Attachment performance of the ectoparasitic seal louse Echinophthirius horridus

Abstract

Marine mammals host a great variety of parasites, which usually co-evolved in evolutionary arms races. However, little is known about the biology of marine mammal insect parasites, and even less about physical aspects of their life in such a challenging environment. One of 13 insect species that manage to endure long diving periods in the open sea is the seal louse, Echinophthirius horridus, parasitising true seals. Its survival depends on its specialised adaptations for enduring extreme conditions such as hypoxia, temperature changes, hydrostatic pressure, and strong drag forces during host dives. To maintain a grip on the seal fur, the louse’s leg morphology is equipped with modified snap hook claws and soft pad-like structures that enhance friction. Through techniques including CLSM, SEM, and histological staining, we have examined the attachment system’s detailed structure. Remarkably, the seal louse achieves exceptional attachment forces on seal fur, with safety factors (force per body weight) reaching 4500 in average measurements and up to 18000 in peak values, indicating superior attachment performance compared to other insect attachment systems. These findings underscore the louse’s remarkable adaptations for life in a challenging marine environment, shedding light on the relationship between structure and function in extreme ecological niches.

High prevalence and low intensity of Echinophthirius horridus infection in seals revealed by high effort sampling

“…The seal louse coevolved with terrestrial ancestors of seals from land into the marine environment millions of years ago 9 , 17 – 19 , hence the seal louse plays an important role as potential vector for a variety of infectious pathogens such as viruses and bacteria 20 , 21 and heartworms ( Acanthocheilonema spirocauda ) 11 , 22 – 24 . Because prevalence and intensity of ectoparasite infection are important biological indicators for predicting host health and inferring evolution 11 , 25 , 26 , precise information on seal louse infection parameters in vulnerable aquatic wildlife are crucial and of parasitological and veterinary relevance 24 , 27 .The seal louse developed biomechanical and physical adaptations for attachment and respiration in the marine environment 15 , 28 , 29 to sustain high pressure, drag forces, and hypoxemia 30 . The sampling of live lice is relevant for experiments on respiration, to investigate feeding and attachment adaptations 29 and reproductive processes in vitro.…”

“…Because prevalence and intensity of ectoparasite infection are important biological indicators for predicting host health and inferring evolution 11 , 25 , 26 , precise information on seal louse infection parameters in vulnerable aquatic wildlife are crucial and of parasitological and veterinary relevance 24 , 27 .The seal louse developed biomechanical and physical adaptations for attachment and respiration in the marine environment 15 , 28 , 29 to sustain high pressure, drag forces, and hypoxemia 30 . The sampling of live lice is relevant for experiments on respiration, to investigate feeding and attachment adaptations 29 and reproductive processes in vitro.…”