Are marine nematodes hyperdiverse? A metagenomic solution.

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A fundamental question in science is how many species are there on earth. The number of taxa that have currently been assigned as species is approximately 1.5 million, although the total number has been estimated at between 10 and 100 million. Thus, a huge deficit exists in our general knowledge of species diversity, but also, there is an extreme negative correlation between taxon body size and the number of species described. Current taxonomical knowledge is heavily biased towards larger taxa and, although the majority of the larger and popular fauna and flora have been described, other important groups such as nematodes have been neglected. Nematodes are the most abundant multicellular organisms on earth and they are found in all habitats, but notably in marine sediments where they can make up between 50-90% of the multicellular fauna. Nematodes are ecologically important in marine sediment ecosystem processes and comprise the majority of the productive and saprophytic trophic base upon which macroorganisms rely. Despite their pivotal role in ecosystem functioning, a current estimate of global nematode diversity (c. 1 million species) remains a matter of conjecture. This massive knowledge gap is the result of the small size and the apparent morphological similarity of nematodes that cause problems in species identification. Also, the laborious procedure of nematode identification can take orders of magnitude more specialist's time to assign individuals to species compared to taxonomists working with larger taxa. Accordingly, in the past few years there has been a noticeable move towards the establishment of a system of species identification using molecular DNA 'barcodes'. The simple concept relies on amplifying and sequencing a standard short DNA sequence in the unknown specimen, and comparing this to a reference library of sequences from identified species. Recent research effort has highlighted the efficiency of adopting a molecular operational taxonomic unit (MOTU) scheme for soil organisms. The MOTUs do not have any formal correlation with published species descriptions, but correlations can be achieved with existing databases, or future classifications in an approach that has been termed 'reverse taxonomy. Molecular identification strategies have caused considerable debate between molecular ecologists and traditional taxonomists. However, with a potential deficit of 960,000 unnamed species, the sheer magnitude of the task means that it is highly unlikely that formal classification of all nematode species will be achieved using classical morphological-based taxonomy alone. MOTU studies to date have studied diversity via sequencing molecular barcodes from a limited number of organisms obtained from environmental samples. However, molecular diversity accumulation curves suggest that there are more undiscovered species present in the meiobenthos. A new technology has been developed very recently called Massively Parallel Sequencing (MPS). MPS is capable of generating 25 million bases of DNA data in a four hour period, which is approximately 100 times faster than current sequencing technology. This project aims to harness this novel analytical power to estimate the actual molecular (and subsequent species) diversity present at different spatial scales throughout littoral communities of UK nematodes and extrapolate this information to estimates of regional and global species richness. The utilization of MPS to quantify nematode molecular biodiversity would represent a major advance towards identifying a crucial biological component of the earth's ecosystems. Furthermore, the project will serve as a template for the use of MPS in assessing the extant biodiversity in any meoi- or microfaunal or floral sample / an application that will be universally applicable to any taxon or hypothesis pertaining to the role of biodiversity in ecosystem functioning.