When morphology stands still: constrained floral evolution in a mega-diverse legume genus

Annals of Botany, vol. 138, pp. 1035–1047

Abstract

BACKGROUND AND AIMS: Changes in floral morphology are key for the evolutionary success of flowering plants. However, many species-rich and ecologically diverse groups show low variation in floral traits. Low morphological variation may be associated with selective pressures and constraints to changes. Nonetheless, because our understanding of floral morphological evolution is focused on plant groups with diverse and specialized floral morphology, there has been little progress in identifying factors underlying floral morphological uniformity. Herein we addressed this issue by asking how the morphology of flowers in the mega-diverse legume genus Mimosa is shaped by constraints. METHODS: We collected floral morphological data across phylogenetically and geographically representative Mimosa species. By integrating morphology into an evolutionary framework, we quantified morphological diversity and tested whether morphological changes are better explained by neutral or adaptive evolutionary models. Then, we accessed evolutionary model parameters to evaluate the role of evolutionary constraints in limiting morphological changes across Mimosa floral whorls. KEY RESULTS: Our results showed that floral morphology is remarkably homogeneous and evolved under evolutionary constraints. Levels of morphological variation and evolutionary parameter estimates vary across floral whorls, indicating that constraint strength differs throughout the flower. CONCLUSIONS: The homogeneous and evolutionarily constrained flowers of Mimosa are unlikely to have been primarily driven by pollinator-mediated selection. We hypothesized that the development and function of flowers in the mimosoid inflorescence constrained trait evolution in this mega-diverse yet morphologically uniform group.

Authors 4

1. Monique Maianne corresponding

   Oklahoma State University · Universidade Federal de São Carlos · Universidade de São Paulo

   Affiliation as printed

   Departamento de Botânica, Universidade Federal de São Carlos , São Carlos, SP 13565-905 ,

   Department of Biology, Oklahoma State University , Stillwater, OK 74078 ,

   Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Universidade de São Paulo , Ribeirão Preto, SP 14040-900 ,

2. Yago Barros‐Souza Aachen Biodiversity Hotspots Research Group Naturalis Biodiversity Center

   Naturalis Biodiversity Center · Universidade Federal de São Carlos · Universidade de São Paulo

   Affiliation as printed

   Biodiversity Hotspots Research Group, Naturalis Biodiversity Center , Leiden 2333 CR ,

   Departamento de Botânica, Universidade Federal de São Carlos , São Carlos, SP 13565-905 ,

   Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Universidade de São Paulo , Ribeirão Preto, SP 14040-900 ,

3. Fabio Andrade Machado

   Oklahoma State University

   Affiliation as printed

   Department of Biology, Oklahoma State University , Stillwater, OK 74078 ,

4. Leonardo Maurici Borges

   Universidade Federal de São Carlos

   Affiliation as printed

   Departamento de Botânica, Universidade Federal de São Carlos , São Carlos, SP 13565-905 ,