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

Abstract

The fish species Synbranchus marmoratus has 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 of S. marmoratus using 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. marmoratus complex, which resulted in the appearance of distinct karyotypic variants in a non-linear fashion related to diploid numbers and in the appearance of similar nonhomologous 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 of Synbranchus genus.A espécie de peixe Synbranchus marmoratus tem sido reportada como um complexo de espécies devido à elevada variabilidade cariotípica intraespecífica a despeito da dificuldade ou impossibilidade de distingui-las usando apenas caracteres morfológicos. O objetivo deste trabalho foi utilizar métodos citogenéticos e moleculares para determinar a delimitação das espécies e compreender a carioevolução de S. marmoratus utilizando amostras coletadas em distintas localidades brasileiras. Dentre os espécimes analisados, um alto grau de variação citogenética relativo aos números diploides e estrutura cariotípica foi observado, com cariótipos mostrando 2n=42, 44 e 46 cromossomos. Adicionalmente, utilizando sequências de três genes mitocondriais, as relações filogenéticas entre cada amostra com cariótipo conhecido foram determinadas, revelando uma divergência nucleotídica significativa entre os cariomorfos. Além disso, as análises indicam que rearranjos cromossômicos ocorreram independentemente nas distintas linhagens do complexo S. marmoratus, o que resultou no aparecimento de distintas variantes cariotípicas de forma não linear em relação aos números diploides e no surgimento de cromossomos similares e não homólogos. Finalmente, a integração de uma abordagem citogenética molecular e filogenética permitiu a determinação de cromossomos específicos que, possivelmente, estão envolvidos em rearranjos e um melhor entendimento sobre os processos evolutivos envolvidos na diferenciação do gênero Synbranchus.

DNA barcoding techniques used to identify the shared ichthyofauna between the Pantanal floodplain and Upper Parana River

“…Other studies have reported that Hoplias malabaricus (Utsunomia et al 2014a), Synbranchus marmoratus (Torres et al 2005;Utsunomia et al 2014b), Rhamdia quelen (Martinez et al 2011), Sternopygus macrurus (de Almeida-Toledo et al 1993), Eigenmannia virescens (Silva et al 2009), E. trilineata (Moys es et al 2010) and Brachyhypopomus pinnicaudatus (Giora 2009) are species complexes, but this is the first time that Leporinus striatus and Pimelodus maculatus are listed as putative species complexes.…”

Karyotype diversity and evolutionary trends in the Asian swamp eel Monopterus albus (Synbranchiformes, Synbranchidae): a case of chromosomal speciation?

“…Once the majority of chromosomal rearrangements involve heterochromatic regions, especially in fish species [26, 27], this explains the centromeric rearrangements in M. albus . The co-localization of CMA 3 positive heterochromatin with the NOR loci also occurs in other synbranchids [25, 28], probably because of local changes in base composition (increase in GC content) due to the so-called GC-biased gene conversion that involves rDNA in many vertebrates, including ray-finned fishes [29].…”

“…They also form small populations, and although they prefer freshwater habitats, these fishes tolerate brackish and saline conditions [1]. On the other hand, as many individuals can be isolated in small lakes during dry years, the capacity of sex reversal observed in synbranchids could contribute to the viability of such populations, increasing the probability of the fixation of genetic differences and speciation processes [25, 28].…”

“…However, Donsakul and Magtoon [17] have also reported that M. albus from the central part of Thailand differs from the other populations, as it has 2n = 18 and NF = 24 (Table 1). Similarly, the Venezuelan Ophisternon aenigmaticum also highlights a karyotype diversification, including 2n = 45 and NF = 51 and 2n = 46 and NF = 52 [20], as well as the Synbranchus marmoratus species from Brazil and Argentina, which presents 2n ranging from 42 to 46 [21–25]. The Synbranchidae family has high karyotype diversity among its species, with 2n ranging from 18 to 46, mainly due to extensive chromosomal rearrangements (fusions/fissions and inversions) (Table 1).…”

Allopatric chromosomal variation in Nematocharax venustus Weitzman, Menezes & Britski, 1986 (Actinopterygii: Characiformes) based on mapping of repetitive sequences

“…Moreover, the availability of refined cytogenetic methods have allowed identifying population polymorphism and unique evolutionary units, even within morphologically similar groups (Bitencourt et al, 2011;Utsunomia et al, 2014).…”