A newly described BIG little pselaphine, and the relationship between size and inquilinity

Jubogaster towai is a newly described genus and species of pselaphine, found recently in a colony of ants (Pheidole xanthogaster) in the Peruvian Amazon. It was named towai, for the son of one of the people who found it, Taku Shimada. What is immediately striking about this pselaphine is its large size (5.1mm for the type specimen) and transverse head. However as only one specimen has been found to date, we cannot be sure of the typical (pun intended) size range of the species. The ants in the colony where our little friend was found seemed to be completely unaware of its presence deep inside the nest. Currently little is known about the ecology, biology, and behaviour of J. towai but we must assume from the circumstances it was found in that it is a true myrmecophile, meaning it lives in association with the ants. That being said, it doesn’t have any of the obvious adaptations of other myrmecophilous pselaphines.

Jubgjaster towai in an ant colony (Pheidole xanthogaster). Photo taken by Taku Shimada, antroom.jp

 Jubogaster has been placed in the tribe (a type of larger grouping) Trogastrini although it does appear to have a lot in common with another tribe, Jubini. This determination was made using molecular techniques. DNA was carefully extracted from the single specimen so as not to damage it. The researchers were able to successfully isolate and amplify a small section of rDNA, which encodes part of the ribosome inside the cell. They then compared this to rDNA from other members of Trogastrini and Jubini as well as members of three other tribes, and some more distantly related beetles for contrast. What they found was that Trogastrini was the best fit for this new genus and species even though it seemed quite different. They also concluded Jubini and Trogastrini are sister groups and have a shared ancestor. 

Photos 1-7 Jubogaster towai from different angles and magnifications Photo: Parker & Maruyama

The most common size of pselaphines is anything up to 3mm but some can be some can be much larger such as Kistneriella termitobia the largest known species at 7.1mm. Anything 3mm or more can be considered large. We don’t know enough about the biology of these little beetles to say with certainty why some are larger than others. However a pattern may be emerging that small pselaphines more often than not are ‘free living’ and not associated with ants, while larger ones are commonly associated with ants. The jury is still out as to whether J. towai or other large pselaphines evolved into inquilines due to their (relatively) large stature, or they became large as an adaptation to become better inquilines. Many bizarre characteristics of some pselaphines have been put down to their inquilinous way of life. There are a number of possible advantages to a larger body size, which may have given natural selection something to work with such as: the abundant food available in ant and termite nests, the comparatively large size of nest galleries, to mimic the size of the host, or as a defensive strategy.

There is on-going research into many aspects of Pselaphine which will hopefully answer some of these questions in the future. You can see the original journal article here.

Parker, J.; Maruyama, M. 2013. Jubogaster towai, a new Neotropical genus and species of Trogastrini (Coleoptera: Staphylinidae: Pselaphinae) exhibiting myrmecophily and extreme body enlargement. Zootaxa 3630 (2): 369-378.

Parker, J. 2013. Personal Communication. Email.