Lake Malawi Research Articles

Ecological speciation in East African freshwater crabs of the genus Arcopotamonautes Bott, 1955 across a lake-river boundary in the Lake Malawi catchment (Potamoidea: Potamonautidae: Potamonatinae)

Abstract Geological, climate and ecosystem changes in Africa likely influenced speciation of Afrotropical freshwater crabs. In total, the subfamily Potamonautinae comprises over 120 species, and this diversity provides a valuable opportunity to explore speciation processes. Here we study diversification of potamonautid crabs in the Lake Malawi catchment, and investigate whether speciation has taken place across a lake-river boundary. Specifically, we reconstruct evolutionary relationships of the Malawi blue crab, Arcopotamonautes orbitospinus (Cunnington, 1907), an endemic of Lake Malawi, and of A. montivagus (Chace, 1953) from rivers and streams draining into Lake Malawi, and smaller lakes within this catchment. Our phylogenetic analysis of over 28,000 single nucleotide polymorphisms shows a monophyletic A. orbitospinus nested within a clade otherwise comprised of A. montivagus from across the Lake Malawi catchment (A. montivagus Group I). We also identified a second allopatric clade of A. montivagus from the Rungwe mountains of Tanzania, and neighbouring Zambia (A. montivagus Group II). Morphological differences were apparent between all three groups. Collectively these results show A. montivagus is a paraphyletic riverine taxon that has diversified in allopatry, and that this species entered Lake Malawi and seeded the specialised heavily armoured lacustrine species, A. orbitospinus. We hypothesise that formation of deep-water conditions within Lake Malawi, together with differences in predation pressures between the rivers and lake, provided ecological opportunities for natural selection to drive speciation across the lake-river boundary. We conclude that geographical separation and ecological adaptation are potentially important drivers of evolutionary diversification in these enigmatic freshwater crabs.

Revealing caprine schistosomiasis and its One Health importance in Malawi: A molecular epidemiological investigation augmented with a praziquantel treatment and GPS animal tracking pilot sub-study

To shed first light on caprine schistosomiasis and its zoonotic potential in Malawi, we conducted a molecular epidemiological investigation, sampling goats (n = 230) across three districts, using faecal miracidia hatching test. Molecular genotyping of miracidia later revealed the prevalence of Schistosoma mattheei to be 0.0 % in Nsanje District (n = 30), 16.7 % in Chikwawa District (n = 30) and 25.3 % in Mangochi District (n = 170). Notably, a miracidium of Schistosoma haematobium was observed from a single goat in Chikwawa. Inspection of carcasses (n = 51) at two local abattoirs in Mangochi District did not find any evidence of caprine schistosomiasis where only a single herd, at Mangochi 3, was infected. Here, despite sampling several other herds nearby, the prevalence was 87.7 % (n = 49), with an animal found excreting 1000 miracidia per 5 g of faeces. At this location, our praziquantel treatment (n = 14) and GPS animal tracking (n = 2) pilot sub-study compared two local goat herds over a three-month period. The daily foraging ranges across a 10 km2 area were recorded, alongside targeted schistosome surveillance within local freshwater intermediate snail hosts. Analysis of GPS data revealed only one herd (infected) to have regular daily water contact with Lake Malawi whereas the other herd (not infected) totally avoided the lake. One week after praziquantel treatment administered at 40 mg/kg, anthelminthic cure rate was 92.3 % while at three months approximately a third of treated animals were shedding schistosome miracidia. Cercariae from several field-caught snails locally were genotyped, inclusive of finding a Schistosoma haematobium-mattheei hybrid. Our findings reveal the focalized nature of caprine schistosomiasis, signposting a novel alert for S. haematobium transmission, and highlight where zoonotic transmission can be intense. To better address zoonotic spill-over from S. mattheei (and/or S. haematobium), the national control programme for schistosomiasis should formally develop targeted surveillance of caprine schistosomiasis and where appropriate, attempt an integrated One Health intervention in future.

African cichlid fishes: morphological data and taxonomic insights from a genus-level survey of supraneurals, pterygiophores, and vertebral counts (Ovalentaria, Blenniiformes, Cichlidae, Pseudocrenilabrinae).

