PURGING INBREEDING DEPRESSION AND THE PROBABILITY OF EXTINCTION - FULL-SIB MATING

Inbreeding depression has been a topic of interest in recent years fro m a number of perspectives, particularly in the captive breeding of en dangered species. Generally, the goal of captive breeding is to avoid the detrimental effects of inbreeding depression and to retain genetic variation for future adaptation. However, an important component of a nother suggested approach to captive breeding is to purge rapidly the population of its genetic load so that its long-term fitness is not co mpromised. I have examined the effectiveness of purging the genetic lo ad by documenting both the reduction in inbreeding depression and the increase of the probability of extinction when there is continous full -sib mating. When the genetic load is the result of lethals, the inbre eding depression is quickly purged without a high probability of extin ction, except when the total genetic load is high. On the other hand, if the load is due to detrimentals of relatively small effect, the gen etic load becomes fixed, the mean fitness is reduced, and the probabil ity of extinction may be greatly increased. In other words, the succes s of such a programme to purge genetic load without an increase in the probability of extinction is highly dependent upon the genetic basis of inbreeding depression, information that is not readily available fo r most species.