Sweeny, Amy; Albery, Gregory; Venkatesan, Saudamini; Fenton, Andy; Pedersen, Amy
In natural populations, it is common for individuals to be infected with parasites. However, some individuals become much more infected than others. This variation is well-documented across a range of hosts and parasites, but it is not always clear what factors determine which individuals in a population become most infected. Importantly, because studies to address this can be difficult and expensive to conduct, we often only have data for short periods of time or in a single location, and therefore don’t know if drivers of infection are consistent in time and space. Answering these questions is important for determining when and where parasites are likely to spread and cause negative impacts on host populations.
A number of environmental factors such as season or climate and host characteristics such as sex, age, and condition are expected to influence disease ecology in wildlife. However, the relationships between these factors and parasite infection are not always consistent, and can actually change over time and between different populations. Here we conducted a long-term, multi-site study of wild wood mouse populations to investigate environmental and host factors which determine the burden of infection with a common gut nematode.
Importantly, because we monitored wood mice and their parasites over 6 years and 5 different woodland populations, we were also able to see if the factors determining infection varied over space and time. Using our extensive dataset, we found that season as well as host body condition and sex of the wood mice were the most important in driving parasitism; however the relationship between each factor and parasite burden varied in magnitude and direction over the years. In addition, we used smaller subsets of the full dataset to investigate what single years or sites showed with regard to factors driving nematode infection and found that effect strength and detection varied across these smaller datasets. These results highlight how dynamic relationships between the environment, hosts, and parasites can be. Furthermore, they show the value of long-term monitoring over spatiotemporal scales for understanding epidemiology in natural populations.