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Efficient Copulation and the Evolutionary Loss of the Avian Intromittent Organ

James V. Briskie and Robert Montgomerie
Journal of Avian Biology
Vol. 32, No. 2 (Jun., 2001), pp. 184-187
Published by: Wiley on behalf of Nordic Society Oikos
Stable URL: http://www.jstor.org/stable/3677665
Page Count: 4
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Efficient Copulation and the Evolutionary Loss of the Avian Intromittent Organ
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Abstract

The absence of an intromittent organ (IO) in most species (>97%) of birds is an enigma: birds are the only terrestrial vertebrates in which insemination typically occurs without the use of an IO. In an earlier review, we evaluated six hypotheses to explain the loss of IOs among birds. We found some support for the influence of sperm competition and female choice, but other hypotheses (e.g. avoidance of sexually transmitted disease) could not be tested because of a lack of empirical data. Wesolowski (1999, J. Avian Biol. 30: 483-485) has criticised our female choice and sexually transmitted disease hypotheses as implausible and insufficient to explain the loss of the IO in birds. Instead, he proposes that IOs were lost to minimise the risk of predation (by shortening duration of copulation) and/or to increase the efficiency of sperm transfer. Here we respond to Wesolowski's (1999) criticisms and test his efficient copulation (EC) hypothesis with data on the duration of copulation in 243 species. Contrary to expectations from the EC hypothesis, copulation durations did not differ significantly between species with and without an IO. Thus we can reject the EC hypothesis as an explanation for the loss of IOs in birds.

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