Evidence of positive selection suggests possible role of aquaporins in the water-to-land transition of mudskippers

Parallel duplication and loss of aquaporin-coding genes during the ‘out of the sea’ transition as potential key drivers of animal terrestrialization

“…The presence of Aqp clades specific to terrestrial animals, such as the Eglps in insects (Finn et al, 2015) or AQP2, AQP5 and AQP6 in tetrapods (Finn et al, 2014; Lorente-Martínez et al, 2018), suggests that the number of aquaporins found in terrestrial animals might be different than the number found in aquatic ones. To test whether there is a correlation between the number of aquaporins and the habitat in which extant species live, we obtained Aqp-coding genes identified in each species and performed a phylogenetic Poisson regression using the habitat as an independent variable.…”

“…a Information from the phylum Nematoda is not discussed as only one terrestrial species was included in our analyses. b Chordate results are proposed by previous studies (Finn et al, 2014;Lorente-Martínez et al, 2018).…”

“…We tested for differences in each of the 4 main subtypes of aquaporins and in all aquaporins together. (Finn et al 2014;Lorente-Martínez et al 2018). The putative function of positively selected Aqp10a (Aqp3-like) in mudskippers' gills (marked with b) is proposed here based on the differential gene expression of its ortholog Aqp10a and paralog Aqp10b in zebrafish in gills (Finn and Cerdà 2011), and the enlarged gill chambers mudskippers have whose function is related to their semiterrestrial lifestyle (i.e.…”

“…chelicerates other than spiders, scorpions and mites), has not yet been explored, let alone in a comparative framework within the context of animal terrestrialization. Only a couple of previous studies have explored the potential key role of aquaporin gene duplications in the adaptation of vertebrates to life on land, with the identification of 3 tetrapod-exclusive classical aquaporins functionally related to water absorption mechanisms (Finn et al, 2014), and some signals of positive selection in semiterrestrial mudskippers' aquaporins (Lorente-Martínez, Agorreta, Torres-Sánchez, & Mauro, 2018). Nevertheless, even though the importance of gene duplication in the origin of new functions and driving adaptation has long been reported (Kondrashov, 2012), the potential role of aquaporin gene duplication and loss in the terrestrialization of lineages other than tetrapods has not yet been explored.…”

Genetic Adaptations in Mudskipper and Tetrapod Give Insights into Their Convergent Water-to-Land Transition

“…Regarding the terrestrial adaptation of tetrapods, there have been some studies to propose genetic signatures associated with essential physiological modifications of ancestral tetrapods such as limb development (as known as fin-to-limb transition), changes in chemoreceptors, and evolution of nitrogen excretion mechanism based on comparative genomics approaches [ 20 , 21 ]. Similarly, as reviewed by You et al [ 22 ], several studies reported unique genetic characteristics of mudskippers related to their land adaptation with the genomics and transcriptomics approaches [ 23 , 24 , 25 ]. Nevertheless, there still have been few studies to compare the genetic signature of land adaptation between mudskipper and ancestor of tetrapods, which can provide candidate genes or insights into biological processes related to the land adaptation of the two distinct vertebrate lineages.…”