Incidental catch of seabirds (bycatch) in fisheries has been identified as a major threat to the conservation of seabird populations. Acquiring accurate, detailed data on seabird bycatch is an ongoing challenge to effective integrated ecosystem management of commercial fisheries. To collect detailed data on seabird bycatch in the Greenland halibut (Reinhardtius hippoglossoides Walbaum, 1792) fishery in northern Canada, we applied two voluntary effort methods with industry partners that asked for additional, detailed information about the nature of the interactions between seabirds and the fishing gear than the data standardly reported in the fishery. We found that the amount of bird bycatch reported in both enhanced datasheets completed by at-sea observers (ASOs) and carcass collections yielded different results when compared to the typical seabird bycatch reporting in the fisheries ASO database. Across three years of data collection (2016, 2018, and 2019), the number of seabirds reported using the enhanced data collection methods were 0.5–11-fold the number from typical ASO database values. We then used these data to model how the differences between data sources may fluctuate across years. These large discrepancies between the methods highlight the challenges with obtaining accurate seabird bycatch data needed to implement a meaningful ecosystem approach to the management.

Benzotriazole UV-Stabilizers (BZT-UVs), compounds added to plastics to reduce ultraviolet degradation, are considered contaminants of emerging concern given their environmental persistence and documented toxicity in humans and animals. UV328 is a BZT-UV that has been recently listed to Annex A of the Stockholm Convention; therefore, understanding species exposure is critical information to fulfill international and domestic regulatory obligations. We evaluated hepatic accumulation of 12 plastic additives (including nine BZT-UVs) in Larus gulls in Atlantic Canada. BZT-UV accumulation was assessed in relation to ingested plastics, hepatic heavy metal accumulation, and body condition. Ninety-six percent of gulls had at least one BZT-UV at detectable hepatic concentrations. The most frequently detected BZT-UVs were UVP (91.4%) and UV328 (76%), suggesting ubiquitous exposure across individuals. We demonstrated interspecific differences in the relationship between ingested plastics and accumulated contaminants, with a positive relationship detected between ingested plastics and both UVP and UV328 in American herring gulls (Larus argentatus smithsonianus), and a positive relationship between hepatic UV328 and Pb concentrations detected in great black-backed gulls (Larus marinus). We provide evidence that Larus gulls feeding at a coastal landfill are highly exposed to BZT-UVs, and that the relationship between ingested plastics and plastic-associated contaminants varies across sympatric species.

The objectives of this research were to assess ingested plastics and accumulated heavy metals in four urban gull species. Additionally, the relationships between ingested plastics and selected demographic and health metrics were assessed. Between 2020-2021 during the non-breeding seasons, 105 gulls (46 American herring gulls (HERG, Larus argentatus smithsonianus), 39 great black-backed gulls (GBBG, Larus marinus), 16 Iceland gulls (Larus glaucoides), 4 glaucous gulls (Larus hyperboreus)) were killed at a landfill in coastal Newfoundland and Labrador, Canada, as part of separate, permitted kill-to-scare operations related to aircraft safety. Birds were necropsied, the upper gastrointestinal tract contents were processed using standard techniques, and livers were analyzed for accumulated As, Cd, Hg, and Pb. The relationships between ingested plastics, demographics, and health metrics were assessed in HERG and GBBG. Across all four species, 85 % of birds had ingested at least one piece of anthropogenic debris, with 79 % ingesting at least one piece of plastic. We detected interspecific differences in plastic ingestion and hepatic trace metals, with increased ingested plastics detected in GBBG compared with HERG. For GBBG, levels of ingested plastic were relatively greater for birds with higher scaled mass index, while HERG with more ingested plastic had higher liver lead concentrations.

