It seems appropriate to end this book with a brief discussion on what the future may hold for molecular ecology. Although it is still a young discipline, molecular ecology has nevertheless changed dramatically over the past 20 years. Molecular data from many different genomic regions are now being acquired almost routinely from a wide range of samples, including blood, tissue, pieces of insect wings, fish scales, seeds, leaves, hairs, toenails, bone, faeces and urine, some of which can be collected without ever seeing the organism that is being genetically profiled. Increasingly refined methods of extraction mean that DNA can be obtained from extremely small samples and, although caveats such as null alleles are more of a concern for particularly small or degraded samples, non-lethal sampling is becoming an increasingly favoured option.
Over the last 10 years or so, microsatellites have emerged as one of the most commonly used type of molecular marker, but their popularity may wane in the future if more precise markers such as SNPs become available for an increasing number of species. There is also a growing movement towards the characterization of individuals and populations based on genes that have a known function, as opposed to selectively neutral markers. Although genome approaches are currently out of reach of most molecular ecologists, they are nevertheless of great interest because of their potential to identify the functions of genes. Microarrays can be used to simultaneously assay hundreds or even thousands of genes, and the increase or decrease in expression of these genes can be monitored under different conditions such as altered light or CO2 availability. Although microarrays for some years were restricted mainly to model organisms such as Arabidopsis, humans and yeast, they are now being used to investigate an increasingly wide range of species. For example, DNA microarrays have been used to quantify gene expression in the digestive tracts of zebra fish (Danoi rerio) to see how gut microbiota affect a wide range of biological processes (Rawls, Samuel and Gordon, 2004), to study the expression of detoxifying genes in different strains of the malaria-transmitting mosquito Anopheles gambiae (David et al., 2005), and to monitor the up-regulation of genes by the tobacco plant Nicotiana attenuata in response to attacks by different types of predators (Heidel and Baldwin, 2004).
Although genomics can provide tremendous benefits to ecologists, it is also true that molecular biologists can benefit from an integrative approach that embraces ecology. The Multinational Coordinating Arabidopsis 2010 Project aims to identify the function of all ~25 000 Arabidopsis genes by the end of 2010, but the adaptive functions of an organism cannot be fully understood without exploring the interactions between its genotype, its phenotype, and the environment in which it lives (Jackson et al., 2002). This is just one reason why interdisciplinary approaches to research are likely to become increasingly commonplace.
It is also probable that in the future we will see more interplay between molecular ecology and a range of traditionally non-ecological applications such as those outlined earlier in this chapter. Applied ecology may also become more prominent because of the growing number of ecological problems that continue to arise around the world following climate change and introduced species. However, although the future should see the growth of molecular ecology continue unabated, we must not lose sight of the accomplishments that have already been made. Molecular genetic data allow us to quantify the genetic diversity and infer the demographic history of a population, identify the likely roles of genetic drift versus local adaptation in the differentiation of populations, pinpoint the origin and subsequent dispersal patterns of introduced species and pathogens, identify hybrids (which can be particularly important in both conservation and evolutionary biology), quantify inbreeding and outbreeding depression in the absence of pedigrees, and ascertain levels of relatedness within both wild and captively-bred populations. This is an incomplete but nevertheless impressive list for such a young discipline and, although we cannot know what the future will bring, few could doubt that the theory, methods and applications of molecular ecology will continue to grow.
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