Abstract
Crater Lake Masoko in Tanzania contains the necessary conditions to facilitate ecological speciation in the haplochromine cichlid Astatotilapia calliptera. The presence of a depth associated gradient in light intensity, temperature and prey availability has led to the formation of a shallow-living littoral ecotype and a deep-living benthic ecotype. Research exploring how natural selection has contributed to the incipient speciation of these ecotypes would benefit from the establishment of reliable fitness proxies that can be applied to wild-caught fish. Here, two proxies, growth rate and male body size, are evaluated as fitness proxies in Astatotilapia calliptera. Growth rate was estimated as a function of body size and age, with age estimated from CT-scan derived otolith thickness measurements. The otolith-based method was validated using laboratory-reared fish of known age and applied to resolve the age distribution of wild caught fish. Male body size was found to strongly predict female courtship rate and socialdominance in laboratory trials, which are likely to determine reproductive success in the natural environment. Collectively, by enabling quantitative estimates of individual fitness, these proxies have considerable potential to further our understanding of the selection pressures driving ecological speciation occurring in Lake Masoko. The methods also have broader potential for contributing to the ecological and evolutionary understanding of other fish species groups.
| Date of Award | 30 Sept 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Martin J Genner (Supervisor) |
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