Abstract
Squalius microlepis was examined from recent and historical collections within the known range of the species with special emphasis on intraspecific variability and variations, and compared to its closest relative species S. tenellus (in total, 193 specimens; 33 absolute and 52 proportional measurements and ratios, and 12 counts including vertebrae). Squalius tenellus was perfectly differentiated in all statistical analyses and can be diagnosed by 76–95 (vs. 64–80) scales in lateral series, 68–83 (vs. 58–77) lateral-line scales, (17)18–20 (vs. 13–16(17)) scales above lateral line, and (7)8–10 (vs. 4–7) scales below lateral line. Squalius microlepis was morphologically heterogeneous, with two phenotypes readily distinguishable (phenotype 1 corresponding to S. microlepis s. str. as defined by its lectotype) by a combination of many characters; those contributing most to the discrimination were number of gill rakers, length of lower jaw (% interorbital width), and head length (% SL). Only phenotype 1 was found in the Ričina-Prološko Blato-Vrljika karst system; most of the specimens from the lower Matica and the Tihaljina-Trebižat karst system were identified as phenotype 2; the sample from karstic poljes near Vrgorac contained both phenotype 1 and 2, and individuals of intermediate morphology. As very limited molecular data exist on the two phenotypes of S. microlepis, we refrain from any taxonomic conclusions until new molecular approaches (and new markers) are used. We also report on a dramatic reduction of the area of distribution and abundance of S. microlepis in recent years.
Highlights
The genus Squalius Banaparte is widely distributed throughout Europe and the Middle East, and shows an especially high diversity in the Mediterranean basin
We report on a dramatic reduction of the area of distribution and abundance of S. microlepis in recent years
Squalius tenellus can be further distinguished by an often slightly incomplete, interrupted or deformed lateral line and scales somewhat irregularly placed on the back and flanks; these traits have not been found in S. microlepis
Summary
The genus Squalius Banaparte is widely distributed throughout Europe and the Middle East, and shows an especially high diversity in the Mediterranean basin. Available data on genetic markers for Squalius microlepis and S. tenellus show that they form a sister-pair in a clade, which is restricted to the Iberian and Apennine Peninsulas and the eastern Adriatic basin (Perea et al 2010; Geiger et al 2014; Schönhuth et al 2018). The CO1 mitochondrial marker do not distinguish them (Perea et al 2010; Geiger et al 2014) while mitochondrial cytb, a combined nuclear data set (RAG+S7), and the combined mitochondrial and nuclear data sets CO1+cytb+RAG+S7 (Perea et al 2010) and CO1+cytb+RAG+S7 (Schönhuth et al 2018) support some divergence
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