Subterranean Fishes of the World

4897

2017

Gouania willdenowi (Risso, 1810), the sole representative of the monotypic clingfish genus Gouania, is endemic to the Mediterranean Sea, where it lives a very cryptic and secretive life in the interstices of pebble beaches. With its wormlike body and small eyes it is perfectly adapted to this extreme environment. Because of a reduced swim bladder and a very patchy distribution of suitable habitats, adult G. willdenowi are very weak active dispersers and dispersal likely happens passively during the pelagic larval phase. Despite being quite common in pebble beaches throughout the Mediterranean, hardly anything is known about its biology, behaviour, phylogeny or taxonomy. DNA-barcoding, species tree analysis (*BEAST) including nine nuclear and one mitochondrial marker, as well as geometric morphometric analyses and MicroCT imaging across the whole Mediterranean Sea, yielded unexpected results regarding the evolutionary history of this genus. Molecular data suggests that the genus Gouania underwent a thus far unrecognized radiation into several fairly divergent species that started around 1.5–4 million years ago, after the Messinian Salinity Crisis. Moreover, whereas little diversity is seen in the western Mediterranean basin, convergently evolved syntopic species pairs (consisting of a gracile, elongate morph and a stockier morph) are found throughout the eastern basin (including the Adriatic Sea). Apparently, the extremely low active dispersal ability of adults implies that dispersal – even over short distances – happens exclusively via larval drift with water currents and that populations/species remain trapped in particular circulation systems. The eastern basin (including the Adriatic Sea) with its numerous islands is characterized by complex local circulation systems that might drive the evolution of locally confined species in the clingfish genus Gouania. To conclude, the radiation of Gouania represents a promising model system for studying rapid radiation and the independent origin of eco-morphologically similar species pairs, and the role of water currents for driving diversification in the marine environment.

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NOBIS Young Researchers’ Day 2017