Ricerc@Sapienza

Mullets are very common fishes included in the family Mugilidae, (Mugiliformes), which
are characterized by both a remarkably uniform external morphology and internal
anatomy. Recently, within this family, different species complexes were molecularly
identified within Mugil, a genus which is characterized by lineages that sometimes
show very different karyotypes. Here we report the results of cytogenetic and molecular
analyses conducted on Mugil hospes, commonly known as the hospe mullet, from
Ecuador. The study aims to verify whether the original described species from the Pacific
Ocean corresponds to that identified in the Atlantic Ocean, and to identify speciesspecific
chromosome markers that can add new comparative data about Mugilidae
karyotype evolution. The karyotype of M. hospes from Ecuador is composed of 48
acrocentric chromosomes and shows two active nucleolar organizer regions (NORs).
In situ hybridization, using different types of repetitive sequences (rDNAs, U1 snDNA,
telomeric repeats) as probes, identified species-specific chromosome markers that
have been compared with those of other species of the genus Mugil. Cytochrome c
oxidase subunit I (COI) sequence analysis shows only 92–93% similarity with sequences
previously deposited under this species name in GenBank, all of which were from
the Atlantic Ocean. Phylogenetic reconstructions indicate the presence of three wellsupported
hospe mullet lineages whose molecular divergence is compatible with the
presence of distinct species. Indeed, the first lineage includes samples from Ecuador,
whereas the other two lineages include the Atlantic samples and correspond to
M. brevirostris from Brazil and Mugil sp. R from Belize/Venezuela. Results here provided
reiterate the pivotal importance of an integrative molecular and cytogenetic approach in
the reconstruction of the relationships within Mugilidae.