Renee A Duckworth

Renee A Duckworth

Associate Professor, Ecology and Evolutionary Biology
Member of the Graduate Faculty
Associate Professor, BIO5 Institute
Primary Department
(520) 626-0734

Research Interest

Dr. Renee Duckworth, Ph.D. is Associate Professor of Ecology and Evolutionary Biology. The ultimate goal of her work is to understand the link between micro and macroevolutionary processes with specific focus on ecological feedbacks and evolutionary diversification. To achieve these goals, she integrates approaches from evolutionary and physiological ecology to quantitative genetic and genomic methods. Her current work uses large-scale field experiments, empirical measures of lifetime fitness and molecular multi-generational pedigree reconstruction to investigate the dynamics of trait evolution in the context of range expansion and species coexistence in passerine birds. Current projects in the lab include the evolution of adaptive introgression, the mechanisms of species coexistence at range margins, the role of adaptive maternal effects in range expansion, and the origin and evolution of animal personality traits.


Duckworth, R. A. (2003). Adaptive dispersal strategies and the dynamics of a range expansion. AMERICAN NATURALIST, 172, S4-S17.

In species undergoing range expansion, newly established populations are often more dispersive than older populations. Because dispersal phenotypes are complex and often costly, it is unclear how highly dispersive phenotypes are maintained in a species to enable their rapid expression during periods of range expansion. Here I test the idea that metapopulation dynamics of local extinction and recolonization maintain distinct dispersal strategies outside the context of range expansion. Western bluebirds display distinct dispersal phenotypes where aggressive males are more dispersive than nonaggressive males, resulting in highly aggressive populations at the edge of their expanding range. I experimentally created new habitat interior to the range edge to show that, as on the range front, it was colonized solely by aggressive males. Moreover, fitness consequences of aggression depended on population age: aggressive males had high fitness when colonizing new populations, while nonaggressive males performed best in an older population. These results suggest that distinct dispersal strategies were maintained before range expansion as an adaptation for the continual recolonization of new habitat. These results emphasize similarities between range expansion and metapopulation dynamics and suggest that preexisting adaptive dispersal strategies may explain rapid changes in dispersal phenotypes during range expansion.

Duckworth, R., Mendonca, M., & Hill, G. (2009). A condition dependent link between testosterone and disease resistance in the house finch. PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, 268(1484), 2467-2472.

Testosterone has recently been proposed as a link between male quality and health and the expression of sexual traits. We investigated the relationship between testosterone and measures of the individual condition and health of males in a natural population of house finches (Carpodacus mexicanus). We also conducted a captive experiment in order to test for the effects of testosterone on resistance to coccidia, which is a common parasite of house finches. Free-living finales in better condition had higher testosterone levels and loiter corticosterone levels than free-living males iii poor condition. In our captive experiment, increased testosterone accelerated the rate of coccidial infection as compared with sham-implanted or gonadectomized males. Although the differences were not significant, free-living males infected with coccidia had louver levels of testosterone and higher levels of corticosterone than males that were not infected. Thus, experimentally elevating testosterone levels in captive males resulted in a higher percentage of infected males, while free-living males with coccidial infection had low testosterone levels. This apparent discrepancy between captive and free-living males iii the association of testosterone and disease may be explained by the condition dependence of testosterone. These results suggest that the testosterone-dependent sexual traits reliably indicate male overall condition and health and, thus, females could benefit front assessing potential mates based on these traits.

Duckworth, R. A. (2010). Aggressive behaviour affects selection on morphology by influencing settlement patterns in a passerine bird. PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, 273(1595), 1789-1795.

The importance of behaviours as instigators or inhibitors of evolutionary change remains largely unresolved and this is in part because there are very few empirical examples of how behaviours affect evolutionary processes. By determining the environment of breeding, aggressive interactions over territories have the potential to strongly impact selection pressures experienced by individuals. Western bluebirds (Sialia mexicana) provide a unique opportunity to investigate the evolutionary importance of aggression, since their highly variable breeding habitat favours distinct foraging techniques and they also compete aggressively for nest boxes, a resource that is easy to manipulate. Here, I show experimentally that more aggressive males compete more effectively for territories with a high density of nest boxes and, as a consequence, aggressive and non-aggressive males are sorted into distinct breeding habitats that differ in the strength of selection on morphological traits. Specifically, males with longer tails and tarsi were favoured in open habitats where high agility is required to forage efficiently, whereas in forested habitats, where agility is less important, selection was weak. These results show that aggression can affect selection on a local scale by determining individual settlement patterns. More generally, because territorial interactions are important across a wide variety of taxa, these results suggest that aggressive behaviour has the potential to impact the evolutionary trajectory of many animal populations.

Duckworth, R. A. (2004). Behavioral correlations across breeding contexts provide a mechanism for a cost of aggression. BEHAVIORAL ECOLOGY, 17(6), 1011-1019.

Identifying correlations among behaviors is important for understanding how selection shapes the phenotype. Correlated behaviors can indicate constraints on the evolution of behavioral plasticity or may reflect selection for functional integration among behaviors. Obligate cavity-nesting birds provide an opportunity to examine these correlations because males must defend limited nest cavities while also competing for mating opportunities and providing parental care. Here, I investigated the role of behavioral correlations in producing a counterintuitive relationship between nest defense and reproductive success in western bluebirds (Sialia mexicana) such that males that defended their nests most intensely had the lowest reproductive success, measured as the number of within and extrapair offspring that fledged. By experimentally measuring aggression across contexts, I show that this cost of nest defense was due to the correlated expression of aggression across the contexts of nest defense and male-male competition coupled with a trade-off between male-male aggression and parental care. In particular, more aggressive males provisioned their females less during incubation and this led to disrupted incubation patterns and fewer fledged offspring. However, aggressive males did not benefit from avoiding parental investment by gaining extrapair fertilizations, and thus, it is unclear how high levels of aggression are maintained in this population despite apparent costs. These results suggest that there are constraints to the evolution of plasticity in aggression and emphasize the importance of considering the integrated behavioral phenotype to understand how variation in behavior is linked to fitness.

Duckworth, R. A., & Badyaev, A. V. (2008). Coupling of dispersal and aggression facilitates the rapid range expansion of a passerine bird. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 104(38), 15017-15022.

Behaviors can facilitate colonization of a novel environment, but the mechanisms underlying this process are poorly understood. On one hand, behavioral flexibility allows for an immediate response of colonizers to novel environments, which is critical to population establishment and persistence. On the other hand, integrated sets of behaviors that display limited flexibility can enhance invasion success by coupling behaviors with dispersal strategies that are especially important during natural range expansions. Direct observations of colonization events are required to determine the mechanisms underlying changes in behavior associated with colonization, but such observations are rare. Here, we studied changes in aggression on a large temporal and spatial scale across populations of two sister taxa of bluebirds (Sialia) to show that coupling of aggression and dispersal strongly facilitated the range expansion of western bluebirds across the northwestern United States over the last 30 years. We show that biased dispersal of highly aggressive males to the invasion front allowed western bluebirds to displace less aggressive mountain bluebirds. However, once mountain bluebirds were excluded, aggression of western bluebirds decreased rapidly across consecutive generations in concordance with local selection on highly heritable aggressive behavior. Further, the observed adaptive microevolution of aggression was accelerated by the link between dispersal propensity and aggression. Importantly, our results show that behavioral changes among populations were not caused by behavioral flexibility and instead strongly implicate adaptive integration of dispersal and aggression in facilitating the ongoing and rapid reciprocal range change of these species in North America.