The skua (Family Stercorariidae) are a group of large, gull-like, predatory seabirds. Two skua species are found in the Antarctic region; the south polar skua (Catharacta maccormicki) and the brown skua (C. lonnbergi). The breeding distribution of the former, is restricted to the Antarctic continent and nearby islands, while the latter has a circumpolar distribution which extends northward from the Antarctic Peninsula and includes many of the Southern Ocean islands. The south polar skua is strictly monogamous, while in contrast, a number of populations of brown skua are comprised in part of communally breeding groups. The brown skua represents the only known example of a communally breeding seabird. In every skua species, breeding females are on average larger and heavier than males. However, in most skua species this dimorphism is relatively small and is of only limited use in sexing individuals. The discovery of sex-specific fragments in the DNA fingerprints of the south polar skua is reported. The multilocus probe pV47-2 hybridised to Hae III restriction fragments which were present exclusively in females and therefore presumably W-linked. The presence of these sex-specific fragments were used to identify female adults and chicks. In addition, the use of these fragments as potentially informative maternal markers is discussed. The parentage of the 13 families from two populations from Ross Island, Antarctica, determined by DNA fingerprinting, revealed a single instance of extra-pair paternity and a single instance of a chick which was parented by neither resident adult. The most likely explanation for the latter is the 'adoption' of a chick from a neighbouring territory. Similarly, DNA fingerprinting was used to assign the sex of individuals of brown skua from a population which breeds on the Chatham Islands, New Zealand. A large proportion of the Chatham Islands population breed in communal groups. Each communal group was shown to be comprised of a single female and two or more males. Consequently, the overall sex ratio amongst breeding birds was biased, with almost twice the number of males as females. In contrast the sex ratio amongst fledgling chicks did not differ significantly from 1:1. The patterns of reproductive success in breeding pairs and communal groups of the brown skua from the Chatham Islands population were determined using multilocus DNA fingerprinting. Sixteen breeding groups were examined, the parentage of 45 chicks produced over three breeding seasons was established using the probes 33.15 and 33.6. No evidence was found of either extra-pair paternity or extra-group fertilisation and there was no evidence of egg dumping by females in any breeding group. These results suggest that long-term banding records for breeding pairs and communal groups accurately reflect the overall reproductive success of these individual groups. In addition, preliminary band sharing analysis indicated that adult members of communal groups were not closely related. These findings are also supported by banding records and are in contrast to the findings of the majority of communally breeding species studied. In the 10 communally breeding groups examined, multiple paternity within a clutch was recorded on two of the 12 occasions in which two chicks were reared. Furthermore, analysis of parentage of the chicks belonging to communal groups in which the adults had remained unchanged for two or more seasons showed that some males had variable reproductive success in different seasons. These records suggest that estimates of reproductive success of individuals based on a single season's data can be misleading. Should temporal changes in paternity (and/or maternity) be shown to be common phenomena in other species, this would have major implications for the interpretation of many parentage studies. The explanation of altruistic behaviour is one of the central issues in contemporary evolutionary theory and behavioural ecology. One of the best known examples of apparent altruism is the helping behaviour which occurs in communal breeding groups such as those found in the brown skua. Within these groups individuals often help to raise offspring which are not their own. This behaviour is an apparent enigma in a world in which organisms are assumed to act in a selfish manner. Consequently, this behaviour has become a focal example at the centre of much evolutionary debate. A variety of theories have been suggested to explain helping behaviour, the most recent is that helping is an unselected consequence of the evolution of communal breeding. This hypothesis is discussed in relation to the recent literature and it is concluded that it does little to advance the current debate. An alternative theoretical approach to helping behaviour is outlined. In conclusion the general findings from the investigation of communal breeding in the brown skua are summarised and these findings are discussed. Finally, possible areas of future research are outlined. / Whole document restricted, but available by request, use the feedback form to request access.
| Identifer | oai:union.ndltd.org:ADTP/276855 |
| Date | January 1993 |
| Creators | Millar, Craig D. (Craig Donald) |
| Publisher | ResearchSpace@Auckland |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Whole document restricted but available by request. Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated., http://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm, Copyright: The author |
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