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Cooperative Breeding in the Southern Anteater-Chat: Sexual Disparity, Survival and Dispersal
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Population and Conservation Biology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Group-living sets the scene for complex social behaviours such as cooperative breeding, and exploring the factors that shape group-living is crucial in understanding these behaviours. This thesis explores the ecology of a population of the facultative cooperative breeding southern anteater-chat (Myrmecocichla formicivora), a group-living bird species endemic to southern Africa. It reveals a breeding system based around a breeding pair and up to three auxiliary males. Despite equal numbers of males and females produced as fledglings there was a surplus of adult males, which remained philopatric. Dispersal was strongly female biased. Females dispersed within their first year, they dispersed further than males, and they lost the benefits of the natal site. The sex skew in the population suggested that these factors drive differential mortality, with juvenile females having much lower annual survival than juvenile males. Adult survival was higher, with female survival only slightly lower than male survival. Dispersal distances suggested that males selected the breeding location, nearer to their natal site. There was no evidence of surplus non-breeding females. On the loss of a breeding female there was no replacement until new females entered the population, yet if a breeding male disappeared the female promptly re-paired with a male from another group. There was no indication of birds floating in the population, and if males were orphaned or widowed they joined other groups as unrelated helpers in preference to floating. There was no sign of inter-group or individual aggression among chats, and unrelated helpers were peacefully accepted into groups, suggesting mutual benefits. In fact all birds in a group helped raise offspring of the breeding pair, and groups with more helpers fledged more offspring, which implies that both direct and indirect fitness benefits can be gained through joining a group and helping. There was surprisingly little inheritance of breeding position by auxiliaries, and strikingly low levels of extra-pair paternity. This study suggests that the Southern anteater-chat group structure arises through male philopatry due to a shortage of breeding females, the benefits of remaining on the natal site and helping, and the potentially high costs of living alone.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. , 50 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 953
Keyword [en]
Southern anteater-chat, Myrmecocichla formicivora, cooperative breeding, social evolution, behavioural ecology, delayed dispersal, family living, Africa
National Category
Evolutionary Biology Zoology
Research subject
Biology with specialization in Population Biology
Identifiers
URN: urn:nbn:se:uu:diva-179070ISBN: 978-91-554-8426-2 (print)OAI: oai:DiVA.org:uu-179070DiVA: diva2:544058
Public defence
2012-09-25, Lindahlsalen, Evolutionary Biology Centre, Norbyvägen 14-18, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2012-09-04 Created: 2012-08-07 Last updated: 2013-01-22
List of papers
1. Group-living in the southern anteater-chat Myrmecocichla formicivora.
Open this publication in new window or tab >>Group-living in the southern anteater-chat Myrmecocichla formicivora.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Group-living sets the scene for complex social behaviours such as cooperative breeding, and exploring the factors that shape group-living is crucial in understanding these behaviours. Here we describe some aspects of the ecology of a population of the facultative cooperative breeding southern anteater-chat (Myrmecocichla formicivora), a group living bird species endemic to southern Africa. We used data from a four year study of individually marked birds, with pedigrees completed using microsatellite genotyping. Southern anteater-chats live in groups of 2-5 individuals - a breeding pair and up to three additional none-breeders. These auxiliary birds were either retained offspring or unrelated individuals, and all birds in a group assisted by feeding at the nest. Our population had a skewed sex ratio of approximately 58% males to 42% females, yet the sex ratio of fledglings was equal, suggesting sex-biased mortality. Helpers were predominantly retained male offspring; however 21% of helpers were unrelated to either of the breeding pair. Southern anteater-chats appear to be non-territorial, with an apparent lack of aggression both within and between groups. Our study confirms that the southern anteater-chat is a facultative cooperative breeder, with both pair breeders and groups with helpers capable of fledging youngsters. We provide evidence suggesting that the breeding system of the southern anteater-chat is based on prompt female dispersal, and male philopatry due to an apparent shortage of mates, potential benefits of the natal site and possible high costs of floating. It appears that ecological constraints promoting delayed dispersal are reinforced by benefits gained from remaining philopatric.

