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| the Nile perch Lates niloticus, a voracious predator introduced into Lake Victoria by humans to satisfy meat demands in the 1950s. Several species of endemic cichlids that were markedly affected are shown. The populations of some of these species declined so much that their genomic structure remained significantly altered even after their numbers climbed back up. in Imamoto, Nakamura, Aibara, Hatashima, ... et Nikaido, 2024. |
Abstract
Within 15,000 years, the explosive adaptive radiation of haplochromine cichlids in Lake Victoria, East Africa, generated 500 endemic species. In the 1980s, the upsurge of Nile perch, a carnivorous fish artificially introduced to the lake, drove the extinction of more than 200 endemic cichlids. The Nile perch predation particularly harmed piscivorous cichlids, including paedophages, cichlids eat eggs and fries, which is an example of the unique trophic adaptation seen in African cichlids. Here, aiming to investigate past demographic events possibly triggered by the invasion of Nile perch and the subsequent impacts on the genetic structure of cichlids, we conducted large-scale comparative genomics. We discovered evidence of recent bottleneck events in 4 species, including 2 paedophages, which began during the 1970s to 1980s, and population size rebounded during the 1990s to 2000s. The timing of the bottleneck corresponded to the historical records of endemic haplochromines” disappearance and later resurgence, which is likely associated with the introduction of Nile perch by commercial demand to Lake Victoria in the 1950s. Interestingly, among the 4 species that likely experienced bottleneck, Haplochromis sp. “matumbi hunter,” a paedophagous cichlid, showed the most severe bottleneck signatures. The components of shared ancestry inferred by ADMIXTURE suggested a high genetic differentiation between matumbi hunter and other species. In contrast, our phylogenetic analyses highly supported the monophyly of the 5 paedophages, consistent with the results of previous studies. We conclude that high genetic differentiation of matumbi hunter occurred due to the loss of shared genetic components among haplochromines in Lake Victoria caused by the recent severe bottleneck.
genetic structure, bottleneck, cichlid, paedophage, genetic diversity
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| Sampling information and localities of 7 haplochromine cichlids endemic to Lake Victoria and Astatotilapia stappersii as an outgroup. These species were included for genetic statistics comparison. a) Pictures of the 8 species. Colored triangles for paedophages and circles for others next to species names correspond to sampling locations on the map. Paedophages, Haplochromis sp. “matumbi hunter,” and H. microdon was shaded by a yellow box. A photo of Astatotilapia stappersii was retrieved from Meier, Marques et al. (2017). b) Sampling localities of all samples in a). The area marked by a red square in the bottom left map represents the location of Mwanza Gulf, Lake Victoria, and the map of the enlarged Mwanza Gulf is shown on the right. The number of samples per species obtained in each sampling locality is shown next to markers colored by species, corresponding to the labels in a). Samples without locality information are noted as unknown. |
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| Pictured on the left is the Nile perch Lates niloticus, a voracious predator introduced into Lake Victoria by humans to satisfy meat demands in the 1950s. On the right, several species of endemic cichlids that were markedly affected are shown. The populations of some of these species declined so much that their genomic structure remained significantly altered even after their numbers climbed back up. photos: Minami Imamoto, Masato Nikaido |
Conclusion:
We successfully demonstrated the population history and phylogenetic relationship of endemic haplochromines by performing large-scale comparative genomics. This study is the first example to present the impacts of the Nile perch upsurge on the genetic structure of Lake Victoria haplochromines. Signatures of bottleneck events in multiple endemic species further supported that the introduction and subsequent expansion of the exotic species Nile perch negatively influenced the demography of endemic species and eventually altered the genetic structure. The previously known hypothesis that piscivores, like paedophages, should have experienced a stronger bottleneck was further supported by inferred evidence of the intense bottleneck in paedophages, especially in matumbi hunters.
Minami Imamoto, Haruna Nakamura, Mitsuto Aibara, Ryo Hatashima, Ismael A Kimirei, Benedicto B Kashindye, Takehiko Itoh, Masato Nikaido. 2024. Severe Bottleneck Impacted the Genomic Structure of Egg-Eating Cichlids in Lake Victoria. Molecular Biology and Evolution. 41(6); msae093. DOI: 10.1093/molbev/msae093
https://phys.org/news/2024-06-nile-perch-invasion-triggered-genetic.html
