Competition for male reproductive investmentelevates testosterone levels in female dunnocks,Prunella modularis

Dunnock (Prunella modularis) Science Article 4

abstract

In many songbirds, females occasionally sing in contexts of high female-female competition. Testosteronemay be involved in the activation of song, because testosterone implants elicit female song in many specieswith rare female song. A possible mechanism for the hormonal control of female song is provided by thechallenge hypothesis, which predicts a rise in testosterone in response to aggressive interactions duringsocially unstable situations. We tested this by comparing faecal testosterone levels in polygynandrous andmonogamous female dunnocks. In groups with two to three females (polygynandry and polygyny) malesprovide less help at each nest than in groups with a single female (monogamy and polyandry). Polygynandrousand polygynous females are aggressive towards one another and attempt to expel rivals. Polygynandrousfemales had signi? cantly higher testosterone levels than monogamous females. Competitionbetween females that was induced by removal of males caused testosterone levels to rise. Further, femaletestosterone levels were correlated with the rate of

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