Keyword
Southern anteater-chat, cooperative breeding, social evolution, behavioural ecology, delayed dispersal, family living, Africa
National Category
Evolutionary Biology
Research subject
Biology with specialization in Population Biology
Identifiers
urn:nbn:se:uu:diva-179071 (URN)
Available from: 2012-08-13 Created: 2012-08-07 Last updated: 2012-09-05
2. Sex specific survival in the southern anteater-chat Mymecocichla formicivora.
Open this publication in new window or tab >>Sex specific survival in the southern anteater-chat Mymecocichla formicivora.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Survival is a key factor behind life-history variation both between and within species. It is also a major influence on sociality in species which delay dispersal and live in family groups. Knowledge of differential survival rates between males and females and juveniles and adults give insights into the costs and benefits of different behavioural and life-history strategies. Here we investigate patterns of survival in a population of the southern anteater-chat (Myrmecocichla formicivora), a facultative cooperatively breeding passerine of southern Africa. Using data from a 9-year mark-capture-recapture study, we examined juvenile and adult sex related variation in survival, and the role of environmental variables (rainfall, temperature) for survival patterns in the population. Annual adult survival probability (mean ± SE) was 0.71 ± 0.03 for males and 0.60 ± 0.04 for females. Juvenile survival was lower for each sex, with juvenile female survival (0.36 ± 0.04) being 35% lower than juvenile male survival (0.55 ± 0.04). Using these estimates we calculated the mean life span (MLS) in years for male southern anteater-chat to be 4.0 ± 0.7, considerably higher than for females at 2.0 ± 0.4. These figures closely matched the population-age structure of the study area, and could explain the high male biased sex skew of adult birds in this population. Higher annual mean temperature was associated with higher survival, whereas higher annual rainfall was associated with lower survival for both sex and age classes. Female survival, particularly female juvenile survival, may be reduced due to prompt dispersal and longer dispersal distances, and the additional costs of breeding early in life. Differential survival can promote male philopatry and this in turn could well encourage the cooperative breeding we see in the southern anteater-chat.

Keyword
Southern anteater-chat, cooperative breeding, social evolution, behavioural ecology, delayed dispersal, family living, Africa
National Category
Evolutionary Biology
Research subject
Biology with specialization in Population Biology
Identifiers
urn:nbn:se:uu:diva-179072 (URN)
Available from: 2012-08-13 Created: 2012-08-07 Last updated: 2012-09-05
3. The rarer sex - female natal dispersal and breeder replacement in the southern anteater-chat Myrmecocichla formicivora.
Open this publication in new window or tab >>The rarer sex - female natal dispersal and breeder replacement in the southern anteater-chat Myrmecocichla formicivora.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Sex biased dispersal is a crucial factor in understanding the mechanism of family dynamics in many cooperative breeders. Female biased dispersal occurs in many cooperatively breeding birds. It is often associated with females dispersing earlier and further, and a male biased sex skew in the population. Here we investigated female dispersal in the southern anteater-chat, a facultative cooperatively breeding passerine of southern Africa. Our study population had a male biased sex skew, and females had lower annual survival than males. Dispersal was strongly female biased, with females dispersing within their first year whereas many males remained philopatric beyond the next breeding season. Breeding females were on average younger than breeding males, and also dispersed further. Each breeding group contained only one female. No females were found floating in the population, and all females were associated with one or more males in a breeding group. It appears that all females disperse in their first year directly to a breeding position. If a female disappeared in the breeding season they were not replaced until new females matured and dispersed the following season, yet if a male breeder disappeared during the breeding season he was almost immediately replaced, indicating that there are no surplus females.

