Does equalization of family sizes reduce genetic adaptation to captivity?

Abstract

Genetic adaptation to captive environments is likely to reduce the reproductive fitness of endangered species when they are reintroduced into natural environments. Equalization of family sizes is predicted to halve genetic adaptation to captivity as it removes selection among families and is recommended in captive management of threatened species. This prediction was evaluated by comparing the reproductive fitnesses of replicate populations of Drosophila maintained using either equal (EFS) or variable family sizes (VFS) for 25 generations in captivity under uncrowded conditions on a medium containing CuSO 4 . After 25 generations, EFS populations produced 8.8% more offspring per pair than their outbred base population on CuSO 4 medium, while VFS produced 17.5% more. Consequently, the rate of genetic adaptation to captivity in EFS was about half that in VFS, as predicted. In simulated 'wild' conditions (crowded, competitive conditions on medium lacking CuSO 4 ), both treatments showed much lower reproductive fitness than their outbred base population, the reductions being 38% in EFS populations and 43% in VFS populations. Surprisingly, reproductive fitness of the two treatments did not differ significantly under these conditions. These results raise doubts about the ability of equalization of family sizes to reduce genetic deterioration that adversely affects reintroduction success for captive populations of endangered species. †

Relaxation of Selection With Equalization of Parental Contributions in Conservation Programs: An Experimental Test With Drosophila melanogaster

“…If this is the case, two important aspects should be noted. First, because equalization of family sizes is supposed to minimize selection, a positive consequence is that adaptation to captivity is also reduced (Allendorf 1993;Frankham et al 2000). Second, the relaxation of selection that occurs under the benign conditions of captivity may have the consequence that the selection coefficients against deleterious mutations are overly reduced.…”

“…The final objective of a conservation program may be the reintroduction into the wild of the captive population (Frankham et al 2000). If this is the case, two important aspects should be noted.…”

“…This has both positive and negative a priori consequences. On the positive side, because selection is minimized, adaptation to captivity is also reduced (Allendorf 1993;Frankham et al 2000), and this is something desirable when the final objective of a conservation program is the reintroduction of the captive population into the wild (Loebel et al 1992;Borlase et al 1993;Couvet and Ronfort 1994;Frankham et al 2000). On the negative side, the reduced purifying selection implies that many deleterious genes segregating in the base population and new mutations appearing during the program will more likely be fixed, with the corresponding consequences on the reproductive capacity of the individuals (see Bryant and Reed 1999).…”

Stress and adaptation in conservation genetics

“…This has been observed in a wide array of experiments in fish, Drosophila, biocontrol insects and plants (see Frankham et al, 2000Frankham et al, , 2002.…”

The efficiency of close inbreeding to reduce genetic adaptation to captivity

“…These strategies are recommended to achieve the other goals of genetic managements, that is, to lower the loss of genetic diversity and the effects of inbreeding depression (Fernández and Caballero, 2001a, b;Theodorou and Couvet, 2003;Meffert et al, 2005). Although equalization of family sizes is expected to halve the rate of genetic adaptation (Allendorf, 1993), experimental results raise doubts about the ability of such breeding schemes to reduce genetic adaptation to captivity and, thus, increase fitness on reintroduction (Loebel et al, 1992;Montgomery et al, 1997;Frankham et al, 2000;Wisely et al, 2003).…”