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Early Career Scientist Seminars

The J.F. Crow Institute for the Study of Evolution at the University of Wisconsin-Madison is inviting early-career evolutionary biologists from outside UW-Madison to apply to participate in an early-career scientist seminar series in spring 2018. Please come share your science with our community! 

The 3-5 speakers selected for the series will be invited to visit UW-Madison. The speaker will present a 50-minute seminar, ideally aimed at evolutionary biologists with a broad range of backgrounds. The speaker will also participate in a 45-minute discussion after the seminar with undergraduate evolution majors. For the day of the seminar we will schedule meetings with faculty and students working in evolutionary biology. The speaker would be responsible for their own travel to Madison, but would receive a $100 honorarium to offset travel costs. If an overnight stay is required, arrangements could be made to stay with a member of the Crow Institute.

 If you have any questions please contact Megan Frayer ( or Jered Stratton (

The application for a Spring seminar has closed. Please check back for future opportunities! 

Riding the wave: testing how rapid evolution shapes the dynamics of range expansions

Christopher Weiss-Lehman

University of Minnesota (Advisor: Allison Shaw) 

Seminar Date: February 22, 2018

Although range expansions have long been modeled as purely ecological phenomena, recent evidence shows that evolutionary changes can shape the expansion process. Multiple possible selection pressures can cause evolution during range expansion, some of them direct outcomes of expansion dynamics. However, neutral processes also can play a significant role in driving evolutionary change during expansion, particularly in the form of gene surfing. The patterns in allele frequency changes produced by adaptive and neutral mechanisms in a single realization of the expansion process and the resulting impacts on expansion dynamics from different mechanisms can be difficult to distinguish. I present results from a highly replicated microcosm experiment with the red flour beetle (Tribolium castaneum) assessing the impact of neutral and adaptive evolutionary changes on range expansion dynamics. Using data from pooled, whole genome sequencing of beetles from the experiment with demographic data on spread rates and trait values, my collaborators and I quantified the relative contributions of adaptive and neutral mechanisms in driving evolutionary changes during expansion. In particular, we demonstrated an important role for gene surfing, as a neutral evolutionary process, in driving increased variance in expansion speeds among replicate populations. I explore this result further by pairing data from the red flour beetle system with a theoretical model exploring the interaction of habitat heterogeneity and rapid evolution in driving variance in expansion patterns. The results I present in this talk demonstrate a clear need to incorporate evolutionary mechanisms when making predictions for range expansions, even over relatively short timescales.


Disentangling the effects of mutation and selection on the evolution of gene expression and regulation

Brian Metzger

University of Chicago (Advisor: Joe Thornton) 

Seminar Date: March 15, 2018

New mutations are the ultimate source of heritable variation. Unfortunately, the action of natural selection alters the types and frequencies of phenotypes observed in natural populations. As a consequence, the relative roles mutation and selection play in shaping patterns of phenotypic variation in natural populations are often difficult to disentangle. This is particularly true for changes in gene expression as the effects of mutations altering gene regulation are difficult to predict. To address this problem, I measured the effects of hundreds of new cis- and trans-regulatory mutations in the absence of natural selection on the expression of the Saccharomyces cerevisiae TDH3 gene. These measurements revealed differences in the effects of cis- and trans-regulatory mutations, indicating that the molecular mechanism by which a mutation alters gene expression plays an important role in the likely phenotypic consequences of that mutation. To determine how natural selection acts on these differences, I compared the effects of these new mutations to the effects of cis- and trans-regulatory polymorphisms segregating amongst over 60 S. cerevisiae strains isolated from a variety of natural environments. This comparison revealed differences in the action of natural selection between cis- and trans-regulatory changes due to differences in the effects of new mutations, including differences in the action of natural selection on the variability in gene expression amongst genetically identical cells, i.e. gene expression noise. These results show how the mutational process helps shape patterns of natural variation by producing biases in the types and frequencies of phenotypic variation.


