Experimental tests of captive breeding for endangered species

Several captive breeding regimes were compared for their ability to maintai n fitness (larval viability) and genetic variation in small populations of the housefly (Musca domestica L.). Populations were either maintained at co nstant sizes of 40, 200, or 2000 individuals or initiated with two pairs of flies and allowed to grow to 40 individuals (low-founder-number population s). Low-founder-number populations without migration exhibited low larval v iability (22%) after 24 generations, compared to larger populations maintai ned at either 200 (49%) or 2000 (69%) individuals, and suffered high extinc tion, with only 44% of the lines surviving 24 generations. Low-founder-numb er populations subjected to two additional founder (bottleneck) episodes, r educing them to two pairs of flies, suffered little additional loss in fitn ess or extinction compared to the single-founder treatments. Migration as l ow as one individual per generation (2.5% migration) significantly offset b oth reduced fitness and rate of extinction. Conversely, fitness was not sig nificantly increased for low-founder-number populations when founders were selected from the top performing 20% of pairs under full-sib mating. Popula tions maintained at 40 individuals were not sustainable, exhibiting low lar val viability (35%) and a high extinction rate (40%) over 24 generations, s imilar to the extinction rates for populations initiated with only four fou nders. Although none of the populations maintained at 200 individuals went extinct, their fitness was reduced by 20% compared to a large control popul ation maintained at 2000 individuals. Electrophoretic variation was signifi cantly correlated with fitness across treatments, but the correlation of fi tness to narrow-sense heritability of two morphometric trails was not signi ficant.