Thermal Change and the Dynamics of Multi-Host Parasite Life Cycles in Aquatic Ecosystems

Abstract

Altered thermal regimes associated with climate change are impacting significantly on the physical, chemical, and biological characteristics of the Earth's natural ecosystems, with important implications for the biology of aquatic organisms. As well as impacting the biology of individual species, changing thermal regimes have the capacity to mediate ecological interactions between species, and the potential for climate change to impact host-parasite interactions in aquatic ecosystems is now well recognized. Predicting what will happen to the prevalence and intensity of infection of parasites with multiple hosts in their life cycles is especially challenging because the addition of each additional host dramatically increases the potential permutations of response. In this short review, we provide an overview of the diverse routes by which altered thermal regimes can impact the dynamics of multi-host parasite life cycles in aquatic ecosystems. In addition, we examine how experimentally amenable host-parasite systems are being used to determine the consequences of changing environmental temperatures for these different types of mechanism. Our overarching aim is to examine the potential of changing thermal regimes to alter not only the biology of hosts and parasites, but also the biology of interactions between hosts and parasites. We also hope to illustrate the complexity that is likely to be involved in making predictions about the dynamics of infection by multi-host parasites in thermally challenged aquatic ecosystems.

Fig. 1

The types of parasite life cycles encountered in aquatic ecosystems vary in complexity from simple direct life cycles (a) in which transmission occurs between two definitive hosts (DH) of the same species, to more complex, indirect life cycles that involve transmission of parasites between multiple obligate intermediate hosts (IH) of different species (b–d). (This figure is available in black and white in print and in color at Integrative And Comparative Biology online).

Fig. 2

Here we use the life cycle of a three-host, indirectly transmitted, parasite as a framework to graphically summarize the various mechanisms by which altered thermal regimes can influence the dynamics of multi-host parasite life cycles in aquatic ecosystems. Inner circle shows hosts, outer circle shows parasite stages. Numbers relate to manuscript sections. (1) Effects on the survival and development of embryonic parasite stages; (2) effects on the survival, activity, and host finding ability of free-swimming infective stages; (3) effects on the susceptibility of intermediate hosts to infective parasites; (4) effects on the survival, growth, and development of parasite stages in intermediate hosts; (5) effects on the ecology and behavior of intermediate hosts; (6) effects on the biology and ecology of definitive hosts; and (7) effects on the performance of adult parasites infecting definitive hosts. Effects of temperature on the interactions between infective parasites and prospective hosts (“A,” “B,” and “C”) are also shown.