Factors eliminating inbreeding depression in a captive herd of speke's gazelle (Gazella spekei)

Abstract

Inbreeding is commonly associated with a lowering of viability and birth weights—a phenomenon known as inbreeding depression. A severe inbreeding depression was encountered in a captive breeding program for Speke's gazelle. Unfortunately, the solution of simply avoiding inbreeding could not be implemented because the entire herd was descended from one import male and three import females. Because of this founder effect, it was impossible to avoid inbreeding. However, laboratory experiments with fruit flies and basic evolutionary theory indicate that animals can rapidly adapt to inbreeding by the selective elimination of the genes responsible for inbreeding depression. These experimental and theoretical results were translated into a breeding program for the Speke's gazelle. The first goal of the breeding program is a demographic goal: increase the total population size as rapidly as possible to the carrying capacity. The other goals all deal with genetic attributes of either parents or offspring: Both parents and offspring should be inbred, and both parents and offspring should have genes from as many different founding ancestors as possible. In this paper, we document that this breeding program does eliminate the inbreeding depression very rapidly, and moreover that the genetic goals of the program aid this elimination exactly as theory predicts. Furthermore, our analysis clearly shows that the gazelles suffered from an inbreeding depression rather than an outcrossing depression. We conclude that inbreeding depressions can be rapidly and effectively reduced by an appropriate breeding program, and hence an inbreeding depression does not constitute an insurmountable barrier to the long‐term maintenance of a species in which inbreeding cannot be avoided.