Life in transition: the evolutionary consequences of ecological and habitat shifts

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Major transitions in habitat and lifestyle traits have featured prominently in the history of life and have shaped the distribution of biodiversity on Earth. Some kinds of transitions have occurred numerous times independently, such as between marine and fresh waters and between predatory and herbivorous feeding modes. Such transitions that are represented by repeated, evolutionarily independent events provide valuable opportunities -- i.e. natural experiments -- to study the predictability of evolutionary responses. My overarching research objective is to elucidate the evolutionary causes and consequences of repeated transitions.***Firstly, my students and I will assess the degree to which transitions impact rates of molecular evolutionary change through time, with a focus upon insects and aquatic invertebrates. We will quantify variability in rates of molecular evolution and test whether rates vary systematically in association with key habitat (e.g. marine/freshwater, benthic/planktonic, terrestrial/aquatic) and lifestyle (e.g. carnivorous/herbivorous, eusocial/solitary, parasitic/free-living) transitions in evolution. This work will represent a substantial step forward in molecular rates research by modeling rate variation across entire phylogenetic trees and by simultaneously investigating the strength of multiple factors in a multivariate context.***Secondly, we will study molecular evolution associated with multiple types of aquatic habitat transitions, each representing a difference between a lower-extinction vs. a higher-extinction environment: ancient lakes vs. surrounding freshwaters, flowing vs. standing waters, and lakes vs. ponds. Using phylogenetically paired sister lineages differing in habitat occupancy, these various habitat regimes will be investigated for their potential association with elevated molecular diversity, population genetic structure, molecular evolutionary rate, and extent of genetic cohesion (vs. clustering into discrete groupings). The results of this work will contribute to understanding the impacts of habitat transitions upon molecular evolution within aquatic life. Furthermore, by explicitly investigating the hypothesis that extinction is important for generating discrete genetic groupings, this work also will contribute towards resolving a puzzle as to why so many taxa exhibit a "barcode gap", which is the disjunction often observed between intraspecific vs. interspecific pairwise DNA sequence divergences.***The results of these studies will reveal whether these transitions provoke general molecular evolutionary responses. Moreover, understanding systematic rate variability is crucial for all who rely upon the molecular clock to provide a timescale for life, including researchers studying macroevolution, biogeography, and climate change impacts using historical reconstructions.**