Cytogenetical and morphological features reveal significant differences among Venezuelan and Brazilian samples of Mugil curema (Teleostei: Mugilidae)

Abstract

Karyotype of M. curema from the Gulf of Mexico and Brazil have been reported as possessing chromosome complement with 2n=28 and FN=48, whereas specimens from Venezuela has been reported as possessing a diploid number 2n=24 and a conserved FN (48). Although at first sight this variation suggests the presence of a chromosomal intraspecific (interpopulational) variability, the possibility that we are dealing with two different species was examined. This work revisit the karyotypes of M. curema from Venezuela and Brazil, including new data on C-banding, and NOR localization, and compares morphologic characteristics of samples from both localities. Thus, besides diploid number, the constitutive heterochromatin distribution and NORs location, mark other differences between M. curema Cytotype 1 (2n=28; FN=48) and Cytotype 2 (2n=24; NF=48). Moreover, morphologic comparison revealed differences in the scale counts and pectoral fin rays: 35 scales in the middle body line and 15 pectoral fin rays in specimens possessing the karyotype 2n=28, compared with 37-39 scales in the middle body line and 17 pectoral fin rays in specimens with the karyotype 2n=24. These differences lead us to suggest that both cytotypes are not related merely to geographic polytipic variations but could correspond to different species.Os cariótipos de M. curema do Golfo do México e do Brasil possuem 2n=28 cromossomos e NF=48. Espécimes da Venezuela, entretanto, apresentam um número diplóide de 28 cromossomos e um NF conservado (48). Apesar desta variação sugerir, a princípio, uma variabilidade intraespecífica (interpopulacional), a possibilidade de estarmos perante diferentes espécies foi investigada. O presente trabalho re-analisa os cariótipos de M. curema da Venezuela e do Brasil, incluindo novos dados sobre bandamento C e localização das NORs e compara caracteres merísticos e morfométricos de amostras de ambas as localidades. Assim, junto com o número cromossômico, a heterocromatina constitutiva e a distribuição das NORs trazem outras diferenças entre M. curema Citótipo 1 (2n=48, FN=48) e Citótipo 2 (2n=48, FN=48). Além disso, as comparações dos caracteres morfológicos revelam diferenças nas contagens, com 35 escamas na linha média do corpo e 15 raios nas nadadeiras peitorais nos espécimes com cariótipo 2n=28, já o cariótipo 2n=24 apresenta 37-39 escamas e 17 raios nas peitorais. Essas diferenças sugerem que ambos citótipos não estão relacionados meramente a variações geográficas politípicas mas que podem corresponder a diferentes espécies.

Classical and molecular cytogenetic characterization of Agonostomus monticola, a primitive species of Mugilidae (Mugiliformes)

“…The latter cytotypes have been found in specimens of Mugil curema from Louisiana and Brasil (2n = 28, NF = 48;LeGrande and Fitzsimons 1976;Nirchio et al 2005) and from Venezuela (2n = 24, NF = 48; Nirchio and Cequea 1998;Nirchio et al 2007, among others). They were originally interpreted (LeGrande and Fitzsimons 1976) to be due to extensive Robertsonian fusions which occurred in an ancestral group with an all-acrocentric chromosome complement (cytotype A) similar to that of M. cephalus.…”

Karyological characterization of <i>Mugil trichodon</i> Poey, 1876 (Pisces: Mugilidae)

“…Karyological information about the Mugilidae shows that NORs are located: on the telomeric region of the long arm of acrocen-tric chromosome pair N°1 in M. cephalus (Rossi et al, 1996), M. platanus (Jordao et al, 1992), and M. liza (Nirchio et al, 2001); on the telomeric region of the long arm of the metacentric chromosome pair N°1 in M. curema from Venezuela (Nirchio et al, 2001); on the telomeric region of the short arm of the subtelocentric chromosome pair N°11 in M. curema from Brazil (Nirchio et al, 2005); and on the short arm of the unique submetacentric chromosome pair (N°24) of Liza aurata, L. ramada, L. saliens and Chelon labrosus (Rossi et al, 1997;Gornung et al, 2001). In Oedalechilus labeo, one pair of NORs that are strikingly different in size is located on the short arms of the only subtelocentric pair (N°9); although there can be an additional, though inactive NOR, in the chromosome complement (Rossi et al, 2000).…”

Karyotype characterization of Mugil incilis Hancock, 1830 (Mugiliformes: Mugilidae), including a description of an unusual co-localization of major and minor ribosomal genes in the family

“…Recent cytogenetic studies carried out on several Mugilidae species from Venezuela (reviewed in Sola et al, 2007Sola et al, , 2008 have provided information regarding several interesting systematic and cytotaxonomic issues within the family. For example, the cytogenetic studies made it possible to establish that Mugil rubrioculus is a separate species from M. curema (Nirchio et al, 2003 and also indicated the likely existence of a species complex within M. curema (Nirchio & Cequea, 1998;Nirchio et al, 2005a). Moreover, the localization of major and minor ribosomal genes revealed that the 48 uniarmed chromosome karyotype, displayed by all the Mugilidae species, with the exception of M. curema, is much more differentiated than the macromorphology of chromosomes would suggest (Sola et al, , 2008.…”