Biology Department

Research Overview

Our research investigates mechanisms of adaptation and speciation in flowering plants. In particular, we are interested in the phenotypic traits responsible for ecological differentiation and reproductive isolation, and the genetics underlying these characteristics. This work encompasses a variety of approaches, with primary emphasis on field experiments conducted in nature. Ongoing investigations are outlined below.

Polyploidy as an evolutionary mechanism

Genome duplication is common in flowering plants, and widely believed to drive adaptation and speciation. Despite its apparent importance, the contributions of polyploidy to phenotypic evolution and reproductive isolation have not been evaluated rigorously. The difficulty of inference has been a major impediment: how does one distinguish the contributions of polyploidy per se from overall genetic divergence? Our research combines studies of naturally occurring polyploid populations with investigations of neopolyploids first generation, spontaneous polyploid mutants to characterize the phenotypic consequences of polyploidization. Current studies are focused on Achillea borealis (Asteraceae), a native perennial herb with tetraploid and hexaploid populations in western North America.

Evolutionary history of polyploid complexes

The nature of polyploid speciation relates to major conceptual issues, in particular, the evolutionary significance of interspecific hybridization. Unfortunately, the genetic features of polyploids present special challenges to phylogenetic inference. Our research combines molecular phylogenetic approaches with genetic and cytogenetic analysis to rigorously evaluate the origins of natural polyploids. Current studies are focused on polyploid complexes in Hedera (English ivy, Araliaceae), Potamogeton (pondweed, Potamogetonaceae) and Achillea ("yarrow," Asteraceae).

Phenotypic and genetic architecture of adaptation

Ecological differentiation drives range expansion and speciation in flowering plants. The phenotypic and genetic underpinnings of adaptation, however, remain poorly understood. Ecologically differentiated plants are typically distinguished by suites of life-history and physiological characteristics, and consequently it is difficult to identify the contributions of particular traits to fitness in different environments. Moreover, ecologically-differentiated plants are often isolated by strong postzygotic reproductive barriers, limiting genetic analysis. To circumvent these difficulties, we are studying a group of closely-related but ecologically divergent populations. The ecological races of Achillea borealis are specialized to local climatic and edaphic conditions in the western U.S. and Canada exhibiting striking divergence in morphological, physiological and life-history characteristics and have a recent historical origin (~100,000 years ago). Our research characterizes associations between phenotypic characters, molecular markers and reproductive fitness in contrasting environments using hybrid pedigrees generated from the ecological races of Achillea.

Ecological races of Achillea borealis (Asteraceae) in western North America