No strong associations between temperature and the host-parasite interaction in wild stickleback

As climate change progresses, thermal stress is expected to alter the way that host organisms respond to infections by pathogens and parasites, with consequences for the fitness and hence population processes of both host and parasite. We used a correlational natural experiment to examine how temperature differences shape the impact of the cestode parasite Schistocephalus solidus on its host, the three-spined stickleback (Gasterosteus aculeatus). Previous laboratory work has found that high temperatures benefit S. solidus while being detrimental to the stickleback. Our study sought to emulate this design in the wild, repeatedly sampling naturally infected and uninfected fish at matched warmer and cooler locations in the Baltic Sea. In our wild study, we found little evidence that temperature was associated with the host-parasite interaction. While infection reduced host condition and reproductive status overall, these effects did not vary with temperature. Host fitness indicators correlated to some extent with temperature, with cooler capture sites associated with larger size but warmer sites with improved reproductive potential. Parasite fitness (prevalence or size) was not correlated with temperature at the capture site. These mismatches between laboratory and field outcomes illustrate how findings from well-controlled laboratory experiments may not fully reflect processes in more variable natural settings. Nonetheless, our findings indicate that temperature can influence host fitness regardless of infection, with potential consequences for both host demography and parasite transmission dynamics in this complex system.Peer reviewe

Segregation in space and time explains the coexistence of two sympatric sub-Antarctic petrels

Biological communities are shaped by competition between and within species. Competition is often reduced by inter- and intraspecific specialization on resources, such as differencet foraging areas or time, allowing similar species to coexist and potentially contributing to reproductive isolation. Here, we examine the simultaneous role of temporal and spatial foraging segregation within and between two sympatric sister species of seabirds, Northern Macronectes halli and Southern Macronectes giganteus Giant Petrels. These species show marked sexual size dimorphism and allochrony (with earlier breeding by Northern Giant Petrels) but this is the first study to test for differences in foraging behaviours and areas across the entire breeding season both between the two species and between the sexes. We tracked males and females of both species in all breeding stages at Bird Island, South Georgia, to test how foraging distribution, behaviour and habitat use vary between and within species in biological time (incubation, brood-guard or post-brood stages) and in absolute time (calendar date). Within each breeding stage, both species took trips of comparable duration to similar areas, but due to breeding allochrony they segregated temporally. Northern Giant Petrels had a somewhat smaller foraging range than Southern Giant Petrels, reflecting their greater exploitation of local carrion and probably contributing to their recent higher population growth. Within species, segregation was spatial, with females generally taking longer, more pelagic trips than males, although both sexes of both species showed unexpectedly plastic foraging behaviour. There was little evidence of interspecific differences in habitat use. Thus, in giant petrels, temporal segregation reduces interspecific competition and sexual segregation reduces intraspecific competition. These results demonstrate how both specialization and dynamic changes in foraging strategies at different scales underpin resource division within a community

Helminth burden and ecological factors associated with alterations in wild host gastrointestinal microbiota

Infection by gastrointestinal helminths of humans, livestock and wild animals is common, but the impact of such endoparasites on wild hosts and their gut microbiota represents an important overlooked component of population dynamics. Wild host gut microbiota and endoparasites occupy the same physical niche spaces with both affecting host nutrition and health. However, associations between the two are poorly understood. Here we used the commonly parasitized European shag (Phalacrocorax aristotelis) as a model wild host. Forty live adults from the same colony were sampled. Endoscopy was employed to quantify helminth infection in situ. Microbiota from the significantly distinct proventriculus (site of infection), cloacal and faecal gastrointestinal tract microbiomes were characterised using 16S rRNA gene-targeted high-throughput sequencing. We found increasingly strong associations between helminth infection and microbiota composition progressing away from the site of infection, observing a pronounced dysbiosis in microbiota when samples were partitioned into high- and low-burden groups. We posit this dysbiosis is predominately explained by helminths inducing an anti-inflammatory environment in the proventriculus, diverting host immune responses away from themselves. This study, within live wild animals, provides a vital foundation to better understand the mechanisms that underpin the three-way relationship between helminths, microbiota and hosts

Impacts of Parasites in Early Life: Contrasting Effects on Juvenile Growth for Different Family Members

