Adaptations to deep diving in seal lice, the exception to the rule that there are no marine insects

Insects are the most evolutionarily and ecologically successful group of living animals, being present in almost all possible mainland habitats; however, they are virtually absent in the ocean, which constitutes more than 99% of the Earth’s biosphere. Only a few insect species can be found in the sea but they remain at the surface, in salt marshes, estuaries, or shallow waters. Remarkably, a group of 13 species manages to endure long immersion periods in the open sea, as well as deep dives, i.e., seal lice. During the evolutionary transition of pinnipeds from land to the ocean, echinophthiriid seal lice had to manage the gradual change to an amphibian lifestyle along with their hosts, some of which may spend more than 80% of the time submerged and performing extreme dives, some beyond 2000 m under the surface. These obligate and permanent ectoparasites have adapted to cope with hypoxia, high salinity, low temperature, and, in particular, conditions of huge hydrostatic pressures. A major remainig question is whether or not seal lice do breath underwater or, on the contrary they dramatically reduce their metabolism to spare oxygen when submerged. During the reported period, we investigated anatomical adaptations to prolongued immersion and also set up a method for measuring oxigen consumption in two media, air and water in small insects, both using state of the art methods.