Abstract Detail

Recent advances in phylogeny and systematics of Brassicaceae 

Cacho, Natalia Ivalu [1], Strauss, Sharon [2].

Untangling the evolutionary ecology of soil specialization in Streptanthus and allies through a combined phylogenetic and ecological approach.

Integration of phylogenies with clade-wide ecological data is expanding our ability to address classic ecological questions. Plant soil specialists contribute greatly to global diversity; yet, the eco-evolutionary forces responsible for generating this diversity are poorly understood. We integrate molecular phylogenies with descriptive and experimental ecological data, creating a powerful framework with which to elucidate forces driving soil specialization. Streptanthus is recognized as an “extraordinary example of adaptive radiation and edaphic specialization” because about 30% of its species are edaphic specialists endemic to serpentine soils and it presents a remarkable morphological and ecological diversity. However, low phylogenetic resolution within Streptanthus, and generally within the Thelypodieae, has limited insights on the origins and history of serpentine use in this group. We present progress on a research program using a much-improved phylogenetic hypothesis for the Streptanthoid Complex (Streptanthus and allied genera Caulanthus, Streptanthella, Stanleya, Thysanocarpus, Thelypodium) as a framework to test hypotheses on the evolutionary ecology of edaphic specialization. Our phylogenetic framework is based on three newly identified and highly variable single copy nuclear regions, three widely used nuclear markers, and two chloroplast regions. Our taxonomic sampling includes >86% of species in Streptanthus and Caulanthus, as well as representatives of several closely allied genera. Using phylogeny and clade-wide field data on soil chemistry and microhabitat bareness (amount of bare ground surrounding plants in natural field sites), we explore the history of specialization to serpentine soil, and the role of chemically similar soils in the evolution of serpentine use. We find evidence that occupation of bare environments, and not of chemically similar soils, preceded shifts to serpentine, and may serve as an evolutionary precursor to harsh elemental soils and environments. In greenhouse experiments, taxa from barer environments are poorer competitors, a tradeoff that may contribute to soil endemism. With chemical profiles of glucosinolates, we study the evolution of chemical plant defense, and test hypotheses of Escalation of Defense (EDH), and of Resource Availability (RAH). Consistent with findings in other groups, we observe low phylogenetic signal in glucosinolate production. Support for both, EDH and RAH, is limited, but glucosinolate defense is correlated with microhabitat bareness, supporting this metric as a potentially underappreciated aspect of soil specialization. We also present progress on the systematics, biogeography, and the evolution of range size and genome size in this group.

1 - Instituto de Biología-National Autonomous University of Mexico, UNAM, Botany, 3er Circuito de Ciudad Universitaria, Mexico, DF, 04510, Mexico
2 - University Of California Davis, Section Of Evolution And Ecology, One Shields Avenue, Davis, CA, 95616, USA

Keywords:
adaptation
edaphic specialization
serpentine
plant secondary chemistry
exaptation
herbivory
plant competitive ability.

Presentation Type: Colloquium Presentations
Session: C2
Location: Salon 8/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 4:15 PM
Number: C2007
Abstract ID:189
Candidate for Awards:None