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Title: Divergence and speciation of East African haplochromine cichlid fish
Author: Tyers, Alexandra Morton
Awarding Body: Prifysgol Bangor University
Current Institution: Bangor University
Date of Award: 2013
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In the Great Lakes of the East African Rift Valley, cichlid fishes have diversified into hundreds of species with great variety of ecomorphological, secondary sexual and behavioural characteristics. A strong role for sexual selection in their speciation is indicated by the presence of many closely related ecologically similar sympatric species which differ in male secondary sexual characteristics. A review of previous research finds that reproductive isolation by direct mate choice may be a common isolating barrier among sympatric species. Observations of partial assortative mating among divergent geographic populations have lead to theories of intralacustrine allopatric speciation of habitat specialists by divergence of signal traits involved in conspecific recognition. Here I demonstrate that signal and preference divergence among populations is not limited to patchily distributed lacustrine endemics, but can also occur in the widely distributed riverine generalist lineage that is phylogenetically basal to the large lacustrine radiations, suggesting a role for divergence of secondary sexual traits in allopatry throughout adaptive radiation. This thesis also adds to the evidence for ecological divergence and peripatric speciation of lacustrine habitat specialists in the absence of significant colour differentiation. In simulated intruder choice tests, males tend to bias aggression towards males of their own species or populations, which may aid in the co-existence of allopatrically diverged populations under secondary sympatry and help to facilitate speciation, or even drive divergence of male traits that are involved in signalling during both courtship and territorial interactions. Results from preliminary investigations into individual variation in mate preference suggest that partial assortative mating among allopatric populations may be due to variation within, rather than among, individuals in their choice of mate. Within-individual variation may be unlikely to cause divergence, but has the potential to aid in colonisation of new areas by a relaxation of directional selection allowing for divergence of male traits by environmental or other social selection pressures. To draw any firm conclusions about the impact of variation in mate choice on speciation, much more data from a wider variety of lineages is needed. Mate choice experiments, carried out as part of a larger ongoing project into sympatric divergence of haplochromine cichlids in isolated crater lakes, found little consistency of female mate choice despite morphological and genetic differentiation of forms. This indicates that, in contrast to previously tested sympatric species of cichHds, at the beginnings of adaptive radiation variety may not be maintained solely through reproductive isolation by direct mate choice. Observations of interactions among animals may frequently reveal unexpected results with regards to what is and is not a species - for example, strong assortative mating among phenotypically similar allopatric populations and that assortative mating alone may not maintain diversity in sympatric populations. Behavioural experiments can complement more modern genetic and genomic techniques and therefore continue to be a valuable tool in the study of speciation and the mechanisms involved in divergence and the maintenance of diversity.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available