Geographic Patterns In Pollen Production In The Plant Ring SpeciesEuphorbia tithymaloidesIn The Caribbean

Abstract

Abstract—We examine investment in male function in the context of geography and floral morphology in the plant ring speciesEuphorbia tithymaloides, which colonized the Caribbean from Mexico/Guatemala along two fronts that roughly correspond to the Greater and the Lesser Antilles and that meet in the vicinity of the Anegada Passage. Our results on investment in pollen relative to ovule production are consistent withE. tithymaloidesrelying on pollinators for reproduction across its range in the Caribbean. We document a geographic pattern of reduction in anther number and pollen:ovule ratios in populations ofE. tithymaloidestowards the Anegada Passage, which is consistent with a possible geographic transition towards a mixed breeding system where selfing has increased importance in this area where its two expansion fronts meet. The reduction in pollen production is correlated with inflorescence morphology, which converges to relatively shorter cyathia towards the Anegada Passage along both fronts. We discuss alternative scenarios and potential drivers of the patterns we document.