Molecular Tools in a Marine Restocking Program for the Endangered Dusky Grouper, Epinephelus marginatus
SABINA DE INNOCENTIIS, ALESSANDRO LONGOBARDI, and GIOVANNA MARINO
ICRAM, Central Institute for Marine Research, Rome, Italy
The duskygrouper (Epinephelus marginatus) is an endangered marine ﬁsh for which a restocking program has been undertaken in the Mediterranean Sea. Genetic variation at six microsatellite loci was assayed to help plan preservation of genetic diversity after release of hatchery-reared juveniles. We estimated relatedness and effective population size within two groups of captive broodstock, assessed geneticvariability of these broodstock and F1 juveniles compared to natural populations, and investigated genetic relationships between hatchery-reared and wild specimens inhabiting the release site. On average, no relatedness was found within captive broodstock and a potentially high number of effective breeders was assessed (Nb D 86.9; CI 95% D 46.0–451.2). However, very few breeders (N D 7) spawnedsuccessfully, and a positive degree of relatedness (rW D 0.0297) was found among this particular subset of individuals. Genetic variability parameters were reduced for the broodstock and F1 juveniles, although not signiﬁcantly. Genetic differentiation was detected among released juveniles and wild conspeciﬁcs collected 75 km away from the target area. However, the pattern of genetic distances from otherwild populations justiﬁes the choice of the broodstock as the best alternative donor stock. Keywords restocking, microsatellite DNA, relatedness, genetic variability, Epinephelus marginatus, conservation
INTRODUCTION Genetic monitoring of restocking programs is highly recommended (Hansen et al., 2000), especially when the aim is restoration of an endangered species. A number of theoreticalspeculations (Ryman, 1991), simulation-based data (Jager, 2005), and case studies (Madeira et al., 2005) show that alarming losses of genetic variability and introgression of new genes into wild populations can result from restocking programs based on hatcheryreared juveniles designed without explicit conservation genetics objectives. Similar problems can also occur, even when the need to use locallyderived broodstock and supportive breeding protocols are respected, if too few breeders are used, or if they are too closely related (Hansen and Jensen, 2005; MachadoSchiafﬁno et al., 2007). The genetic objective in hatchery-based
Address correspondence to Sabina De Innocentiis, ICRAM, Central Institute for Marine Research, Via di Casalotti, 300, 00166 Rome, Italy. E-mail: email@example.com projects is to minimize the random loss of genetic diversity, and to avoid the possible loss of ﬁtness due to either mating among related individuals (inbreeding depression) or mating among individuals adapted to very different habitats (outbreeding depression) (Tallmon et al., 2004). Homogenization or replacement of locally adapted genotypes, resulting from a numerical and/orﬁtness advantage of the released individuals, i.e., “genetic swamping,” should be kept to a minimum. To achieve these goals, two kinds of breeding approaches are currently recommended: (1) minimizing kinship among breeders (Ballou and Lacy, 1995) and controlling the effective number of breeders (Saillant et al., 2005) to prevent inbreeding and/or drift acceleration; and (2) taking into account thestock structure of the species, i.e., evaluating the genetic differentiation among donor and recipient populations (Brown et al., 2000) to provide protection from introgression and outbreeding depression for the future generations. Although the International Union for the Conservation of Nature and Natural Resources (IUCN) has called for recovery
S. DE INNOCENTIIS ET AL.