The chronic toxicity of short chain perfluoroalkyl sulfonic acids (PFSAs), such as perfluorobutanesulfonic acid (PFBS) and perfluorohexanesulfonic acid (PFHxS), are relatively understudied despite the increasing detection of these compounds in the environment. We investigated the chronic toxicity and bioconcentration of PFBS and PFHxS using northern leopard frog (Rana [Lithobates] pipiens) tadpoles. We exposed Gosner stage (GS) 25 tadpoles to either PFBS or PFHxS at nominal concentrations of 0.1, 1, 10, 100, and 1000 μg/L until metamorphosis (GS42). We then assessed tadpole growth, development, stress, and immune metrics, and measured fatty acid (FA) composition and PFSA concentrations in liver and whole-body tissues. Tadpole growth and development measures were relatively unaffected by PFSA exposure. However, tadpoles exposed to 1000 μg/L PFBS or PFHxS had significantly increased hepatosomatic indexes (HSI) relative to controls. Further, tadpoles from the 1000 μg/L PFHxS treatment had altered FA profiles relative to controls, with increased total FAs, saturated FAs, monounsaturated FAs, and omega-6 polyunsaturated FAs. In addition, tadpoles from the 1000 μg/L PFHxS treatment had a higher probability of waterborne corticosterone detection. These results suggest that PFBS and PFHxS influence the hepatic health of tadpoles, and that PFHxS may alter lipid metabolism in tadpoles. We also observed a higher probability of tadpoles being phenotypically female after exposure to an environmentally relevant concentration (0.1 μg/L) of PFHxS, suggesting that PFHxS may exert endocrine disrupting effects on tadpoles during early development. The measured bioconcentration factors (BCFs) for both compounds were ≤ 10 L kg-1 wet weight, suggesting low bioconcentration potential for PFBS and PFHxS in tadpoles. Many of the significant effects observed in this study occurred at concentrations several orders of magnitude above those measured in the environment; however, our work shows effects of PFSAs exposure on amphibians and provides essential information for ecological risk assessments of these compounds.

Factors such as host species, phylogeny, diet, and both timing and location of sampling are thought to influence the composition of gut-associated bacteria in insects. In this study, we compared the faecal-associated bacterial taxa for three Coenagrion and one Enallagma damselfly species. We expected high overlap in representation of bacterial taxa due to the shared ecology and diet of these species. Using metabarcoding based on the 16S rRNA gene, we identified 1513 sequence variants, representing distinct bacterial ‘taxa’. Intriguingly, the damselfly species showed somewhat different magnitudes of richness of ZOTUs, ranging from 480 to 914 ZOTUs. In total, 921 (or 60.8% of the 1513) distinct ZOTUs were non-shared, each found only in one species, and then most often in only a single individual. There was a surfeit of these non-shared incidental ZOTUs in the Enallagma species accounting for it showing the highest bacterial richness and accounting for a sample-wide pattern of more single-species ZOTUs than expected, based on comparisons to the null model. Future studies should address the extent to which faecal bacteria represent non-incidental gut bacteria and whether abundant and shared taxa are true gut symbionts. Graphical Abstract Pictures of odonates adopted from Norske Art databank under Creative Commons License (CC BY 4.0).

Trophic interactions are at the core of several key ecological processes and theories as they determine the flow of material and energy within and across communities and habitats. Odonates provide a rich and diverse taxonomic group with several features (e.g. trophic position, hunting behavior, olfaction) that make them a very interesting biological model for the study of trophic interactions in aquatic and terrestrial habitats. Moreover, odonates undergo incomplete metamorphosis with aquatic larvae and terrestrial adults, which provides opportunities to investigate ontogenetic diet variation and trophic links between aquatic and terrestrial systems. They are also important predators regulating prey populations and mediating community processes such as trophic cascades. Finally, recent studies on odonates have pioneered whether local adaptation and phenotypic plasticity can counterbalance the negative impacts of global change on resource acquisition and fitness. This chapter reviews recent studies investigating the trophic features and role of odonates in aquatic and terrestrial ecosystems as well as their importance for investigating the impact of global change on trophic ecology, local adaption, and community processes. Many of the insights highlighted in this chapter go beyond odonates and have helped to advance key concepts in trophic ecology.

