Understanding the determinants of parasite infection in different hosts is one of the main goals of disease ecology. Evaluating the relationship between parasite–host specificity and infection parameters within host communities and populations may contribute to this understanding. Here we propose two measures of specificity that encompasses phylogenetic and ecological relatedness among hosts and investigated how such metrics explain parasite infection prevalence and mean infection intensity (MII). We analysed the parasites associated with an anuran community in an area of Atlantic Forest and used the number of infected hosts and the net relatedness index to calculate the phylogenetic and ecological specificities of the parasites. These specificity measures were related to infection metrics (prevalence and MII) with generalized linear mixed models at community (all hosts) and population (infected host species) scales. Parasite prevalence was correlated with the number of infected hosts and, when considering only multi-host parasites, was positively related to parasite ecological specificity at community and population scales. Thus, parasite species have similar prevalences in ecologically closer hosts. No relationship was found for parasite MII. Incorporating ecological characteristics of hosts in parasite specificity analyses improves the detection of patterns of specificity across scales.

Predicting how elevated temperatures from climate change alter host–parasite interactions requires understandings of how warming affects host susceptibility and parasite virulence. Here, the effect of elevated water temperature and parasite exposure level was tested on parasite prevalence, abundance and burden, and on fish growth, using Pomphorhynchus laevis and its fish host Squalius cephalus. At 60 days post-exposure, prevalence was higher at the elevated temperature (22 °C) than ambient temperature (18 °C), with infections achieved at considerably lower levels of exposure. Whilst parasite number was significantly higher in infected fish at 22 °C, both mean parasite weight and parasite burden was significantly higher at 18 °C. There were, however, no significant relationships between fish growth rate and temperature, parasite exposure, and the infection parameters. Thus, whilst elevated temperature significantly influenced parasite infection rates, it also impacted parasite development rates, suggesting warming could have complex implications for parasite dynamics and host resistance.

Parasite ecologists are often interested in the repeatability of patterns in parasite communities in space and/or time, because of implications for the dynamics of host-parasite interactions. Field studies usually examine temporal and spatial variation in isolation or limit themselves to a small number of host populations. Here, we studied the macroparasite communities of 12 populations of three-spined stickleback, Gasterosteus aculeatus L., on North Uist, Scotland, separated by small geographical distances, during the breeding season in 2 consecutive years (2007 and 2008) to determine: (1) the extent of spatial variation in macroparasite communities, (2) whether this variation is consistent across years, and (3) whether habitat characteristics can explain differences in macroparasite community composition among populations. We found substantial variation in parasite communities among populations. Generally, measures of parasite community composition were higher in 2008 than in 2007, but this effect of year was consistent across populations, such that the relative differences in these measures among populations changed little between years. These data suggest that there is short-term stability in the spatial variation in macroparasite communities of North Uist sticklebacks. However, none of the 5 habitat characteristics measured explained spatial variation in any measure of parasite community composition.

Within the distribution of Ligula intestinalis, a tapeworm affecting freshwater fishes, there are genetically distinct and well-separated phylogenetic clusters. East Africa is represented by a single monophyletic clade which is understudied compared with Euro-Mediterranean clades. The present field investigation in the Lake Baringo and Naivasha catchments, Kenya, revealed that this L. intestinalis clade was highly host-specific, present in only 2 of 12 fishes examined; Barbus paludinosus in Naivasha and Barbus lineomaculatus in Baringo. In infected fish, cestodes comprised up to 20% of body weight. Only 1 parasite was recorded per fish, a contrast to infected fishes in Europe where mixed infections are commonplace. In B. lineomaculatus in Baringo, only fish of greater than 64 mm in length were parasitized. The highest parasite prevalence was recorded in fish of 70–77 mm in length, and reduced for lengths of 78–84 mm. Parasitized fish were significantly associated with a particular type of habitat, occurring most frequently in shallow littoral areas, and being absent from open water and rocky shore habitats. Uninfected fish were present in all habitats. This relationship between spatial occupancy and parasite prevalence is suggested to arise from behavioural alterations induced by the parasite that promotes completion of the parasite life cycle.

Gastrointestinal parasite infections are widespread among wild ungulates. Because many of these parasites infect multiple host species, inter-specific interactions among hosts potentially play an important role in parasite transmission dynamics in ungulate communities. In this study, the effects of inter-specific contact on parasitism rates in 11 sympatric African bovids was examined using habitat overlap among species as a measure of cross-species contact rates. Across individual hosts, strongyle nematode abundance increased with increasing numbers of bovid species occupying a habitat. Furthermore, comparative analyses show a positive association between strongyle prevalence and level of habitat overlap across taxa. These findings suggest that among sympatric bovids, contact between species contributes significantly to the transmission of generalist nematode parasites. For a more host-specific parasite group, coccidia, parasite abundance and individual probability of infection declined in hosts living in bovid rich habitats. This pattern may reflect enhanced inter-specific competition among parasites in these areas. Finally, similar to strongyle abundance, individual parasite richness also increased among hosts occupying habitats with higher numbers of bovid species. No association between habitat overlap and parasite richness was detected at higher taxonomic scales, however, which suggests that contact between host species may not contribute to parasite colonization of new host taxa.