The iconic freshwater cichlid fishes (Cichlidae) comprise about 1750 validly named species and hundreds more that are known, but not yet described and named. Cichlids are an important source of protein for millions of people on several continents, are model organisms in studies of evolution, speciation, ecology, development, behaviour and physiology and are popular as aquarium fishes. Yet, comparative studies of cichlid internal anatomy are rare. Even their osteology has not been taxonomically surveyed. The cichlid postcranial skeleton has been especially neglected. Here, I provide the first survey in cichlids of the considerable variation in numbers of vertebrae, supraneurals and dorsal- and anal-fin supports (pterygiophores), as well as the patterns with which the pterygiophores insert between the neural or haemal spines. The study includes some 1700 specimens of nearly 400 cichlid species. Focusing on the largest subfamily, the African cichlids or Pseudocrenilabrinae, the survey furnishes data from species in all but one of its 166 genera. Limited data from species in the other cichlid subfamilies (Etroplinae, Ptychochrominae and Cichlinae) and from the related leaffishes, Polycentridae, are also presented. Key examples of pterygiophore insertion patterns from throughout the range of variation are illustrated and discussed. Detailed analytical tables and all raw data are provided in supplementary files.A bizarre specialisation in Cyprichromis is noted, evidently for the first time. Uniquely in this Lake Tanganyikan genus, five to seven anal pterygiophores are abdominal in position, located anterior to the anal fin and inserting toward or between successive pairs of pleural ribs.Taxonomic changes: The most speciose tribe of African cichlids, currently known as Haplochromini, is correctly called Pseudocrenilabrini. Based chiefly on the molecular phylogenetic findings of other workers, I propose four pseudocrenilabrine subtribes, one occurring in rivers and three endemic to Lake Malawi. I also re-assign the Lake Tanganyikan tribe Tropheini as another subtribe of Pseudocrenilabrini, in line with numerous molecular studies placing tropheines firmly within this tribe. The remaining genera of Pseudocrenilabrini remain incertae sedis in this tribe pending clarification of their phylogenetic relationships.The character complex here surveyed is a promising source of taxonomically and phylogenetically informative characteristics distinguishing or uniting cichlid taxa at multiple hierarchical levels, from species through subfamily. This reference set of novel character data can also provide information for palaeontological studies of African cichlids. These attributes are skeletal features potentially available for study in well preserved fossils and may help determine their correct taxonomic placement.

Molecular epidemiology and population genetics of Schistosoma mansoni infecting school-aged children situated along the southern shoreline of Lake Malawi, Malawi.

In areas of low disease endemicity, highly sensitive diagnostic tools to identify, diagnose, and monitor intestinal schistosomiasis transmission are needed to reliably measure the burden and risk of infection. Here, we used highly sensitive molecular diagnostic methods to investigate Schistosoma mansoni prevalence and transmission along the southern shoreline of Lake Malawi, five years post-disease outbreak. Faecal and urine samples were provided by school-aged children situated along the southern shoreline of Lake Malawi. Kato-Katz faecal-egg microscopy and point-of-care circulating cathodic antigen (POC-CCA) rapid diagnostic tests were then performed to diagnose infection with S. mansoni. Urine-egg microscopy was also used to diagnose infection with Schistosoma haematobium. In addition, Schistosoma miracidia were isolated from faecal material using a standard miracidium hatching technique. A two-step real-time PCR approach was then used to diagnose infection with S. mansoni using DNA isolated from faecal samples. Furthermore, isolated miracidia were genotyped to species level through PCR and Sanger sequencing. Phylogenetic analyses were then carried out to identify which previously defined S. mansoni cox1 lineage group S. mansoni miracidia were most closely related to. The measured prevalence of S. mansoni infection varied considerably depending on which diagnostic assay was used. When compared to real-time PCR, faecal-egg microscopy had a sensitivity of 9% and a specificity of 100%. When POC-CCA 'trace' results were considered positive, POC-CCA had a sensitivity of 73% and a specificity of 81% when compared to real-time PCR. However, when considered negative, POC-CCA sensitivity was reduced to 56%, whereas specificity was increased to 90%. In addition, a high degree of S. haematobium DNA was detected in DNA isolated from faecal samples and motile S. haematobium miracidia were recovered from faecal samples. Schistosoma mansoni miracidia were closely related to two independent cox1 lineage groups, suggesting multiple recent introduction and colonisation events originating from surrounding east African countries. Intestinal schistosomiasis is now highly prevalent along the southern shoreline of Lake Malawi just five years post-disease outbreak. In addition, a high prevalence of urogenital schistosomiasis persists. The revision of ongoing schistosomiasis control programmes in this area is therefore recommended. Our study also highlights the need for reliable diagnostic assays capable of distinguishing between Schistosoma species in multispecies co-endemic areas.

