Updating taxonomic biogeography in the light of new methods – examples from the Collembola

Abstract

The aim of this article is to review the consequences of advances in molecular genetics for researchers of Collembola biogeography. Gene sequence data have generally confirmed existing high-level taxonomy, but complicated species-level taxonomy by uncovering extensive cryptic diversity. Several commonly recorded European Collembola ‘species’ have proved to be complexes of closely related taxa, reducing the value of many older (pre-1990) records to near-zero. It seems likely that many more cryptic species of Collembola remain to be uncovered, even in well studied areas in Europe. The inevitable proliferation of genetically defined ‘species’ will be awkward to integrate into existing databases, which are based on morphospecies. Eventually the results will transform our understanding of Collembola biodiversity, since molecular data contain greatly more information, notably estimates of divergence times. In ancient and relatively pristine ecosystems (e.g. Antarctica, oceanic islands) genetic data can be used to show both extreme isolation of endemics (pre-dating ice ages) and the arrival of European/North American invasives. Collembola from the genus Lepidocyrtus in several very different areas show patterns of intra-specific divergence dated in the millions of years, a pattern likely to be repeated in other genera.
An exciting approach to speeding up these genetic studies comes from the advent of high throughput pyrosequencing technology, which already allows mass identification of mixed life forms from clustering then sequencing DNA amplicons (‘metabarcoding’), raising the possibility of automating the identification of bulked soil faunal extracts. A trial of this using soil extracts from Tenerife identified an apparent endemic Friesea species, along with mainland invasive species. These next generation techniques rely on Molecular Taxonomic units (MOTUs), identified purely by sequence analysis (usually of mtCOI), so vigilance will always be needed against the spurious identification of sequence artefacts such as nuclear copies of mitochondrial genes (NUMTS). A new risk of relying simply on high throughput sequence analysis is the possibility of inventing non-existent ‘species’ from irrelevant DNA.