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Minimizing selection Selection can be minimized by making the captive environ- ment similar to the wild environment. However, this is largely impractical as the success of captive breeding is predicated upon removing predators and minimizing parasites and disease and generally providing a benign environment. Further, space is severely constrained in most zoos; therefore, natural ranges cannot be provided for large species to assist in encouraging normal behaviour. Equalizing family sizes removes selection between families and restricts it to selection among siblings within families and is expected to halve the rate of genetic adaptation to captivity (Haldane 1924; King 1965; Frankham & Loebel 1992; Allendorf 1993; Lande 1995). Equalization of family sizes is recommended in the genetic management of cap- tive populations (see Borlase et al. 1993; Frankham et al. 2002). The current recommendation to minimize kinship (Ballou & Lacy 1995; Fernandez et al. 2004) is equivalent to equalization of family sizes when there are equal founder contributions, or becomes so within a few generations when founder contributions are unequal (Montgomery et al. 1997). An empirical test has shown that equalization of family sizes does halve genetic adaptation to captivity (Table 1; Frankham et al. 2000). However, when the popu- lations were tested in a simulated wild environment, there was no significant improvement in reproductive fitness of the equalization of family sizes treatment, compared to the variable family size treatment. Further, neither minimizing kinship nor equalizing founder representation resulted in improved wild fitness in comparison to random breeding controls, in spite of having lower inbreeding levels than the controls (Loebel et al. 1992; Montgomery et al. 1997). Reducing genetic diversity by fragmentation Genetic adaptation to captivity can be reduced by frag- menting populations of threatened species across institutions and relying upon small Ne and genetic drift to reduce genetic diversity in individual populations, while retain- ing it at the species level (Margan et al. 1998). Captive populations of endangered species are typically dispersed among many institutions because the breeding capacities of individual zoos are limited, and there is a need to minimize the impact of catastrophes (e.g. fires, extreme weather and diseases). As inbreeding depression and loss of genetic diversity are inevitable in small isolated populations, management of endangered species in captivity has changed from isolated populations at individual institutions towards maintaining the total population as effectively a single random mating population by regular translocation of animals among institutions. However, the effectively single population strategy is costly, increases the risk of spreading disease (Anderson 1991; Woodford & Rossiter 1994), and is @ 2007 The Author Journal compilation @ 2007 Blackwell Publishing Ltd GENETIC ADAPT A TION TO CAPTIVITY 5 1.5 1.0 Ul Ul (I) .5 u: 0.5 . Single large I1'Il Several small (pooled) I1'Il Control 0.0 0 L{) 0 0 L{) 0 0 0 0 (I) :!2 L{) C\I 0 L{) C\I 0 L{) L{) L{) Ul ~ X .,... X X L{) C\I X X co [ll C\I C\I '<t X C\I co C\I + + 0 L{) 0 C\I X X co '<t Fig. 1 Effect of fragmentation of captive populations upon fitness when populations are reintroduced into the wild (from Margan et al. 1998). Reproductive fitness of the single large (solid black), several small (pooled) (hatched), base population (T92) and new wild population (T9S) tested under crowded, competitive simulated wild conditions (all competitive indices are relative to T9S, mean 64.8). not the optimum strategy for minimizing genetic adaptation or retaining genetic diversity. We evaluated the frag- mentation strategy using populations maintained for 50 generations in captivity by comparing wild fitness in single large populations vs. that in several populations of the same total size (Margan et al. 1998). For example, we compared populations withNe of 100, with 2 of Ne = 50 and 4 of Ne = 25. The combining of the several smaller populations was done after 50 generations, with 8-10 generations of random mating being allowed prior to fitness measurements. In all com- parisons, the combined several small treahnents gave superior fitness to the single large population in the wild environment, and the superiority usually increased with degree of fragmentation (Fig. 1). Further, genetic diversity was higher in the several small population combinations than in the single large ones, as predicted by theory (with no extinctions) (Kimura & Crow 1963; Robertson 1964; Lande 1995). If a strategy involving several small populations, main- tained separately and then pooled, is as good genetically, or better than populations maintained as a single large unit, then it should be favoured as it also reduces the risks and costs associated with regular translocations. Technology- assisted reproductive techniques such as artificial in- semination, in-vitro fertilization, gamete and embryo freezing, are not yet available for most endangered species, and are expensive to develop. Consequently, most mixing among captive populations involves costly translocation of live individuals. Accidents and stress can cause serious injury to translocated animals, as well as animals at the release site. Translocations may also introduce infectious disease, and could cause the extinction of a captive population (Cooper 1993; Griffith et al. 1993; Jacobson 1993;