Anthropogenic activities along the Lake Nyasa catchments alter the habitat and genetic diversity of a Lake Salmon, Opsaridium microlepis

The Lake Salmon, Opsaridium microlepis is an economically important fish along the Lake Nyasa. However, the species is under threat of extinction due to anthropogenic activities such as agriculture, mining, urbanization, and deforestation. Consequently, the fish species is currently regarded as a threatened species, and the International Union for Conservation of Nature (IUCN) has red-listed the species due to an apparent decline in abundance. The current study assesses the potential impact of human activities on the genetic diversity of O. microlepis using partial mitochondrial cytochrome oxidase subunit I (COI) sequences and microsatellite loci. The results indicate that genetic diversity is lower in the areas affected by human activities compared to relatively pristine areas. The results from this study may suggest that human activities taking place in the catchments are likely to contribute to the alteration of the genetic diversity of O. microlepis species. Thus, immediate measure is required to control anthropogenic activities in the areas to protect the species and other aquatic organisms from possible threats of extinction.

Hydrological dynamics of the shire river: Insights from baseflow and recession analysis

The Shire River, a vital waterway in Malawi, plays a pivotal role in the country's economy, serving as a source of electrical power and irrigation for surrounding communities. This study investigates the hydrological dynamics of the Shire River by examining its flow components and the influence of baseflow under varying climatic conditions. Through meticulous baseflow separation using the Eckhardt recursive digital filter and recession analysis, Lake Malawi emerges as the primary contributor to the river's baseflow, sustaining approximately 80%–82% of total flows annually of which about 78% is contributed during wet seasons. Moreover, an inverse relationship between baseflow and rainfall is observed, highlighting the significance of baseflow augmentation during drier periods. Baseflow analysis of wettest and driest years further elucidates precipitation's impact on baseflow fluctuations, emphasizing the intricate interplay between precipitation patterns and baseflow dynamics. Therefore, to ensure the sustainable management of the Shire River, it is crucial to implement policies that support the conservation of groundwater resources and the efficient allocation of water during varying climatic conditions. Overall, this study provides valuable insights into the hydrological processes of the Shire River, contributing to enhanced understanding and sustainable management of this essential water resource.

A whole-body micro-CT scan library that captures the skeletal diversity of Lake Malawi cichlid fishes

Here we describe a dataset of freely available, readily processed, whole-body μCT-scans of 56 species (116 specimens) of Lake Malawi cichlid fishes that captures a considerable majority of the morphological variation present in this remarkable adaptive radiation. We contextualise the scanned specimens within a discussion of their respective ecomorphological groupings and suggest possible macroevolutionary studies that could be conducted with these data. In addition, we describe a methodology to efficiently μCT-scan (on average) 23 specimens per hour, limiting scanning time and alleviating the financial cost whilst maintaining high resolution. We demonstrate the utility of this method by reconstructing 3D models of multiple bones from multiple specimens within the dataset. We hope this dataset will enable further morphological study of this fascinating system and permit wider-scale comparisons with other cichlid adaptive radiations.

Evolution and morphological diversity of the genus Diploneis (Bacillariophyta) in Lake Malawi, with description of six new species

ABSTRACT Lake Malawi, one of the world’s oldest and most important freshwater systems, harbours a remarkable biotic diversity partly due to variable fluctuations in climate and lake level. Over time, these fluctuations have contributed to the emergence and development of different ecological niches and microhabitats that have facilitated diversification within the lake. Despite our extensive knowledge of different animal groups, the evolutionary history of species-rich diatom groups in Africa and, particularly, in Lake Malawi has yet to be studied. Here, we used a combination of morphological, molecular, and paleontological data to assess the species richness and evolutionary processes of the diatom genus Diploneis in this lake. The comprehensive dataset revealed four putative new endemic species from modern and two apparently extinct Diploneis species from the fossil record of the lake, described here as new to science. Morphological analyses showed that all these new species exhibit remarkable differences and unique morphological patterns that were recently discovered in Diploneis species from nearby Lake Tanganyika. Molecular phylogenetic analyses revealed that the four new species now living in Lake Malawi are nested within a clade of Lake Tanganyika Diploneis species but do not form a monophyletic group. This suggests that the new Lake Malawi Diploneis species are derived from one or more Tanganyikan ancestors and that more than one colonization event probably occurred. However, further analyses are needed to elucidate their origin.

