Costs and benefits of competitive traits in females: aggression, maternal care and reproductive success

Recent research has shown that female expression of competitive traits can be advantageous, providing greater access to limited reproductive resources. In males increased competitive trait expression often comes at a cost, e.g. trading off with parental effort. However, it is currently unclear whether, and to what extent, females also face such tradeoffs, whether the costs associated with that tradeoff overwhelm the potential benefits of resource acquisition, and how environmental factors might alter those relationships. To address this gap, we examine the relationships between aggression, maternal effort, offspring quality and reproductive success in a common songbird, the dark-eyed junco (Junco hyemalis), over two breeding seasons. We found that compared to less aggressive females, more aggressive females spent less time brooding nestlings, but fed nestlings more frequently. In the year with better breeding conditions, more aggressive females produced smaller eggs and lighter hatchlings, but in the year with poorer breeding conditions they produced larger eggs and achieved greater nest success. There was no relationship between aggression and nestling mass after hatch day in either year. These findings suggest that though females appear to tradeoff competitive ability with some forms of maternal care, the costs may be less than previously thought. Further, the observed year effects suggest that costs and benefits vary according to environmental variables, which may help to account for variation in the level of trait expression.Research was supported by National Science Foundation (NSF) grants to EK (BSC 05-19211 and IOS 08-20055) and an NSF Doctoral Dissertation Improvement Grant to KC (09-10036). KC was also supported by NSF Graduate Research Fellowship (www.nsfgrfp.org)

Hormones and Life History: An Integrative Approach

Research proposal submitted to the National Science Foundatio

Proximate Factors Accounting for Stable Sex and Age Differences in the Winter Distribution of Dark-eyed Juncos (Junco h. hyemalis)

Research proposal submitted to the National Science Foundatio

Hormones and avian life histories: exploring the mechanistic and functional bases of fecundity trade-offs in a male bird

Research proposal submitted to the National Science Foundatio