Molecular genetics
Why do we need to use molecular genetics?
In conservation biology it is often necessary to understand the extent to which populations are genetically related to, or isolated from, each other. The loss of genetic variability is thought to be detrimental to a population because it may reduce the ability of that population to adapt or respond to environmental change. Such reduced ‘fitness’ of the population following a loss of genetic variability may occur as a result of a number of factors, such as inbreeding. Small populations are most vulnerable to such effects, as the rate at which genetic variability is lost depends upon the effective number of breeders in a population over time. As a consequence, small populations with low growth rates and/or low reproductive fitness are sometimes thought to have undergone an historic genetic ‘bottleneck’. However, immigration of individuals from other populations, may strongly counteract the negative effects of small population size. Therefore, understanding population structuring, and the forces controlling it, provides valuable information to guide conservation strategies and management.
In this project modern molecular genetic techniques (e.g. microsatellite markers and mtDNA sequences) will be used to investigate evidence for stock separation of basking sharks throughout the NE Atlantic and further afield. Obtaining a better understanding of basking shark population genetic structure using these approaches will indicate the relative importance of those population processes, past and present, which are likely to influence the genetic diversity and stability of populations in the future. Additionally, depending upon the level of population or stock differentiation, it may be possible to use some of the population genetic markers to assign body parts (such as fins), recovered from commercial products, to specific stocks/areas.
How do you carry out the genetic analysis?
The genetic analysis requires small tissue samples taken from basking sharks from as wide a geographical range as possible. These tissue samples will be taken by biopsy from free-ranging basking sharks using specially developed, benign techniques. Designated surveys will be undertaken off SW England to locate sharks for biopsy. Tissue samples from SW England and NW Scotland have already been collected as part of our previous tagging project, but additional samples will be obtained from strandings, incidental bycatch and commercial catches of known origin. These samples are then subsequently analysed in the laboratory.
We need your basking shark tissue samples!
The project team also has extensive links with international agencies and individuals worldwide and samples will be sought from colleagues within Europe, North America, the Caribbean, South Africa, Australia, New Zealand and Japan. Nonetheless, we would be very pleased to receive any basking shark tissue samples that you would be willing to donate. Your contribution will, of course be fully acknowledged. Please contact us before sending any samples – basking sharks are now listed on Appendix II of CITES and so require the necessary permits to be issued before they can be moved internationally.
So how will this new knowledge be used?
The demography of populations is defined by interactions between extrinsic ecological factors such as environmental stochasticity (or chance environmental events) and intrinsic ecological factors like social behaviour, reproductive strategies and migration patterns. For instance, t he impact of historical fishing is believed to have contributed to a loss of genetic diversity and inbreeding of the survivors. The current potential for inbreeding depression, an important measure of a population’s ‘genetic health’, will be derived for basking sharks from quantitative assessment of inbreeding measured using microsatellite data (Wright’s inbreeding coefficient Fis, 1951) .
The results from the genetic analyses of known individuals (males and females) will be interpreted in relation to satellite tagging data to examine sex- and age-related dispersal mechanisms (i.e. are females more site faithful than males?). Interpretation of the movements and distribution patterns revealed by tagging data (in terms of the probability of individual sharks belonging to spatially or temporally discrete local populations) will be evaluated against genetic evidence of population structure. If sufficient samples are available, the mixing dynamics by life stage and sex will be determined. This information provides the basis for an understanding of the impact of exploitation on basking shark populations, and will help to indicate the scale of management actions needed to ensure their sustainability.
