gesneriinae subtribe using geometric morphometrics from flower photographs in strict lateral view. For each flower photograph, 32 landmarks were placed (6 landmarks and 26 semi-landmarks). Two landmarks were positioned at the tips of the petal lobes, two at the base of the petal lobes, and two at the base of the corolla.

Pollinator information was obtained from field-based information or inferred from flower characteristics for species with unstudied pollination biology in the field.

The phylogeny of the Gesneriinae subtribe (Gesneriaceae) species was reconstructed in *BEAST from DNA sequences of 5 nuclear genes (CYCLOIDEA, CHI, UFR3GT, F3H, and GAPDH ).