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1. Behavioural mechanisms underlying parasite-mediated competition for refuges in a coral reef fish

   https://doi.org/10.1038/s41598-019-52005-y  

   Forrester, Graham E. ; Chille, Erin ; Nickles, Katie ; Reed, Kiran ( October 2019 , Scientific Reports)

   Parasites have been increasingly recognized as participants in indirect ecological interactions, including those mediated by parasite-induced changes to host behaviour (trait-mediated indirect interactions or TMIIs). In most documented examples, host behaviours altered by parasites increase susceptibility to predation because the predator is also a host (host-manipulation). Here, we test for a TMII in which a parasitic copepod modifies the predator-prey interaction between a small goby host and several larger predatory fish. Gobies compete for crevices in the reef to avoid predation and goby mortality increases more rapidly with increasing refuge shortage for parasitized gobies than for those free of parasites. We found interactive effects of refuge shortage and parasitism on two behaviours we predicted might be associated with parasite-mediated competition for refuges. First, as refuge-shortage increases, the rate of aggression among gobies increases and parasitism intensifies this interaction. Second, goby proximity to refuges increases as refuges become scarce, but parasitism nullifies this increase. In combination, these parasite-induced changes in behaviour may explain why parasitized gobies are poor competitors for refuges. Because the parasite is not trophically transmitted via host manipulation, these altered behaviours in parasitized gobies are likely coincidental to infection.

    

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2. Unhealthy herds and the predator–spreader: Understanding when predation increases disease incidence and prevalence

   https://doi.org/10.1002/ece3.9918  

   Richards, Robert L. ; Elderd, Bret D. ; Duffy, Meghan A. ( March 2023 , Ecology and Evolution)

   Disease ecologists now recognize the limitation behind examining host–parasite interactions in isolation: community members—especially predators—dramatically affect host–parasite dynamics. Although the initial paradigm was that predation should reduce disease in prey populations (“healthy herds hypothesis”), researchers have realized that predators sometimes increase disease in their prey. These “predator–spreaders” are now recognized as critical to disease dynamics, but empirical research on the topic remains fragmented. In a narrow sense, a “predator–spreader” would be defined as a predator that mechanically spreads parasites via feeding. However, predators affect their prey and, subsequently, disease transmission in many other ways such as altering prey population structure, behavior, and physiology. We review the existing evidence for these mechanisms and provide heuristics that incorporate features of the host, predator, parasite, and environment to understand whether or not a predator is likely to be a predator–spreader. We also provide guidance for targeted study of each mechanism and quantifying the effects of predators on parasitism in a way that yields more general insights into the factors that promote predator spreading. We aim to offer a better understanding of this important and underappreciated interaction and a path toward being able to predict how changes in predation will influence parasite dynamics.

    

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3. Predation shifts coevolution toward higher host contact rate and parasite virulence

   https://doi.org/10.1098/rspb.2021.2800  

   Walsman, Jason C. ; Cressler, Clayton E. ( July 2022 , Proceedings of the Royal Society B: Biological Sciences)

   Hosts can avoid parasites (and pathogens) by reducing social contact, but such isolation may carry costs, e.g. increased vulnerability to predators. Thus, many predator–host–parasite systems confront hosts with a trade-off between predation and parasitism. Parasites, meanwhile, evolve higher virulence in response to increased host sociality and consequently, increased multiple infections. How does predation shift coevolution of host behaviour and parasite virulence? What if predators are selective, i.e. predators disproportionately capture the sickest hosts? We answer these questions with an eco-coevolutionary model parametrized for a Trinidadian guppy–Gyrodactylusspp. system. Here, increased predation drives host coevolution of higher grouping, which selects for higher virulence. Additionally, higher predator selectivity drives the contact rate higher and virulence lower. Finally, we show how predation and selectivity can have very different impacts on host density and prevalence depending on whether hosts or parasites evolve, or both. For example, higher predator selectivity led to lower prevalence with no evolution or only parasite evolution but higher prevalence with host evolution or coevolution. These findings inform our understanding of diverse systems in which host behavioural responses to predation may lead to increased prevalence and virulence of parasites.

