Download Milana V, Angiulli E, Sola L, Rossi AR Combining cytogenetic and

Milana V, Angiulli E, Sola L, Rossi AR
Combining cytogenetic and molecular data in taxonomically debated fish species: two case
studies.
Combined molecular and cytogenetic approaches were adopted to investigate the debated-taxonomic
status of fish species, belonging to unrelated families, characterized by different ecology, biology and
distribution range. In details, our aim was to verify the morphological assignment of samples, to
identify cytotaxonomic markers and to reconstruct phylogenetic relationships.
The first case regards species of the genus Pseudoplatystoma (Pimelodidae), distributed in the major
river basins of South America, where they represent important fisheries resources and play an
important ecological role due to their piscivirous and migratory habits. Traditional taxonomy
recognized three species, but recent morphological analyses raised their number to eight, including
two new species, P. orinocoense and P. metaense, distributed exclusively in the Orinoco basin. These
two species were found to have very conservative karyotypes (2n=56) and similar cytogenetic
features in terms of both constitutive heterochromatin distribution and number and location of
minor and major ribosomal genes. The analysis of cytochrome b (1110 bp) and a fragment of COI
gene (432 bp) confirmed the assignment of P. metaense and P. orinocoense specimens to the two
distinctive Pseudoplatystoma molecular clades identified in the Orinoco basin. The gene
genealogies obtained with these two mitochondrial markers confirms that the identified molecular
clades provide support for the recognition of only some of the eight described morphospecies.
The second case regards some Italian endemic Leuciscinae species (Cyprinidae), the Toscana stream
chub, Squalius lucumonis, an endangered species restricted to the Tyrrhenian drainage basins of
Central Italy (Tiber, Arno, Ombrone, and Serchio) along with three sympatric species, S. squalus,
Telestes muticellus and Rutilus rubilio. The taxonomic status of S. lucumonis was repeatedly questioned
by several authors, who argued that it could represent a hybrid between two of the previously
mentioned sympatric species. The analysis of cytochrome b (1110 bp) and of a non-coding nuclear
region, Cyfun P (Cyprinid formerly unknown nuclear Polymorphism), confirmed the validity of the
four different taxa and proved to be useful to exclude the presence of hybrids. Comparative
chromosomal localization of minor ribosomal genes through FISH with 5S rDNA probe showed
that these chromosomal regions are differentially distributed among the four species and represent
useful cytotaxonomic markers in leuciscine fishes.