Absence of a genetic bottleneck in a wild rabbit (Oryctolagus cuniculus) population exposed to a severe viral epizootic

Infectious diseases and their demographic consequences are thought to influ ence the genetic diversity of populations. In Europe, during the last 50 ye ars, the European rabbit (Oryctolagus cuniculus) has suffered two important viral epizootics: myxomatosis and rabbit viral haemorraghic disease (RVHD) . Although mortality rates were very high, the impact of these diseases on genetic diversity has never been assessed directly. The subject of this pap er is a wild rabbit population in France, which has been studied since the beginning of the 1980s. The first outbreak of RVHD occurred in 1995 and pro voked a demographic crash. The population, sampled for the first time in 19 82 and 1994, was sampled again at the end of 1996 to examine the impact of the epizootic on genetic diversity. In spite of the observed high mortality rate (approximate to 90%), analysis of 14 polymorphic loci (allozymes and microsatellites) showed no loss in genetic diversity after the epizootic. D etermination of temporal changes in allele frequencies indicated that the p opulation evolved under genetic drift. The temporal method of Waples demons trated a significant decrease in the effective population size (N-e) correl ated with the demographic crash due to the epizootic. However, the populati on had only been studied for two generations after the epizootic and the re mnant population size probably stayed high enough (approximate to 50 indivi duals) to keep its genetic diversity at the precrash level. These results s uggest that, contrary to what is usually thought and in spite of the subseq uent high mortality rates, past epizootics (especially myxomatosis) may hav e had little effect on the genetic diversity of wild rabbit populations in Europe.