Aggregation of macroparasites among hosts is nearly universal among parasite-host associations. Researchers testing hypotheses on origins of parasite aggregation and its importance to parasite and host population ecology have used different measures of aggregation that are not necessarily measuring the same thing, potentially clouding our understanding of underlying epidemiological processes. We highlight these differences in meanings by exploring properties and interrelationships of six common measures of parasite aggregation, and provide a "user's guide" to inform researchers' decisions regarding their application. We compared the mathematical expressions of the different measures of aggregation, and ran two series of simulations and analyses. The first simulations tested the effect of random removals of parasites on aggregation levels under different conditions, while the second explored interrelationships between the measures, as well as between other individual parasitological sample measures (i.e. mean abundance, prevalence) and aggregation. Results of simulations and analyses showed that the six measures of aggregation could be separated readily into three groups: the variance-to-mean ratio (VMR) together with mean crowding, patchiness with k of the negative binomial, and Poulin's D with Hoover's index. These three pairs of measures showed differing responses to random parasite removals and differing relations with mean abundance and/or prevalence, highlighting that metrics capture different variation in other sample measures and different attributes of aggregation. We used results of our simulations and analyses, and a literature review, to list the properties, advantages, and disadvantages of each aggregation metric. We provide a comprehensive exploration of what is assessed by each metric, as a guide to metric choice. We implore researchers to provide enough information such that aggregation measures from each group are reported or can be readily calculated. Such steps are needed to allow large-scale analyses of variation in degrees of aggregation within and among parasite-host associations, to uncover epidemiological processes shaping parasite distributions.

Abstract Trophic interactions are at the core of several key ecological processes and theories as they determine the flow of material and energy within and across communities and habitats. Odonates provide a rich and diverse taxonomic group with several features (e.g. trophic position, hunting behavior, olfaction) that make them a very interesting biological model for the study of trophic interactions in aquatic and terrestrial habitats. Moreover, odonates undergo incomplete metamorphosis with aquatic larvae and terrestrial adults, which provides opportunities to investigate ontogenetic diet variation and trophic links between aquatic and terrestrial systems. They are also important predators regulating prey populations and mediating community processes such as trophic cascades. Finally, recent studies on odonates have pioneered whether local adaptation and phenotypic plasticity can counterbalance the negative impacts of global change on resource acquisition and fitness. This chapter reviews recent studies investigating the trophic features and role of odonates in aquatic and terrestrial ecosystems as well as their importance for investigating the impact of global change on trophic ecology, local adaption, and community processes. Many of the insights highlighted in this chapter go beyond odonates and have helped to advance key concepts in trophic ecology.

Aggregation of macroparasites among hosts is a near-universal pattern, and has important consequences for the stability of host-parasite associations and the impacts of disease. Identifying which potential drivers are contributing to levels of aggregation observed in parasite-host associations is challenging, particularly for observational studies. We apply beta regressions in a Bayesian framework to determine predictors of aggregation, quantified using Poulin's index of discrepancy (D), for 13 species of parasites infecting Icelandic Rock Ptarmigan (Lagopus muta) collected over 12 years. 1,140 ptarmigan were collected using sampling protocols maximizing consistency of sample sizes and of composition of host ages and sexes represented across years from 2006-2017. Parasite species, taxonomic group (insect, mite, coccidian, or nematode), and whether the parasite was an ecto- or endoparasite were tested as predictors of aggregation, either alone or by modulating an effect of parasite mean abundance on D. Parasite species was an important predictor of aggregation in models. Despite variation in D across samples and years, relatively consistent aggregation was demonstrated for each specific host-parasite association, but not for broader taxonomic groups, after taking sample mean abundance into account. Furthermore, sample mean abundance was consistently and inversely related to aggregation among the nine ectoparasites, however no relationship between mean abundance and aggregation was observed among the four endoparasites. We discuss sources of variation in observed aggregation, sources both statistical and biological in nature, and show that aggregation is predictable, and distinguishable, among infecting species. We propose explanations for observed patterns and call for the review and re-analysis of parasite and other symbiont distributions using beta regression to identify important drivers of aggregation-both broad and association-specific.

