THE INFLUENCE OF MATING SYSTEM AND OVERLAPPING GENERATIONS ON EFFECTIVE POPULATION-SIZE

The effective population size (N-e) depends strongly on mating system and generation time. These two factors interact such that, under many circumstances, N-e is close to N/2, where N is the number of adults. T his is shown to be the case for both simple and highly polygynous mati ng systems. The random union of gametes (RUG) and monogamy are two sim ple systems previously used in estimating N-e, and here a third, lotte ry polygyny, is added. Lottery polygyny, in which all males compete eq ually for females, results in a lower N-e than either RUG or monogamy. Given nonoverlapping generations the reduction is 33% for autosomal l oci and 25% for sex-linked loci. The highly polygynous mating systems, harem polygyny and dominance polygyny, can give very low values of N- e/N when the generation time (T) is short. However, as T is lengthened , N-e approaches N/2. The influence of a biased sex ratio depends on t he mating system and, in general, is not symmetrical. Biases can occur because of sex differences in either survival or recruitment of adult s, and the potential for a sex-ratio bias to change N-e is much reduce d given a survival bias. The number of juveniles present also has some influence: as the maturation time is lengthened, N-e increases.