Biology subjects

Sawasawa, W.

Publications and source records attributed to Sawasawa, W..

3 recordsLinked to original sources

bioRxiv2026

Population divergence in growth allometry of annual killifishes across ephemeral habitats in Malawi floodplain systems

Body size is a fundamental determinant of ecological performance, and variation in length- weight relationships can provide insight into how populations respond to local environmental conditions. Annual killifishes inhabit highly seasonal wetlands characterized by substantial environmental heterogeneity, yet population-level variation in growth allometry remains poorly understood. We investigated growth allometry in 18 populations of two annual killifish species, Nothobranchius kirki and N. wattersi, distributed across ephemeral habitats in Malawi. Length- weight relationships were analyzed separately for each species using linear mixed-effects models, with locality incorporated as a random effect. Environmental variation among localities was summarized using principal component analysis of water quality variables, and population- specific allometric coefficients were subsequently related to environmental gradients. Significant population-level variation in growth trajectories was detected in both species, indicating divergence in allometric scaling among localities. Divergence was more pronounced in N. wattersi, which exhibited a broader range of population-specific allometric coefficients than N. kirki. Populations also differed significantly in relative body condition after accounting for body length and sex. Environmental gradients explained a significant proportion of variation in allometric slopes in N. kirki, whereas no significant relationship was detected in N. wattersi. Thus, the species exhibiting weaker allometric divergence showed stronger environmental associations, while the species exhibiting greater divergence showed little correspondence with measured environmental variables. These results demonstrate substantial spatial heterogeneity in growth allometry among populations of annual killifishes inhabiting seasonal wetlands. Furthermore, the contrasting environmental associations observed between species suggest that population divergence in growth trajectories may arise through different ecological and evolutionary processes, even among closely related taxa occupying similar habitats.

ecology↗

bioRxiv2024

Introgression dynamics of sex-linked chromosomal inversions shape the Malawi cichlid adaptive radiation

Chromosomal inversions contribute to adaptive speciation by linking co-adapted alleles. Querying 1,375 genomes of the species-rich Malawi cichlid fish radiation, we discovered five large inversions segregating in the benthic subradiation that each suppress recombination over more than half a chromosome. Two inversions were transferred from deepwater pelagic Diplotaxodon via admixture, while the others established early in the deep benthic clade. Introgression of haplotypes from lineages inside and outside the Malawi radiation coincided with bursts of species diversification. Inversions show evidence for transient sex linkage and a striking excess of protein changing substitutions points towards selection on neuro-sensory, physiological and reproductive genes. We conclude that repeated interplay between depth adaptation and sex-specific selection on large inversions has been central to the evolution of this iconic system.

evolutionary biology↗

bioRxiv2024

Population genomic analysis reveals cryptic population structure in the commercially important Lake Malawi cichlid Copadichromis mloto

Fish is an important source of animal protein for many people living around Lake Malawi. The evaluation of population structure and genetic diversity can yield useful information for management and conservation of fish species but is complicated in Lake Malawi by the close genetic relatedness of species of the recent cichlid adaptive radiation. In this study, we analysed whole-genome sequencing data of "true utaka", a group of cichlids previously common in fisheries, but that has faced strong decline due to overfishing. Our analysis of 223 individuals collected from fishermens catches along the western shoreline of Lake Malawi confirmed that Copadichromis mloto (C. sp. "virginalis kajose") is the true utaka most targeted by fisheries. Genetic principal component analysis, phylogenetic inference, and admixture analysis revealed complex patterns of population structure. The presence of at least three geographically widespread genetic clades that have remained separate despite gene flow and partial sympatry hints at the presence of currently undescribed, cryptic species diversity in C. mloto. This result leads us to suggest that, despite the lack of obvious habitat barriers, benthic and pelagic species of Malawi cichlids might harbour unidentified species diversity and calls for further genetic and taxonomic research to define appropriate conservation units.

genomics↗