Leuciscus (Pisces, Cyprinidae) karyotypes: Transect of Portuguese populations

Abstract

The presently described Iberian chubs - Leuciscus carolitertii and L. pyrenaicus - sampled throughout their distribution ranges in Portugal were cytogenetically analyzed. Their chromosome numbers were consistently 2n = 50, except for two specimens of L. carolitertii, which exhibited a supernumerary chromosome in some of the metaphases. The karyotypes were found to be highly typical for other Leuciscus taxa, as well as for European leuciscine cyprinids: the chromosome sets are dominated by metacentric and submetacentric elements with a reduced number of acrocentric pairs (three to four); the largest pair of the complements belongs typically to this latter category. The chubs from northern drainages, assignable to L. carolitertii, have apparently a more stable karyotype structure (12M:30S:8A) than the chubs from L. pyrenaicus, which have 12M:32S:6A, but may exhibit in the most southern river basins (Guadiana, Mira, Aljezur, Bordeira and Arade) more variable karyotypes. Besides, these data support the very recent discovery of two genetically distinct Leuciscus taxa in this region of the Iberian Peninsula, suggesting the stochastic fixation of structural chromosome rearrangements in these small and isolated drainages, which may be affected by bottlenecks due to significant variations in hydrological regimes. The NORs were apparently located in one small submetacentric pair of chromosomes and the presence of a heteromorphic sex chromosome system of the ZW/ZZ type was also evidenced for the Iberian endemic chubs.<br>A análise citogenética dos dois endemismos de Leuciscus atualmente descritos na Península Ibérica foi efetuada em amostras obtidas ao longo da sua área de distribuição. Apresentaram um valor diplóide de 2n = 50, com exceção de dois exemplares de L. carolitertii, os quais exibiam um cromossomo supranumerário em algumas metáfases. Caracterizaram-se por um padrão cariológico idêntico ao dos restantes táxons do mesmo gênero, igualmente partilhado pelos Leuciscinae europeus: um elevado número de cromossomos metacêntricos e submetacêntricos e um número reduzido de acrocêntricos (três a quatro pares), incluindo-se neste último grupo o maior par do complemento. As NORs localizaram-se tipicamente num par de submetacêntricos de reduzidas dimensões, existindo também evidências de um sistema cromossômico de determinação sexual do tipo ZW/ZZ. Porém, os espécimes do norte, L. carolitertii, aparentaram possuir um cariótipo mais estável em termos estruturais (12M:30S:8A) do que os do sul, pertencentes a L. pyrenaicus (12M:32S:6A). Esta espécie exibiu, nas suas populações mais meridionais que se localizam nas bacias do Mira, Aljezur, Bordeira e Arade, alterações da referida fórmula cromossômica, fato que vem em apoio da recente descoberta de dois taxóns de Leuciscus geneticamente diferenciados no sul da Península Ibérica, sugerindo a fixação de rearranjos cromossômicos estruturais nestas pequenas e isoladas bacias hidrográficas, com grandes variações dos seus regimes hidrológicos produzindo os chamados" efeitos de gargalo"

Comparative molecular cytogenetic analysis of three Leuciscus species (Pisces, Cyprinidae) using chromosome banding and FISH with rDNA

“…Heteromorphic sex chromosomes have been reported in L. cephalus, L. aula, L. souffia muticellus, L. carolitertii and L. pyrenaicus (Fontana et al 1970;Vujosevic et al 1983;Collares-Pereira et al 1998). In the present study, however, no such chromosomes were detected in the species examined, suggesting that the previously reported heteromorphic chromosomes might be a local polymorphism rather than a true sex chromosome.…”

“…About 20 among 35 putative species of the genus Leuciscus as well as other taxa included in the family Leuciscinae so far cytogenetically investigated indicated a considerable great karyological similarity (e. g. Tsingenopoulos and Karakousis 1996; Ráb et al 1996;Collares-Pereira et al 1998;Bianco et al 2004). Their karyotypes (2n = 50) were characterized by mainly biarmed elements, suggesting a high evolutionary position among cyprinid fish, and one pair of large A chromosomes which has been proposed as their cytogenetic markers (Cataudella et al 1977;Buth et al 1991;Ráb and Collares-Pereira 1995;Boron 2001;Rabova et al 2003).…”

“…One NOR-bearing chromosome pair (with NORs located on the short arms) observed in the karyotype of L. cephalus is the most common NOR phenotype among Leuciscinae (Collares-Pereira et al 1998;Rabova et al 2003). L. cephalus displayed a rather plesiomorphic state of the NOR character.…”

Chromosomes of Iberian Leuciscinae (Cyprinidae) Revisited: Evidence of Genome Restructuring in Homoploid Hybrids Using Dual-Color FISH and CGH

“…Besides basic Giemsa-stained chromosome counts and karyotype morphology [Collares-Pereira, 1985;Ráb and Collares-Pereira, 1995;Collares-Pereira et al, 1998], silver and chromomycin-A 3 bandings added little information to the differentiation of the genomes of these cyprinid fish [Rodrigues and Collares-Pereira, 1996;Gante et al, 2004;Gromicho and Collares-Pereira, 2004;Gromicho et al, 2006a;Monteiro et al, 2009;Pereira et al, 2009]. On one hand, results were consistent with the overall karyotypic pattern of the subfamily, whereas suggesting some degree of divergence by the presence of more than one chromosome pair bearing the NORs.…”

“…The karyotype structure in this group varies between 5-7 metacentric, 15-18 submetacentric and 2-4 subtelo-to acrocentric chromosome pairs and fundamental number ranges from 92 to 96 ( fig. 1 e) [Collares- Pereira, 1985;Ráb and Collares-Pereira, 1995;Collares-Pereira et al, 1998;Gromicho et al, 2006a;Monteiro et al, 2009;Nabais et al, 2013].…”