Monday, September 22, 2014

Living in the dark

Their world is always dark. They don't have eyes not even antennae. They live in soil, mosses, or in leaf litter. Minimalistic, small creatures called protura, sometimes nicknamed coneheads. These animals are tiny (0.5-2mm length) wingless insects that lack pigmentation which means they are usually white or pale brown. These little critters were overlooked for a long time and only discovered 1907 in a botanical garden at the University of Genoa.

Not much is known about this group and the natural history of its species. They seem to have a preference for forest soil with population densities of several 10 000 per square meter. Perhaps they feed on mycorrhizal fungi . Because the first leg pairs are held pointing forwards scientists use to believe that proturans were predators of small mites. Today it is thought that this most peculiar character is most likely a functional compensate of the lack of antenna and its sensory features. 

About 800 species of protura are known but identification is notoriously difficult. Diagnostic characters are very inconspicuous and difficult to recognize. Taxonomic work requires patience, special skills and a lot of experience. A pilot study just published in PLoSONE describes efforts to determine if DNA Barcoding might be a useful additional approach to delimiting and determining proturan species.

About 100 specimens were subjected to a non-destructive DNA extraction method. Due to the minuteness of proturans, species can only be determined unambiguously after a clearing treatment in which all tissues are removed and subsequent slide mounting of the specimen. The authors used two molecular markers, the standard DNA Barcoding for animals (COI) and a fragment of the nuclear 28S rDNA. 

Remarkably, morphological determination in all species exactly mirrors molecular clusters. The investigation revealed unusually huge genetic COI distances among the investigated proturans, both maximal intraspecific distances (0–21.3%), as well as maximal congeneric interspecifical distances (up to 44.7%).

This study is part of a larger research project which is dedicated to explore the role of the protura in the evolution of insects. Past findings indicated a relationship to the group of the diplura. The last common ancestor of both groups dates back more than 440 million years (Ordovician Period) which is around the time when land plants appeared.

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