Local adaptations, comparative trophic ecology and phylogenetic analysis of the haplochromine Cichlids of lake Kanyaboli, a satellite lake of lake Victoria,Kenya

Abstract

The satellite lakes of Lake Victoria region have been noted as potential refugia of haplochromine cichlids that have gone extinct in Lake Victoria. These lakes include lakes Kanyaboli, Sare and Namboyo in Kenya, Nawampasa, Nabugabo, Mburo, Kachera, Bunyoni and Mulehe in Uganda and Lake Ziwa la Wanawake in Tanzania. Some of these lakes harbour relict populations of haplochromine cichlids that have gone extinct in the main lake and could therefore play an important role in their conservation. This thesis presents a detailed analysis of local adaptations, trophic ecology, molecular phylogenetics and population genetic structure of haplochromine cichlids of Lake Kanyaboli, one of the small lakes in the Yala swamp wetland of Lake Victoria basin and provides an insight into its evolutionary, ecological and conservation importance. Morphometric and meristic measurements were analysed in six common extant haplochromine cichlids of Lake Kanyaboli. Lake Kanyaboli is characterized by low alpha species diversity. The six haplochromine cichlids found are morphologically generalized and are characterized by high body depth - standard length ratio and jaw length - head length ratio. Only the dentition and trophic apparatus show specialization related to diet. The morphometric, meristic and dentition characters show a departure from the cladistically determined plesiomorphic character states of the Lake Victoria haplochromines. The observed low species diversity can be attributed to the small size of the lake that limits space for ecological speciation and also the homogeneity of the habitats especially lack of rocky and sandy habitats that may restrict gene flow between populations. The trophic relationships in the six haplochromines were examined and related to the teeth and jaws structure. Gut content analysis revealed that 8 different food items are consumed. The contribution of each food type to the diet of the fishes, as determined by the percentage frequency of occurrence were as follows: Algae 34.8%, chironomidiChaoborus larvae 64.3%, other insects 33.9%, mollusks 15.2%, fish embryos 16.1%, fish eggs 6.25%, plant remains 43.8% and detritus 37.5%. No single species feed exclusively on a single food item. Diet overlap was measured by co-efficient of similarity and was found to be common, probably due to the high food abundance in the lake. However, for each species certain food items contribute higher proportions of the fish diet and their dentition structure are best adapted to exploit the particular food types. Astatotilapia nubila can be classified as an insectivore, Astatotilapia 'big eye' as an algivore, Lipochromis maxillaris as a paedophage, Xystichromis phytophagus as a plant feeder, Astatoreochromis alluaudi as a molluscivore and Pseudocranilabrus multicolor victoriae as an algivore. Trophic resource partitioning therefore exists in this haplochromine community, despite being morphologically generalized. Feeding represents the most explicit axis of niche differentiation among the haplochromines and promotes their co-existence. All the six species were restricted to the fringing papyrus during the day while L. maxillaris, A. alluaudi and Xphytophagus move inshore during the night. The phylogenetic status of six extanct haplochromine species and their phylogenetic relationships was established by directly sequencing the first 369bp of the mitochondrial DNA Control Region via PCR amplification. The population genetic structure and genetic variability of the endangered Xystichromis phytophagus was inferred from the mtDNA