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Preserved assemblages of invertebrate remains in lacustrine sediment reveal temporal variations of community composition and environmental conditions. However, records for large tropical lakes are scarce. Lake Victoria, the largest tropical lake, has a dynamic history of changes in water level, biogeochemistry and fish community composition over the past ~17,000 cal yr BP.In order to quantify changes in the invertebrate assemblage of Lake Victoria from the late Pleistocene throughout the Holocene, we examined chitinous remains of Cladocera and larval dipterans (Chironomidae and Chaoboridae) from a sediment core (37 m water depth) dated from ~13,700 cal yr BP to present.We identified four major phases in the invertebrate assemblage throughout this period of lake history. Firstly, Chironomidae and Chaoboridae appeared at low abundances during the earliest stages of lake inundation in the late Pleistocene, at a time when Cladocera were notably absent. Secondly, chaoborids and chironomids increased in abundance during the mid‐Holocene, which coincided with high diatom production toward the end of the Holocene African Humid Period. Thirdly, starting ~4,700 cal yr BP, Alona, a predominantly littoral cladoceran genus, consistently appeared in the invertebrate assemblage alongside changes in mixing regimes and persisted throughout the late Holocene to the present. Fourthly, the arrival of both Chydorus and Bosmina longirostris marked the establishment of an abundant cladoceran assemblage at ~1,350 cal yr BP. The assemblage then gradually shifted toward the increasing dominance of B. longirostris, a planktonic cladoceran.Several of the observed changes in the invertebrate assemblage occurred concurrently with changes in climatic conditions in East Africa and diatom productivity that have been previously recorded in Lake Victoria. This multi‐millennial record of sedimentary invertebrate assemblages in Lake Victoria elucidates some of the temporal development of these communities throughout most of the dynamic modern history of the ecosystem. [ABSTRACT FROM AUTHOR]

Octopus cyanea (Gray, 1849), abundant in the South‐West Indian Ocean (SWIO), constitutes a vital resource for both subsistence and commercial fisheries. However, despite this socioeconomic importance, and recent indications of overfishing, little is known about the population structure of O. cyanea in the region. To inform sustainable management strategies, this study assessed the spatio‐temporal population structure and genetic variability of O. cyanea at 20 sites in the SWIO (Kenya, Tanzania, Mozambique, Madagascar, Mauritius, Rodrigues, and the Seychelle Islands) by complementary analysis of mitochondrial DNA (mtDNA) noncoding region (NCR) sequences and microsatellite markers. MtDNA analysis revealed a shallow phylogeny across the region, with demographic tests suggesting historic population fluctuations that could be linked to glacial cycles. Contrary to expectations, NCR variation was comparable to other mtDNA regions, indicating that the NCR is not a hypervariable region. Both nuclear and mtDNA marker types revealed a lack of genetic structure compatible with high gene flow throughout the region. As adults are sedentary, this gene flow likely reflects connectivity by paralarval dispersal. All samples reported heterozygote deficits, which, given the overall absence of structure, likely reflect ephemeral larval recruitment variability. Levels of mtDNA and nuclear variability were similar at all locations and congruent with those previously reported for harvested Octopodidae, implying resilience to genetic erosion by drift, providing current stock sizes are maintained. However, as O. cyanea stocks in the SWIO represent a single, highly connected population, fisheries may benefit from additional management measures, such as rotational closures aligned with paralarval ecology and spanning geopolitical boundaries. [ABSTRACT FROM AUTHOR]

Tropical freshwater lakes are well known for their high biodiversity, and particularly the East African Great Lakes are renowned for their adaptive radiation of cichlid fishes. While comparative phylogenetic analyses of extant species flocks have revealed patterns and processes of their diversification, little is known about evolutionary trajectories within lineages, the impacts of environmental drivers, or the scope and nature of now‐extinct diversity. Time‐structured palaeodata from geologically young fossil records, such as fossil counts and particularly ancient DNA (aDNA) data, would help fill this large knowledge gap. High ambient temperatures can be detrimental to the preservation of DNA, but refined methodology now allows data generation even from very poorly preserved samples. Here, we show for the first time that fish fossils from tropical lake sediments yield endogenous aDNA. Despite generally low endogenous content and high sample dropout, the application of high‐throughput sequencing and, in some cases, sequence capture allowed taxonomic assignment and phylogenetic placement of 17% of analysed fish fossils to family or tribe level, including remains which are up to 2700 years old or weigh less than 1 mg. The relationship between aDNA degradation and the thermal age of samples is similar to that described for terrestrial samples from cold environments when adjusted for elevated temperature. Success rates and aDNA preservation differed between the investigated lakes Chala, Kivu and Victoria, possibly caused by differences in bottom water oxygenation. Our study demonstrates that the sediment records of tropical lakes can preserve genetic information on rapidly diversifying fish taxa over time scales of millennia. [ABSTRACT FROM AUTHOR]

Background: Researchers in the developing countries often have inadequate scientific writing skills to publish their research in international peer reviewed journals. Objectives: To improve the research-and proposal-writing skills of researchers and to evaluate the impact of this intervention. Methods: An off-the-shelf online course (AuthorAID, developed by INASP) was embedded in the Tanzania Fisheries Research Institute's (TAFIRI) website and offered to the institute researchers in Tanzania. The 8-week course was followed by a 2-day face-to-face workshop that used the course material contextualized to local conditions, and the combination was repeated one more time. Results: A total of 47 participants completed the course and attended the workshop: 21 (54%) completed the course in 2016 and 26 (67%) in 2017. The number of papers published annually by TAFIRI staff more than tripled between 2016 and 2019 after the AuthorAID intervention, most of them (114, or 91%) by researchers who had undergone the training. Conclusion: Embedding and contextualizing proven learning materials, such as the AuthorAID online course, can be an economical and effective approach to improving the writing skills of scientists in developing countries. [ABSTRACT FROM AUTHOR]

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.

There is considerable potential for nuclear genomic material in environmental DNA (eDNA) to inform us of population genetic structure within aquatic species. We tested if nuclear allelic composition data sourced from eDNA can resolve fine scale spatial genetic structure of the cichlid fish Astatotilapia calliptera in Lake Masoko, Tanzania. In this ∼35 m deep crater lake the species is diverging into two genetically distinguishable ecomorphs, separated by a thermo-oxycline at ∼15 m that divides biologically distinct water masses. We quantified population genetic structure along a depth transect using single nucleotide polymorphisms (SNPs) derived from genome sequencing of 530 individuals. This population genetic structure was reflected in a focal set of SNPs that were also reliably amplified from eDNA - with allele frequencies derived from eDNA reflecting those of fish within each depth zone. Thus, by targeting known genetic variation between populations within aquatic eDNA, we measured genetic structure within the focal species., Competing Interests: The authors have no competing interests to declare., (© 2023 The Authors.)