Does equalization of family sizes reduce genetic adaptation to captivity?

Genetic adaptation to captive environments is likely to reduce the reproduc tive fitness of endangered species when they are reintroduced into natural environments. Equalization of family sizes is predicted to halve genetic ad aptation to captivity as it removes selection among families and is recomme nded in captive management of threatened species. This prediction was evalu ated by comparing the reproductive fitnesses of replicate populations of Dr osophila maintained using either equal (EFS) or variable family sizes (VFS) for 25 generations in captivity under uncrowded conditions on a medium con taining CuSO4. After 25 generations, EFS populations produced 8.8% more off spring per pair than their outbred base population on CuSO4 medium, while V FS produced 17.5% more. Consequently, the rate of genetic adaptation to cap tivity in EFS was about half that in VFS, as predicted. In simulated 'wild' conditions (crowded, competitive conditions on medium lacking CuSO4), both treatments showed much lower reproductive fitness than their outbred base population, the reductions being 38% in EFS populations and 43% in VFS popu lations. Surprisingly, reproductive fitness of the two treatments did not d iffer significantly under these conditions. These results raise doubts abou t the ability of equalization of family sizes to reduce genetic deteriorati on that adversely affects reintroduction success for captive populations of endangered species.