How did mygalomorph spiders get to the Balearic Islands?

Trapdoor spiders are robust and hairy, living in tubes protected by a small camouflaged door from where they attack their victims. This group, with sixteen families and more than 2.600 species -among which we can find the tarantula-, are animals of great biogeographical interest for their little capacity of dispersion which makes their distribution reflect the geological and climate difficulties that occur in their habitat. A study of the University of Barcelona showed the origins of the Nemesia, a species of mygalomorph spider spread in the Mediterranean area. According to the study, published in the scientific journal Journal of Biogeography, these species were originated in the Iberian Peninsula and established in the Balearic Islands due the land bridges which linked and separated the islands with the continent in consecutive moments.

The scientific study, led by professor Miquel A. Arnedo and Doctor Elisa Mora, from the Department of Evolutionary Biology, Ecology and Environmental Sciences and the Biodiversity Research Institute (IRBio), also signed by the researchers Angeliki Paspati (UB-IRBio), and Arthur E. Decae, from Ghent University (Belgium).

Colonization in two stages

More than eleven million years, the ancestors of the current Balearic Nemesia were spreading from the Betic region to the territory which would end up scattering to form the current islands. Researchers of the University of Barcelona used molecular phylogenetic techniques to establish the evolutionary relations between the Nemesia of the islands and the ones from the peninsula, and compared the results with tectonic movements, established by geology, which shaped the Mediterranean orography. “The first fragmentation happened during the marine transgression of the Tortonian – between 11,6 and 7,2 million years ago-, when the ancestors of some species isolated from the ones distributing in the area of the Balearic Islands and Betic region. Between 5,9 and 5,3 million years ago the islands met again with the peninsula due the Messinian salinity crisis, that is, the drying of the Mediterranean Sea which followed the temporary shutdown of the old corridors that connected it with the Atlantic Ocean” says Miquel Arnedo.

Glaciations open the way to Minorca

This temporary reconnection of the islands was the way through which a species of mygalomorph spiders – Iberesia- reached Majorca, and later Minorca. “During the quaternary glaciations, the ancestors of Iberesia used the drawdown that provoked a connection between Majorca and Minorca, to colonize the latter”, says the researcher.

According to the researcher, these results prove the lack of capacity of dispersion of these spiders and the relevance of tectonic movements in the configuration of the current diversity of the Mediterranean Basin. Nemesia are a proof of this diversity, since different species have been found in all the Mediterranean Basin and the main islands of the sea. “The research, with similar methods, will continue with the study of the Nemesia fauna origins in the other islands of the western Mediterranean Sea; Corsica, Sardinia and Sicily. And we want to go further with the phylogeographical patterns and those of space structuring of the genetic diversity of these groups in the Balearic Islands” says Miquel Arnedo.

Article reference:

Mora, E.; Paspati, A.; Decae, A. E., i Arnedo, M. «Rafting spiders or drifting islands? Origins and diversification of the endemic trap-door spiders from the Balearic Islands, Western Mediterranean». Journal of Biogeography, octubre de 2016. DOI: 10.1111/jbi.12885

Image: Trapdoor spiders are robust and hairy.