Fluorescence in situ hybridization of rDNA, telomeric (TTAGGG)n and (GATA)n repeats in the red abalone Haliotis rufescens (Archaeogastropoda: Haliotidae)

摘要

The red abalone Haliotis rufescens (Swainson, 1822) is the largest species of abalone in the world and the most desirable commercially for size and light meat color (Oakes and Ponte 1996). Red abalone supports an important fishery on the California coast, and it is well suited for farming, as both land based and ocean based operations. Natural populations have been reported from Sunset Bay, Oregon in United States to Turtle Bay, Baja California in Mexico (Cox 1962; Lindberg 1992).Because of its commercial importance, several intensive studies have been carried out in abalones, including population genetic analysis, seed production, and ecology (Lindberg 1992; González and Scoresby 1996; Hamm and Burton 2000; Zú?iga et al. 2000; Del Río-Portilla and González-Avilés 2001). However, the abalone fishery have has undergone a major decline since the 1960s (Tegner et al. 1989), and overexploitation, pollution, habitat degradation and epidemic disease have probably been the main factors to these declines (Burton and Tegner 2000).To date, few studies have been carried out in order to know genetic markers for population structure in the red abalone. Traditional allozyme studies have not detected any significant population differences, therefore molecular tools like microsatellites and mitochondrial markers have been used in order to detect such differences (Kirby et al. 1998). In addition, cytogenetic analyses are also useful tools in population genetic studies. In this context, Ag-NORs and rDNA-FISH technique have been applied in Crassostrea angulata chromosomes, revealed high Ag-NORs and rDNA-FISH polymorphisms between natural populations. Differences found in localization of chromosomal rDNA could be related to the plasticity in molluscs to survive under a wide range of environmental conditions (Cross et al. 2003). Moreover, these results are in agreement with the NOR-bearing chromosome variability found with other molluscs (Pascoe et al. 1996; Martínez-Expósito et al. 1997; Torreiro et al. 1999; Martínez et al. 2002). In reference to gastropod molluscs, few studies have been carried out, mainly because of the low number of species analyzed with cytogenetic molecular markers. In fact, available karyological data in gastropods indicate that less than 20 species have been analyzed cytogenetically using molecular techniques. However, to date, more than 300 species have been examined by conventional cytogenetics (Vitturi et al. 2002). In reference to abalones, nowadays there are not available karyological studies by FISH. In fact, 65 species have been reported for Haliotidae (Lindberg 1992), while only 15 species have been cytogenetically described (Gallardo-Escarate et al. 2004). Moreover, karyological studies belonging from California abalones have only been performed on the black abalone H. cracherodii (Minkler 1977) and recently on the red abalone H. rufescens (Gallardo-Escárate et al. 2004).In order to apply fluorescence in situ hybridization (FISH) in the red abalone, and thus contribute with new cytogenetic information, we organized the present paper with the followings aims: a) to examine the localization of 18S-5.8S-28S rDNA, b) to detect all rDNA-FISH clusters, c) to find telomeric sequences with (TTAGGG)n DNA probe and d) to ascertain the presence of (GATA)n microsatellites.