ORIGINAL ARTICLE Spatial and temporal variation of genetic diversity and estimation of effective population sizes in Atlantic salmon (Salmo salar, L.) populations from Asturias (Northern Spain) using microsatellites Yaisel Juan Borrell Æ David Bernardo Æ Gloria Blanco Æ Emilia Va ´zquez Æ Jose ´ Antonio Sa ´nchez Received: 15 February 2007 / Accepted: 1 August 2007 / Published online: 17 August 2007 Ó Springer Science+Business Media B.V. 2007 Abstract Rivers in Asturias (northern Spain) constitute the southern limit of the distribution of Atlantic salmon (Salmo salar L.) in Europe, a biological resource facing one of the more serious challenges for conservation today. In this work, eight microsatellite loci have been used to analyse samples collected in 1993 and 1999 from four Asturian rivers (Esva, Narcea, Sella, and Cares), obtaining information about the temporal and the spatial genetic variation in these populations and, in addition, estimations of their effective population sizes. The temporal analysis revealed a general decrease in all the estimated genetic variability parameters when samples from 1993 (mean A (1993) = 6.47, mean H O(1993) = 0.472, mean H E(1993) = 0.530) were compared with those obtained in 1999 (mean A (1999) = 6.16, mean H O(1999) = 0.460, mean H E(1999) = 0.490). This reduction was particularly notable for the case of the Esva river. Our results pointed to a pattern of spatial genetic differentiation inside the Asturian region (F ST (1993) = 0.016 P \ 0.01; F ST (1999) = 0.023 P \ 0.01). Using the standard Temporal Method we found estimates of N e ^ (Esva) = 75.1 (33.2–267.2); N e ^ (Cares) = 96.6 (40.0–507.5), N e ^ (Sella) = 106.5 (39.1–9396.4) and N e ^ (Narcea) = 113.9 (42.0–3693.3). The use of likelihood-based methods for the N e ^ estimations improved the results (smaller CIs) for the Esva and Cares rivers (N e ^ (Esva) = 63.9 (32.3–165.3); N e ^ (Cares) = 76.4 (38.8–202.0) using a Maximum likelihood approach) and suggested the presence of larger populations for the Sella and Narcea rivers (N e ^ &200). These results showed that the Asturian Atlantic salmon populations (in particular Esva and Cares river populations) could be close to the conservation genetic borderline for avoiding inbreeding depression although we discuss some implications of the analysis of temporal genetic change in populations with overlapping generations. Keywords Salmo salar Á Effective population size Á Microsatellite DNA Á Temporal variation Á Loss of diversity Introduction A keystone of knowledge in any attempt of species con- servation and/or management is the effective size of a population (N e ) (Berthier et al. 2002; Kalinowski and Waples 2002; Shrimpton and Heath 2003). The N e can be defined as the size of an ideal population (Wright–Fisher model) in which genetic drift occurs at the same rate as in the studied population (Wright 1931). The standard Tem- poral Method (Krimbas and Tsakas 1971; Nei and Tajima 1981; Waples 1989) is by far the most widely used genetic approach for estimating contemporary N e ^ (Waples and Yokota 2007). This method is based on the relationship between N e ^ and the standardized variance of change in gene frequency (F ^ ) of samples taken at two or more points in time (Waples 1989). Other authors have proposed to use Maximum likelihood-based methods to obtain information about the full distribution of allele frequency and obtain smaller bias and less conservative confidence intervals (CIs) for the point estimates N e ^ (Wang 2001). Effective size is relevant in conservation biology since it influences the rate of loss of genetic diversity, the rate of fixation of deleterious alleles and the efficiency of natural selection at Y. J. Borrell Á D. Bernardo Á G. Blanco Á E. Va ´zquez Á J. A. Sa ´nchez (&) Departamento de Biologı ´a Funcional. Laboratorio de Gene ´tica Acuı ´cola. IUBA, Universidad de Oviedo, c/Julia ´n Claverı ´a s/n. 33071, Oviedo, Asturias, Spain e-mail: jafsp@uniovi.es 123 Conserv Genet (2008) 9:807–819 DOI 10.1007/s10592-007-9400-5