Lake Tanganyika Research Unit

Mpulungu, Zambia

Lake Tanganyika Research Unit

Mpulungu, Zambia
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Koblmuller S.,University of Graz | Nevado B.,Royal Belgian Institute Of Natural Sciences | Nevado B.,University of Oxford | Makasa L.,Lake Tanganyika Research Unit | And 11 more authors.
Hydrobiologia | Year: 2016

Stenotopic specialization to a fragmented habitat promotes the evolution of genetic structure. It is not yet clear whether small-scale population structure generally translates into large-scale intraspecific divergence. In the present survey of mitochondrial genetic structure in the Lake Tanganyika endemic Altolamprologus (Teleostei, Cichlidae), a rock-dwelling cichlid genus comprising A. compressiceps and A. calvus, habitat-induced population fragmentation contrasts with weak phylogeographic structure and recent divergence among genetic clades. Low rates of dispersal, perhaps along gastropod shell beds that connect patches of rocky habitat, and periodic secondary contact during lake level fluctuations are apparently sufficient to maintain genetic connectivity within each of the two Altolamprologus species. The picture of genetic cohesion was interrupted by a single highly divergent haplotype clade in A. compressiceps restricted to the northern part of the lake. Comparisons between mitochondrial and nuclear phylogenetic reconstructions suggested that the divergent mitochondrial clade originated from ancient interspecific introgression. Finally, ‘isolation-with-migration’ models indicated that divergence between the two Altolamprologus species was recent (67–142 KYA) and proceeded with little if any gene flow. As in other rock-dwelling cichlids, recent population expansions were inferred in both Altolamprologus species, which may be connected with drastic lake level fluctuations. © 2016 The Author(s)

Takeuchi Y.,Kyoto University | Ochi H.,4 4 7 Higashimon cho | Kohda M.,Osaka City University | Sinyinza D.,Lake Tanganyika Research Unit | Hori M.,Kyoto University
Ecology of Freshwater Fish | Year: 2010

Abstract - Tropical fish communities are highly diverse with large numbers of allied species coexisting. Concerns have been raised about changes in such communities caused by anthropogenic disturbances, but little is known about long-term changes. We investigated changes in the littoral fish community of Lake Tanganyika. A 10 × 40-m quadrat was placed on a rocky shore in the southern part of the lake, and fish censuses were conducted once a year during most years in 1988-2008. In total, 54 cichlid and 6 non-cichlid species were recorded. Aufwuch feeders were most abundant, followed by plankton feeders, detritus feeders, piscivores, shrimp eaters, zoo-benthos eaters, and scale eaters. Species richness and abundance were sustained over the study period, with biodiversity, as evaluated by the Shannon-Wiener index, remaining high. However, Mantel tests between the Bray-Curtis index and the difference in years between compared censuses revealed that the species composition of the community gradually changed with time. The fish community gradually underwent a change that may be due to low anthropogenic impacts on food condition. Our results promote awareness about the conservation of diversity in Lake Tanganyika. © 2010 John Wiley & Sons A/S.

Egger B.,University of Basel | Sefc K.M.,University of Graz | Makasa L.,Lake Tanganyika Research Unit | Sturmbauer C.,University of Graz | Salzburger W.,University of Basel
Journal of Heredity | Year: 2012

In the extremely species-rich haplochromine cichlid fishes of the East African Great Lakes, prezygotic isolation between closely related species is often maintained by color-assortative mating. In 1998, local fisherman working for the ornamental fish trade released different color morphs of the cichlid genus Tropheus into a small harbor basin in the southern part of Lake Tanganyika. This artificial amalgamation of color morphs provides a unique possibility to study mating patterns in cichlids in a natural environment over time. In a precursor study, we analyzed genotypes and phenotypes of almost 500 individuals sampled between 1999 and 2001 and uncovered a marked degree of color-assortative mating, which depended on the level of color pattern dissimilarity between morphs. Twelve years after introduction of nonindigenous morphs, we again sampled Tropheus individuals from the harbor basin and an adjacent, originally pure population and analyzed phenotypes (coloration) and genotypes (mitochondrial control region and 9 microsatellite loci) to assess the current status of the admixed population. Principal component analyses of color score data and population assignment tests demonstrate an increasing level of introgressive hybridization between morphs but also some ongoing color-assortative mating within morphs. The observed mating pattern might have been influenced by fluctuating environmental conditions such as periodic algal blooms or increased sedimentation causing turbid conditions in an otherwise clear lake. © The American Genetic Association. 2012. All rights reserved.

Sefc K.M.,University of Graz | Hermann C.M.,University of Graz | Steinwender B.,University of Graz | Steinwender B.,The New Zealand Institute for Plant and Food Research Ltd | And 7 more authors.
Ecology and Evolution | Year: 2015

Assortative mating promotes reproductive isolation and allows allopatric speciation processes to continue in secondary contact. As mating patterns are determined by mate preferences and intrasexual competition, we investigated male-male competition and behavioral isolation in simulated secondary contact among allopatric populations. Three allopatric color morphs of the cichlid fish Tropheus were tested against each other. Dyadic male-male contests revealed dominance of red males over bluish and yellow-blotch males. Reproductive isolation in the presence of male-male competition was assessed from genetic parentage in experimental ponds and was highly asymmetric among pairs of color morphs. Red females mated only with red males, whereas the other females performed variable degrees of heteromorphic mating. Discrepancies between mating patterns in ponds and female preferences in a competition-free, two-way choice paradigm suggested that the dominance of red males interfered with positive assortative mating of females of the subordinate morphs and provoked asymmetric hybridization. Between the nonred morphs, a significant excess of negative assortative mating by yellow-blotch females with bluish males did not coincide with asymmetric dominance among males. Hence, both negative assortative mating preferences and interference of male-male competition with positive assortative preferences forestall premating isolation, the latter especially in environments unsupportive of competition-driven spatial segregation. Empirical work on the evolution of premating isolation has focused on mating preferences, and few studies address the role of male-male competition. We tested agonistic interactions and reproductive isolation between allopatric color morphs of a cichlid fish. Our results demonstrate (1) that color morph-dependent asymmetric dominance will oppose positive assortative preferences of allopatric taxa in secondary contact and hence interfere with speciation, and (2) that asymmetric reproductive isolation can also occur due to a lack of positive assortative female preferences when there is no dominance of one color morph over the other. © 2015 The Authors.

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