The geographical extent of mtDNA introgression was determined in the watershed where they were first discovered, as well as in neighboring drainages. To test the likelihood of the latter possibility we utilized an experimental approach that involved the assessment of physiological performance of introgressed char at different levels of biological organization, including the molecular, subcellular and whole animal levels. The results provide supporting evidence for a mitochondrial genome influence on enzyme structure and function, as well as an influence at the sub-cellular level of mitochondrial function. Taken together, the results demonstrate that mtDNA variation resulting from introgressive hybridization can be functionally important and may be selectively maintained in natural populations. These findings are of particular interest to population and conservation biologists, as mtDNA variation is traditionally believed to be of neutral consequence.
Hybrids are viable and, as male hybrids are normally fertile, backcrossing is possible.
Difficulties in the morphological identification of hybrids precluded studies of natural hybridization until the advent of protein electrophoresis. Evidence of second generation hybrids in the wild is equivocal but a circumstantial case exists for interspecific introgression defining the genetic character of some salmon populations. At the intraspecific level, a compelling case can be made for introgressive hybridization between distinct European and North American population groups, coming into secondary contact after differentiating in isolation during previous Pleistocene glacial period. Secondary contact during the current interglacial period appears to influence the genetic character of populations on both continents. Presently, both inter and intraspecific hybridization appear to be increasing due to anthropogenic factors, including transfers and introductions of non-native salmon and trout as part of stocking and aquaculture programmes.