Spider diversity

Female Aganippe sp. Image: WA Museum

Mygalomorphae is an infraorder of spiders including several families comprising e.g. tarantulas as well as the famous Australian funnel-web spiders. Quite a few species of this group are short-range endemics which makes them exceptionally well-suited for monitoring conservation status of terrestrial ecosystems. Mygalomorph spiders have been proposed as bioindicators for monitoring ecological changes despite secretive habits and a challenging taxonomy as only males can be reliably identified to species. 

A sexually-mature male mygalomorph will typically spend several weeks travelling above ground, looking for females. Not only does this make him vulnerable to predators such as birds or ghost bats, he also has a problem in case he is lucky enough to find a female as in some cases she will simply kill and eat him if he is unable to escape after mating.

A large portion of all specimens collected and stored in museums are juveniles or females, which have very limited morphological features that can be used for species-specific classification. The life of an adult mygalomorph spider male is usually short and they only mature into a male at certain times of year. That makes taxonomy within this group rather difficult as species have typically been classified by the adult male's unique sex organ. 

Sure enough, DNA Barcoding of spiders becomes increasingly popular and a new publication from Australia shows once more how little we really know in terms of biodiversity.

To assess mygalomorph diversity and the distribution of species in the Pilbara, we employed a molecular barcoding approach. Sequence data from the mitochondrial DNA cytochrome c oxidase subunit I (COI) gene were obtained from 1134 specimens, and analysed using Bayesian methods. Only a fraction of the total mygalomorph fauna of the Pilbara has been documented, and using a species boundary cut-off of 9.5% sequence divergence, we report an increase in species richness of 191%.

191% increase with a very conservative cut-off value (9.5%) in a limited bioregion. This is a remarkable number largely owing to the fact that male spiders needed for morphological determination are so rarely available. A big step forward and the authors seem quite excited about the possibilities:

Barcoding provides a rapid, objective method to help quantify mygalomorph species identifications and their distributions, and these data, in turn, provide crucial information that regulatory authorities can use to assess the environmental impacts of large-scale developments.