Experimental test of the effects of supportive breeding on wild populations
Supportive breeding is currently being used in the management of threatened populations, but the effects of this management strategy remain relatively untested. The common house fly, Musca domestica, was used as a model to assess the relative effectiveness of supportive breeding strategies for endangered species management. Captive populations were subjected to one of two captive breeding treatments, and served as the source of migrants for "wild" populations, which received either 5% or 50% of their total census size from captive migrants each generation. One "wild" population treatment served as a control and received no migrants. Measures of fitness were assessed from each population for nine generations. Within the captive populations, analyses found highly significant declines in fitness across generations, with much higher total fitness in the equalized breeding strategy as compared to the structured breeding scheme. Captive population fitness did not prove to be a good predictor of "wild" population fitness after reintroduction, but the inbreeding co-efficient of the captive populations were found to be correlated with recipient "wild" population fitness. This suggests that captive breeding programs with goals of future reintroduction to the wild should focus on overall kinship as opposed to fitness levels and make every attempt to minimize the co-efficient of inbreeding within the captive population. "Wild" populations that received low levels of ideally bred captive migrants performed significantly better than control populations, which received no outside migration. No other "wild" population treatments were found to differ significantly from the control populations, which may be due in part to the small population sizes that limited the effects of selection and migration and strengthened the influence of factors such as genetic drift and inbreeding. It is likely that the constraints of small population size led to the control populations having the lowest overall fitness. Based on this study, it does not appear that sweeping generalizations can be made about the effects of migrant breeding treatment and level of migration on wild populations. Further research is warranted before supportive breeding programs are implemented for a broader range of threatened and endangered species.
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