Few studies of wild animal performance account for parasite infections: A systematic review

Abstract

1. Wild animals have parasites. This inconvenient truth has far-reaching implications for biologists measuring animal performance traits: infection with parasites can alter host behaviour and physiology in profound and sometimes counterintuitive ways. Yet, to what extent do studies on wild animals take individual infection status into account? 2. We performed a systematic review across eight scientific journals primarily publishing studies in animal behaviour and physiology over a 5-year period to assess the proportion of studies which acknowledge, treat or control for parasite infection in their study design and/or analyses.3. We explored whether parasite inclusion differed between studies that are experimental versus observational, conducted in the field vs the laboratory and measured behavioural vs physiological traits. We also investigated the importance of other factors such as the journal, the trait category (e.g. locomotion, reproduction) measured, the vertebrate taxonomic group investigated and the host climatic zone of origin. 4. Our results show that parasite inclusion was generally lacking across recent studies on wild vertebrates. In over 680 filtered papers, we found that only 21.9% acknowledged the potential effects of infections on animal performance in the text, and only 5.1% of studies treated animals for infection (i.e. parasite control) or considered infection status in the statistical analyses (i.e. parasite analysis). Parasite inclusion, control and analysis were higher in laboratory compared to field studies and higher for physiological studies compared to behavioural studies but did not differ among journals, performance trait categories and taxonomic groups. Among climatic zones, parasite inclusion, control and analysis were higher in tropical, subtropical and temperate zones than in boreal and polar zones.

On the use of antibiotics in plasticity research: Gastropod shells unveil a tale of caution

“…This suggests that the populations examined in these studies likely had a low pathogen load and/or genotypes with a low susceptibility to pathogens, and also that in the absence of antibiotic treatment, shell thickness plasticity may be undetectable using commonly applied sample sizes in some P. acuta populations. Given the general lack of researchers considering potential confounding effects of parasite and pathogen infection during animal studies (Chrétien et al, 2022), we do not know how many previous P. acuta studies remained unpublished because there were more genotypes with high susceptibility to pathogens among sampled snails. Even if some pathogens do not directly affect snail mortality, they may have prevented researchers from being able to detect plastic responses.…”

Mechanisms and consequences of infection‐induced phenotypes

“…Recognition of the pivotal role that parasites play in the variability of animal phenotypes in nature is surprisingly low (Chretien et al, 2023).…”

“…Recognition of the pivotal role that parasites play in the variability of animal phenotypes in nature is surprisingly low (Chretien et al, 2023). Several contributions to this special feature present practical guidance for researchers working in a range of disciplines to assess the role of infection in their study system, including behaviour (Salerno et al, 2023; Stockmaier et al, 2023; Tillman & Adelman, 2023; Vindas et al, 2023), performance (Chretien et al, 2023), physiology (Alves & Aubin‐Horth, 2023; Lopes, 2023; Seguel et al, 2023; Wu, 2023) and epigenetics (Ngo et al, 2023). Yet, there are still many unanswered questions.…”

“…Although the complex interactions among host phenotypes and parasite infection have been studied by researchers for decades, phenotypic variation driven by infection has often historically been overlooked rather than interpreted as ecologically relevant with important evolutionary consequences (Ezenwa et al, 2016;Minchella, 1985). Still today, many researchers do not consider parasites as important sources of intra-and interindividual variation in the phenotypic traits of their study organisms (Chretien et al, 2023). This special feature highlights the various ways that parasites drive variation in host phenotypes.…”

“…This special feature highlights the various ways that parasites drive variation in host phenotypes. The contributed articles highlight diverse host–parasite systems across a broad range of taxa and include perspective and concept articles (Adamo, 2023; Lopes, 2023; Pavey & Vyas, 2023; Poulin et al, 2023; Stockmaier et al, 2023; Tillman & Adelman, 2023), a systematic literature review (Chretien et al, 2023), a meta‐analysis (Wu, 2023) and observational and experimental research conducted in laboratory and field settings (Alves & Aubin‐Horth, 2023; Ngo et al, 2023; Salerno et al, 2023; Seguel et al, 2023; Vindas et al, 2023; Will et al, 2023). In this Editorial, we contextualize each featured article's contribution to our understanding of how parasites generate intra‐ and interindividual differences in host phenotypes, how this trait variation reverberates across levels of biological organization from cells to communities and the role of the host's external environment in modulating these effects.…”