Keyword
Southern anteater-chat, cooperative breeding, social evolution, behavioural ecology, delayed dispersal, family living, Africa
National Category
Evolutionary Biology
Research subject
Biology with specialization in Population Biology
Identifiers
urn:nbn:se:uu:diva-179073 (URN)
Available from: 2012-08-13 Created: 2012-08-07 Last updated: 2012-09-05
4. From helping to breeding – male choice in the southern anteater-chats Myrmecocichla formicivora.
Open this publication in new window or tab >>From helping to breeding – male choice in the southern anteater-chats Myrmecocichla formicivora.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Dispersal choice is important in understanding population structure and dynamics. Here we examine male choice in the facultative cooperative breeding southern anteater-chat Myrmecocichla formicivora based on a four year study in South Africa. The sex ratio in our study population was male biased, with many males remaining philopatric. All groups consisted of one or more adult males associated with one adult female. We found a significant positive effect of auxiliary number on group productivity (both number of young fledged, and first year survival), while controlling for potentially confounding variables (territory and breeder identity). The majority of auxiliaries, 54%, were related to both birds in the breeding pair, with another 25% related to one member of the pair, and 21% related to neither of the breeders. There was no evidence of males floating within our study population, and it appears that if males lose their family due to mortality they join other groups as unrelated non-breeding auxiliaries rather than float. No aggression was observed between individual southern anteater-chats, and unrelated group members helped rear offspring in the group they had joined. Despite the presence of, and helping by unrelated group members there was very little evidence of breeding position inheritance (1/24 auxiliaries unrelated to the breeding female) or extra-pair paternity (2.4% of fledglings). This study suggests that the southern anteater-chat group structure arises through male philopatry due to a lack of breeding females and potentially high costs of living alone.

Keyword
Southern anteater-chat, cooperative breeding, social evolution, behavioural ecology, delayed dispersal, family living, Africa
National Category
Evolutionary Biology
Research subject
Biology with specialization in Population Biology
Identifiers
urn:nbn:se:uu:diva-179074 (URN)
Available from: 2012-08-13 Created: 2012-08-07 Last updated: 2012-09-05
5. Development of a suit of microsatellite markers for the southern anteater-chat Myrmecocichla formicivora.
Open this publication in new window or tab >>Development of a suit of microsatellite markers for the southern anteater-chat Myrmecocichla formicivora.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We tested the cross amplification of 37 microsatellite markers for their suitability in genotyping the southern anteater-chat Myrmecocichla formicivora, an opportunistic cooperatively breeding passerine bird endemic to southern Africa. Fourteen microsatellite markers were identified as having suitable characteristics, with minor deviation from Hardy-Weinberg equilibrium and little evidence of null alleles. These 14 Primer pairs were combined in 4 multiplexes and run on 183 individual samples from our study population of southern anteater-chat on Benfontein Nature Reserve, near Kimberley in central South Africa. The loci ranged from 3-34 alleles per locus, and observed heterozygosity ranged from 0.45 -0.93. We then tested these 14 microsatellites for their use in examining paternity in a population of southern anteater-chat being studied on Benfontein Nature Reserve, near Kimberley in South Africa. Of the population of 183 individuals (the 2011 population) 93% of the offspring could be allocated a mother, 97% a father, and 87% a parent pair with 95% confidence. The remainder could be allocated at the 80% confidence level. Where mothers could be assigned from observations this was in 100% agreement with the microsatellite results, giving us good support for the accurate assignment of parentage in our population.

Keyword
Southern anteater-chat, cooperative breeding, social evolution, microsatellites, genotyping, cross-amplification, behavioural ecology, delayed dispersal, family living, Africa
National Category
Evolutionary Biology
Research subject
Biology with specialization in Population Biology
Identifiers
urn:nbn:se:uu:diva-179075 (URN)
Available from: 2012-08-13 Created: 2012-08-07 Last updated: 2012-09-05

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Output format
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