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Researcher Rebecca Clark on the R/V Odyssey
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Photo: Chris Johnson |
VOYAGE OF THE ODYSSEY - GENETICS
Even though the backbone of the Voyage is the toxicology research, we will also be collecting data and doing work in several other areas whenever such work does not interfere with our primary focus. We feel that such additional research will add support to the on-going research and maximize the benefits that can accrue from this three year study. A prime example of this work is work on DNA fingerprinting that will be carried out in the laboratory of William Amos of Cambridge University. The place where animals are sampled may bear little relation to where they have fed or spent most of their lives. However, genetic analyses help in assigning individuals to populations which assists in defining migratory patterns, which in turn aids in interpreting other analyses.
Genetic studies
It is expected that approximately 10-15 samples will be collected from a maximum of six species at a maximum of fifty geographic locations. Given how little we know about the worldwide distribution and movements of most species of whale, such a sample resource will prove invaluable for a wide spectrum of current and future research. Broadly, the foreseeable benefits can be divided into those which accrue from the Voyage data set alone, and those which would accrue to related and collaborative studies.
Stand alone benefits
1)Type specimens and the regulation of whaling
Recent studies have highlighted the benefits of being able to take an unknown sample of whale meat and match it to a control sample, thereby establishing the species and oceanic region of origin. The Voyage of the Odyssey should result in a unique reference database of genetic type specimens. Such a resource would provide an invaluable tool for the regulation of possible future commercial whaling operations, as well as for the identification of samples from stranded whales.
2)A temporal transect and global change
Current genetic studies are hampered by a lack of information about historical status. Low genetic variability may be interpreted either as the natural characteristic of a species, or as the consequence of severe population depletion. Equally, genetic homogeneity may indicate extensive dispersal patterns or unnatural mixing caused by human disruption of the marine environment. The Voyage of the Odyssey will provide an opportunity to assemble an invaluable reference data set for future studies, describing both the distribution and levels of genetic variability among the target species.
3)Stock identity
Stock identity has been the subject of intense debate for many years: what is a stock and how should it be managed. Unfortunately, many species of whale are distributed globally and most individual whales are capable of swimming thousands of miles in their lifetime. Consequently, the relationship between different populations remains for the most part obscure. Photo-identification studies can help to reconstruct general patterns of movement, but they will never be able to elucidate functional relationships between populations: in other words, gene flow.
Most on-going population genetic studies focus on one or at best a few different populations within a species. The only significant exception is that of the humpback whale but, even here, some populations remain unsampled. To construct a realistic population model for any given species, data must be collected from as many sub-populations/geographic regions as possible. The voyage of the Odyssey provides a unique opportunity to do this.
In terms of methodology, all samples will be typed for two classes of genetic marker: nuclear and mitochondrial. Mitochondrial genes are inherited only from the mother, and hence tell us only about female lineage. By contrast, nuclear markers are inherited equally from both parents. Both approaches are informative, but one used without the other can be misleading. For example, a common pattern among mammals is for females to remain faithful to the region where they were born and for males to disperse, a system which minimizes inbreeding. In such species, a mitochondrial study would probably indicate a highly fragmented population structure, with each natal area appearing isolated from every other. By contrast, a nuclear genetic study of the same species could indicate a single homogeneous population.
Genetic variability and population size
It is common knowledge that bottlenecked populations, those that have been reduced to very small numbers, often show reduced genetic variability. Conversely, large populations tend to be highly polymorphic. In other words, levels of genetic variability tend to correlate with population size. The flip side of this relationship is that by measuring genetic diversity, an indirect relative assessment of population size can be obtained. The Voyage sample set should provide an ideal opportunity to calibrate genetic methods for population size estimation with sightings surveys and other methods such as the acoustic surveys that will be going on concurrently.
Collaborative benefits of genetic studies
1)A context for single population studies
Few populations can be considered 'closed', lacking both immigration and emigration, particularly in the marine environment. At the same time, most cetacean studies focus on a single study population. Clearly, many aspects of a single population study would be improved if rates of immigration and emigration could be determined. For example, immigrants might differ considerably in their pollutant loads, thereby artificially conflating inter-individual variability.
The Voyage sample set will provide a context for single population studies. Wherever populations are differentiated genetically, a worldwide reference set will facilitate the identification of immigrant individuals. Similarly, destination populations for emigrants may be identified by the fact that they appear genetically closer to the study population. Those wishing to construct population genetic models will benefit greatly from data concerning the genetic character of neighboring populations.
2)Assistance in Interpretating Toxicology Studies
In order to interpret observed levels of toxins in the body tissues of individual cetaceans it is vital to know as much as possible about past behavior of the cetaceans. Clearly, the current position of an animal may not necessarily represent the environment in which it has spent the majority of its life. Genetic analysis allows us to add an extra dimension to the reconstruction of global migration patterns, and hence will aid in the interpretation of other analyses.
3)Stimulation of Future Studies
It is a truism to state that one never knows what one will find until one looks. Again, with the possible exception of the humpback whale, no one has yet examined a cetacean species on such a global scale as we are proposing in the Voyage of the Odyssey. Whereas many of the results which the Voyage will yield may well be in line with expectations, there are equally likely to be some surprises. Such leads will form the basis of exciting new lines of research.
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