Welcome to the Estes lab in the Department of Biology at Portland State University! Our lab studies a variety of fundamental questions in evolutionary biology; however, our main research interests are focused on determining the population genetic patterns and molecular genetic underpinnings of adaptive evolution and the role that new mutations play in the evolutionary process. Current research addresses the following topics, which we investigate using a variety of tools and approaches that include: laboratory experimental evolution with Caenorhabditis elegans and congeners, genomics technology and classical genetic methods.

 

Genetics of adaptation

The efficiency of natural selection is weakened in small populations. This situation can lead to substantial fitness losses for such populations due to accumulated mutational damage. Previous work found that experimental lines of C. elegans exhibiting reduced fitness and compromised behavioral responses due to the accumulation of spontaneous mutations were able to regain original levels of average fitness when maintained in large population sizes exposed to natural selection. We believe that recovery of ancestral levels of fitness was due to the buildup of secondary, compensatory mutations. With the Patrick Phillips (Univ. of Oregon) Dee Denver (Oregon State Univ.) labs, we are now addressing the patterns and mechanisms of compensatory evolution at several levels of biological organization using whole-genome sequencing and other array-based technologies. This work is supported by the National Science Foundation.

 

Natural variation in oxidative stress & aging in C. briggsae

A new avenue of research for our lab centers on the effects of mitochondrial-generated reactive oxygen species (ROS) on variation in fitness, aging and lifespan among natural populations of C. briggsae. These investigations are based on a foundation of previous work by Charlie Baer (Univ. of Florida) and Dee Denver (Oregon State Univ.) that revealed considerable variation in laboratory fitness and spontaneous mutation rates among natural isolates of C. briggsae and C. elegans. We have conducted the first survey of natural variation in reproductive schedule and lifespan among C. briggsae isolates and, with the Keith Garlid physiology lab (Biology, PSU), are exploring the relationships between natural variation in ROS production, metabolic rates, oxidative stress resistance and lifespan.

 

Correlations & constraints

How do multiple phenotypic characters evolve together? A key determinant of the long-term patterns of multivariate evolution may be the pattern of pleiotropic mutational input. We have addressed the degree to which new mutations that influence different complex traits are integrated by pleiotropy, and the evolutionary implications of such integration. We have measured the effects of selection on the structure of the mutational variance-covariance matrix and have found that detectable mutations generally produce large, manifold effects only on suites of functionally related traits, a pattern that may aid natural selection in eradicating harmful mutations from populations. Of considerable interest is whether such modular genetic effects are a feature of adaptive mutations. Hence one goal of future research is to determine both the frequency and properties of mutations more likely to be relevant for adaptive evolution.

Other work on evolutionary constraints includes an analysis of evolutionary rates with Steve Arnold (Oregon State Univ.), which suggests that long-term morphological stasis is likely due to adaptation to a phenotypic optimum within a stable adaptive zone. And most recently, Michael Westphal (Morgan lab, Kansas State Univ.), Michael LeMaster (Western Oregon Univ.) and I have studied the role of genetic correlations in constraining phenotypic evolution of coloration traits among populations of the common garter snake, Thamnophis sirtalis.

 

Garter snake mating systems

My postdoctoral research, conducted at Oregon State Univ. with Steve Arnold and Robert Mason, sought to understand the evolutionary causes and consequences of mating systems in natural populations. The main objectives are to establish how pre- and post-mating factors help to define the mating system and how aspects of the mating system influence offspring fitness correlates.We have found evidence for extensive multiple paternity, with at least some offspring sired by mates from a previous season, and that populations exhibit asymmetric behavioral isolation. Ongoing work with Mason PhD student, Chris Friesen, is addressing the potential for genetic benefits to female multiple mating and the potential implications of hybrid performance on realized migration rates. We use populations of the red-sided garter snake, T. sirtalis parietalis, in Manitoba, Canada as a model system for this work.