Format: ORAL

Kathleen M. Kay1, Kathleen Darragh2, Dena L. Grossenbacher3, Pedro Jurez1, Santiago Ramrez4, Kathryn Uckele1, Oscar M. Vargas5

1 Department of Ecology and Evolutionary Biology, University of California, Santa Cruz; Santa Cruz, CA, USA 2 Department of Biology, Indiana University, Bloomington, IN, USA 3 Department of Biology, California Polytechnic State University, San Luis Obispo, CA, USA 4 Center for Population Biology, University of California, Davis; Davis, CA, USA 5 Department of Biological Sciences, California State Polytechnic University, Humboldt; Arcata, CA, USA

The evolution of hummingbird pollination is common across angiosperms throughout the Americas, presenting an opportunity to examine convergence in traits, genetics, and selective environments to better understand how complex phenotypes arise. We examine many independent shifts from bee to hummingbird pollination in the Neotropical spiral gingers (Costus; Costaceae) and address common explanations for the prevalence of these transitions. We reconstruct ancestral pollination states on a well-resolved phylogeny and examine variation in traits and environmental correlates across independent shifts. Using a phylogenomic approach, we assess historical introgression events to determine if convergence could involve the sharing of alleles across species. We further dissect the genetic basis of a recent bee-to-bird shift and compare those findings to genetic changes underlying floral traits in other Costus species. We also test the hypothesis that hummingbird pollination is adaptive in high-elevation pollination environments relative to bee pollination by translocating flowering plants of both types across an elevational gradient in Costa Rica. A consistent set of traits predict hummingbird pollination, but not the stereotypical ‘hummingbird’ traits of long, red flowers. We find many shifts to hummingbird pollination, no reversals, a single shared phenotypic optimum across hummingbird flowers, and little evidence of introgression. Our genetic investigations find large effect color and scent loci, small effect morphology loci, and some overlap in loci across independent floral transitions. In contrast to other clades, we find no association between pollination and climate, and mixed evidence that hummingbird pollination is adaptive in montane environments. Evolutionary shifts to hummingbird pollination in Costus are highly convergent and directional, involve a surprising set of traits when compared with other plants with analogous transitions, and refute the generality of several common explanations for the prevalence of transitions from bee to hummingbird pollination.