Sexes often differ in foraging and diet, which is associated with sex differences in size, trophic morphology, use of habitats, and/or life history tactics. Herein, strikingly similar diets were found for adult sexes of a dragonfly (Leucorrhinia intacta), based on comparing 141 dietary taxa identified from the metabarcoding of mitochondrial DNA archived in feces. Arthropods in > 5% of samples included five species of dipterans, two hemipterans, two spider species and one parasitic mite. The mite was not traditional prey as its presence was likely due to DNA contamination of samples arising through parasitism or possibly via accidental consumption during grooming, and therefore the mite was excluded from diet characterizations. Common prey species were found with statistically indistinguishable frequencies in male and female diets, with one exception of an aphid more often found in male diets, although this pattern was not robust to corrections for multiple statistical tests. While rare prey species were often found in diets of only one sex, instances of this were more frequent in the more oft-sampled females, suggesting sampling artefact. Sexes did not differ in the mean prey species richness in their diets. Overall, sexes showed statistically indistinguishable diets both on a prey species-by-species basis and in terms of multivariate characterizations of diet composition, derived from presence-absence data of prey species analyzed via PERMANOVA and accumulation curves. Males and females may have similar diets by being both opportunistic and generalist predators of arthropods, using the same foraging habitats and having similar sizes and flight agilities. Notably, similarities in diet between sexes occur alongside large interindividual differences in diet, within sexes. Researchers intending on explaining adaptive sex differences in diet should consider characteristics of species whose sexes show similar diets.

AbstractTesting hypotheses in ecological and evolutionary parasitology can require testing whether host traits or coinfecting parasites explain variation in parasitism by focal species. However, when host traits and coinfecting parasites are considered separately, relations between either and parasitism by focal species can be spurious—a problem that is addressed when both are considered together. We assessed whether abundances of focal parasites related to host age/sex and coinfecting parasites for three endoparasites and nine ectoparasites of Icelandic Rock Ptarmigan (Lagopus muta) collected over 12 yr (2006–2017), and quantified the variation in focal parasitism explained by these predictors. Host traits and coinfecting parasites explained significant variation in abundance of all nine focal parasite species for which models converged, when those models were based on groups of parasites sharing tissue tropism and/or transmission pathways and included year as a random effect. We found a single spurious relation: a host age–sex interaction effect that was removed once concurrent parasitism was considered. When considering focal parasites within groups of coinfecting parasites, we found cases of positive, negative, and lacks of correlations. The amount of variation in focal parasite abundance explained by host traits versus coinfecting parasites depended on the focal parasite and its group. Overall variation explained was both related to the prevalence of the focal parasite, possibly due to underlying parasite aggregation, and similar to variation explained in other models in ecology and evolution. We conclude that host traits and coinfecting parasites often combine to determine infection by focal species. Future studies should also explore the mechanisms underlying parasite–parasite relations and their potential impacts on host demography for this and other study associations, and assess relative effects of host traits and coinfecting parasites on focal parasitism.