Assesing wave power potential in Nkhatabay, Malawi

Background: This thesis is an investigation of the wave power resource on Lake Malawi, precisely Nkhatabay, focusing on the spatial distribution of wave power of the said places exposed to the highest wave power. Findings: The main objective of this study was to determine the wave potential of Lake Malawi in Malawi in order to allow design and usage of wave energy in Malawi. Methods: The study methodology employed to achieve this main objective entails an analysis of measured wave data recorded at wave recording station along Lake Malawi. Conclusion: The analysis provided a general description of wave power at the location for which wave data exist. From this analysis,it was found that Nkhatabay is exposed to average wave power of approximately 202 KW/m annually. Data was collected from the Department of Climate Change and Meteorological Services (DCCMS), who have implanted a Lake buoy at Usisya in Nkhatabay. The data gathered was analyzed using Microsoft excel and R studio to come up with graphs for proper description of results. Power calculations were conducted as well to determine the output of turbines used with respect to the wave data observed.

Preying on cyprinid snout warts (pearl organs) as a novel and peculiar habit in the Lake Malawi cichlid Docimodus evelynae

Cichlid fishes in the African Great Lakes have undergone explosive speciation, acquiring markedly varying ecologies and diets. There are multiple lineages of scale-eating cichlids, and their natural history and evolutionary ecology is only partially understood. We examined the feeding habit of Docimodus evelynae, a known scale eater, in Lake Malawi. The stomach contents of young individuals mainly consisted of unknown 1 mm hard, white warts (> 30%). To clarify the origin of these warts, we conducted an X-ray fluorometer analysis, and found they were rich in sulphur but low in silicon and calcium, suggesting they were epidermal tissues. Histological and morphological analyses revealed they were multicellular and cup-shaped. These characteristics matched only those of the pearl organs of the coexisting cyprinid Labeo cylindricus. DNA was extracted from the warts found in the stomach of five D. evelynae individuals, followed by PCR using primers targeting the partial COI gene of L. cylindricus. The resulting sequences exhibited 98% similarity to those of L. cylindricus. Pearl organs, never reported as a primary food for fish, could offer a substantial nutritional source based on calorific calculations. Understanding how this peculiar diet is foraged is essential for full comprehension of the food-web structure in this lake.

Detection of male genital schistosomiasis (MGS) associated with human, zoonotic and hybrid schistosomes in Southern Malawi

BackgroundMale Genital Schistosomiasis (MGS) remains an often-overlooked chronic sequela of urogenital schistosomiasis in endemic areas of sub-Saharan Africa. As part of a 2-year longitudinal study on Hybridization of UroGenital Schistosomiasis (HUGS) in Malawi, a MGS sub-study was conducted to assess whether hybrid schistosomes were incriminated.MethodsDuring recruitment, demographic, health and socio-economic data were collected through individual questionnaire interviews in Mthawira community from Nsanje District along Shire River and Samama community from Mangochi District along Lake Malawi shoreline. Urine and semen samples were collected and analysed to determine the identity of schistosome infection. Urine filtration and microscopy, direct microscopy of semen and its sediments (after centrifugation) were performed. Thereafter, the sediments were examined by molecular DNA analysis with a novel two-tube real-time PCR assay. The participants were also screened for Human papilloma virus (HPV) and other sexually transmitted infections (STIs).ResultsTwenty-two men were recruited for the sub-study, 8 in Nsanje District and 14 in Mangochi District, with a median age of 22.0 years. By microscopy, ten (45.7%) participants had Schistosoma ova in their urine, 11 (50.0%) in semen while 16 (72.7%) were positive by real-time PCR. One participant had both S. haematobium and S. mattheei ova in his semen, three showed symptoms, and one had a mixed infection of S. mansoni and possible S. haematobium-S. mattheei hybrid. Twelve men had detectable high-risk HPV serotypes 16, 18 and others while six had Trichomonas vaginalis and other STIs.ConclusionZoonotic and hybrid schistosomes can cause MGS similar to human schistosomes, which can be co-infected with HPV and STIs, thereby posing a new challenge in diagnosis, management and control measures in resource poor settings. Increased awareness of these infections among local communities and primary healthcare workers and improvement of disease management are needed and advocated.

