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Title of Dissertation: GENETIC MANAGEMENT, INBREEDING DEPRESSION AND OUTBREEDING DEPRESSION IN CAPTIVE POPULATIONS Jonathan D. Ballou, Doctor of Philosophy, 1995 Dissertation directed by: Dr. Gerald S. Wilkinson Associate Professor Department of Zoology The patterns and severity of inbreeding and outbreeding depression in organisms have been used to address fundamental questions relat­ ing to basic evolutionary issues of population genetic structure and dynamics. In addition, the genetic structure of populations, and the effect it has on the severity of inbreeding and outbreeding depres­ sion, play a critical role in the conservation of small populations. This dissertation examines three issues relating to populations ge­ netics of small populations. The first chapter presents a method, based on the concept of mean kinship, for managing pedigreed popula­ tions for maximum retention of genetic diversity. Using Monte Carlo simulations, the mean kinship strategy is compared to and found more effective at maintaining gene diversity than other strategies recom­ mended for this purpose. The second chapter investigates the poten­ tially confounding effects of inbreeding and outbreeding depression in captive populations. It has been hypothesized that outbreeding, not inbreeding, is responsible for the observed depression often Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. documented in captive populations. Several models for detecting joint effects of inbreeding and outbreeding depression are presented and applied to data from five populations. While the data structure of four of the populations complicate the analyses, inbreeding ef­ fects are present in all populations and there is no evidence of outbreeding depression. Recognizing that inbreeding depression is a common problem in small populations, the last chapter addresses the question: can inbreeding depression be eliminated through selection against deleterious and lethal alleles (i.e. purging)? Selection for healthy, inbred animals (who are less likely to carry deleterious alleles than non-inbred individuals) theoretically can purge a pop­ ulation of deleterious or lethal alleles. This chapter presents an analysis of 24 captive populations of mammals for evidence of pur­ ging by comparing inbreeding depression in descendants of inbred animals to that in descendants of non-inbred individuals. The re­ sults suggest that while the unintentional purging that has already taken place in populations may reduce inbreeding depression to some extent, it has not been sufficient to eliminate depression. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. GENETIC MANAGEMENT, INBREEDING DEPRESSION AND OUTBREEDING DEPRESSION IN CAPTIVE POPULATIONS by Jonathan Davis Ballou Dissertation submitted to the Faculty of the Graduate School of The University of Maryland in partial fulfillment of the requirements for the degree of Doctor of Philosophy 1995 Advisory Committee: Associate Professor Gerald S. Wilkinson, Chair/Advisor Associate Professor Lin Chao Assistant Professor Wolfgang Stephan Assistant Professor Michele Dudash Dr. Robert Lacy Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.