To understand the diversity and strength of predation in natural communities, researchers must quantify the total amount of prey species in the diet of predators. Metabarcoding approaches have allowed widespread characterization of predator diets with high taxonomic resolution. To determine the wider impacts of predators, researchers should combine DNA techniques with estimates of population size of predators using mark-release-recapture (MRR) methods, and with accurate metrics of food consumption by individuals. Herein, we estimate the scale of predation exerted by four damselfly species on diverse prey taxa within a well-defined 12-ha study area, resolving the prey species of individual damselflies, to what extent the diets of predatory species overlap, and which fraction of the main prey populations are consumed. We identify the taxonomic composition of diets using DNA metabarcoding and quantify damselfly population sizes by MRR. We also use predator-specific estimates of consumption rates, and independent data on prey emergence rates to estimate the collective predation pressure summed over all prey taxa and specific to their main prey (non-biting midges or chironomids) of the four damselfly species. The four damselfly species collectively consumed a prey mass equivalent to roughly 870 (95% CL 410-1,800) g, over 2 months. Each individual consumed 29%-66% (95% CL 9.4-123) of its body weight during its relatively short life span (2.1-4.7 days; 95% CL 0.74-7.9) in the focal population. This predation pressure was widely distributed across the local invertebrate prey community, including 4 classes, 19 orders and c. 140 genera. Different predator species showed extensive overlap in diets, with an average of 30% of prey shared by at least two predator species. Of the available prey individuals in the widely consumed family Chironomidae, only a relatively small proportion (0.76%; 95% CL 0.35%-1.61%) were consumed. Our synthesis of population sizes, per-capita consumption rates and taxonomic distribution of diets identifies damselflies as a comparatively minor predator group of aerial insects. As the next step, we should add estimates of predation by larger odonate species, and experimental removal of odonates, thereby establishing the full impact of odonate predation on prey communities.

Measures of parasitism often differ between hosts. This variation is thought due in part to age or sex differences in exposure to parasites and/or susceptibility to parasitism. We assessed how often age or sex biases in parasitism were found using a large, multi‐year (2006–2017) dataset of 12 parasite species of Icelandic rock ptarmigan ( Lagopus muta ). We found host traits (i.e. age and/or sex) accounted for significant variation in abundance of 11 of the 12 parasite species. We often found increased abundance among juvenile hosts, although significant adult biases were observed for three parasite species. Additionally, higher levels of parasitism by many species were observed for female hosts, contrary to frequent male biases in parasitism reported for other vertebrates. Abundance of six parasite species was best explained by interactions between host age and sex; some degree of decrease in abundance with host age was present for both male and female hosts for four of those parasite species. We consider various host and parasite traits that could account for observed singular and repeated patterns of age and/or sex biases in parasitism (e.g. age‐ and sex‐related grouping behaviours, age‐specific mortality in relation to parasitism, acquisition of greater immunity with age). This work provides a foundation for future studies investigating age‐related differences in acquired immunity and age‐specific parasite‐mediated mortality for males and females, as well as studies on interactions between co‐infecting parasite species.

Field experiments where parasites are removed through treatment and contaminant levels in host tissues are recorded can provide insight into the combined effects of parasitism and contaminants in wild populations. In 2013 and 2014, we treated northern common eider ducks (Somateria mollissima) arriving at a breeding colony with either a broad-spectrum antihelminthic (PANACUR®) or distilled water, and measured their blood lead (Pb) levels. Breeding propensity and clutch sizes were inversely related to Pb in both treatment groups. In comparison, a negative effect of Pb on resight probability the following year was observed only in the anti-parasitic treatment (APT) group. These contrasting patterns suggest a long-term benefit to survival of intestinal parasitism in eiders experiencing Pb exposure. The arrival date of hens explained some, but not all, of the effects of Pb. We weigh the merits of different hypotheses in explaining our results, including protective bioaccumulation of Pb by parasites, condition-linked thresholds to costly reproduction and the direct effects of APT on eider health. We conclude that variation in helminth parasitism influences survival in this migratory bird in counterintuitive ways.

Studies on parasite-mediated selection often focus on single parasite taxa infecting single species of hosts. However, host populations experience infections by multiple parasite taxa simultaneously; coinfection is expected to influence how host- and/or parasite-related factors affect host exposure and susceptibility to various parasites, and the resulting patterns of infection. We sampled adult dragonflies from a population of Leucorrhinia intacta (Hagen) in eastern Ontario, Canada. Dragonflies were exposed to parasitism by both water mites (Arrenuridae) and gregarines (Eugregarinidae). We tested for covariation between these ecto- and endoparasites, while considering potential sex and age biases in host sampling and patterns of infection. Mite parasitism differed dramatically between host sexes: nearly all collected males were parasitized, whereas only half of females were infested. This was likely due to differences in age distributions between sexes in sampled dragonflies. Water mite and gregarine parasitism showed strong, negative covariation, and coinfection occurred far less often than expected by chance, although these patterns were restricted to samples of females which, unlike male samples, likely included many old and young dragonflies. We report the first observation of negative covariation between internal and external parasite taxa in an anisopteran host and suggest this relationship between water mites and gregarines may be more widespread among Odonata and perhaps other insects than previously surmised. We advance hypotheses based on host age-parasitism relationships as well as variable parasite-mediated selection to help explain the sex specificity of observed coinfection patterns in our samples.

