Molecular Organization and Evolution of 5S rDNA in the Genus Merluccius and Their Phylogenetic Implications
Daniel Campo ÆGonzalo Machado-SchiafﬁnoÆJose Luis Horreo ÆEva Garcia-Vazquez
Received:25November 2008/Accepted:29January 2009/Published online:27February 2009ÓSpringer Science+BusinessMedia, LLC 2009
Abstract The molecular organization of the 5S rRNA gene family has been studied in a wide variety of animal taxa, including many bony ﬁshspecies. It is arranged in tandemly repeated units consisting of a highly conserved 120base pair–longregion, which encodes for the 5S rRNA, and a nontranscribed spacer (NTS)of variable length, which contains regulatory elements for the transcription of the coding sequence. In this work, a comparative analysis of 5S ribosomal DNA (rDNA)organization and evolution in the 12species of the genus Merluccius , which are dis-tributed in the Atlantic and Paciﬁcoceans, was carried out. Two main types of 5S rDNA (typesA and M) were iden-tiﬁed,as differentiated by the absence or presence of a simple sequence repeat within the NTS. Four species exhibited the 2types of 5S rDNA, whereas the rest showed only 1type. In addition, the species M. albidus and M. bilinearis showed 2variants (Sand L) of type-M 5S rDNA, which differentiated by length. The results obtained here support the hypothesis of a 5S rRNA dual system as an ancient condition of the Piscine genome. In contrast, some inconsistencies were found between the phylogeny of the genus Merluccius based on mitochondrial genes and that obtained from nuclear markers (5SrDNA, microsatellite loci, and allozyme data). Hybrid origin of the American species M. australis is suggested based on these results.
Keywords Merluccius Á5S rDNA ÁCoding sequence ÁNTS A ÁNTS M ÁMolecular evolution ÁPhylogeny ÁIncongruence ÁSpeciation ÁHybridization
The minor class of ribosomal DNA (rDNA)comprises the 5S rRNA gene family, which is arranged in higher eukaryotes in several thousands of copies of tandemly repeated units. Each unit consists of a highly conserved coding sequence of 120base pairs (bp)encoding for the 5S rRNA, and a ﬂankingregion of variable length that is not transcribed (nontranscribedspacer [NTS])and contains some regulatory elements for the transcription of the cod-ing sequence (Sajdaket al. 1998; Wasko et al. 2001). Because it is nontranscribed, the NTS is neutral and it is expected to freely mutate. However, the 5S rDNA ﬁtsin a
concerted evolution model (Drouinand Moniz de Sa
`1995), which allows for the homogenization of the repeated sequences, thus decreasing intraindividual and intrapopu-lation heterogeneity (Dover1982). For this reason, the NTS has been widely employed as a molecular marker for species identiﬁcationand phylogenetic studies, although its application for this last purpose in closely related species is being currently discussed (Pasoliniet al. 2006).
Many studies have been published dealing with the structure, chromosomal location, and sequence variation of the 5S rRNA genes in fungi (Krameret al. 1978; Cihlar and Sypherd 1980; Tabata 1980; Cassidy and Pukkila 1987; Duchesne and Anderson 1990; Amici and Rollo 1991), plants (Ganalet al. 1988; Nedi et al. 2002), and animals (Brownet al. 1977; Bogenhagen et al. 1980; Bogenhagen and Brown 1981; Komiya et al. 1986), including freshwater
and marine ﬁshes(Penda
´s et al. 1994; Mora ´n et al. 1996; Electronic supplementary material The online version of this
article (doi:10.1007/s00239-009-9207-8) contains supplementary material, which is available to authorized users.
D. Campo (&) ÁG. Machado-SchiafﬁnoÁJ. L. Horreo ÁE. Garcia-Vazquez
Departamento de Biologia Funcional, Universidad de Oviedo, C. Julian Claveria s/n,33006Oviedo, Spain e-mail:firstname.lastname@example.org
J Mol Evol (2009)68:208–216DOI 10.1007/s00239-009-9207-8