Bats are known to host zoonotic viruses, including henipaviruses that cause high fatality rates in humans (Nipah virus and Hendra virus). However, the determinants of zoonotic spillover are generally unknown, as the ecological and demographic drivers of viral circulation in bats are difficult to ascertain without longitudinal data. Here we analyse serological data collected from African straw‐coloured fruit bats ( Eidolon helvum ) in Ghana over the course of 2 years and across four sites, comprising three wild roosts and one captive colony. We focus on antibody affinity to five henipavirus antigens: Ghanaian bat henipavirus (GhV), Nipah virus (NiV), Hendra virus (HeV), Mojiang virus (MojV) and Cedar virus (CedV). In the wild roosts, we detected seasonal variations in henipavirus antibody binding, possibly associated with bat life‐history cycles and migration patterns. In the captive colony, we identified increases in antibody affinity levels among pregnant bats, suggesting possible shifts in the immune system during pregnancy. These bats then pass maternal antibodies to their pups, which wane before antibody affinity levels rise later in life following initial infections and/or reactivation of latent infections. These results improve our understanding of the links between bat ecology and viral circulation, including for GhV, a locally‐circulating African henipavirus.

Climate change may exacerbate the impact of invasive parasites from warmer climates through pre‐existing temperature adaptations. We investigated temperature impacts on two closely related marine parasitic copepod species that share the blue mussel (Mytilus edulis) as host: Mytilicola orientalis has invaded the system from a warmer climate 90 years to adapt. In laboratory experiments with temperatures 10–26°C, covering current and future temperatures as well as heat waves, the development of both life cycle stages of both species accelerated with increasing temperature. In the parasitic stages, the growth of the established invader increased evenly from 10°C to 22°C, whereas the recent invader barely grew at all at 10°C and grew faster already at 18°C. In contrast, temperature had little effect on the transition success between life cycle stages. However, the highest temperature (26°C) limited the egg development success of the established invader and the host entry success of both species, whereas the infection success of the established invader increased at 18°C and 22°C. In general, our experiments indicate that the main effect of temperature on both species is through development speed and not life cycle stage transition success. Based on regional long‐term temperature data and predictions, the numbers of completed life cycles per year will increase for both parasites. The established invader seems better adapted for low current temperatures (around 10°C), whereas the more recent invader barely develops at these temperatures but can cope in high temperatures (around 26°C). Hence, pre‐existing temperature adaptations of the recent invader may allow the species to better cope with heat waves.

The straw-coloured fruit bat (Eidolon helvum) is widespread in sub-Saharan Africa and is widely hunted for bushmeat. It is known to harbour a range of paramyxoviruses, including rubuloviruses and henipaviruses, but the zoonotic potential of these is unknown. We previously found a diversity of paramyxoviruses within a small, captive colony of E. helvum after it had been closed to contact with other bats for 5 years. In this study, we used under-roost urine collection to further investigate the paramyxovirus diversity and ecology in this colony, which had been closed to the outside for 10 years at the time of sampling. By sampling urine weekly throughout an entire year, we investigated possible seasonal patterns of shedding of virus or viral RNA. Using a generic paramyxovirus L-gene PCR, we detected eight distinct paramyxovirus RNA sequences. Six distinct sequences were detected using a Henipavirus-specific PCR that targeted a different region of the L-gene. Sequence detection had a bi-annual pattern, with the greatest peak in July, although different RNA sequences appeared to have different shedding patterns. No significant associations were detected between sequence detection and birthing season, environmental temperature or humidity, and no signs of illness were detected in any of the bats in the colony during the period of sample collection.

An increase in temperature due to climate change may affect the geographic ranges of invasive parasites and alter their impact on native hosts. Our goal was to determine if the effects of infection by two species of invasive endoparasitic copepods on native blue mussel hosts (Mytilus edulis) change with increasing temperatures. We investigated this with a laboratory experiment using temperatures that represent annual mean and mean summer water temperatures of past observations and future predictions for the study area, the European Wadden Sea (10–26 °C). Over a period of 8–20 weeks, infection with Mytilicola intestinalis lowered mussel condition and infection with Mytilicola orientalis decreased mussel shell growth. High temperatures decreased mussel growth and condition in general, but only at low temperatures (10–14 °C) the parasite-induced loss of condition was evident compared to uninfected mussels. Mussel mortality and reproductive activity were not affected by parasite infection, although both were impacted by temperature: the highest temperature (26 °C) increased mussel mortality, and gamete ripening only occurred at lower temperatures (10–18 °C). Taken together, these results suggest that both infection and high temperatures have independent negative effects. However, an increase in temperature does not worsen the effect of infection on individual mussel hosts, and neither does infection decrease host tolerance for long-term exposure to high temperatures. These findings add to our understanding of the interplay between increasing temperature and the interaction between invasive parasites and native hosts, and help predicting host and parasite dynamics in systems affected by species invasions and climate change.

Biological invasions have become a topic of concern due to their increasing occurrence and ecological and economic consequences. This chapter examines the stages, mechanisms and effects of biological invasions from a parasitological point of view, focusing on parasitic protists, microsporidians, fungi, oomycetes, helminths and arthropods. We present hypotheses and mechanisms underlying biological invasions of parasites and hosts, such as the enemy release hypothesis, spillover, spillback, disease acquisition and invasional meltdown. We illustrate these mechanisms and the effects of biological invasions on parasite–host interactions and native ecosystems with examples from aquatic environments. In terms of effects, we discuss direct competitive and consumer–resource interactions and indirect density- and trait-mediated effects by invasive parasites, ranging from the individual to the community and ecosystem level. We conclude the chapter with some remarks on management and mitigation aspects.

The increase in heatwave frequency and severity due to climate change can threaten intertidal organisms that already experience large temperature fluctuations. Habitat-forming species can mitigate temperature extremes by creating protective microhabitats. While Pacific oysters (Magallana gigas) are known to provide thermal refuge on tropical rocky shores, their influence on temperate intertidal mudflat systems has not been investigated before. We examined the thermal environment within oyster reefs in the European Wadden Sea by recording temperatures in two microhabitat types (crevices between oysters and oyster-formed tidal pools) and comparing them to adjacent mudflats. Temperatures were measured over one year using biomimetic loggers that replicate the thermal properties of the blue mussel (Mytilus edulis), a key co-inhabitant of oyster reefs. Crevices between oysters provided cooler microhabitats particularly in summer when mean temperatures were 0.2-0.4 ± 0.02-0.05 °C lower and daily minimum temperatures were 1.0 ± 0.43 °C lower than on surrounding mudflats, while cumulative heat exposure was only moderately lower and day maximum temperatures were lower than mudflat values only at one of two sites. In contrast, tidal pools had higher day maximum temperatures than the surrounding mudflat across the year. These results demonstrate that oysters can provide localized thermal buffering in temperate mudflat systems, especially through reduced mean temperatures in crevices. However, the effect is less pronounced than in tropical rocky environments. Our findings highlight the context-dependent role of ecosystem engineers in modifying thermal landscapes, with potential implications for species persistence under climate change.