This chapter discusses insect behavioral responses to parasites. Dividing behaviors conceptually into those that occur before and after infection, we start by reviewing the evidence that insects identify and avoid potentially infectious environments to minimize negative consequences of infection. Behavioral responses following infection according to their adaptive value to either the insect host or to the parasite will then be considered. One section covers sickness behaviors proposed to benefit the host by conserving energetic resources during infection; another section discusses evidence for altered host behavior as a parasite adaptation enhancing parasite survival or transmission. The mechanistic link between behavior and immunity in insects is briefly discussed, and provide a summary of methods and techniques becoming standard to studying behavior of model insect species in the context of infection. The chapter concludes by discussing future directions in the study of insect behavioral responses to parasites.

Studies generally have neglected parasite-centric views in explorations of whether the oft-seen patterns of parasite aggregation are adaptive. Using simulation models, we explored the effects of aggregation on coinfection with hetero- or conspecific parasite species characterised by different mean abundances. Increasing aggregation increased the probability of conspecific co-occurrence for parasites with low mean abundances, and increased median numbers of conspecifics for all species. In comparison, increasing aggregation generally decreased the probability, intensity and diversity of heterospecific co-occurrence, irrespective of mean abundance. Researchers should weigh the respective costs and benefits of increasing co-occurrence with conspecifics and decreasing coinfection with heterospecifics in explaining aggregation.

Parasite species often show differential fitness on different host species. We developed an equation-based model to explore conditions favouring host species exploitation and discrimination. In our model, diploid infective stages randomly encountered hosts of two species; the parasite's relative fitness in exploiting each host species, and its ability to discriminate between them, was determined by the parasite's genotype at two independent diallelic loci. Relative host species frequency determined allele frequencies at the exploitation locus, whereas differential fitness and combined host density determined frequency of discrimination alleles. The model predicts instances where populations contain mixes of discriminatory and non-discriminatory infective stages. Also, non-discriminatory parasites should evolve when differential fitness is low to moderate and when combined host densities are low, but not so low as to cause parasite extinction. A corollary is that parasite discrimination (and host-specificity) increases with higher combined host densities. Instances in nature where parasites fail to discriminate when differential fitness is extreme could be explained by one host species evolving resistance, following from earlier selection for parasite non-discrimination. Similar results overall were obtained for haploid extensions of the model. Our model emulates multi-host associations and has implications for understanding broadening of host species ranges by parasites.This article is part of the themed issue 'Opening the black box: re-examining the ecology and evolution of parasite transmission'.

The patterns and mechanisms by which biological diversity is associated with parasite infection risk are important to study because of their potential implications for wildlife population's conservation and management. Almost all research in this area has focused on host species diversity and has neglected parasite diversity, despite evidence that parasites are important drivers of community structure and ecosystem processes. Here, we assessed whether presence or abundance of each of nine helminth species parasitizing lesser snow geese (Chen caerulescens) was associated with indices of parasite diversity (i.e. species richness and Shannon's Diversity Index). We found repeated instances of focal parasite presence and abundance having significant positive co-variation with diversity measures of other parasites. These results occurred both within individual samples and for combinations of all samples. Whereas host condition and parasite facilitation could be drivers of the patterns we observed, other host- or parasite-level effects, such as age or sex class of host or taxon of parasite, were discounted as explanatory variables. Our findings of recurring and positive associations between focal parasite abundance and diversity underscore the importance of moving beyond pairwise species interactions and contexts, and of including the oft-neglected parasite species diversity in infection-diversity studies.