Influence of Geographical Isolation on Genetic Diversity of Redbelly Tilapia, Coptodon zillii Gervais, 1848 and Microhabitat Transformation Modulated by Gill Ectoparasitic Helminthes

The study investigated the genetic diversity of the redbelly tilapia (Coptodon zillii) from three Egyptian aquatic ecosystems; Rayyan Lake, Burullus Lake, and the River Nile with the microhabitat utilization patterns of three gill parasites (monogenea, digenea, and copepoda). Results rejected the null hypothesis that geographical isolation does not affect genetic diversity, revealing distinct evolutionary divergence among the populations. Phylogenetic analysis showed strong bootstrap support (94-100%), dividing the Egyptian isolates into two sub-populations: one with Burullus Lake and the Nile River isolates and another with the Rayyan Lake isolate evolving separately. Additionally, the study dismissed the assumption that microorganisms exhibit identical microhabitat usage. Each parasite taxon displayed unique attachment, distribution, and feeding strategies, leading to specific microhabitat transformations. Digenean Centrocestis formosanus formed cysts within gill cartilage, monogeneans lodged between gill lamellae, and copepods (Ergasillus sieboldi) gripped filaments using specialized antennae. These adaptations suggest resource partitioning facilitates coexistence in shared environments. The findings highlight how ecological and evolutionary factors shape genetic divergence in the redbelly tilapia and parasite niche specialization. The discussion explores potential drivers of clustering patterns and evolutionary relationships among tilapia isolates, as well as strategies for microhabitat utilization. Overall, the study underscores the role of environmental heterogeneity in influencing both host genetics and parasite ecological dynamics.