Biogeography of parasitism in freshwater fish: spatial patterns in hot spots of infection

Abstract

Contrary to species occurrence, little is known about the determinants of spatial patterns of intraspecific variation in abundance, particularly for parasitic organisms. In this study, we provide a multi‐faceted overview of spatial patterns in parasite abundance and examine several potential underlying processes. We first tested for a latitudinal gradient in local abundance of the regionally most common parasite species and whether these species achieve higher abundances at the same localities (shared hot spots of infection). Secondly, we tested whether intraspecific similarity in local abundance between sites follows a spatial distance decay pattern or is better explained by variation in extrinsic biotic and abiotic factors between localities related to local parasite transmission success. We examined the infection landscape of a model fish host system (common and upland bullies, genus Gobiomorphus: Eleotridae) across its entire distributional range. We applied general linear models to test the effect of latitude on each species local abundance independently, including the abundance of each co‐infecting species as another predictor. We computed multiple regressions on distance matrices among localities based on abundance of each of the four most common trematode species, as well as for geographic distance, biotic and abiotic distinctness of the localities. Our results showed that the most widely distributed parasites of bullies also achieve the highest mean local abundances, following the abundance – occupancy relationship. Variation in local abundance of any focal parasite species was independent of latitude, the abundance of co‐occurring species and spatial distance or disparity in biotic attributes between localities. For only one parasite species, similarity of abundance between sites covaried with the extent of abiotic differences between sites. The lack of association between hot spots of infection for co‐occurring species reinforces the geographic mosaic scenario in which hosts and parasites coevolve by suggesting non‐deterministic, species‐specific variation in parasite abundance across space.

Spatial covariation of local abundance among different parasite species: the effect of shared hosts

“…It is probably safe to say that densities of S. anguillae and T. opisthorchis generally covary positively across localities, at both the metacercarial and adult stages. This clashes with the results reported for these two species on a much larger spatial scale, with the two species achieving their highest metacercarial abundances in completely different places across New Zealand (Blasco-Costa et al 2015). Hotspots of infection for S. anguillae were found in the northern part of the North Island and in south-central South Island, whereas those for T. opisthorchis occurred toward the southern tip of the North Island and the west coast of the South Island.…”

“…Various pairs of species from this set of five trematodes share either one, two, or all three hosts at different life cycle stages. Previously, spatial covariation in abundance has been investigated by Blasco-Costa et al (2015) in four of these five species; it was found that even pairs of species with identical life cycles and sharing all their hosts had completely independent patterns of abundance hotspots throughout their range. However, this earlier study focused on abundance of a single life stage, used a host-centric measure of abundance, and was performed on a very large scale (all of New Zealand) involving a broad range of environmental conditions (Blasco-Costa et al 2015).…”

“…Previously, spatial covariation in abundance has been investigated by Blasco-Costa et al (2015) in four of these five species; it was found that even pairs of species with identical life cycles and sharing all their hosts had completely independent patterns of abundance hotspots throughout their range. However, this earlier study focused on abundance of a single life stage, used a host-centric measure of abundance, and was performed on a very large scale (all of New Zealand) involving a broad range of environmental conditions (Blasco-Costa et al 2015). Here, using a completely different data set, we focus on a much smaller scale where conditions are likely less heterogeneous, we investigate abundance of two life stages (metacercariae and adults) and we use a measure of abundance that captures the parasite population size rather than the severity of infections incurred by hosts.…”

Parasite–Parasite Interactions in the Wild: How To Detect Them?

“…Studies should include further reporting and deciphering of interaction mechanisms and consequences (e.g., [62]) in model study systems as well as the development of a predictive theory of multi-parasite epidemics, integrating the different levels of organization and the various highlighted mechanisms [63,64]. Biogeographical studies will help to discern potential interactions between parasite species manifesting at large spatial scales by identifying the underlying processes (geographic, abiotic, biotic) that are responsible for the spatial distribution of co-occurring parasite species, and also explain their similar or dissimilar hot-spots of infection [65]. New tools such as next-generation sequencing (NGS) and network analyses will help to better interpret the complex epidemiological patterns observed at each organizational level.…”

Community structure of metazoan parasites from Pimelodus blochii in two rivers of the Western Brazilian Amazon: same seasonal traits, but different anthropogenic impacts

“…organic and inorganic conditions) and/or to the host (e.g. feeding, behaviour, physiology, sex) (Blasco-Costa et al 2014;Oliveira et al 2017). Furthermore, the abundance of parasites with complex life cycles may be strongly dependent of the population density of intermediate and definitive hosts, superposing time and space (Blasco-Costa et al 2014).…”