Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)




Daniel A Cristol

Committee Member

John P Swaddle

Committee Member

Michael D Lamar


Choosing a high-quality mate contributes strongly to increased reproductive success in birds. Female birds assess quality in males, in part, via condition-dependent signals such as male songs and plumage. The production of attractive signals can be disrupted by environmental stressors, however, including environmental toxins. Mercury, a globally-increasing pollutant, is one such toxin. Mercury exposure has been shown to affect song, plumage, bill color, and mating behaviors in male birds, but the effect of these changes on the outcome of female mate choice is unknown. These effects on condition-dependent signals indicate that mercury could potentially alter males’ attractiveness to females, as females use such traits to assess quality of potential mates. We sought to determine if male attractiveness to females is affected by dietary mercury exposure, using zebra finches as our model system. Males were either exposed to dietary mercury (1.2 ppm) or unexposed (0.0 ppm), and then assessed by unexposed females in three types of mate preference trials: song-only phonotaxis trials, that observed female preference for mercury-exposed or unexposed songs; two-choice association preference trials, that observed female preference for mercury-exposed or unexposed males in neighboring cages; and aviary pairing trials, in which females were given the opportunity to pair with either a mercury-exposed male or unexposed male. In phonotaxis trials and association trials, females did not spend more time near songs or males of one treatment over the other. In aviary pairing trials, females were equally likely to pair with males of either treatment. While mercury exposure is known to reduce reproductive output in zebra finches and other birds, our results suggest that females are not incorporating mercury-induced variation in male traits into their mate choice decisions. This raises questions about the future evolution of the avian mate choice system in an environment increasingly affected by toxins, as females experience fitness losses as a result of potentially poor mate choice decisions. If this is the case, then females are likely to respond to this sexual selection pressure by including toxin-mediated trait variation in their quality assessment mechanisms.



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