An improved method for estimating inbreeding depression in pedigrees

Fitness is expected to decrease with inbreeding in proportion to the amount of deleterious genetic variation present in a population. The effect of inbreeding on survivorship is usually modeled as a negative exponential relationship, and this model has been widely used to estimate the amount of deleterious genetic variation in populations. Linear regression has traditionally been used to estimate the parameters ol the model, including the number of lethal equivalents. This article describes an alternative method for estimating parameters and their confidence limits: the maximum likelihood approach. The accuracy of regression and maximum likelihood estimates of the number of lethal equivalents is compared through simulation. The maximum likelihood approach is found to be both median unbiased and capable of estimating confidence limits with nearly the stated degree of accuracy, while the linear regression approach is found to be median biased. The significance of this on previous estimates of inbreeding depression is discussed.