Relatedness, polyandry and extra-group paternity in the cooperatively-breeding white-browed scrubwren (Sericornis frontalis?) |
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| Authors: | Linda A Whittingham Peter O Dunn Robert D Magrath |
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| Institution: | (1) Division of Botany and Zoology, Australian National University, Canberra, ACT 0200, Australia, AU;(2) Department of Biological Sciences, Lapham Hall, P.O. Box 413, University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA Tel.: 414-229-2252; Fax: 414-229-3926; e-mail: whitting@csd.uwm.edu, US |
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| Abstract: | We used DNA fingerprinting to examine the genetic parentage and mating system of the cooperatively breeding white-browed
scrubwren, Sericornis frontalis, in Canberra, Australia. Our analyses revealed a remarkable variety of mating tactics and social organization. Scrubwrens
bred in pairs or multi-male groups that consisted of a female and two or more males. Females were always unrelated to the
pair male or alpha (dominant) male. Among multi-male groups we found three different mating tactics. Firstly, when alpha and
beta (subordinate) males were unrelated, they usually shared paternity in the brood. This resulted in both males gaining reproductive
benefits directly. Secondly, when beta males were not related to the female but were related to the alpha males, beta males
sired offspring in some broods. In this situation, beta males gained reproductive benefits both directly and potentially indirectly
(through the related alpha male). Thirdly, when beta males were related to the female or both the female and alpha male, they
remained on their natal territory and did not sire any offspring. Thus beta males gained only indirect reproductive benefits.
Overall, when group members were related closely, the dominant male monopolized reproductive success, whereas when the members
were not related closely the two males shared paternity equally. This positive association between monopolization of reproduction
and relatedness is predicted by models of reproductive skew, but has not been reported previously within a single population
of birds. Other cooperatively breeding birds with both closely related and unrelated helpers may show a similar variety of
mating tactics. Finally, we found that extra-group paternity was more common in pairs (24% of young) than in multi-male groups
(6%), and we discuss three possible reasons for this difference.
Received: 21 May 1996 / Accepted after revision: 14 December 1996 |
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| Keywords: | Cooperative breeding DNA fingerprinting Reproductive skew Mating systems Kin selection |
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