Ecomorphological adaptation in three mudskippers (Teleostei: Gobioidei: Gobiidae) from the Persian Gulf and the Gulf of Oman

We hypothesise that the body shapes of three mudskipper species (Boleophthalmus dussumieri, Periophthalmus waltoni, and Scartelaos tenuis) are ecomorphological adaptations to different epi- and infaunal habitats. We investigated: (i) the association between burrow density and selected ecological variables; (ii) the phylogenetic relationships among these species, based on two mtDNA and one nDNA markers; (iii) their geometric morphometrics and ancestral shape reconstructions, based on two-dimensional landmark configurations; and (iv) their body surface-to-volume ratios (SAV), based on a geometric model. Boleophthalmus dussumieri and S. tenuis are more closely related, and more elongated than P. waltoni; the body of S. tenuis also has a higher SAV, and its elongated shape appears to be a divergent trait. P. waltoni is found in a wide range of conditions, including vegetated habitats; B. dussumieri is associated with low-energy conditions and fine unvegetated deposits; and S. tenuis is associated with high-energy conditions and coarser, non-cohesive sediments. These results suggest that body elongation in Scartelaos species is a divergent locomotory adaptation to marine habitats characterised by semi-liquid and less cohesive sediments. The more compact body shape of Periophthalmus species is hypothesised to have evolved from a gobionelline ancestor, and is proposed to be a preadaptation to subaerial locomotion in semi-terrestrial habitats.