Local adaptation, coadaptation, and population boundaries

Coadaptation can occur either because of local adaptation in a geographically widespread population and/or because of intrinsic adaptation to the state of other genes or chomosomes. In either event, hybridization between animals with differently coadapted gene or chromosomal complexes can result in a decrease 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 populations 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 population boundaries can be detected through mating behavior, a pedigree analysis that can detect outbreeding depressions and distinguish them from inbreeding depressions, or genetic and karyotypic surveys. Once an outbreeding depression has been detected, it can be used to redefine the boundaries of the populations to be managed. Basically, the outbreeding depression is avoided by preventing hybridization between animals with the different coadapted complexes. In some cases, formal subspecific designations have been used to define the population boundaries. 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 systematics. 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.