    

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4. Winter Tick Burdens for Moose Are Positively Associated With Warmer Summers and Higher Predation Rates

   https://doi.org/10.3389/fevo.2021.758374  

   Hoy, Sarah R. ; Vucetich, Leah M. ; Peterson, Rolf O. ; Vucetich, John A. ( November 2021 , Frontiers in Ecology and Evolution)

   Climate change is expected to modify host-parasite interactions which is concerning because parasites are involved in most food-web links, and parasites have important influences on the structure, productivity and stability of communities and ecosystems. However, the impact of climate change on host–parasite interactions and any cascading effects on other ecosystem processes has received relatively little empirical attention. We assessed host-parasite dynamics for moose ( Alces alces ) and winter ticks ( Dermacentor albipictus ) in Isle Royale National Park over a 19-year period. Specifically, we monitored annual tick burdens for moose (estimated from hair loss) and assessed how it covaried with several aspects of seasonal climate, and non-climatic factors, such as moose density, predation on hosts by wolves ( Canis lupus ) and wolf abundance. Summer temperatures explained half the interannual variance in tick burden with tick burden being greater following hotter summers, presumably because warmer temperatures accelerate the development of tick eggs and increase egg survival. That finding is consistent with the general expectation that warmer temperatures may promote higher parasite burdens. However, summer temperatures are warming less rapidly than other seasons across most regions of North America. Therefore, tick burdens seem to be primarily associated with an aspect of climate that is currently exhibiting a lower rate of change. Tick burdens were also positively correlated with predation rate, which could be due to moose exhibiting risk-sensitive habitat selection (in years when predation risk is high) in such a manner as to increases the encounter rate with questing tick larvae in autumn. However, that positive correlation could also arise if high parasite burdens make moose more vulnerable to predators or because of some other density-dependent process (given that predation rate and moose density are highly correlated). Overall, these results provide valuable insights about interrelationships among climate, parasites, host/prey, and predators. 

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5. Female common cuckoo calls dampen the mobbing intensity of great reed warbler hosts

   https://doi.org/10.1111/eth.13126  

   Marton, Attila ; Fülöp, Attila ; Bán, Miklós ; Hauber, Márk E. ; Moskát, Csaba ; Goymann, ed., Wolfgang ( January 2021 , Ethology)

   To avoid mobbing attacks by their hosts during egg laying, some avian brood parasites have evolved traits to visually and/or acoustically resemble predator(s) of their hosts. Prior work established that reed warblers (Acrocephalus scirpaceus), a small host species of the brood parasitic common cuckoo (Cuculus canorus), delayed returning to the nest when confronted by either the calls of the female cuckoo or that of the predatory sparrowhawk (Accipiter nisus). It remains less clear, however, whether female cuckoo calls also suppress the nest defences of larger and more aggressive hosts. Such hosts typically attack vigorously, and can even hurt the brood parasitic intruders, instead of fleeing in the face of danger. Here, we tested whether the female cuckoo calls dampen mobbing intensity in a much largerAcrocephalushost of the common cuckoo, the great reed warbler (A. arundinaceus). We presented great reed warbler pairs with female common cuckoo models at their nests without and then with playing back the female‐specific bubbling calls of the cuckoo. As controls, we tested the hosts’ responses to harmless collared dove (Streptopelia decaocto) models, also without and then with the playbacks of dove calls. We found that the playback of female brood parasite calls reduced the aggression of hosts towards the cuckoo models as compared to model presentations without female calls, but we detected no such effect of the control calls with dove models. Our results revealed that female cuckoo calls effectively suppress the antiparasitic responses of great reed warbler hosts, which could aid parasites to approach the nest undiscovered and to evade the costly attacks of this large host. Therefore, the female call can be regarded as a general part of the cuckoo's trickery repertoire for successful parasitism.

    

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