Revealing rhizobial fitness across symbiotic and free-living environments: identifying fitness tradeoffs and genomic variants

Liana Burghardt

University of Minnesota (Advisor: Peter Tiffin)

Seminar Date: March 22, 2018

When living in symbiosis with legume hosts, rhizobial bacteria convert atmospheric nitrogen into a plant-available form. In exchange, rhizobia receive carbon in the form of dicarboxylates and a favorable environment for reproduction. Rhizobia do not always live in symbiosis and the majority of the population at any given time is free-living in the soil. Little is known about how adaptation to the free-living environment affects the stability of the mutualism or the extent to which host genotype mediates competitive outcomes between closely related microbial strains. Here we present a variant of the ‘evolve and re-sequence’ approach that provides a robust method to estimate bacterial fitness and identify genetic variants responsible for fitness. We show that plant hosts impose strong selection on rhizobial populations, symbiotic fitness and free-living fitness are not correlated, and there is a trade-off between success in soil and in resource-rich liquid media. Selection in hosts caused strong shifts in allele frequency across the genome and these shifts were particularly strong for variants in genes associated with motility, transcriptional master regulators of nitrogen fixation, and genes involved in host/rhizobia signaling. Our work demonstrates the potential power of select and re-sequencing approaches to characterize fitness in microbial species as well as the naturally occurring allelic variants responsible for that variation. In the case of rhizobia, characterizing soil- and host-specific selection and identifying the causative rhizobial genes may allow for manipulation of this symbiosis to increase agricultural yields and provide insight into the biological processes that govern ecosystem productivity.


Variable hybridization outcomes reflect variable reproductive isolation

Elizabeth Mandeville 

University of Wyoming (Advisors: Katie Wagner and Annika Walters) 

Seminar Date: April 12, 2018

Interspecific hybridization can reveal mechanisms of reproductive isolation between related species, and also has long term implications for the evolution of hybridizing taxa. Although hybridizing species are often distributed across heterogeneous environments in the context of variable communities, variation in outcomes of hybridization is still incompletely understood. My recent work quantifies variation in hybridization across replicate instances of hybridization in fish taxa in the mountain west, specifically suckers and trout. Comparison of these two empirical instances of hybridization is informative about how hybridization varies across a large geographic area. My collaborators and I analyzed hybridization among six Catostomus species across the Upper Colorado River basin and found extreme variation in hybridization across locations. Different hybrid crosses were present in different locations, despite similar species assemblages. Within hybrid crosses, hybridization varied from only first generation hybrids to extensive hybridization with backcrossing. Similarly, our study of hybridization between introduced rainbow trout and native Yellowstone cutthroat trout revealed variation in extent of hybridization across 27 replicate tributaries, but patterns of variation were slightly different. Species always hybridized when sympatric, but the degree and direction of backcrossing varied. The next challenge in our work will be identifying precisely why hybridization outcomes vary. Variation might result from uneven fitness of hybrids across locations, polymorphism in genetic incompatibilities, chance, unidentified historical contingencies, or some combination thereof. We are currently investigating these possible mechanisms in both study systems. Our results suggest that one or a few instances of hybridization represent all interactions between the focal species.


Ecology, sexual selection, and phenotypic diversification

Justa Heinen-Kay

University of Minnesota (Advisor: Marlene Zuk)

Seminar Date: April 26, 2018 

Sexual traits are often the most flamboyant aspects of biodiversity and are critically important in generating and maintaining species boundaries. The classic paradigm is that natural and sexual selection act in opposite directions, with sexual selection favoring trait elaboration while natural selection provides a braking force. However, this often fails to reflect what is observed in nature because the evolutionary dynamics of sexual traits are rarely that simple. My research takes a novel, integrative approach to understanding the evolution of sexual traits that involves ecology, social dynamics, trait interactions, physiology, and plasticity. First, I will discuss some of my dissertation work with Bahamian mosquitofish that demonstrates divergence in conspicuous signals, behaviors, and male genitalia driven by population-level differences in predation due to natural variation over 1000’s of years and human impacts on the environment over 10’s of years. Next, I will discuss my postdoctoral research that takes the question of how natural and sexual selection interact a step further to investigate what happens when one evolutionary force overpowers the other. This work centers on Pacific field crickets in Hawaii that rapidly experienced the evolutionary loss of male song due to selection from a deadly parasitoid fly. My work has shown both plastic and pleiotropic influences on female reproductive investment and exploratory behaviors following rapid spread of the silencing mutation. Together, my research sheds light on how the interplay between natural and sexual selection influences diversification, and the causes and consequences of sexual trait evolution in the wild.