Profile of Alexandra Tyers
General Research Theme:
Divergence and speciation of East African haplochromine cichlid fish.
The majority of the cichlid fish species found in the East African Rift Valley belong to the haplochromini tribe. These fish are found in many of the river systems throughout East Africa, but it is due to their rapid adaptive radiation and explosive speciation within the Great Lakes, particularly Malawi and Victoria, that has lead to their frequent use as a model system in evolutionary biology. Among the hundreds of endemic species found within each lake there are eco-morphological and behavioural adaptations to suit all habitats and available food sources. Many closely related cichlid species are reproductively isolated by mate choice and territorial males tend to be more aggressive to similar-coloured males, facilitating coexistence of divergent colour morphs or species. The beautiful diversity of colour within and among sympatric species and geographic populations makes these not only a very useful, but also very charismatic, group of organisms with which to test theories of vertebrate evolution and speciation
Sympatric divergence of haplochromine cichlids in isolated Tanzanian crater lakes
The recent discovery of haplochromine cichlids in several small isolated crater lakes in Tanzanian has lead to the development of a collaborative project to investigate sympatric divergence by combining full genome sequencing with more traditional ecological field work and aquarium based behavioural experiments. My main contribution to this project is design and implementation of several large scale aquarium based mate choice experiments to test for reproductive isolation between putative species and consistency of female choice for different male phenotypes (putative/incipient species).
Divergence and speciation of Lake Malawi haplochromine cichlid fish from non-rocky habitats
Much of the exceptional diversity of lacustrine cichlids can be explained by geographic variation among isolated populations of the rocky-shore habitat specialists. However, there are also many other types of habitat specialists, which have received much less attention. The main focus of my thesis research was to compare patterns of assortative mating among taxa from different habitats with different degrees of population structuring, by investigating divergence and reproductive isolation among allopatric populations of non-rock restricted taxa in the Lake Malawi catchment.
Individual differences in female mate preference
Mate preferences are a major force in the process of speciation. Not only does the development of assortative mating reduce gene flow between diverging taxa and provide pre-zygotic reproductive isolation between closely related species without the need for geographical or ecological separation, consistent individual variation in preference within a population has the potential to influence evolution by sexual selection. Because of its potential to drive evolutionary change, I have developed and interest in the nature of individual variation in behaviour, which is often overlooked in population level studies of mate preference.
The maintenance of rare morph colour polymorphism in Lake Malawi haplochromine cichlids
Blotch polychromatism is widespread among East African cichlids and recent laboratory based behavioural experiments suggest that intrasexual aggression may be a major contributing factor to it's maintenance: lack of recognition of rare morphs by conspecifics may result in an advantage through reduced aggression. We investigated these issues in the polychromatic Lake Malawi cichlid fish, Pseudotropheus callainos, using laboratory behavioural choice trials and field observations.
In the lakes of the East African Rift Valley, cichlid fish have diversified into hundreds of species with great variety of ecomorphological, secondary sexual and behavioural characteristics. Due to their repeated rapid adaptive radiation and diversity of naturally and sexually selected traits, these charismatic groups of animals are frequently used as a model system in evolutionary biology.
- Tyers, A.M., Challis, R.J., Ngatunga, B., Genner M.J. & Turner, G.F. (In Prep). Assortative mating associated with divergence of male courtship colour among geographically isolated Astatotilapia.
- Tyers, A.M., Bavin, D., Cooke, G.M. Griggs, C. & Turner, G.F. (2014). Peripheral isolate speciation of a Lake Malawi cichlid fish from shallow muddy habitats. Evolutionary Biology, DOI: 10.1007/s11692-014-9277-4
- Tyers AM & Turner GF. (2013) Signal and preference divergence among populations of the non-endemic basal Lake Malawi cichlid fish Astatotilapia calliptera (Perciformes: Cichlidae). Biological Journal of the Linnean Society. 110: 180-188.