Differences in thermal tolerance and locomotion capacity support distinct dispersal strategies in marine larvae Halarachnidae mites

Halarachnidae mites are obligate ectoparasites infesting the respiratory tract of marine mammals. Larvae disperse and it is generally accepted that infestation occurs during nose to nose host interaction. However, mite infested hosts can exhibit sneezing and catarrh that could act as a long-distance dispersal mechanism. It is currently unknown if larvae can survive the external to the hosts environmental conditions and locate new hosts. We evaluated the thermal tolerance of two species of Halarachnidae mites, Orthohalarachne attenuata and O. diminuata , and tested if they survive extreme temperature conditions exposing larvae to constant temperatures. Then, we tested if larval age influences thermal tolerance between these two species. Finally, we studied the locomotion capacities as it can be a complementary mechanism to survive external host conditions while searching for new hosts. Orthohalarachne attenuata has a higher thermal tolerance than O. diminuata when exposed to a combination of high and low temperatures and time of exposure, which is compatible with the hypothesis of a full larval development in the respiratory system organs and dispersion to the external environment. Age does not seem to influence thermal performance. Finally, O. diminuata has a much higher locomotion capacity than O. attenuata . Our experiments show that O. attenuata has an overall higher thermal tolerance than O. diminuata although a lower locomotion. Together, our results indicate that Halarachnidae mites larvae have different strategies to withstand the environmental conditions outside the host but compatible with the hypothesis that larvae can disperse far through host sneezing and survive.