Phenotypic plasticity of the gastropod Melanoides tuberculata in the Nile Delta: A pollution-induced stabilizing selection

Highlights: • Manzala lagoon is one of the most polluted lakes in the Nile-Delta of Egypt. • Phenotypic plasticity of the Melanoides tuberculate was assessed using geometric morphometric. • Polluted sites have very limited morphological variation relative to unpolluted sites. • Stabilizing selection is the dominated mechanism of the natural selection in the polluted sites. - Abstract: To understand the effect of metal pollution on the speciation process, we conducted comparative analyses of six populations of the gastropod Melanoides tuberculata, which dominated the Manzala lagoon (Nile Delta, Egypt). Geometric morphometric analysis was implemented to quantify the phenotypic plasticity of the species. The results from both Canonical Variate Analysis and Relative Warp indicated an overall decrease in the morphological breadth of M. tuberculata in the polluted sites. The favored phenotypes in the polluted sites have moderate whorl section, moderate ovate aperture, less-prominent radial ornament, and overall moderate-spired shells. Lack of morphological variations and dominance of intermediate phenotypes in the polluted sites indicate that stabilizing selection is driving the morphological pattern of this species. Moreover, analysis by using the partial least square model confirmed that metal pollution is the major predictor of the observed shape variations, whereas other biotic/abiotic traits are a minor predictor.