Molecular and cytogenetic analyses of cryptic species within the Synbranchus marmoratus Bloch, 1795 (Synbranchiformes: Synbranchidae) grouping: species delimitations, karyotypic evolution and intraspecific diversification

Ricardo Utsunomia,José C Pansonato-Alves,Fausto Foresti,Fernando F Mendonça,Claudio Oliveira,Guilherme J Costa-Silva,Priscilla C Scacchetti

doi:10.1590/1982-0224-20140039

Ricardo Utsunomia, José C Pansonato-Alves + Show 5 more

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https://doi.org/10.1590/1982-0224-20140039

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Abstract

The fish species Synbranchus marmoratushas been reported to exist as a species complex due to high intraspecific karyotypic variability in spite of the difficulty or impossibility to distinguish them using morphological traits alone. The goal of this work was to use cytogenetic and molecular methods to determine the species delimitations and understand the karyoevolution ofS. marmoratususing samples collected from distinct Brazilian localities. Among the analyzed specimens, a large degree of cytogenetic variation related to diploid numbers and karyotype structure was observed, with karyotypes showing 2n=42, 44 and 46 chromosomes. In addition, using sequences of three mitochondrial genes, the phylogenetic relationships between every sample with a known karyotype were determined, which revealed significant nucleotide divergence among the karyomorphs. Also, the analyses indicate that chromosomal rearrangements occurred independently within the distinct lineages of S. marmoratuscomplex, which resulted in the appearance of distinct karyotypic variants in a non-linear fashion related to diploid numbers and in the appearance of similar non-homologous chromosomes. Finally, the integration of both molecular cytogenetic and phylogenetic approaches allowed the determination of specific chromosomes possibly involved in rearrangements and a better understanding about the evolutionary processes involved in the differentiation ofSynbranchusgenus.

Highlights

Cryptic species are defined as two or more morphologically indistinguishable species that are incapable of interbreeding (Bickford et al, 2007)
Considering the wide distribution of S. marmoratus throughout the waters of South and Central America, the purpose of this study was to characterize the karyotypes of distinct groups within this species and determine whether divergent species exist within the current S. marmoratus grouping, to analyze the relationships between the sampled taxa and to investigate the history of chromosomal rearrangements in this species as a whole
The analyses provided evidence for the existence of two main clades within S. marmoratus (I and II), one of which can be further subdivided into four subclades (IA, IB, IC and ID)

Summary

Introduction

Cryptic species are defined as two or more morphologically indistinguishable species that are incapable of interbreeding (Bickford et al, 2007) Such species likely arise through interespecific reproductive isolation, which can be caused by pre-zygotic means, such as gametic incompatibility and/or ecological isolation (Miyatake et al, 1999; Landry et al, 2003), or by post-zygotic means, such as hybrid inviability and/or sexual selection against hybrids (Orr, 1995; Noor et al, 2001; Presgraves et al, 2002). Such complexes have already been studied in a variety of fish orders, including Characiformes, Synbranchiformes, and Gymnotiformes (Moreira-Filho & Bertollo, 1991; Torres et al, 2005; Milhomem et al, 2008)

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