Replicated Functional Evolution in Cichlid Adaptive Radiations.

AbstractAdaptive radiations highlight the mechanisms by which species and traits diversify and the extent to which these patterns are predictable. We used 1,110 high-speed videos of suction feeding to study functional and morphological diversification in 300 cichlid species from three African Great Lake radiations of varying ages (Victoria, Malawi, and Tanganyika) and an older, spatially dispersed continental radiation in the Neotropics. Among African radiations, standing diversity was reflective of time. Morphological and functional variance in Lake Victoria, the youngest radiation, was a subset of that within Lake Malawi, which itself was nested within the older Tanganyikan radiation. However, functional diversity in Neotropical cichlids was often lower than that in Lake Tanganyika, despite being much older. These two radiations broadly overlapped, but each diversified into novel trait spaces not found in the youngest lake radiations. Evolutionary rates across radiations were inversely related to age, suggesting extremely rapid trait evolution at early stages, particularly in lake radiations. Despite this support for early bursts, other patterns of trait diversity were inconsistent with expectations of adaptive radiations. This work suggests that cichlid functional evolution has played out in strikingly similar fashion in different radiations, with contingencies eventually resulting in lineage-specific novelties.

Influence of large scale climate drivers on hydro-climate variability in Dwangwa River Basin, Malawi

Large-scale climate processes such as the Indian Ocean Dipole (IOD) have significant roles in modulating rainfall and hydrological systems. Understanding such processes can inform adaptation measures for climate change and variability, as well as water resource management and planning. This study investigated the impact of the Indian Ocean Dipole (IOD) on rainfall and discharge variability in the Dwangwa River Basin (DRB) in Malawi, a key inflow to Lake Malawi. Specifically, the study analysed annual rainfall variability trends from 1985 to 2015 using the Coefficient of Variation (CV) and the annual Precipitation Concentration Index (PCI). The significance and direction of rainfall and discharge trends were quantified using the Mann–Kendall trend test at α = 0.05 significance level. To evaluate the association between rainfall and IOD, the Pearson product moment used three IOD phases: positive, negative, and neutral. Simple linear regression was utilised to check the response of the river during the concerned IOD phases. The study found CVs between 20 and 30%, typical of climates with moderate monthly rainfall variability. The PCI ranged from 20 to 30%, suggesting a strongly seasonal and highly variable temporal intra-annual rainfall distribution in the DRB. Moreover, the Mann–Kendall test statistics showed insignificant decrease in annual rainfall trends. Further, the findings demonstrated an insignificant negative correlation between rainfall and positive IOD, with rainfall increases associated with negative IOD, whereas positive IOD is associated with decreased river discharge. Consequently, El Niño and a positive IOD could cause DRB to have low water availability. Therefore, the study demonstrates that rainfall is experiencing a decreasing trend, which is driven by large-scale mechanics.

A geospatial analysis of local intermediate snail host distributions provides insight into schistosomiasis risk within under-sampled areas of southern Lake Malawi

BackgroundAlong the southern shoreline of Lake Malawi, the incidence of schistosomiasis is increasing with snails of the genera Bulinus and Biomphalaria transmitting urogenital and intestinal schistosomiasis, respectively. Since the underlying distribution of snails is partially known, often being focal, developing pragmatic spatial models that interpolate snail information across under-sampled regions is required to understand and assess current and future risk of schistosomiasis.MethodsA secondary geospatial analysis of recently collected malacological and environmental survey data was undertaken. Using a Bayesian Poisson latent Gaussian process model, abundance data were fitted for Bulinus and Biomphalaria. Interpolating the abundance of snails along the shoreline (given their relative distance along the shoreline) was achieved by smoothing, using extracted environmental rainfall, land surface temperature (LST), evapotranspiration, normalised difference vegetation index (NDVI) and soil type covariate data for all predicted locations. Our adopted model used a combination of two-dimensional (2D) and one dimensional (1D) mapping.ResultsA significant association between normalised difference vegetation index (NDVI) and abundance of Bulinus spp. was detected (log risk ratio − 0.83, 95% CrI − 1.57, − 0.09). A qualitatively similar association was found between NDVI and Biomphalaria sp. but was not statistically significant (log risk ratio − 1.42, 95% CrI − 3.09, 0.10). Analyses of all other environmental data were considered non-significant.ConclusionsThe spatial range in which interpolation of snail distributions is possible appears < 10km owing to fine-scale biotic and abiotic heterogeneities. The forthcoming challenge is to refine geospatial sampling frameworks with future opportunities to map schistosomiasis within actual or predicted snail distributions. In so doing, this would better reveal local environmental transmission possibilities.Graphical

