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Environmental and genetic components of variation in body size of a cooperative breeder, the purple-crowned fairy-wren

Khadraoui, M (2017) Environmental and genetic components of variation in body size of a cooperative breeder, the purple-crowned fairy-wren. Master's Thesis / Essay, Ecology and Evolution.

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An animal's body size is a trait of major importance for its metabolism, physiology, ecology and fitness. It is thus likely to be under various forms of selection. Climate change is thought to have had various effects on avian body size across the world. However, the intensity and direction of the effect remains controversial. Environmental and genetic variation are likely to influence variation in body size, and measuring their effects with quantitative genetic tools is essential to understand and predict phenotypic temporal trends. Here, I used a 12-year dataset of tarsus length measurements and investigated the effects of environmental factors on this morphological trait in a cooperative breeder, the purple-crowned fairy-wren (Malurus coronatus coronatus). I also estimated the genetic component of variation in body size in this species. Adult tarsus length measurements varied from 20.6 to 26.7mm, and the study population showed a weak increase in size over the study period (p = 0.02), but it was not strongly linked with rain- and temperature-related climatic variables. Social group size during the nesting period varied from 2 to 10 individuals, and larger groups were associated with smaller birds. On the contrary, larger brood sizes (ranging from 1 to 4 chicks) consistently yielded larger birds, with broods of 4 having a mean+SE tarsus of 24.08+0.08mm and single-individual broods 23.63+0.09mm. While the study of climatic effects on animal body size has become increasingly popular in the last decade, the influence of climate change on growth remains poorly understood. The social environment, its interaction with climate and their combined influence on growth should come back to focus for us to understand and predict temporal trends in animal body size. Environmental factors generally explained a low amount of phenotypic variation, and the heritability of tarsus length after accounting for sex was of 0.48. The cross-sex genetic correlation of male and female tarsus length was 0.63. This estimate and the observed sexual dimorphism suggest that males and females are under contrasting selection pressures and may have a limited possibility to evolve towards their respective optimal body size. Overall, this study provides a first step towards understanding the evolution of body size in the purple-crowned fairy-wren, and calls for more detailed analyses to determine whether the observed change is a plastic response or a microevolutionary change.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Ecology and Evolution
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 08:32
Last Modified: 15 Feb 2018 08:32

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