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 in breeding on survivorship is usually modeled as a negative exponential relat ionship, and this model has been widely used to estimate the amount of dele terious genetic variation in populations. Linear regression has traditional ly been used to estimate the parameters of the: model, including the number of lethal equivalents. This article describes an alternative method for es timating parameters and their confidence limits: the maximum likelihood app roach. The accuracy of regression and maximum likelihood estimates of the n umber of lethal equivalents is compared through simulation. The maximum lik elihood approach is found to be both median unbiased and capable of estimat ing confidence limits with nearly the stated degree of accuracy, while the linear regression approach is found to be median biased. The significance o f this on previous estimates of inbreeding depression is discussed. (C) 199 8 Wiley-Liss, Inc.