Use of Single Family Lines to Preserve Genetic Variation in Laboratory Colonies

Two genetic processes, drift and selection, can lead to losses of genetic traits in laboratory colonies and subsequent poor performance in the field. Genetic drift can be detected from changes in frequencies of selectively neutral alleles, especially allozymes, and can be avoided by maintenance of large population sizes. In contrast, selection may not be detected or avoided easily in large colonies, potentially resulting in the loss of traits essential for performance or adaptation to the field. This loss can be minimized if important alleles are made homozygous by mildly inbreeding independent family lines. The number of lines needed to prevent confidently the loss of alleles was calculated for a range of initial frequencies. For arrhenotokous or diploid species, only 25 or 50 single family lines, respectively, are needed to preserve common alleles, which are the alleles that seem most likely to be important to field performance. The relevance of these results to laboratory rearing, especially for classical biological control and conservation of endangered species, is discussed.