Climate change threatens world’s parasites


Climate change impacts on parasites: Parasite traits and abiotic and biotic interactions leading to parasite vulnerability under climate change. We list the most important biological traits of parasites that could amplify their vulnerability to extinction under climate change, the most likely changes to host–parasite interactions and various mitigation strategies likely to be used by both parasites and hosts adapting to disrupted climates. From Royal Society Open Science [open access].

Climate change impacts on parasites: Parasite traits and abiotic and biotic interactions leading to parasite vulnerability under climate change. We list the most important biological traits of parasites that could amplify their vulnerability to extinction under climate change, the most likely changes to host–parasite interactions and various mitigation strategies likely to be used by both parasites and hosts adapting to disrupted climates. From Royal Society Open Science [open access].


Why care about parasites?

Why should that matter?

Parasites are icky, right?

Dangerous, too.

And nobody ever thanked you for calling s/he a parasite, right?

Well consider this [emphasis added] from a team of scientists from the University of California, Berkeley, the University of Connecticut, the University of Zurich, the University of Michigan, and the Smithsonian’s National Museum of Natural History and just published [open access] in the prestigious journal Royal Society Open Science:

[T]he geographical boundaries and ecology of ectoparasites can be affected by aridity, salt spray, elevation and cold, while endoparasites can be affected by precipitation, soil type, temperature and other variables. A changing climate alters the availability of parasite niche space, driving a combination of habitat loss and range shifts, and potentially decreasing population growth and reproductive rates, all potentially encouraging primary extinctions.

That loss of parasite biodiversity may have cascading effects in resource–consumer webs, and change the productivity and stability of ecosystems in unpredictable ways that are often overlooked in the literature . Some estimate that up to 70% of all animal species are parasites, making parasitism the most common consumer strategy on Earth, and parasites account for a significant portion of biomass and up to 78% of food web links in any given ecosystem. Their presence and diversity has also been suggested as an indicator of ecosystems with a low degree of human degradation. In addition, evolutionary specializations like host behaviour modification can increase biomass flow between free-living hosts up to 20-fold, while adaptations like host castration can drastically limit host population size. Recent research has also highlighted that within-host interactions and competition between parasites can dilute disease risk for hosts in counterintuitive ways. As demonstrated in the Ribeiroia trematode–amphibian experimental system, parasite and host biodiversity can dilute both disease risk and parasite-induced host mortality at the population level. Just as decreasing diversity in free-living species often increases the dominance of the most abundant species, parasite extinctions could have unpredictable effects on the structure of disease communities, as some pathogens could experience competitive release as rare species go extinct.

More on the study from the University of California, Berkeley:

Photogenic animals, from polar bears to people, aren’t the only creatures under threat from global climate change. A new review led by UC Berkeley suggests the phenomenon threatens parasites with extinction, which could have big consequences for ecosystems.

The vast majority of research into parasites and environment change focuses on how hosts, particularly humans, will be harmed. Few studies have addressed how the loss of parasite biodiversity may affect other aspects of host health, ecosystem connectedness and health  and biodiversity as a whole. Previous research suggests that parasites are up to 10 times more vulnerable to extinction than are their hosts.

In the new study, the researchers suggest that parasites are as prone to extinction due to climate change as any other taxonomic group. The study predicts that losing parasites could destabilize ecosystems in many ways, such as by increasing more virulent disease or by altering the food web or changing host physiology. The study found that parasites in hosts with variable internal temperatures, parasites of large-bodied hosts, host-specific parasites and parasites with complex life cycles will likely be the most vulnerable to extinction due to climate change.

“This is the first comprehensive review of how climate change may affect parasite biodiversity, from the point of view of parasite conservation,” said Carrie Cizauskas, who led the research as a postdoctoral affiliate in the lab of Wayne Getz, a professor of wildlife ecology in the Department of Environmental Science, Policy and Management. Colin Carlson, a graduate student in the same department, is co-lead author of the review.

The research was published today in the journal Royal Society Open Science.

Previous work from this group has called for further research into parasite vulnerability from parasites’ perspectives, rather than primarily focusing on hosts, and also outlined ways to potentially conserve parasites. In the new study, the authors outline actionable items for researching the vulnerability of parasites. A forthcoming review from Cizauskas and Carlson attempts to quantify these parasite extinction risks using existing data and modeling.

The team outlines a protocol for identifying vulnerable parasites by a set of key risk factors, including host specificity, parasite life cycle complexity and climatic tolerance. The next step involves identifying important unanswered questions in parasite ecology, such as how host phylogeny predicts parasite extinction, or whether parasite extinctions will be clustered in particular ecosystems. Finally, they suggest proposing how ecological disciplines may be used to identify gaps in parasite research data.

“Ultimately, our goal is for this review to act as a catalyst for further research efforts and discussions regarding the important and little-addressed topic of parasite vulnerability in the face of climate change,” Cizauskas said.

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