Drift effects on the multivariate floral phenotype of Calceolaria polyrhiza during a postglacial expansion in Patagonia

Abstract

Quaternary environmental changes substantially impacted the landscape and promoted rapid evolutionary changes in many species; however, analyses of adaptive phenotypic variation in plants have usually neglected the underlying historical context. Here we associate phylogeography and phenotypic evolution by analyzing the divergence of Calceolaria polyrhiza multivariate floral phenotype after a Pleistocene postglacial expansion in Patagonia. Phenotypic matrix (P) properties (size, shape, orientation and phenotypic integration) of six refugium and six recent populations from two different phylogroups were compared following different approaches. We found that P-matrix shape and orientation remained stable despite the strong phylogeographic footprint of postglacial expansion. However, average proportional reductions in matrix size supported the expectation that drift had a significant effect on the floral phenotype in the northern phylogroup. When phylogeographic history was not included in the analyses, results overestimated phenotypic differences, whereas under explicit phylogeographic control, drift appeared as the best explanation for matrix differences. In general, recent populations showed a larger phenotypic divergence among them but a lower overall phenotypic variation than refugium populations. Selection skewers analyses indicated a lower potential response to selection in recently colonized populations than in refugium populations. We discuss that the combination of phylogeographic analyses with geographic distribution of functional phenotypic (genotypic) variation is critical not only to understand how historical effects influence adaptive evolution, but also to improve field comparisons in evolutionary ecology studies.