Temporal change in inbreeding depression in life-history traits in captive populations of guppy (Poecilia reticulata): evidence for purging? L.-K. LARSEN *, C. PE ´ LABON*, G. H. BOLSTAD*, A ˚ . VIKEN  , I. A. FLEMING à & G. ROSENQVIST* *Department of Biology, Centre for Conservation Biology, Norwegian University of Science and Technology (NTNU), Trondheim, Norway  The Norwegian Biodiversity Information Centre, Trondheim, Norway àOcean Sciences Centre, Memorial University of Newfoundland, St. John’s, NL, Canada Introduction An increasing number of populations are presently turning into ‘‘island’’ populations as a consequence of habitat fragmentation. The reduction of population size generally provokes a loss of genetic variability as a result of genetic drift and inbreeding (i.e. mating among relatives). Small populations consequently face several challenges. Mildly deleterious alleles can be fixed by genetic drift and the reduced genetic variation hampers the population’s ability to respond to selective challenges induced by environmental changes (Allendorf & Luikart, 2007). Additionally, these populations are more vulner- able to stochastic and demographic factors. Finally, the increase in homozygosity resulting from inbreeding tends to reduce individual and population fitness, a phenom- enon known as inbreeding depression. Together, these consequences may substantially increase the risk of extinction in small populations (Mills & Smouse, 1994; Saccheri et al., 1998; Keller & Waller, 2002). The decline in fitness caused by inbreeding has focused the attention of geneticists and evolutionary biologists ever since Darwin’s early experiments on selfing in plants (Darwin, 1876). Since then, inbreeding depression has been documented for a wide range of organisms, including mammals (Lynch, 1977; Lacy & Ballou, 1998; Hedrick & Kalinowski, 2000; Meagher et al., 2000), birds Correspondence: Line Kristin Larsen, Department of Biology, Centre for Conservation Biology, Norwegian University of Science and Technology (NTNU), N – 7491, Trondheim, Norway. Tel.: +47 735 96090; fax: +47 735 96100; e-mail: linekris@bio.ntnu.no ª 2011 THE AUTHORS. J. EVOL. BIOL. 24 (2011) 823–834 JOURNAL OF EVOLUTIONARY BIOLOGY ª 2011 EUROPEAN SOCIETY FOR EVOLUTIONARY BIOLOGY 823 Keywords: captive breeding; deleterious alleles; fish; genetic load; inbreeding coefficient; life-history traits; purging; selection. Abstract Inbreeding depression, which generally affects the fitness of small populations, may be diminished by purging recessive deleterious alleles when inbreeding persists over several generations. Evidence of purging remains rare, especially because of the difficulties of separating the effects of various factors affecting fitness in small populations. We compared the expression of life-history traits in inbred populations of guppy (Poecilia reticulata) with contemporary control populations over 10 generations in captivity. We estimated inbreeding depression as the difference between the two types of populations at each generation. After 10 generations, the inbreeding coefficient reached a maximum value of 0.56 and 0.16 in the inbred and control populations, respectively. Analysing changes in the life-history traits across generations showed that inbreeding depression in clutch size and offspring survival increased during the first four to six generations in the populations from the inbred treatment and subsequently decreased as expected if purging occurred. Inbreeding depression in two other traits was weaker but showed similar changes across generations. The loss of six populations in the inbred treatment indicates that removal of deleterious alleles also occurred by extinction of populations that presumably harboured high genetic load. doi: 10.1111/j.1420-9101.2010.02224.x