Identification of a New Mullet Species Complex Based on an Integrative Molecular and Cytogenetic Investigation of Mugil hospes (Mugilidae: Mugiliformes).

Mauro Nirchio,Anna R Rossi,Valentina Milana,Claudio Oliveira,Fabilene G Paim

doi:10.3389/fgene.2018.00017

Abstract

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 species-specific 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 well-supported 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.

Highlights

Mullets is the popular name of fishes included in the Mugilidae, a species rich family that is the only representative of the order Mugiliformes
Each fish received an intra-abdominal injection of 0.0125% colchicine (1.0 ml/100 g body weight) 50 min before being sacrificed by administering a numbing overdose of benzocaine (250 mg/L) as recommended by the Guidelines for the Euthanasia of Animals of the American Veterinary Medical Association (AVMA, 2013)
This morphological character is shared with M. brevirostris, which inhabits the opposite side of the Americas

Summary

Introduction

Mullets is the popular name of fishes included in the Mugilidae, a species rich family that is the only representative of the order Mugiliformes. In Mugilidae, most of the classical morphological characters used in species identification and/or systematics have poor diagnostic power and morphometric variability is limited (Schultz, 1946; Thomson, 1997; González-Castro, 2007; González-Castro and Ghasemzadeh, 2016). Cytogenetic and molecular studies have provided important data for understanding the systematic relationships and evolutionary pathways among mullet species (Harrison et al, 2007; Sola et al, 2007; Durand et al, 2012; Durand and Borsa, 2015) These studies have shown that it is necessary to use integrative approaches to study mugilids. Molecular phylogenetic analyses have been used successfully in the investigation of chromosome evolution in some fish groups as those of the genus Characidium (PansonatoAlves et al, 2014) and Triportheus (Yano et al, 2014), and in Geophagus brasiliensis (Alves-Silva and Dergam, 2015)

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