Revealing bovine schistosomiasis in Malawi: Connecting human and hybrid schistosomes within cattle

In Malawi, the putative origin of a newly described Schistosoma haematobium-mattheei hybrid human schistosome was assessed upon a seminal molecular parasitological survey of cattle. Using miracidia hatch test (MHT) and carcass inspection at slaughter, mean prevalence of bovine schistosomiasis was 49.1% (95% CI: 43.7–54.6%) and 10.3% (95% CI: 6.0–16.2%) respectively, though significant spatial heterogeneity was noted. Approximately 2.0% of infected cattle, and only those from Mangochi District, shed S. haematobium-mattheei and/or S. haematobium in faeces. To quantify schistosome (re)infection dynamics, where a S. haematobium-mattheei hybrid was present, we undertook a novel pilot GPS-datalogging sub-study within a specific herd of cattle (n = 8) on the Lake Malawi shoreline, alongside a praziquantel (40 mg/kg) treatment efficacy spot check. At sub-study baseline, all GPS-tagged cattle had proven daily water contact with the lake. Each animal was patently infected upon MHT, with older animals shedding less miracidia. At one month review, whilst parasitological cure was 100.0%, from six weeks onwards, (re)infection was first noted in the youngest animal. By three-month review, all animals were patently (re)infected though only miracidia of S. mattheei were recovered, albeit in much lower numbers. To conclude, infection with S. mattheei is particularly common in cattle and demonstrates a previously cryptic burden of bovine schistosomiasis. Within Mangochi District, bovine transmission of both S. haematobium-mattheei hybrids and S. haematobium are now incriminated, with unequivocal evidence of contemporary zoonotic spill-over. Future control of urogenital schistosomiasis here in the southern region needs to develop, then successfully integrate, a One Health approach with appropriate mitigating strategies to reduce and/or contain bovine schistosomiasis transmission.

Isotope Hydrology and Hydrogeochemical Signatures in the Lake Malawi Basin: A Multi-Tracer Approach for Groundwater Resource Conceptualisation

Reliance on groundwater is outpacing natural replenishment, a growing imbalance that requires detailed and multi-faceted water resource understanding. This study integrated water-stable isotopes and hydrogeochemical species to examine hydrogeochemical processes during groundwater recharge and evolution in the Lake Malawi basin aquifer systems. The findings provide insights into groundwater source provenance, with non-evaporated modern precipitation dominating recharge inputs. Grouped hydrochemical facies exhibit five groundwater water types, prominently featuring Ca-Mg-HCO3. Modelled hydrogeochemical data underscore dominant silicate dissolution reactions with the likely precipitation of calcite and/or high-Mg dolomitic carbonate constrained by ion exchange. Isotope hydrology reinforces water resource system conceptualisation. Coupled isotopic-hydrogeochemical lines of evidence reveal a discernible spatial-seasonal inhomogeneity in groundwater chemical character, revealing a complex interplay of meteoric water input, evaporative effects, recharge processes, and mixing dynamics. Findings show that measurable nitrate across Malawi highlights a widespread human impact on groundwater quality and an urgent need for detailed modelling to predict future trends of nitrate in groundwater with respect to extensive fertiliser use and an ever-increasing number of pit latrines and septic systems arising from rapid population growth. This study not only refined the Lake Malawi basin aquifer systems conceptualisation but also provided isotopic evidence of groundwater and lake water mixing. This study sets a base for groundwater management and policy decisions in support of the Integrated Water Resources Management principles and Sustainable Development Goal 6 objectives for groundwater sustainability in the transboundary Lake Malawi basin.

