The function and evolution of snapping defence in termite soldiers
Jan Šobotník, Eliška Cintulová , Aleš Buček , Aaron Mullins , David Sillam-Dussès , Yves Roisin , Thomas Bourguignon , Paul Bardunias , Jan Šobotník
(1) Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic; Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic ; Okinawa Institute of Science and Technology Graduate University, Onna-son, Okinawa, Japan ; Fort Lauderdale Research & Education Center, University of Florida, Ft. Lauderdale, Florida, USA ; Université Paris 13 – Sorbonne Paris Cité, Laboratory of Experimental and Comparative Ethology, Paris, France ; Evolutionary Biology and Ecology, Université Libre de Bruxelles, Bruxelles, Belgium ; Okinawa Institute of Science and Technology Graduate University, Onna-son, Okinawa, Japan ; Department of Zoology, Florida Atlantic University, Davie, Florida, USA ; Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic
Termites constitute an enormous biomass in the tropics, and as such are the subjects of intense predation and competition. To cope with this plethora of risks, they have developed numerous sophisticated defensive strategies. The most efficient of these strategies against natural enemies is found in the snapping soldiers. In general, soldier survival improves with decreasing duration of contact to the opponent, which can be achieved either by snapping, or by rapid application of defensive chemicals that are ultimately exhausted leaving the soldier defenceless. The snapping action is achieved by pushing two slender elongated mandibles against each other resulting in the deformation of mandibles and stored kinetic energy. Once optimal pressure is achieved, the left mandible springs over the right, and the hit is delivered with devastating power. Snapping mandibles occur in two distinct forms, symmetric or asymmetric, that considerably differ in the underlying mechanics. Both left and right symmetric snapping mandibles are equivalent and both deliver a simultaneous hit to either side. In asymmetric snapping mandibles only the left mandible is deformed and the hit is oriented in a more forward direction. The cuticle of snapping mandibles has unique mechanical properties with no comparison to cuticles of other insects, and this feature is responsible for extremely high speed-of-motion during the snapping process. The speed-of-motion can reach up to 260 km per hour in symmetric and over 500 km per hour in asymmetric mandibles, exceeding thus the speed observed in any other land animal. Very similar snapping mandibles evolved at least six times in the Kalotermitidae undescribed genus from Cameroon, Termes-group, Neocapritermes-group, Pericapritermes-group, Promirotermes and Orthognathotermes, and the functional and structural properties of the mandibles reveal a remarkable degree of similarity in spite of independent origins.