Does your lip stick? Evolutionary aspects of the mouth morphology of the Indo-Pacific clinging goby of the Sicyopterus genus (Teleostei: Gobioidei: Sicydiinae) based on mitogenome phylogeny.

<p class="rtejustify">Sicydiinae gobies have an amphidromous life cycle. Adults grow, feed, and reproduce in rivers, while larvae have a marine dispersal phase. Larvae recruit back to rivers and settle in upstream habitats. Within the Sicydiinae subfamily, the&nbsp;<em>Sicyopterus </em>genus, one of the most diverse (24 species), is distributed in the tropical islands of the Indo‐Pacific. One of the characters used to determine <em>Sicyopterus </em>species is the upper lip morphology, which can be either smooth, crenulated, or with papillae, and with (2 or 3) or without clefts. The mouth is used as a secondary locomotor organ along with the pelvic sucker. It is thus strongly related to the climbing ability of species and is of major importance for the upstream migration and the colonization of insular freshwater systems. The mouth also has an important role in the feeding mechanism of these herbivorous species. In this paper, we have established a molecular phylogeny of the genus based on the 13 mitochondrial protein‐coding genes to discuss the relationship between 18 Sicyopterus species. There is a well‐supported dichotomy in the molecular phylogeny of the <em>Sicyopterus</em> genus and this separation into two clades is also morphologically visible, with the distinction of species with three clefts and species with 0 or 2 clefts on the upper lip. The mouth morphology can thus be separated with regard to the molecular phylogeny obtained. The evolution of the mouth morphology is discussed in terms of the adaptation of the <em>Sicyopterus</em> genus to settlement and life in tropical insular river systems.</p>