Uncovering deep mysteries: The underwater life of an amphibious louse

International audienceDespite the incredible success of insects in colonizing almost every habitat, they remain virtually absentin one major environment – the open sea. A variety of hypotheses have been raised to explain why just afew insect species are present in the ocean, but none of them appears to be fully explanatory. Lice belongingto the family Echinophthiriidae are ectoparasites on different species of pinnipeds and river otters, i.e.they have amphibious hosts, who regularly perform long excursions into the open sea reaching depths ofhundreds of meters (thousands of feets). Consequently, lice must be able to support not only changes intheir surrounding media, but also extreme variations in hydrostatic pressure as well as breathing in a lowoxygen atmosphere. In order to shed some light on the way lice can survive during the diving excursionsof their hosts, we have performed a series of experiments to test the survival capability of different instarsof Antarctophthirus microchir (Phthiraptera: Anoplura) from South American sea lions Otaria flavescens,when submerged into seawater. These experiments were aimed at analyzing: (a) immersion tolerancealong the louse life; (b) lice’s ability to obtain oxygen from seawater; (c) physiological responses andmechanisms involved in survival underwater. Our experiments showed that the forms present in nondivingpups – i.e. eggs and first-instar nymphs – were unable to tolerate immersion in water, while followinginstars and adults, all usually found in diving hosts, supported it very well. Furthermore, as long asthe level of oxygen dissolved in water was higher, the lice survival capability underwater increased, andthe recovery period after returning to air declined. These results are discussed in relation to host ecology,host exploitation and lice functional morphology