Abstract Detail

Systematics Section/ASPT

Lee, Chris [1], Whitton, Jeannette [2].

Evidence for adaptive radiation in Townsendia from phylogenetic inference and ecological niche modeling.

Townsendia (Asteraceae) includes approximately 28 taxa that are distributed throughout the Rocky Mountain regions of the Yukon and Alaska to New Mexico and parts of Mexico. This group exemplifies a range of growth habits including upright biennials, sprawling annuals and acaulescent perennials as well as both apomictic and sexual reproduction. In addition, species differ in range size, with some taxa spanning from Yukon to Colorado but others restricted to lone hillsides in Wyoming; these differences appear to be correlated with edaphic ranges, from soil generalists to, e.g., gypsophilous endemics. Nonetheless, this great morphological, ecological and reproductive variation belies the low levels of genetic variation seen in the plastid and nuclear ribosomal DNA. With ~5000bp of sequencing data, a phylogeny for Townsendia remains unresolved, while the three outgroup genera, Boltonia, Dichaetophora, and Astranthium show high levels of genetic divergence. Combined, these three outgroups include only nine taxa and generally share similar morphological characteristics. These various lines of evidence suggest that Townsendia has diversified rapidly, and may represent a case of adaptive radiation. Adaptive radiation is the rapid diversification of organisms into a variety of ecological niches and can occur when an ancestral taxon chances upon underutilized resources following colonization, extinction of previous taxa, or evolution of a key innovation.. We have combined the results of phylogenetic analysis with tests of ecological niche divergence between putative sister taxa to assess evidence for ecological divergence as a factor in this diversification. We used ecological niche modeling implemented in Maxent to measure the predicted niche overlap of closely related Townsendia. These values were compared against the background environmental distribution to seek general trends for niche divergence or conservatism in the group. Our results so far have found evidence for niche conservatism in sister taxa with greater genetic distance, but this trend reverses to one of niche divergence with decreased genetic distance between pairs of sister species. Well-defined species circumscriptions within Townsendia initially suggested a straightforward phylogeny for the group. Although we have found this original assumption false, the confluence of phylogenetic inference, niche modeling and taxonomic studies suggest adaptive radiation as a possible explanation for the observed patterns.

1 - University of British Columbia, Botany, Room #3529 - 6270 University Boulevard, Vancouver, BC, V6T1Z4, Canada
2 - University Of British Columbia, Department Of Botany, 3529-6270 UNIV BLVD, VANCOUVER, BC, V6T 1Z4, Canada

Keywords:
Asteraceae
niche modeling
Phylogeny
adaptive radiation
Maxent.

Presentation Type: Oral Paper:Papers for Sections
Session: 30
Location: Payette/Boise Centre
Date: Tuesday, July 29th, 2014
Time: 2:30 PM
Number: 30005
Abstract ID:778
Candidate for Awards:George R. Cooley Award