Abstract

This research focuses on the effect of salinity gradient on genetic diversity, population structure, adaptive evolution, and community structure of benthic macroinvertebrates. It will fill the gap between ecology patterns and the genetic mechanisms underlying them to learn how augmented salinity serves as a selection agent affecting the community resilience and biodiversity. The secondary data synthesis method was used, which combined the datasets of peer-reviewed literature, environmental surveillance programs, and biodiversity databases of freshwater, estuarine, and coastal systems. Measures of genetic diversity, allelic richness (), observed heterozygosity (), expected heterozygosity (), and nucleotide diversity (), were tabulated and standardised. FST was used to determine the degree of population differentiation, and environmental association analysis was used to determine adaptive signatures. Relationships among salinity and genetic variation and community structure were assessed using multivariate techniques, including Principal Coordinate Analysis (PCoA) and Redundancy Analysis (RDA), as well as regression and meta-analytic models. Salinity increased genetic diversity tremendously as  decreased from 8.4 ± 1.2 to 4.3 ± 0.9 and  from 0.75 ± 0.04 to 0.54 ± 0.06. The nucleotide diversity (0.0065 to 0.0031) decreased by more than 50%. The degree of population differentiation became much higher (up to 0.28), which suggests that there was limited gene flow. Salinity and genetic diversity were found to be strongly negatively correlated ( up to 0.72, p < 0.001). Salinity had strong positive relationships with adaptive loci, such as Na⁺/K⁺-ATPase ( = 0.71) and aquaporins ( = 0.64). The richness of the species changed to 15 ± 3 instead of 42 ± 5, and the Shannon diversity was reduced to 1.89 compared to 3.21, which shows significant changes in the composition of the community. Salinity acts as a dominant environmental filter driving genetic erosion, population divergence, and adaptive specialization in benthic macroinvertebrates. While adaptive mechanisms support short-term persistence, reduced genetic diversity may limit long-term resilience to environmental change. These findings highlight the need for integrative ecological-genomic approaches to better predict biodiversity responses under increasing salinization.

Keywords: Salinity gradient, Genetic diversity, Benthic macroinvertebrates, Adaptive evolution, Population structure, Environmental filtering, Freshwater salinization