Evol Ecol Res 3: 129–155 (2001) Full PDF if your library subscribes.
Comparative studies of reaction norms in Arabidopsis. I. Evolution of response to daylength
Heidi Pollard,1 Mitchell Cruzan1,2 and Massimo Pigliucci1,2*
1Department of Botany and 2Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996-1100, USA
Author to whom all correspondence should be addressed.
The evolution of reaction norms (the genotype-specific manifestation of different phenotypes in response to environmental variation) has rarely been addressed from within a phylogenetic comparative framework, despite general agreement that we need a better understanding of how historical and deterministic processes (e.g. selection and constraints) interact to yield a particular pattern of variation of phenotypic plasticity within and across species. In this study, we compare the reaction norms to daylength in eight accessions of Arabidopsis thaliana from Scandinavia and three closely related species, A. arenosa, A. lyrata subsp. petraea and A. suecica. We find that across-environment means evolved continuously and very rapidly within this group, while plasticity (calculated as the difference between the character value under short photoperiod minus the expression of the same trait under long photoperiod) changed only rarely and especially at the base of the A. thaliana clade. Character means co-evolved in a fashion that identifies two functional sets of traits, one during the vegetative phase and the other during the reproductive phase, with trade-offs between characters expressed across the two phases. With a few exceptions, plasticities of different traits tended to evolve largely independently of each other. Several plasticities evolved in concert with their corresponding across-environment means, but by following a pattern of negative correlations that cannot be explained by simple geometrical considerations in environment-phenotype space. Neither the mean nor the plasticity of a focal trait, flowering time, were correlated with differences in phylogenetic relatedness, geographical distance or latitudinal differential. This suggests that neither genetic drift nor adaptation to large-scale geographical factors occurred.
Keywords: Arabidopsis, comparative method, daylength, intraspecific phylogeny, reaction norms, phenotypic plasticity.
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