Extra-pair fertilization in yellow warblers

Beth Collins (Ph.D student with Dr. Robert Browne, advisor; Dr. Dave Anderson, co-advisor) is conducting this research primarily to identify factors that lead to extra-pair fertilizations in yellow warblers (Dendroica petechia), a brightly colored passerine species. The range of yellow warblers is very widespread, with a continuous breeding range that extends from northern Canada to northern South America. This work will examine populations of yellow warblers on Isla Espaņola in Galāpagos, Ecuador and in eastern North America for a minimum of two breeding seasons. Although much work has been done with yellow warblers, intraspecific variation in mating systems and extra-pair fertilizations has not been fully assessed.

Beth has chosen to use an avian system, and yellow warblers specifically, as an investigative model organism that she believes will contribute significantly to our understanding of extra-pair fertilizations (EPFs) and hence our understanding of male and female reproductive strategies. There is evidence that these birds maintain socially monogamous pair bonds, but there is sufficient variation is the frequency of EPFs to suggest alternative mating strategies exist. Extra-pair fertilizations (EPFs) by cuckolding males in a socially monogamous species could potentially increase the variance in male reproductive success with implications leading to possible selective consequences in mating systems.

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Galapagos yellow warbler; note the red cap


The main focus of this research is to elucidate the underlying biological basis controlling the frequency of extra-pair fertilizations (EPFs) in yellow warblers by measuring the following: male testosterone levels, male song complexity, breeding synchrony within populations, breeding synchrony among neighboring females, population density, nesting density, and male plumage characteristics.

Annual visits to the same population will also provide data on long-term survival of offspring and males making it possible to analyze long-term reproductive strategy success. This data can be used to compare the long-term success of reproductive strategies in males with low frequency of EPFs versus males that utilize high frequencies of EPFs. A multiple year study will also allow determination of whether EPF rates are constant over time for individual males or if there are annual strategy differences for individual males.

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