Molecular evolution of echolocation genes in freshwater and marine cetaceans

Abstract

Throughout their evolutionary history, cetaceans faced two environmental transitions, which resulted in extraordinary radiation events and in morphological, physiological and behavioral adaptations to life underwater. The first event was the colonization of marine environments by cetaceans' terrestrial ancestors, followed by the invasion of freshwater systems and the recolonization of marine ecosystems. Freshwater ecosystems are highly distinct from the oceans in temperature, acoustic, depth and physical complexity, representing a dramatic change in the selective pressures affecting sensorial traits, such as echolocation. These changes drove the multiple origins of the river dolphins and their differentiation from marine odontocetes. River dolphins share a series of echolocation parameters and morphological characters related to hearing, suggesting that convergent evolution may have played a role in the evolution of freshwater and marine odontocetes. Echolocation, a complex biosonar, has evolved independently in both dolphins and bats and allows them the production, emission and processing of high frequency sounds for spatial orientation. The molecular convergence between this groups and inside Odontoceti is widely documented, especially for genes associated with sound reception and cochlear development. Thus, it is possible to hypothesize that the convergent evolution of these genes was favored by the wide variety of physical and acoustic differences between marine and riverine environments. Therefore, our main goal is to study the molecular convergence between freshwater and marine dolphins, focusing on the following genes: SLC26A5, Tmc1, Cdl14, Cdh23 and SMPX, and species: Inia geoffrensis, Sotalia fluviatilis, Sotalia guianensis, Lipotes vexillifer and Pontoporia blainvillei. We will conduct molecular evolution analysis, especially those that estimate natural selection acting upon these genes throughout evolution. (AU)