Local adaptation, coadaptation, and population boundaries

Abstract

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 choniosomes. In either event, hybridization between animals with differently 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 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 bccn detected, it can be used to redefine the boundaries of the populations to be managed. Basically, the outbreeding depression is avoided by prevcnting 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 populationthinking 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. Key words: outbreeding depression, population boundariesReceived for publication September 17, 1985; accepted October 22, 1985. Address reprint requests to Alan R. Templeton, Department of Biology, Washington University, INTRODUCTION The Definition of CoadaptationThe word "coadaptation" was used first by Dobzhanslq [1948] to describe the phenomenon that sets of genes derived from different geographical populations of the fruit fly species Drosophilu pseudoobscuru resulted in reduced fitness when brought together by hybridization, particularly in the generations following the initial hybrids. Subsequent work [Brncic, 1954;Templeton et al, 1976; Wallace et al, 19531 revealed that coadapted gene complexes can be found within a large number of Drosophilu species, although some Drosophilu species show no evidence for coadaptation despite being widespread geographically [McFarquhar and Robertson, 1963 ; Richardson and Kojima, 1965, Singh, 19721.The Drosophilu studies indicate that coadapted ene complexes are a common but not universal phenomenon. This inference should be applicable to the vast majori...

Refugial Origins of Reindeer (Rangifer Tarandus L.) Inferred From Mitochondrial Dna Sequences

“…Prolonged isolation may also have led to adaptive differences between the two lineages (cf. Templeton et al 1986), as indicated from the conspicuous adaptations to forest habitat seen in the woodland caribou (Banfield 1961;Cumming 1992). Although the existence of haplotypes of northern origin in the more southerly distributed populations and vice versa indicates recent events of gene flow, the limited mixture of haplotypes may suggest some degree of reproductive isolation.…”

An investigation of inbreeding depression and purging in captive pedigreed populations

“…When this was tried in a zoo population of Speke's gazelle (Gazella spekei), the level of inbreeding depression was reported to be dramatically reduced after only two or three generations (Templeton and Read, 1984), leading to support for this approach (Ralls and Ballou, 1986;Templeton et al, 1986). However, reanalysis of the same data failed to find evidence of genetic improvement .…”

Mitochondrial DNA differentation in chamois (genus Rupicapra) : implications for taxonomy, conservation, and management

“…Apart from the maintenance of genetic variability within populations, the preservation of the integrity of locally well adapted gene pools is one of the major issues in conservation genetics (cf Templeton et al 1986). Sound knowledge of systematic relationships in a given taxon, especially within the problematic range from geographically separated populations to closely related species, is thus essential for restocking operations, for promoting gene flow by translocation of animals, and for assessing priorities in the preservation of particular populations.…”