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Gayana (Concepción) - Cromosomas de Girella laevifrons (Tschudi 1846) (Osteichthyes: Kyphosidae)

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Gayana (Concepción)

versión On-line ISSN 0717-6538

Gayana (Concepc.) v.74 n.2 Concepción  2010

http://dx.doi.org/10.4067/S0717-65382010000200007 

Gayana 74(2): 136-138, 2010. ISSN 0717-652X

 

Comunicación breve

 

Chromosomes of Girella laevifrons (Tschudi 1846) (Osteichthyes: Kyphosidae)

 

Cromosomas de Girella laevifrons (Tschudi 1846) (Osteichthyes: Kyphosidae)

 

Irma Northland-Leppe1, Drina Véjar1, Pedro Jara-Seguel2*, Nelson Fuentes1 & Cristian Núñez1

1 Departamento Biomédico, Facultad de Ciencias de la Salud, Universidad de Antofagasta, Antofagasta-Chile. *E-mail: pjara@uct.cl

2 Escuela de Ciencias Ambientales, Facultad de Recursos Naturales, Universidad Católica deTemuco, Temuco-Chile.


RESUMEN

El número cromosómico y la morfología del cariotipo de Girella laevifrons (Tschudi 1846) son descritos por primera vez. G. laevifrons presenta un número cromosómico 2n = 48 y su cariotipo está constituido por 24 pares de cromosomas acrocéntricos en ambos sexos, similar a lo documentado previamente para otras especies del género Girella Gray, 1835.


ABSTRACT

The chromosome number and karyotype morphology of Girella laevifrons (Tschudi 1846) are described for the first time. G. laevifrons presents a chromosome number of 2n = 48 and its karyotype is formed in both sexes by 24 acrocentric chromosome pairs, similar to what has been described for other species of Girella Gray, 1835.


Girella laevifrons (Tschudi 1846) is an abundant fish species distributed in the Pacific coast and islands from Guañape in Peru to El Tabo in Chile (8°S to 33°S; Pequeño & Sáez 2008). At present, genetic studies on G. laevifrons are not available and basic aspects, such as chromosome number and karyotype structure, remain unknown. The lack of genetic studies on G. laevifrons contrasts with the varied systematics research centered in other species of Girella, which include information on karyotypes, C and Ag-NOR banding, allozyme electrophoresis, PCR-RFLP markers, and gene sequences (Hinegardner & Rosen 1972, Ueno & Ojima 1991, Yagishita et al. 2002, Matsuoka 2002, Hardie & Hebert 2004, Itoi et al. 2007, Saito et al. 2008). The characterization of karyotype changes (e.g., numerical and/or structural) among related fish species is important to understand processes of genetic variation, genome evolution and speciation, as well as to delimit taxa (Winkler et al. 2004).

Here we describe for the first time the karyotype morphology of G. laevifrons and compare it with that already reported for other species of the genus.

Ten specimens including five males and five females of G. leavifrons were collected at the Pacific coast in a beach located in front of the Universidad de Antofagasta, San Jorge Bay, Chile (23° 42 'S; 70° 26 'W). The cytological protocol described by Northland-Leppe et al. (2009) was followed. Chromosomes were measured in photomicrographic enlargements of ten metaphases. The karyotype was made up with the chromosomes ordered on the basis of decreasing length.

Male and female individuals of G. laevifrons showed a diploid chromosome number 2n = 48 (NF = 48); the karyotype is composed only by acrocentric chromosomes (Fig. 1). Chromosomes are small (length < 4.0 \xva). Chromosomes lack secondary constriction and satellites. Sex chromosomes were not identified using conventional Giemsa staining.

Resemblance in chromosome number and karyotype morphology was observed among G. laevifrons and the Japanese species G. melanichthys Richardson, 1846 and G. punctata Gray, 1835 (Nishikawa & Karasawa 1972, Ueno & Ojima 1991). However, conspicuous secondary constrictions co-localized with Ag-NOR bands in one pair of large chromosomes described in kidney cells of G. melanichthys (Ueno & Ojima 1991) were not observed in chromosomes of G. laevifrons obtained from gill cells. The absence of secondary constrictions in G. laevifrons may be due to technical artefacts, or by the existence of functional differences of ribosomal genes among different tissues of different species (Sánchez et al. 1990). The use of Fluorescence in situ hybridization aimed to locate rDNA would help clarify this issue.

The karyotype resemblance among species of Girella is remarkable and can also be extended to species of Kyphosus Lacepede, 1801 (Table 1). Karyological resemblance between these two genera of the family Kyphosidae is also seen in DNA C-values. C-values of Girella fall within the range documented for Kyphosus and other genera of Kyphosidae (Table 1). These genome similarities (i.e., chromosome number and morphology, DNA C-values), although pardal, support the close relationship among Girella and Kyphosus previously proposed by Yagishita et al. (2002) based on molecular phylogenies. Interestingly, G. mezina Jordán & Starks, 1907 and G. punctata Gray, 1835 included in that same phylogeny appeared as very close species, which is consistent with the karyotype resemblances discussed in the present work.

Figure 1. Karyotype of Girella laevifrons, 2n = 48.

Figura 1. Cariotipo de Girella laevifrons, 2n = 48.


Table I. Cytogenetic characters of species of Kyphosidae from Chile and Japan. 2n, somatic chromosome number; FN, arms fundamental number; L, largest chromosome length; S, shortest chromosome length; CV(pg), haploid DNA content in picograms (C-value).

Tabla I. Caracteres citogenéticos de especies de Kyphosidae de Chile y Japón. 2n, Número cromosómico somático; FN, número fundamental de brazos; L, longitud del cromosoma más largo; S, longitud del cromosoma más corto; C V(pg), contenido de ADN haploide en picogramos (valor C).

Finally, despite recent advances ongenetic studies in Girella species, several issues remain unclear. Additional research using conventional and/or molecular cytogenetic techniques could be applied to study G. laevifrons and insular Chilean species of Girella (e. g., G. albostriata Steindachner, 1898; G. feliciana Clark, 1938; G. nigricans) (Pequeño & Sáez 2000). These studies would allow envisaging mechanisms of karyotype evolution within the genus. Advances in this field have been documented by Takai & Ueno (1997) for species of the genus Kyphosus in which some characters (e. g. chromosome number and morphology, Ag-NOR location, some C-bands) are conserved and perhaps have been retained from the common ancestor of the group, whereas karyotype modification would be mainly caused by amplification of constitutive heterochromatin.

ACKNOWLEDGEMENTS

Our thanks to two anonymous reviewers for their comments.

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Recibido: 12.05.10

Aceptado: 09.09.10