May 14, 2010
by Asta Audzijonyte, Monterey Bay Aquarium Research Institute, USA
The history of species and populations leaves traces in their genes. Analysis of genetic diversity therefore can provide information about the events that affected organisms tens, thousands or millions of years ago. Indeed, molecular analyses have revolutionised our view on the extent and age of Earth’s biodiversity (i.e. plants and animals are just a tiny fraction of the total biodiversity) and intra-specific dynamics.
For example, the main paradigm in marine ecology was that of open marine populations widely connected by dispersing larvae over thousands of kilometres. Yet, application of high resolution molecular markers and statistical approaches is now revealing a surprising amount of genetic structuring on geographical scales of tens or hundreds of kilometres, including in organisms thought to be highly dispersing. These findings have great implications in conservation attempts. If dispersal in marine populations is indeed limited, local population extinctions, perhaps commonly caused by human activities such as fishing, may not be easily balanced by new recruits.
There are at least two factors explaining the increasing role of genetics in marine ecology, systematics and conservation. First, and most importantly, genomic methodologies are for the first time providing access to a wide range of molecular markers in non-model organisms, and hence a broader and more realistic picture of how different forces of selection and neutral differentiation are acting on different parts of the genome. As genetics, based on one or two genes, is turning into genomics, i.e. analysis based on a large number of genes from across the entire genome, its power is increasing. Second, the flux of genomic data has been accompanied by new hypotheses and improved statistical approaches, incorporating computer simulations, and statistical predictions of dispersal and population structure. Finally, when it comes to marine populations, availability of extensive physical oceanographic data and advances in hydrodynamic ocean modelling is promoting development of tools for predicting dispersal and connectivity, which can now be used to generate hypotheses of genetic structuring. These, in turn, can be validated with actual data from the field.
Genetics can and does provide crucial information in marine biodiversity management. Models of marine reserves suggest that life history characteristics and dispersal potential are essential in predicting how a species will respond to protection. Yet, for most marine organisms dispersal distances are not known even to an order of magnitude. Given that observing dispersal of larvae directly is prohibitively difficult, use of population genomics is the most effective way to go. Recent technological and theoretical advances now makes population genomics well equipped to provide such answers. Genomic studies are now revealing several important features of wild populations, which must be taken into account when designing sustainable fisheries. First, not only many marine species are subdivided into subpopulations, but often these populations have local important genetic adaptations to specific conditions. Second, in a number of species only a very small proportion of adults contribute to each year’s reproductive output. This means that effective size population of reproducing population can be several orders of magnitude smaller than the actual population size, and that leads to faster then previously believed loss of genetic diversity in severely exploited species. Finally, recent research has demonstrated that strong selection imposed by exploitation (e.g. removing large individuals) eliminates their genes (e.g. responsible for fast growth) from populations and causes evolutionary changes. These changes may take thousands of generations to reverse. All these findings now start to shed light on the long-observed but poorly understood annual variability in reproductive success for marine populations.
Another powerful and growing application of genomic technologies is in the quick and accurate molecular identification of organisms and even their quantification. Genomic technologies can be more rapid than conventional morphological approaches, and are also suitable to identify eggs and planktonic larvae that cannot be distinguished through visual means. Application of genomic sensors is now in the early stages of allowing these identifications to be made in real time and in situ, without transporting samples to the laboratory. Possibly, such genomic sensors will be used routinely to study plankton samples or monitor invasive species in the not too distant future.
Genetics has already proven to be an irreplaceable tool in studies of natural systems, and recent technological and theoretical advances will improve the quality and extend its use. Surely, like every developing scientific field it does not and will not proceed without mistakes. Yet, the very fact that mistakes are being discovered and corrected indicates that our understanding of the processes governing nature’s genetic diversity is improving.
(*Asta Audzijonyte completed her PhD at the University of Helsinki, Finland in 2006. Her doctoral research was on molecular systematics, phylogeography and phylogenetics of aquatic organisms in boreal lakes, and Baltic and Caspian seas. In 2008, she started working at Monterey Bay Aquarium Research Institute (MBARI) studying population dynamics and connectivity of deep sea invertebrates. In November 2007, Asta visited Phillip England and Rasanthi Gunasekera at the CSIRO Marine Laboratories in Hobart en route to MBARI. She helped give a rapid start to the CERF Marine Biodiversity Hub project on connectivity of deep sea squat lobsters, and set the foundation for a productive relationship between MBARI and the CERF Hub in this research area. While in Hobart, she took part in a workshop describing genetic options and approaches to assist marine biodiversity management. The workshop was attended by researchers and managers from CSIRO, Department of the Environment, Water, Heritage and the Arts (DEWHA), Australian Antarctic Division, and the University of Montana.)