April 13, 2021
Department Ecology and Evolutionary Biology, University of Arizona
" Phylogenomic Studies of Character Evolution in New World Astragalus (Fabaceae) "
Co-Sponsored Seminar Presented by UCLA’s Department of Ecology and Evolutionary Biology and the Mildred E. Mathias Botanical Garden
Both diversification (the formation of new species) and disparification (differentiation related to diverging ecological niches) have been at work in shaping species radiations. Classic examples of adaptive radiations are well known for extremes of ecological differentiation and associated morphological divergence, but perhaps lesser known are nonadaptive radiations, in which rapid diversification was not apparently accompanied by matching disparification. The approximately 500 species of the Neo-Astragalus clade of Astragalus L. (Fabaceae) in the Americas are estimated to have shared a common ancestor as recently as 4.5 million years ago, however, as largely temperate, perennial herbaceous plants, these species are rather ecologically similar in comparison to classic examples of plant adaptive radiations. I explored potential cryptic (or difficult to observe) differentiation among Neo-Astragalus species by examining character evolution and homoplasy in morphological traits as well as the hyperaccumulation of selenium using phylogenies I estimated from whole chloroplast genomes and nuclear ribosomal DNA cistrons sequenced from a combination of specimens collected in the field and existing herbarium specimens. About two dozen Neo-Astragalus species are selenium hyperaccumulators that are not only restricted to soils already rich in the element but also accumulate it to the point they are highly toxic to most herbivores. After characterizing the extent of selenium accumulation in these and potentially closely related species using analytical chemistry techniques, I reconstructed the evolutionary history of the trait in Neo-Astragalus. Convergent evolution in this trait could be indicative of other kinds of cryptic but ecologically important disparification that may have occurred during the evolution of Neo-Astragalus in the Americas and in Astragalus as a whole.
Host: Victoria Sork