Using luminescence dating to constrain lake sediment records: A new age model for the 1.38 Ma lake Malawi drill core, Eastern Africa

The 2005 Lake Malawi deep scientific drill core is the longest and most continuous high-resolution record from the continental tropics, extending to ∼1.38 Ma. While extensive sets of paleoclimate proxy data have been generated from this core, a gap in directly dated sediment, between ∼74 ka and ∼590 ka (28–167 m below lake floor), has limited the understanding of climatic drivers in this system. Previous age models fill the gap in direct dates by tuning to the global δ18O stack and interpreting paleomagnetic excursions, but these methods and the resulting models remain disputed. We fill this gap in chronology using luminescence dating, with 31 samples collected at ∼4 m resolution in this section of the core. Luminescence dating can sometimes be limited by relatively large uncertainties (typically ∼7%) and difficulty estimating the water content history of samples. We overcome these limitations by employing a high sampling density and using the sediment record to understand changes in water content during the burial period. This yields a vastly improved and robust age model that indicates changes in sedimentation rates not discernible in prior age models.

Sitwe 23, a Complex ESA/MSA Locality in the Northern Luangwa Valley, Zambia

This paper describes the lithic aggregates from Sitwe 23 (SW23), a Stone Age locality in a previously unstudied region of the northern Luangwa Valley, Zambia. This area yielded two surface lithic scatters containing abundant artifacts derived from Pleistocene sediments on uplifted terrain and exposed by recent erosion on two adjacent terraces. The scatters are time-averaged palimpsests formed by deflation, but most of the lithics lack evidence of significant fluvial transport or post-depositional damage, indicating minimal horizontal displacement. Typological and attribute analyses of samples from both spurs reveal predominantly simple and expedient core and flake technologies, as well as sophisticated biface manufacture and Levallois technique producing flakes and points that are differentially distributed between the terraces. The artifacts identified in this analysis include types conventionally considered diagnostic of the Acheulean, Sangoan, and Middle Stone Age, suggesting that the collections may document one or more temporal windows during the Chibanian age (770–126 ka). Whether artifacts in these samples were originally deposited sequentially or concurrently is not yet known and alternative hypotheses are presented and discussed. The collections are compared to sites in Zambia and the northern Lake Malawi basin and found to be similar technologically but typologically different. Given the paucity of previously known Ston Age archaeological sites in the region, our work now demonstrates that northern Luangwa has significant archaeological potential and deserves further study.

A first report of Pseudosuccinea columella (Say, 1817), an alien intermediate host for liver fluke, in Malawi

Starting in October 2021, quarterly malacological surveys have been undertaken in Malawi, with the sampling of 12 specified freshwater habitats throughout a calendar year. Each survey monitors the presence of aquatic intermediate snail hosts of medical and veterinary importance. In March 2023, the alien lymnaeid species Pseudosuccinea columella was encountered for the first time in the surveys, in Nsanje District. This species identity was later confirmed upon DNA analysis of mitochondrial ribosomal 16S sequences. In July 2023, P. columella was also noted at single sites within Mangochi and Chikwawa Districts, and again in Nsanje District, with an additional location observed. Of particular importance, our sampled location in Mangochi District was directly connected to Lake Malawi, which expands the species list of invasive molluscs in this lake. While P. columella is a well-known intermediate snail host for human and animal fascioliasis, screening collected snails for trematode cercariae, alongside molecular xenomonitoring, did not yield equivocal evidence of active fluke infection. However, the newly recognized presence of this alien intermediate snail host within Lake Malawi, and along the Shire River Valley, flags a new concern in altered local transmission potential for human and animal fascioliasis.Graphical

Ethical issues in Lake Malawi fisheries: a case of Karonga District

ABSTRACT The fisheries sector, exemplified here by Malawi’s Karonga District, illustrates the global consequences of insufficient ethical considerations, leading to the depletion of fisheries resources. Using data spanning from 2012 to 2021, including frame surveys and catch assessment surveys, this study employs ethical theories and the ethical matrix to identify and analyse ethical issues. The observed concerns include illegal fishing, heightened investment in a limited resource fishery, consumption of the critically endangered Chambo species, the environmental impact of trawl surveys, technological overreliance, and inadequate resource support from local politicians. Recommendations encompass ending open-access fisheries, revising biomass assessment methods, promoting mindset change, implementing poverty alleviation programmes, promoting aquaculture development, and enhancing the establishment of freshwater protected areas as sites for biodiversity conservation.