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Determining the genetic makeup of Dolomedes plantarius
It is widely recognized in conservation biology that, once a species reaches very low population levels, demographic and stochastic events can rapidly induce changes in its genetic makeup. These are usually manifested as a loss of genetic variability. Reduced genetic variability can have a negative impact on individual fitness (by reducing survival and/or fecundity) and thus on population viability, increasingly the likelihood of extinction. Since genetic variability provides the basis of a species' potential to evolve in the face of changing environmental conditions, genetic issues are increasingly emphasized in conservation programs. The conservation of genetic diversity is now one of the three major conservation priorities of the IUCN.
Despite an active conservation programme, the D. plantarius population at Redgrave and Lopham Fen NNR, UK, has remained very small for at least nineteen years and experienced breeding failure in some years. Even after restoration of the fen's hydrology in 1999, the population failed to show any significant or sustained recovery. This suggested that this population may have suffered a reduction in fitness as a consequence of the loss of genetic variability following bottlenecks in population size. This prompted English Nature (now Natural England) to include genetic research in its programme of measures to ensure population recovery.
Genetic study of D. plantarius at the University of East Anglia
English Nature contributed funding towards a PhD place, within Professor Godfrey Hewitt's research group at the University of East Anglia, to start to investigate the conservation genetics of D. plantarius.
Marija Vugdelic's Research at UEA
Marija began a PhD studentship studying the conservation genetics of D.plantarius in autumn 2002 and completed her thesis in 2006. Her main aim was to determine the genetic makeup of D. plantarius, with her primary focus on the endangered UK population at Redgrave and Lopham Fen. She also analysed populations from the entire distribution range and reconstructed the species phylogeny to give insight into genetic partitioning within the species as whole, and to place UK populations within this context. In her thesis she examined the implications of our new understanding of the genetic makeup of this species for future conservation management decisions. Click here to download an abstract of her thesis.
Genetic study of D. plantarius at the University of Nottingham
Since 2007 work on the conservation genetics of Dolomedes has been continued by Dr Sara Goodacre's group at the University of Nottingham.
Andrew Holmes' Research
Andrew undertook a year's research for a Masters degree (MRes) on the conservation genetics of D. plantarius in 2007/08. He developed a reliable methodology for extracting DNA from shed skins which represents an important advance in our ability to sample from small and endangered populations. This enabled him to examine loss in nucleotide diversity in a sequence of skins collected from the endangered population at Redgrave and Lopham Fen, UK, over the last 17 years. He found there had been significant reduction over this period. Andrew also developed work begun by Marija on bacterial endosymbiontic infections in the English D. plantarius populations. He found that the spiders were infected by at least four different endosymbiont species. Levels of infection were generally higher in the Pevensey Levels than in the Redgrave and Lopham Fen population and this difference was significant for one of the species. Click here to download an abstract of his thesis.
Future research on the genetics of Dolomedes
Sara Goodacre's group continues its close links with the D. plantarius Recovery Programme and particularly with the proposed translocation programme They are involved both in decision-making about appropriate provenance of spiders for release and in genetic monitoring of changes in the genetic make-up and diversity of the new populations. They will also continue to build on other two aspects Marija Vugdelic's work: understanding the relationships between D. plantarius populations across Europe and continuing to build the phylogenetic tree for the entire genus. Because of this, we still welcome Dolomedes samples from all over the world.
Call for samples
DNA for analysis can be extracted even from small and degraded tissue samples, by applying appropriate laboratory protocols. With rare species such as D. plantarius is essential that (i) the tissue collection should use non-destructive means wherever possible and (ii) where required, appropriate licencing should be obtained in the country of origin. The sources of DNA for genetic analysis include:
- fresh tissue (ideally individual legs, which excise easily and re-grow as juvenile spiders change their skin) preserved in 100% ethanol,
- dry museum specimens;
- ethanol-preserved specimens;
- shed skins.
Fresh tissue samples are the most reliable source of high quality DNA samples but, although the latter three sources are usually degraded tissue samples, they can often yeild very useful fragments of DNA. Andrew Holmes' (above) success in developing a technique for obtaining DNA from shed skins now means that these benign samples can make a very valuable contribution to genetic studies.
If you have access to shed skins or other tissue samples, and would like to contribute to this study, please click here for more information.