Population size, selection, and mutation-accumulation

One of the primary goals in the management of endangered species is the determination of a minimum viable population size. Population size is a major determinant of genetic variability and is theorized to correlate with long term evolutionary potential and the ability to cope with environmental change. However, there is little empirical evidence to support this theory and no empirical tests of the minimum viable population size required to avoid the effects of genetic stochasticity (random genetic drift and inbreeding).; Using housefly populations recently established from the wild, fitness, the ability to survive variable or stressful environmental conditions, genetic variability, and changes in life history traits due to adaptation to the captive environment were assayed. Two treatments were maintained at the effective population sizes suggested for long-term evolutionary potential (N{dollar}rmsb{lcub}e{rcub}{dollar} = 500) and short-term sustainability (N{dollar}rmsb{lcub}e{rcub}{dollar} = 50). A third treatment, founder-flush, assessed the relative importance of founding numbers and rate of inbreeding on genetic variation, fitness, and evolutionary potential.; Conservation programs are being established without clear expectations as to the long term effects of captive breeding. The research presented here provides empirical evidence on the effects of (1) different effective populations sizes, (2) different founding numbers, (3) the number of generations spent in captivity, (4) and the effects of relaxed selection on compromising future adaptability, fitness, and genetic variation.; Populations with effective population sizes close to 500 were immune to the effects of genetic stochasticity over the course of 24 generations. An effective population size of 50 was not sufficient to protect populations from genetic deterioration for even the short-term, and extinction occurred as rapidly as 37 generations. Founder-flush populations were found to maintain normal levels of additive genetic variance, and their fitness was greater than that of lines inbred slowly to a similar level. However, this fitness was very environment dependent and their viability dropped to that of similarly inbred lines under variable or stressful conditions.; Adaptation to the captive environment and mutation-accumulation due to relaxed or altered selection were found to have rapid effects that may thwart reintroduction attempts. These effects, particularly mutation-accumulation, are often overlooked in captive breeding programs.