The Chavez Lab



Hybrid zones (red text) and intraspecific transects (blue text) in different environmental settings.

Genomics of Speciation and Adaptation

We are interested in the evolution of isolating barriers between diverging lineages and especially the role that ecology and divergent adaptations have in the formation of these barriers. We are addressing these questions with empirical research on taxa that are at different stages of divergence and in different environments and have focused largely in taxa that have formed hybrid zones and that occur along environmental gradients.

Our primary study system is the Tamiasciurus tree squirrel. These squirrels live in heterogenous forest environments that span a wide range of abiotic and biotic conditions. Thus, there are rich opportunities to study local adaptation and divergent adaptations. Furthermore, multiple hybrid zones in different environments are formed between T. douglasii (Douglas squirrel) and T. hudsonicus (red squirrel). In total, there are rich opportunities to investigate how the environment has lead to genetic adaptation, reproductive isolation, and reproductive incompatibility. We have generated de novo genome and transcriptome assemblies for this study system and are collecting population-level genomic (e.g., whole-exome, RADseq) and phenotypic data to understand which genomic regions underlie ecologically important traits and may be involved in divergent adaptations and reproductive isolation.

Ecology and Behavior of Reproductive Isolation

Ecological and behavioral interactions can play an integral role in the speciation process through the evolution of divergent adaptations and assortative mating behaviors. Tamiasciurus squirrel hybrid zones (T. hudsonicus X T. douglasii) provide a rich opportunity to study the role of divergent behaviors and ecology in hybrid zone dynamics and reproductive isolation. As has been shown in multiple studies, Tamiasciurus tree squirrels are model organisms for studies in behavioral ecology, life history evolution, and species interactions. We are conducting field studies on a Tamiasciurus hybrid zone population in the North Cascades to understand key ecological and behavioral factors that shape prezygotic and postzygotic mechanisms of reproductive isolation (e.g., hybrid fitness, assortative mating, resource selection), as well as how environmental factors contribute to the evolution of ecologically important traits (e.g., fur coloration, bite-force biomechanics).


Macroevolutionary Patterns of Color Variation

Color patterns are a key fitness trait in animals because they have important roles in visual signaling, concealment, and thermoregulation. The squirrel family has one of the greatest diversity of color patterns among mammal families. Variation in color patterns appears associated with body size, as many of the largest squirrel species are polymorphic in color patterns and have the greatest contrast between color patches, whereas many of the smallest squirrels have a cryptic appearance. To date, biologist know little about why squirrels, especially tree squirrels, possess such a range of color patterns. We are using a comparative methods approach to study the relationship between color pattern variation, body size, and other variables.

The Evolution of Venom in Shrews

Venom is known to have evolved in only a handful mammalian species. The origin of venom and selective pressures for venom adaptations are poorly understood. We are using molecular approaches (genomics, transcriptomics, and proteomics) to study when and how venom genes have evolved. We are also beginning studies to identify the ecological and life history factors that have led to the evolution of venom in some shrew species.