Zoo zyxw Biology 5:115-125 (1986) Local Adaptation, Coadaptation, and Population Boundaries Allan R. Templeton, Helmut Hemmer, Georgina Mace, Ulysses S. Seal, William M. Shields, and David S. Woodruff zyxw Department of Biology, Washington University, St. Louis, Missouri (A. R. zyx I), institute of Zoology, Johannes Gutenberg University, Mainz, Federal Republic of Germany (ti. H.), Zoological Society of London, London, England (G.M.), Minnesota Zoological Gardens, Apple Valley (U.S.S.), Department of Environmental and Forest Biology, State University of New York, Syracuse (W M.S.), and Department of Biology, University of California, San Diego La Jolla (D.S. W.) zyxwvutsr Coadaptation can occur either because zyxwv of local adaptation in a geographically widespread population and/or because of intrinsic adaptation to the state of other genes or choniosomes. In either event, hybridization between animals with differ- ently coadapted gene or chromosomal complexes can result in a dccrease in fertility, viability, etc. in the initial hybrids and especially in later generations. This is known as an outbreeding depression. Moreover, releasing animals not adapted to the local environment can seriously hamper the effectiveness of a reintroduction program, and hybridization can also destroy the local adaptation. Coadapted gene complexes are best detected through studies on natural popula- tions because the adaptive nature of the complex is often only apparent in the natural environment. In the absence of information on natural populations (but ideally as a supplement), the presence of coadapted gene complexes and popula- tion boundaries can be. detected through mating behavior, a pedigree analysis that can detect outbreeding depressions and distinguish them from inbreeding depres- sions, or genetic and karyotypic surveys. Once an outbreeding depression has bccn detected, it can be used to redefine the boundaries of the populations to be managed. Basically, the outbreeding depression is avoided by prevcnting hybrid- ization between animals with the different coadapted complexes. In some cases, formal subspecific designations have been used to define the population bounda- ries. Unfortunately, many subspecific designations were made before population- thinking influenced taxonomy. It is important to emphasize the need to undertake modern biological studies and to collect additional information useful for system- atics. If modern biological studies indicate that the subspecies have little or no biological significance, it is best to treat the animals as a single population and disregard the subspecific designations. Key words: outbreeding depression, population boundaries Received for publication September 17, 1985; accepted October zyxwv 22, 1985. Address reprint requests to Alan R. Templeton, Department of Biology, Washington University, St. Louis, MO 63130. zyxwvut 0 1986 Alan zyxwvut R. Liss, Inc.