Abundance data applied to a novel model invertebrate host shed new light on parasite community assembly in nature

Abstract

Understanding how environmental drivers influence the assembly of parasite communities, in addition to how parasites may interact at an infracommunity level, are fundamental requirements for the study of parasite ecology. Knowledge of how parasite communities are assembled will help to predict the risk of parasitism for hosts, and model how parasite communities may change under variable conditions. However, studies frequently rely on presence–absence data and examine multiple host species or sites, metrics which may be too coarse to characterise nuanced within‐host patterns. We utilised a novel host system, the freshwater mussel Anodonta anatina, to investigate the drivers of community structure and explore parasite interactions. In addition, we aimed to highlight consistencies and inconsistencies between PA and abundance data. Our analysis incorporated 14 parasite taxa and 720 replicate infracommunities. Using Redundancy Analysis, a joint species distribution model and a Markov random field approach, we modelled the impact of both host‐level and environment‐level characteristics on parasite structure, as well as parasite–parasite correlations after accounting for all other factors. This approach was repeated for both the presence and abundance of all parasites. We demonstrated that the regional species pool, individual host characteristics (mussel length and gravidity) and predicted parasite–parasite interactions are all important but to varying degrees across parasite species, suggesting that applying generalities to parasite community construction is too simplistic. Furthermore, we showed that PA data fail to capture important density‐dependent effects of parasite load for parasites with high abundance, and in general performs poorly for high‐intensity parasites. Host and parasite traits, as well as broader environmental factors, all contribute to parasite community structure, emphasising that an integrated approach is required to study community assembly. However, care must be taken with the data used to infer patterns, as presence‐absence data may lead to incorrect ecological inference.

Population‐level effects of parasitism on a freshwater ecosystem engineer, the unionid mussel Anodonta anatina

“…Jokela et al., 1993; Walker, 2017), particularly for the virulent R. campanula (Müller et al., 2015; Taskinen et al., 1994), but these studies still record native mussels being able to reproduce at low infection intensities. We have also previously recorded gravid mussels at low infection intensities of R. campanula (Brian & Aldridge, 2021), suggesting that understanding the degree of infection is as important as understanding its presence (Brian & Aldridge, 2020). Nevertheless, our results highlight that even intermediate infection intensities are correlated with mussel castration, showing the need to understand the presence and distribution of this highly virulent parasite across individuals and populations.…”

“…The non‐endangered unionid duck mussel Anodonta anatina (Linnaeus 1758) was chosen as our study species as it is common throughout Europe (Lopes‐Lima et al., 2017), and is infected with a broad range of parasites (Brian & Aldridge, 2019, 2021). We collected 60 mussels from each of two sites that are hydrologically connected but separated by approximately 20 km: the River Great Ouse at Brandon Creek (52.5002°N, 0.3650°E; henceforth BC) and the Old West River at Stretham, a tributary of the Great Ouse (52.3343°N, 0.2243°E; henceforth OW).…”

Don't move a mussel? Parasite and disease risk in conservation action

“…(b) Possible outcomes of translocation with respect to pathogen spread. The first two columns specify whether the source and recipient populations respectively have a single-host pathogen (SHP; i.e., a pathogen that does not require another host in the life cycle), a multihost pathogen (MHP) or no pathogens (NP) prior to translocation multiple macro-and microparasites simultaneously (Brian & Aldridge, 2021b;Richard et al, 2020), leading to a complex set of possible interactions. Consider again a median translocation size of 50 from a mussel population that now has two pathogens, both at a conservative 5% prevalence.…”

“…Different pathogens are found in different populations (e.g., Chittick et al, 2001); translocations should ensure they are not spreading pathogens to new locations, which requires understanding pathogen geography and diversity. Withinpopulation variation is also important: differences in filtering behaviour or sizes of individuals can influence parasite communities (Brian & Aldridge, 2021b). Assessing these factors may be difficult for endangered species, but recently developed nondestructive methods may help (e.g., Brian & Aldridge, 2021a).…”

“…This important determinant of risk has three key facets: how the pathogen responds to different host densities, how biotic and abiotic aspects of the habitat influence pathogen spread, and how pathogen exposure varies temporally (Brian & Aldridge, 2021b). This is particularly important when mussels cannot be screened for pathogens extensively: if we know how a pathogen spreads, or what times of year are important in its life-history, we can better predict the risk of it successfully establishing somewhere new, and how risk varies among scenarios.…”