The Guppy as a Conservation Model: Implications of Parasitism and Inbreeding for Reintroduction Success COCK VAN OOSTERHOUT, ∗ § ALAN M. SMITH, ∗ BERND H ¨ ANFLING, ∗ INDAR W. RAMNARINE,† RYAN S. MOHAMMED,† AND JOANNE CABLE‡ ∗ Molecular Ecology and Fisheries Genetics Laboratory, University of Hull, Hull, HU6 7RX, United Kingdom †Department of Life Sciences, University of the West Indies, St. Augustine, Trinidad, West Indies ‡School of Biosciences, Cardiff University, Cardiff CF10 3TL, United Kingdom Abstract: Ex situ conservation is of increasing importance to prevent the extinction of endangered animals in the wild. Despite low success rates of reintroduction programs few researchers have investigated empirically the efficacy of captive breeding regimes for the release of captive-bred vertebrates. We used guppies (Poecilia reticulata) from two populations in Trinidad to compare different conservation breeding regimes. The upper Aripo population was chosen for its small effective population size (N e ≈ 100) and genetic isolation, which makes it representative of many endangered natural populations. By contrast, the lower Aripo population is a genetically diverse, much larger population (N e ≈ 2400). We examined three captive-breeding regimes: (1) inbreeding fish crossed with their full siblings, (2) minimized inbreeding, no consanguineous matings, and (3) control fish crossed at random. We kept pedigree records for all regimes so that we could calculate inbreeding coefficients over four generations. The body size and fertility of guppies was significantly reduced due to inbreeding depression. The genetic load of sterile equivalents was particularly high for the lower Aripo population. Body size also declined due to breeding conditions in the captive environment. After four gener- ations in captivity, the fish were released into a mesocosm in Trinidad. Captive-bred guppies were extremely susceptible to gyrodactylid parasites (58% survival rate) compared with their wild counterparts (96% survival). A reduced level of immunogenetic variation due to inbreeding and lack of exposure to natural parasites may have rendered captive-bred individuals more prone to infectious disease. The threat of disease outbreak is particularly high when naive captive-bred hosts are released in wild populations. Susceptible, captive-bred hosts could facilitate the transmission of parasites throughout the wild population, thus initiating an epi- demic. This risk could potentially be reduced by prior exposure to parasites before release and gradual release of captive-bred individuals. Keywords: captive breeding, ex situ conservation, genetic variation, Gyrodactylus, immunocompetence, in- breeding depression, MHC, parasites, Poecilia reticulata, resistance to gyrodactylids, sterile equivalents El Guppy como Modelo de Conservaci´ on: Implicaciones del Parasitismo y la Endogamia para el ´ Exito de Reintro- ducci´ on Resumen: La conservaci´ on ex situ cada vez es m´ as importante para la prevenci´ on de la extinci´ on de an- imales silvestres en peligro. No obstante las bajas tasas de ´ exito de los programas de reintroducci´ on, pocos investigadores han estudiado emp´ ıricamente la eficacia de los m´ etodos para la liberaci´ on de vertebrados criados en cautiverio. Utilizamos guppies (Poecilia reticulata) de dos poblaciones en Trinidad para comparar diferentes m´ etodos de reproducci´ on para la conservaci´ on. La poblaci´ on de la cuenca alta del r´ ıo Aripo fue seleccionada por su aislamiento y tama˜ no poblacional efectivo peque˜ no (N e ≈ 100), lo que la hace represen- tativa de muchas poblaciones naturales en peligro. En contraste, la poblaci´ on de la cuenca baja del Aripo es una poblaci´ on mucho m´ as grande (N e ≈ 2400) y diversa gen´ eticamente. Examinamos tres m´ etodos de §email c.van-oosterhout@hull.ac.uk Paper submitted November 13, 2006; revised manuscript accepted July 2, 2007. 1573 Conservation Biology Volume 21, No. 6, 1573–1583 C 2007 Society for Conservation Biology DOI: 10.1111/j.1523-1739.2007.00809.x