Identifying the role of selection in the expression of aggressive phenotypes in song sparrows, Melospiza melodia

WCU Author/Contributor (non-WCU co-authors, if there are any, appear on document)
Jessica Anna Krippel (Creator)
Western Carolina University (WCU )
Web Site:
Jeremy Hyman

Abstract: Evolutionary theory predicts that selection should minimize variation inbehavioral traits if they are associated with reproductive success. Yet, some behavioraltraits, such as territorial aggression, show high levels of variation. Selection may play arole in maintaining this variation, if individuals with differing aggressive phenotypes usealternative tactics to obtain similar reproductive success. In this study, we examined therole of selection in the maintenance of individual variation by measuring the fitnessconsequences of territorial aggression in an urban population of song sparrows,Melospiza melodia. Song sparrows are socially, but not genetically monogamous due tothe presence of extrapair fertilizations (EPFs). We tested the hypothesis that aggressivemale song sparrows would not achieve greater annual reproductive success thanunaggressive males due to trade-offs associated with aggressive phenotypes. Wepredicted: 1) that aggression would show a positive relationship with nest productivity,but that aggressive males would face a trade-off between the energy required to defendhigh quality territories and paternal investment in nestling growth; and 2) that aggressivemales would be more likely to seek or obtain extrapair fertilizations, but that they wouldface a trade-off between seeking extrapair fertilizations and losing paternity in their social nests. We did not uncover a relationship between aggression and annual reproductivesuccess or nest productivity, but we did find a significant, positive relationship betweenaggression and nestling growth rate. Nestling growth rates have been shown to affectboth the recruitment and reproductive success of offspring, and thus, aggressive malesong sparrows could achieve greater fitness by producing more successful offspring thanunaggressive males. Our study indicates that aggressive male phenotypes may be favoredvia selection on their offspring that acts well after fledging and emphasizes theimportance of examining multiple components of reproductive success when investingthe role of selection in maintaining individual variation in behavioral traits.

Additional Information

Language: English
Date: 2014
Song sparrow -- Behavior -- Genetic aspects
Aggressive behavior in animals
Natural selection

Email this document to