Customer Reviews

Genetics and the Extinction of Species

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When this book was prepared at the dawn of the new millennium it was an attempt by leading experts in the field of conservation biology to review the role that genetics could play in conservation and management decisions given the recent developments in molecular techniques (PCR, automated sequencing) and population genetic theory (coalescence theory). However, since then there have been even more rapid advances due to automation and many of the molecular techniques have been sidelined by the rush to sequence DNA for a multitude of species currently on the threshold of extinction or requiring intensive conservation focus.
But what role does genetics play in the extinction process itself? Are populations really likely to die out simply as a result of dwindling genetic variability, through either a reduction in heterozygosity or a loss of rare alleles? A loss of genetic variability can be the result of demographic events, and in turn genetic uncertainty can alter the survival and reproductive probabilities of individuals, leading to a decrease in population size. Sometimes it can be difficult to unravel cause and effect. However, ultimately it is deterministic anthropogenic activities that impact most unfavourably on the health of species and their habitat through pollution, overexploitation, land development and the introduction of alien and pest species. Stochastic ecological and genetic factors that occur in nature are intensified by the activities of man and can then further threaten the persistence of populations and species. These extinction risks are clearly and concisely explained in the opening chapter by theoretician Russell Lande.
By definition, species that are endangered are rare and persist in small populations. It is these small, often highly fragmented and/or isolated populations that are of interest to conservation biologists. The problems inherent in small population size include: loss of genetic variation; inbreeding depression; random events in the survival and reproduction of individuals; and increased susceptibility to environmental factors (e.g. changes in climate, food supply and the nature and numbers of competitors, predators and parasites). These are all factors that conservation managers must take into account when managing endangered species or populations. Therefore, though genetic data must be considered in the decision-making process, there is a need to explain to non-geneticists what sort of information is required, how it can contribute to practical conservation and the means by which it can be applied in real situations. This is the aim of this anthology of papers from the leading experts in the field of conservation genetics.
The contents are wide-ranging if some chapters are a little esoteric. For example, the chapter by Paul Harvey and Helen Steers in which they describe the method for inferring population dynamic history directly from DNA sequence data acquired from individuals in the field is quite conceptually difficult, though the use of historical data and phylogenies has become increasingly important since then as more and more sequence data is forthcoming. As with the other authors (and all good scientists) they also deal with the current limitations of the technique, limitations and problems arising from unrealistic assumptions in the model and possible solutions.
Today, the practical application of phylogenetic information is clearer as stark choices have to be made by conservation mangers as to what to save, often at the expense of another species. How best to measure the allocation of genetic diversity among taxa? How best to conserve different amounts of biodiversity? Bill Amos tackles two problems associated with the measurement of genetic diversity and genetic distance, with the emphasis placed on microsatellite of short-tandem repeat data. There are two case studies concerned with the extinction, endangerment and conservation of Hawaiian birds and a fine chapter on the use of genetics in plant conservation. Kathryn Rodrìguez-Clark takes a critical look at some past assumptions and methods in captive breeding, notably the classical view that loss in population heterozygosity should be proportional to loss in adaptive variation. This has resulted in misplaced emphasis on slowing the loss of neutral variation and inbreeding depression without taking into account the ultimate goal of retention of adaptive potential.
This excellent series of papers places genetics at the forefront of biodiversity conservation while dealing with its current limitations. It is recommended for conservation managers with limited genetic knowledge who wish to better understand the role of genetics in the extinction process and how genetic information can be exploited for use in both ex-situ breeding programmes and situ conservation projects. However, it is a little out of date now.