Parasites in extreme environments

Parasites are not only the most abundant form of life on earth, they are also essential contributors to ecosystem health. Such ecosystems may comprise extreme environments that would appear to make completing a parasite life cycle difficult, if not impossible. Yet, parasites have evolved remarkable adaptations that have allowed them to complete their life cycles in seemingly inhospitable environments (e.g. see Tinsley, 1999). However, such environments are rarely stable and the increasing influence of climate change is particularly challenging to parasite survival. In this special issue, seven invited reviews examine different examples of extreme environments and their influence on parasite-host relationships.

Digenean trematodes have complex indirect life cycles yet they have successfully colonized the deep oceans and Rodney Bray provides an overview of the rich diversity of digenean trematodes parasitizing fish in such hostile environments. Ralph Vanstreels and colleagues look at host-parasite associations of arthropods infesting birds and pinnipeds in one of the most extreme environments on our planet, Antarctica. In contrast, the focus of Elizabeth Warburton and Ian Beveridge in their two articles is arid environments where hosts are typically not abundant. Warburton looks at the evolution of virulence, breadth of host spectra, and life cycle strategies, whereas Beveridge compares helminth and arthropod parasite communities occurring in macropodid, vombatid and notoryctid marsupials as well as in rodents in arid, semi-arid and humid zones of Australia.

Freshwater ecosystems are among the most diverse and endangered in the world and among these are what are termed intermittent rivers. As Alan Lymbery and colleagues explain, these rivers may cease to flow at any time, with isolated pools providing ecological refuges. They discuss the threat posed by climate change to fish and parasite communities in intermittent rivers. Alejandro Aleuy and Susan Kutz are concerned with the impact of climate change on parasite dynamics, primarily in the Arctic. They show how a detailed understanding of the complex ecological processes involved in the survival of nematode parasites in extreme and changing conditions is essential.

Leeches are fascinating animals which are very successful parasitic worms. As such, they deserve much more attention in the parasitology literature. In this review, Anna Phillips and colleagues tackle an unusual topic in leech biology by providing insights into their extreme biology that have allowed them to survive and flourish in a range of seemingly inhospitable environments. They discuss the morphological, physiological, and behavioral adaptations of leeches living in such environments which include extremes in temperature, moisture, salinity, pressure, light, and pollution.

Finally, I want to thank Susan Kutz for suggesting this topic as a Special Issue, and Ian Beveridge for Ian Beveridge’shis suggestions with the initial planning.