Parasitism experienced early in ontogeny can have a major impact on host growth, development and future fitness, but whether siblings are affected equally by parasitism is poorly understood. In birds, hatching asynchrony induced by hormonal or behavioural mechanisms largely under parental control might predispose young to respond to infection in different ways. Here we show that parasites can have different consequences for offspring depending on their position in the family hierarchy. We experimentally treated European Shag (Phalacrocorax aristoteli) nestlings with the broad-spectrum anti-parasite drug ivermectin and compared their growth rates with nestlings from control broods. Average growth rates measured over the period of linear growth (10 days to 30 days of age) and survival did not differ for nestlings from treated and control broods. However, when considering individuals within broods, parasite treatment reversed the patterns of growth for individual family members: last-hatched nestlings grew significantly slower than their siblings in control nests but grew faster in treated nests. This was at the expense of their earlier-hatched brood-mates, who showed an overall growth rate reduction relative to last-hatched nestlings in treated nests. These results highlight the importance of exploring individual variation in the costs of infection and suggest that parasites could be a key factor modulating within-family dynamics, sibling competition and developmental trajectories from an early age

Asymmetry in pay-off predicts how familiar individuals respond to one another

Familiarity influences individual decision-making in many vertebrate species. Here, we propose that familiarity modulates behaviour to different extents depending on the social context of the interaction. Specifically, the more that one player stands to gain relative to the other, the less important familiarity will be in influencing their responses to one another. We test this prediction using pairs of male guppies (Poecilia reticulata) in three competitive scenarios of increasing asymmetry in outcome to the two players: schooling under potential threat (similar outcomes), competing for a defensible food source (some asymmetry) and competing for a receptive female (strongly asymmetrical outcomes). Males show a graded response as asymmetry increases, with familiarity producing marked behavioural differences under potential threat, minor changes when competing for food, but none at all in competition for mating opportunities. This suggests that mutualistic benefits can arise as a by-product of selfish behaviour, supporting the role of pseudo-reciprocity in the evolution of cooperation

Data from: Asymmetry in pay-off predicts how familiar individuals respond to one another

Familiarity influences individual decision-making in many vertebrate species. Here, we propose that familiarity modulates behaviour to different extents depending on the social context of the interaction. Specifically, the more that one player stands to gain relative to the other, the less important familiarity will be in influencing their responses to one another. We test this prediction using pairs of male guppies (Poecilia reticulata) in three competitive scenarios of increasing asymmetry in outcome to the two players: schooling under potential threat (similar outcomes), competing for a defensible food source (some asymmetry) and competing for a receptive female (strongly asymmetrical outcomes). Males show a graded response as asymmetry increases, with familiarity producing marked behavioural differences under potential threat, minor changes when competing for food, but none at all in competition for mating opportunities. This suggests that mutualistic benefits can arise as a by-product of selfish behaviour, supporting the role of pseudo-reciprocity in the evolution of cooperation

Context-dependent male familiarity data

This file contains the data for all three experiments in the paper: behaviour under predation threat, competing for food and competing for mates. Each experiment is in a separate tab of an Excel file. Column heading should be clear with reference to the manuscript. All data was collected experimentally using a lab-bred population

Indirect effects of parasitism: costs of infection to other individuals can be greater than direct costs borne by the host

Parasitic infection has a direct physiological cost to hosts but may also alter how hosts interact with other individuals in their environment. Such indirect effects may alter both host fitness and the fitness of other individuals in the host's social network, yet the relative impact of direct and indirect effects of infection are rarely quantified. During reproduction, a host's social environment includes family members who may be in conflict over resource allocation. In such situations, infection may alter how resources are allocated, thereby redistributing the costs of parasitism between individuals. Here, we experimentally reduce parasite burdens of parent and/or nestling European shags (Phalacrocorax aristotelis) infected with Contracaecum nematodes in a factorial design, then simultaneously measure the impact of an individual's infection on all family members. We found no direct effect of infection on parent or offspring traits but indirect effects were detected in all group members, with both immediate effects (mass change and survival) and longer-term effects (timing of parents' subsequent breeding). Our results show that parasite infection can have a major impact on individuals other than the host, suggesting that the effect of parasites on population processes may be greater than previously thought

Chick Growth Rates

Growth rates of all individual chicks in the experiment with all explanatory variables tested, including treatment, productivity, rank, sex, nest etc

Chick data (2011)

Data from the year of anti-parasite treatment for each individual chick in the experiment: growth rate and survival, along with anti-parasite treatment group and unmanipulated traits such as hatch date, sex and rank