Geographical differentiation in floral traits along the distribution range of the Patagonian oil-producing Calceolaria polyrhiza: do pollinators matter?

COSACOV, A.; COCUCCI, A.A.; SÉRSIC, A.N.

ANNALS OF BOTANY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2014 vol. 113 p. 251 - 266

0305-7364

Background and Aims: The underlying evolutionary and ecological processes of pollinator driven floral diversification are still poorly understood. The Grant-Stebbins model suggests that differences in geographical ranges of the more effective pollinator could result in ?pollination ecotypes?. To test this hypothesis, we studied geographical phenotypic variation of Calceolaria polyrhiza and its pollinators, two oil-collecting bee species that differ significantly in body size and geographical distribution. This system conform a specialist oil-flower/oil-bee plant-pollinator interaction endemic to Patagonia. Methods: We measured six floral and seven vegetative traits in 46 populations distributed across the entire species range. We selected 24 sites and retrieved their climatic and edaphic parameters; we captured 2-16 bees/site of the most frequent pollinator species and measured a critical flower-bee fitting trait involved in effective pollination. We examined geographical pattern of phenotypic variation and its relationship with biotic and abiotic factors using uni- and multivariate analyses. Mantel permutation test was used to explore decoupled geographic variation between corolla area and fit-related floral traits. Key Results: Body length of pollinators and floral fit-related traits were strongly correlated with one another. Geographic variation of mechanical-fit related traits is decoupled from variation in corolla size. This latter floral trait has a geographical pattern concurrent with that of vegetative traits and is mainly affected by climatic gradients. Conclusions: The relationship between floral operative distance and bee length remained significant even in models that included various environmental variables and an allometric predictor one. We conclude that in this system pollinators play a key role in shaping floral phenotype at a geographical scale, promoting the differentiation of two floral ecotypes. The abiotic environment also has an important role, mainly affecting floral size. Decoupled geographical variation between fit-related traits and floral size is suggested to represent a strategy to maintain plant-pollinator phenotypic matching in this environmentally heterogeneous area.