Potential new research project
Although field work is continuing in MAR-ECO, researchers are actively involved in analysing the results thus far.
Post-doc David Rees has proposed a research project to put together an interesting new tool for use in fish taxonomy. The potential project will involve collaboration between a number of MAR-ECO researchers.
Renaissance biologist brings DNA toolbox to fish taxonomy
Correct identification of many deep-water fish species is hampered by numerous difficulties. These are largely the result of insufficient data, given the difficulties and costs of collecting deep-sea specimens. Adaptation to a largely uniform, but relatively hostile environment has, in some cases, resulted in ‘cryptic’ species that are morphologically very similar. In other cases, sexual dimorphism, differences between larval and adult forms and other morphological differences have resulted in the over-splitting of some species. The application of genetic techniques gives taxonomists new tools to help resolve some of these systematic questions.
David Rees began his research career at the University of Durham with an eye to a career in wildlife conservation. Work in ecology led to an interest in evolutionary biology and a PhD at the University of East Anglia, where he studied colonisation and speciation in beetles on the Canary Islands. Subsequent postdoctoral research positions in Bergen, Norway and Québec, Canada took him to Costa Rica and the Canadian and Norwegian Arctic. The arctic fieldwork gave him his first experiences with marine organisms where he studied genome size and polar gigantism in Arctic crustaceans.
The MAR-ECO project has collected a number of deep-water species that pose major taxonomic questions. Rees has worked together with MAR-ECO researchers Tracey Sutton, Ingvar Byrkjedal and Filipe Porteiro, among others, to put together a research proposal to address these problems in four important groups. Their approach will integrate the DNA methods Rees has learned with traditional taxonomic methods.
It is Rees’s first foray into vertebrate biology outside purely ecological studies. He is greatly looking forward to it; he feels that it is always nice to work with interesting groups of animals. Rees feels that having a renaissance approach has given him a solid biological overview of evolutionary questions that many specialists may not have. Although the drawback of working in different fields is that he has to learn so much new material each time he begins a new one.
Four species challenges
(1) Ridgeheads (genus Melanphaidae) are bathypelagic (deep, open water) fish. They have significant biomass in the deep open ocean waters and thus may be of significant potential economic importance in future fisheries. The different species within this group are difficult to differentiate based on morphological differences alone.
(2) The deep-sea hatchetfishes (family Sternoptychidae, genus Maurolicus) are even more difficult to differentiate. The genus, Maurolicus previously contained only one species; this has now been split into 15 different species. However, morphological differences can be extremely difficult to assess and species identification has been often based on the geographical location of capture.
(3) The deep-sea smelts (family Bathylagidae) are another group where it is difficult to identify species based on morphology alone. These fish live in the mid to deep open ocean waters and are also of significant biomass in these waters, and thus potentially economically interesting species. Interestingly, the larval forms of the deep-sea smelts are much more diverse morphologically than the adult forms.
(4) Very little is known about the black swallowers and deep-sea swallowers (family Chiasmodoutidae). Again, morphological similarities makes species differentiation difficult.
What about ‘barcoding’?
Distinguishing species on the basis of morphology alone was generating a ‘bottle-neck’ principally because there are simply not enough taxonomic specialists working in this area, or enough material to work with. The idea of "DNA-barcoding" was postulated as a way assist taxonomists with this bottleneck. "DNA-barcoding" uses species-specific segments of DNA as ‘name-tags’ or ‘barcodes’ for each species. For target organisms, a specific portion of a selected gene would be sequenced. For most species such sequences would have relatively low variation between species compared to between species.
These "DNA-barcodes" could then be used to help identify different life-history stages, to asses morphological and geographical differences and to identify ‘cryptic’ species, which might appear very similar morphologically.
The trick is to identify the best sequence to use for this purpose. Significant amounts of work in this area have been done in some animal groups, particularly mammals. Fish scientists will use this experience and build on it. The technique involves duplicating the sequence in question. This process is facilitated by the use of particular primers. Researchers will begin by testing the effectiveness of primers that have previously been developed and used in genetic work with mammals and other organisms.
Tests of the effectiveness of DNA-barcoding, for species identification and for highlighting taxonomic trouble-spots, will be conducted in parallel with other DNA studies. These will use both mitochondrial and nuclear DNA sequences. Rees explains that because mitochondrial DNA tends to evolve more quickly than nuclear DNA, the mitochondrial genes have higher variability and are better used for distinguishing among different populations than deeper evolutionary scales. It is important to consider sequences from several genes because different genes have different rates of mutation (change) and so may give different pictures of evolutionary history.
Working with MAR-ECO provides Rees with a couple of advantages for his work. First, he is part of a large international collaboration of research specialists, something that is a significant advantage in taxonomic work. Second, research collaboration means that the strengths and knowledge of each participant can be maximised. Third, he has access to the very large fish collection from the MAR-ECO, G.O.Sars expedition, summer 2004.
Results from this project will not only test a new, potentially very valuable tool (barcoding) for species identification, but will also provide important information about fish species that are being and will continue to be affected by new fisheries initiatives in the open and deep ocean.