Macroevolution of panicoid inflorescences: a history of contingency and order of trait acquisition

REINHEIMER RENATA; A. C. VEGETTI; RUA G.H.

ANNALS OF BOTANY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2013 p. 1 - 16

0305-7364

? Background and Aims Inflorescence forms of panicoid grasses (Panicoideae s.s.) are remarkably diverse and they look very labile to human eyes; however, when performing a close inspection one can identify just a small subset of inflorescence types among a huge morphospace of possibilities. Consequently, some evolutionary constraints have restricted, to some extend, the diversification of their inflorescence. Developmental and genetic mechanisms, the photosynthetic type, and plant longevity have been postulated as candidate constraints for Angiosperms and panicoids in particular; however it is not clear how these factors opperate and which of these have played a key role during the grass inflorescence evolution. To gain insigths into this matter we investigate the macroevolutionary aspects of panicoid inflorescences.? Methods The inflorescence aspect (lax versus condensed), homogenization, truncation of the terminal spikelet, plant longevity and photosynthetic type were the traits selected for this study. Maximum Likelihood and Bayesian Markov chain Monte Carlo methods were used to test different models of evolution and to evaluate the existence of evolutionary correlation among the traits. For those cases in which the correlation was confirmed, test of contingency and order of trait acquisition were preformed to further explore the patterns of such co-evolution.? Key Results Data reject the independent model of inflorescence trait evolution and confirmed the existence of evolutionary contingency. Results support the general trend of homogenization being a prerequisite for the posterior loss of the terminal spikelet of the main axis. There was no evidence for temporal order in the gain of homogenization and condensation; consequently, the homogenization and condensation could occur simultaneously. The correlation between inflorescence traits with plant longevity and photosynthetic type is not confirmed.? Conclusions The findings indicate that the lability of the panicoid inflorescence is just apparent. Indeed, we found that the history of the panicoids inflorescence is a combination of inflorescence trait contingency and order of character acquisition. These indicate that developmental and genetic mechanisms may be important constrains that have limited the diversification of the inflorescence form in panicoid grasses.