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Morphological responses to simulated wind in the genus Brassica (Brassicaceae): allopolyploids and their parental species¹

²Department of Botany and Ecology and Evolution, 437 Hesler Biology, University of Tennessee, Knoxville, Tennessee 37996 USA

ABSTRACT

Thigmomorphogenesis refers to the widespread ability of sessile organisms to modify their morphology in response to a variety of mechanical stimulations, from direct contact with the stem by insects or other plants to flexure caused by wind, water, or snow. In this paper we investigated the differences in the reaction norms to wind exposure of seven species of the Brassicaceae that constitute a well-studied complex of known phylogenetic relationships. The goals included the characterization of differences between allopolyploids and their parental species and the comparison of wild and fast-cycling accessions within each species. We found statistically significant variation for plasticity among species or accessions for several characters, but the majority of the phenotypic variance was accounted for by overall (across-environment) differences among species and accessions and not by variation in plasticity. Allopolyploids displayed an array of behaviors when compared to their parents, from co-dominance to complete dominance to exceeding both parental means. Furthermore, fast-cycling plants showed distinct features from their wild relatives, suggesting that wild populations should be included with artificially selected lines in ecological studies. We proposed further steps to gain a more comprehensive understanding of thigmomorphogenetic responses, by integrating current research on the molecular bases of thigmomorphogenesis with insights into the ecology and evolution of plants exposed to wind.

Key Words: Brassica • phenotypic plasticity • Raphanus • thigmomorphogenesis • wind