Molecular evidence for the freshwater lifestyle conquer in two Italian endemic representatives of the Gobiidae family: Padogobius nigricans and Padogobius bonelli
Author(s)
Macali, Armando
Date Issued
June 16, 2017
Type
Doctoral Thesis
Abstract
Evolutionary transitions between marine and freshwater habitats are rare events that can have
profound impacts on aquatic biodiversity. Marine–freshwater transitions are a particularly
interesting aspect of the evolutionary biology of many fish groups. Within Mediterranean fish
biodiversity, one of the most enigmatic group in terms of adaptive radiation on evolutionary
time scale is represented by the Gobiidae family (Teleostei). Mediterranean representatives of
Gobiidae are divided in three distinct evolutionary lineages: Pomatoschistus lineage, with
marine and freshwater species; Aphia lineage, composed of exclusively marine species
inhabiting the Mediterranean and North-East Atlantic; Gobius lineage, including a radiation in
the inland Ponto-Caspian region (Benthophilines), as well as species inhabiting the
Mediterranean, North-eastern Atlantic, and Atlantic coast of Africa. Within Gobius lineage, one
intriguing open question is related to the origin of the genus Padogobius. Padogobius is
represented by only two species: P. nigricans Canestrini, 1867, endemic to Central and
Northern Italy, and P. bonelli (Bonaparte, 1846), known from the North-Eastern Italy and
adjacent areas. Both species are pure freshwater inhabitants. Nevertheless, whether the
adaptation to the freshwater habitats evolved only once or independently is still debated.
In this dissertation I inferred a more comprehensive analysis of species-level relationships of
the major representatives of Mediterranean gobies, linking evolutionary marine/freshwater
ecological transitions to the paleohistory of the Mediterranean basin. I implemented a time
calibrated species tree inference with ancestral state reconstruction encompassing the search for
a sister group of Padogobius to test the monophyly of the freshwater habit. All the
reconstruction proposed in this study converge in the definition of the polyphyletic origin of the
genus Padogobius. The results provide strong support for a multiple independent origin of the
freshwater habit in the two endemic Italian species P. bonelli and P. nigricans. Additionally,
the results from species tree inference propose new insight in the relationships among members
of Mediterranean Gobius lineage, previously not considered. Molecular dating of the radiation
of Gobius species and Padogobius representatives are consistent with the oceanographic and
tectonic history of the basin, enhancing of the role of the Messinian Salinity Crisis in shaping
Mediterranean biodiversity.
Additional information
Dottorato di ricerca in Ecologia e gestione delle risorse biologiche
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