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Testing alternative hypotheses for the decline of cichlid fish in Lake Victoria using fish tooth time series from sediment cores.

ABSTRACT: Lake Victoria is well known for its high diversity of endemic fish species and provides livelihoods for millions of people. The lake garnered widespread attention during the twentieth century as major environmental and ecological changes modified the fish community with the extinction of approximately 40% of endemic cichlid species by the 1980s. Suggested causal factors include anthropogenic eutrophication, fishing, and introduced non-native species but their relative importance remains unresolved, partly because monitoring data started in the 1970s when changes were already underway. Here, for the first time, we reconstruct two time series, covering the last approximately 200 years, of fish assemblage using fish teeth preserved in lake sediments. Two sediment cores from the Mwanza Gulf of Lake Victoria, were subsampled continuously at an intra-decadal resolution, and teeth were identified to major taxa: Cyprinoidea, Haplochromini, Mochokidae and Oreochromini. None of the fossils could be confidently assigned to non-native Nile perch. Our data show significant decreases in haplochromine and oreochromine cichlid fish abundances that began long before the arrival of Nile perch. Cyprinoids, on the other hand, have generally been increasing. Our study is the first to reconstruct a time series of any fish assemblage in Lake Victoria extending deeper back in time than the past 50 years, helping shed light on the processes underlying Lake Victoria's biodiversity loss.

SUBMITTER: Ngoepe N

PROVIDER: S-EPMC10950456 | biostudies-literature | 2024 Mar

REPOSITORIES: biostudies-literature

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Testing alternative hypotheses for the decline of cichlid fish in Lake Victoria using fish tooth time series from sediment cores.

Ngoepe Nare N Merz Alenya A King Leighton L Wienhues Giulia G Kishe Mary A MA Mwaiko Salome S Misra Pavani P Grosjean Martin M Matthews Blake B Mustaphi Colin Courtney CC Heiri Oliver O Cohen Andrew A Tinner Willy W Muschick Moritz M Seehausen Ole O

Biology letters 20240320 3

Lake Victoria is well known for its high diversity of endemic fish species and provides livelihoods for millions of people. The lake garnered widespread attention during the twentieth century as major environmental and ecological changes modified the fish community with the extinction of approximately 40% of endemic cichlid species by the 1980s. Suggested causal factors include anthropogenic eutrophication, fishing, and introduced non-native species but their relative importance remains unresolv ...[more]

PMID: 38503343

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Project description:BackgroundEfficient communication requires that signals are well transmitted and perceived in a given environment. Natural selection therefore drives the evolution of different signals in different environments. In addition, environmental heterogeneity at small spatial or temporal scales may favour phenotypic plasticity in signaling traits, as plasticity may allow rapid adjustment of signal expression to optimize transmission. In this study, we explore signal plasticity in the nuptial coloration of Lake Victoria cichlids, Pundamilia pundamilia and Pundamilia nyererei. These two species differ in male coloration, which mediates species-assortative mating. They occur in adjacent depth ranges with different light environments. Given the close proximity of their habitats, overlapping at some locations, plasticity in male coloration could contribute to male reproductive success but interfere with reproductive isolation.MethodsWe reared P. pundamilia, P. nyererei, and their hybrids under light conditions mimicking the two depth ranges in Lake Victoria. From photographs, we quantified the nuptial coloration of males, spanning the entire visible spectrum. In experiment 1, we examined developmental colour plasticity by comparing sibling males reared in each light condition. In experiment 2, we assessed colour plasticity in adulthood, by switching adult males between conditions and tracking coloration for 100 days.ResultsWe found that nuptial colour in Pundamilia did respond plastically to our light manipulations, but only in a limited hue range. Fish that were reared in light conditions mimicking the deeper habitat were significantly greener than those in conditions mimicking shallow waters. The species-specific nuptial colours (blue and red) did not change. When moved to the opposing light condition as adults, males did not change colour.DiscussionOur results show that species-specific nuptial colours, which are subject to strong divergent selection by female choice, are not plastic. We do find plasticity in green coloration, a response that may contribute to visual conspicuousness in darker, red-shifted light environments. These results suggest that light-environment-induced plasticity in male nuptial coloration in P. pundamilia and P. nyererei is limited and does not interfere with reproductive isolation.

Dataset Information

Testing alternative hypotheses for the decline of cichlid fish in Lake Victoria using fish tooth time series from sediment cores.

Publications

Testing alternative hypotheses for the decline of cichlid fish in Lake Victoria using fish tooth time series from sediment cores.

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