In this post, Functional Ecology and Journal of Animal Ecology showcases each article that can be found in our cross-journal special feature on Mechanisms and consequences of infection-induced phenotypes.
This collection of studies brings together biologists working on a wide range of host-parasite systems and topics—from molecular biology and animal behaviour to comparative physiology and community ecology—to synthesize our current state of understanding of host-parasite relationships and brainstorm how we can move this research area forward in an uncertain future.
Editorial
Mechanisms and consequences of infection-induced phenotypes
Researchers studying animal phenotypes often overlook the potential influence of parasites hiding inside their study organisms. Yet, most wild animals host parasites, which can alter individual phenotypes (e.g. morphology, physiology, behaviour). The time is ripe to acknowledge, critique and discuss the implications of infection on host phenotypes across taxonomic boundaries and biological levels of organization.
Functional Ecology
Controlling host behaviour can be costly for parasites. In some parasitic systems, such as insect parasitoids, this physiological cost can be paid for by the mother parasite, her offspring or both. Determining who pays the physiological cost of manipulating host behaviour, and why, promises exciting insights into how parasitic manipulation evolved.
Behavioural defences against parasites across host social structures
This review synthesizes how different levels of host sociality should affect how individuals change their behaviour to avoid, resist and tolerate infections, how this benefits themselves, and how it affects their group members (and the entire group). Animals in colonial groups (such as ants and bees) often rely on whole-colony health more than their own and infected individuals have an interest not to harm colony by transmitting parasites to others. Therefore, behavioural anti-parasite strategies are often targeted at protecting the group rather than the individual.
Searching while sick: How does disease affect foraging decisions and contact rates?
This work explores how changes in food searching behavior arise during infection, their consequences for contact rates among sick and healthy individuals, and how environmental factors could help shape these links. For example, temperature, urbanization, and overall habitat structure have been shown to affect food searching behaviors and disease prevalence in many animals.
Anticipating infection: How parasitism risk changes animal physiology
Determining how the disease environment experienced by animals impacts their physiology, survival and reproduction has major implications for our knowledge of how parasites affect populations beyond their consumptive effects. If the physiological changes triggered in uninfected animals help reduce disease burden or speed up recovery from disease, they can have cascading effects on disease dynamics; therefore, they are important to study and understand.
The authors artificially increased myo-inositol levels in uninfected fish, but this did not make them behave like Schistocephalus-infected fish. However, when they treated infected fish with lithium, they behaved more like healthy sticklebacks, but not for all behaviours. They spent less time swimming close to the surface, were less active, took longer to feed in a new environment, and spent more time frozen after a predator attack—a way to hide in plain sight from their bird predators.
The authors observed two fungal species that act as hyperparasites (parasites of other parasites) of Ophiocordyceps and drastically reduced its ability to fully develop and release spores. Ophiocordyceps fungi are found around the globe. By learning how they interact with different environments, we can begin to understand their disease dynamics and unravel how these, and other parasitic manipulators, thrive.
An extended epiphenotype for an extended phenotype in Toxoplasma gondii infected feral house mice
The authors found that DNA from Toxoplasma-infected mice was chemically modified in a way that should increase the expression of the arginine vasopressin gene. Why is that important? If we increase the production of this gene in a lab, we can get even uninfected mice to reduce their fear. So, Toxoplasma causes chemical modifications in mice brains, likely manipulating mice behavior and making it more likely that infected mice will soon find themselves on the dinner menu of cats. Kangaroo Island is currently amidst a feral cat control program to save native fauna. Removing cats should also help to break the transmission of Toxoplasma and eventually help wildlife and sheep from this harmful infection.
In nature, most animals are simultaneously infected with a diverse range of parasites. Some of these parasites, like gastrointestinal (GI) worms, can cause profound changes in the host that affect co-occurring parasites. In this study, focusing on two different GI worms (Cooperia and Haemonchus) infecting wild African buffalo, we examined if and how worms modify host immunity and tissue morphology and the consequences of these modifications for a protozoan parasite, coccidia, that also resides in the GI tract.
Brain-infecting parasites leave lasting effects on behaviour even in resistant hosts
Observing Medaka, the common pet fish known as Japanese Rice fish, the authors have now documented lasting behavioural effects in hosts resisting infection. Despite repeated attempts to infect these fish, they resisted infection. Yet, the infection attempts resulted in the fish developing a more social personality and becoming more physically active. In consequence, important aspects of animal and human behaviour can in theory be dictated by known and unknown parasite encounters.
Journal of Animal Ecology
Few studies of wild animal performance account for parasite infections: A systematic review
This literature review suggests that parasites are sorely under-acknowledged by researchers in recent years despite growing evidence that infections can modify animal performance. Given the ubiquity of parasites in the environment, the authors encourage scientists to consider individual infection status when assessing performance of wild animals.
In light of the microbiome revolution sweeping through ecology and evolutionary biology, the authors hypothesise that the composition of symbiotic microbial communities living within individual parasites influences the nature and extent of their effect on host phenotype. The interests of both the parasite and its symbionts are aligned through the latter’s vertical transmission, favouring joint contributions to the manipulation of host phenotype.
Predation cues amplify the effects of parasites on the personality of a keystone grazer
Group infection status strongly influenced behavioural reaction norms: uninfected individuals grouped with an infected snail were more responsive to predation risk, exhibiting increased climbing behaviour and spending less time in the water. Here parasites are influencing personality indirectly by inducing avoidance behaviours in healthy individuals, although only in high-risk environments.
