Parallel phenotypes of Littoraria angulifera emerge across ecoregions, as a response to urbanization

Abstract Cities are emerging as the fastest-growing ecosystems on Earth. While evidence is accumulating that a diverse array of species exploits urban habitats, the mechanisms by which urbanization drives natural selection and shapes phenotypic responses remain poorly understood, particularly in tropical coastal areas. Here, we evaluate the repeatability of phenotypic changes exhibited by the snail Littoraria angulifera , a species closely associated with mangrove trees that thrives in anthropogenic habitats following forest clearing. We compared urban and non-urban populations from three ecoregions along the Caribbean coast of Colombia. Our analysis revealed significant differences in size structure, abundance, onset of sexual maturity, and feeding structures between urban and non-urban populations. Parallel urban phenotypes—characterized by smaller body sizes, increased abundance, earlier sexual maturation, and distinctive radular morphology—have emerged across ecoregions. The unique radular morphology observed in urban snails likely reflects adaptations to the textural differences in anthropogenic habitats. Meanwhile, the consistent patterns in body size and sexual maturation suggest selection for “fast-living” phenotypes, driven by altered thermal regimes resulting from reduced shading after mangrove clearing and the proliferation of impervious surfaces. These findings align with documented phenotypic responses in various terrestrial species to the urban heat island effect, highlighting the broader role of thermal reaction norms as a unifying mechanism shaping the evolution of ectothermic organisms in urban environments.