Applications of mitochondrial DNA analysis in conservation: a critical review

Patterns of variation in mitochondrial DNA (mtDNA) increasingly are being investigated in threatened or managed species, but not always with clearly defined goals for conservation. In this review I identify uses of mtDNA analysis which fall into two different areas: (i) 'gene conservation' - the identification and management of genetic diversity, and (ii) 'molecular ecology' - the use of mtDNA variation to guide and assist demographic studies of populations. These two classes of application have different conceptual bases, conservation goals and time-frames. Gene conservation makes extensive use of phylogenetic information and is, in general, most relevant to long-term planning. Appropriate uses here include identification of Evolutionarily Significant Units and assessment of conservation priority of taxa or areas from an evolutionary perspective. Less appropriate are inferences about fitness from within-population diversity and about species boundaries. Molecular ecology makes more use of allele frequencies and provides information useful for short-term management of populations. Powerful applications are to identify Management Units and to define and use naturally occurring genetic tags. Estimating demographic parameters, e.g migration rate and population size, from patterns of mtDNA diversity is fraught with difficulty, particularly where populations are fluctuating, and is unlikely to produce quantitative estimates sufficiently accurate to be useful for practical management of contemporary populations. However, through comparative studies, mtDNA analysis can provide qualitative signals of population changes, allowing efficient targeting of resource-intensive ecological studies. Thus, there are some relatively straightforward uses of mtDNA, preferably in conjunction with assays of nuclear variation, that can make a significant contribution to the long-term planning and short-term execution of species recovery plans.