Search for: All records

The abundances of free-living species have changed dramatically in recent decades, but little is known about change in the abundance of parasitic species. We investigated whether populations of several parasites have shifted over time in two shore crab hosts, Hemigrapsus oregonensis and Hemigrapsus nudus, by comparing the prevalence and abundance of three parasite taxa in a historical dataset (1969–1970) to contemporary parasite abundance (2018–2020) for hosts collected from 11 intertidal sites located from Oregon, USA, to British Columbia, Canada. Our data suggest that the abundance of the parasitic isopod Portunion conformis has varied around a stable mean for the past 50 years. No change over time was observed for larval acanthocephalans. However, larval microphallid trematodes increased in prevalence over time among H. oregonensis hosts, from a mean of 8.4–61.8% between the historical and contemporary time points. The substantial increase in the prevalence of larval microphallid trematodes could be owing to increased abundances of their bird final hosts, increased production of parasite infective stages by snail intermediate hosts or both. Our study highlights the variability among parasite species in their temporal trajectories of change. 

Human‐altered shorelines make up approximately 14% of the coastline in the United States, with consequences for marsh ecosystems ranging from altered physical and biological variables, to direct loss of intertidal marsh habitat, to diminished land–sea connectivity. Trophically transmitted parasites that require connectivity between upland host species and marsh host species to complete their complex lifecycles could be particularly sensitive to the effects of shoreline alterations. They can additionally respond to gradients in natural physical and biological factors, including the host communities, that are often sharp at the land–sea ecotone. Across 27 salt marshes over 45 km, we evaluated the effects of environmental variables and three types of land use (undeveloped; single‐house adjacent to the marsh with small‐scale shoreline armoring; and single‐house adjacent to the marsh without shoreline armoring), on infection prevalence and intensity of the trematodeMicrophallus basodactylophallusin its second intermediate crab host,Minuca pugnax. The first intermediate hosts ofM. basodactylophallusare Hydrobiid snail species that are obligate marsh residents, while the definitive hosts are terrestrial rodents and raccoons. Thus, trematode transmission must depend on cross‐boundary movement by the definitive hosts. We found that although there was a trend of lower infection prevalence at undeveloped forested sites, there was no significant effect of adjacent land development on infection prevalence or intensity. Instead host, biotic and abiotic factors were correlated with infection; namely, largerM. pugnaxhad higher prevalence and intensity ofM. basodactylophallus, and higher soil moisture and lower density of the ribbed mussel (Geukensia demissa) were associated with increasedM. basodactylophallusprevalence. The small, indirect influence of upland development suggests that movement of definite hosts across the ecotone may be largely unaffected. Further, the robust trematode levels signify the ecosystem and the species interactions, upon which its complex lifecycle depends, are largely intact.

 

We examined body size scaling relationships for two developmental life stages of parasitic helminths (egg and adult) separately in relationship to latitude (i.e. Bergmann's rule), temperature and temperature seasonality. Given that helminth eggs experience environmental conditions more directly, whereas adults live inside infected host individuals, we predict stronger environmentally driven gradients of body size for eggs than for adults.

Global.

Present day.

Parasitic helminths.

We compiled egg size and adult body size data (both minimum and maximum) for 265 parasitic helminth species from the literature, along with species latitudinal distribution information using an extensive global helminth occurrence database. We then examined how the average helminth egg and adult body size of all helminth species present (minimum and maximum separately) scaled with latitude, temperature and temperature variability, using generalized linear models.

Both the egg size and the adult body size of helminths tended to decrease towards higher latitudes, although we found the opposite body size scaling pattern for their host species. Helminth sizes were also positively correlated with temperature and negatively, but more weakly, with temperature seasonality.

Instead of following the body size patterns of their hosts, helminth parasites are more similar to other ectotherms in that they follow the converse Bergmann's rule. This pattern did not differ between helminth developmental stages, suggesting that mean annual temperature and seasonality are unlikely to be related mechanistically to body size variation in this case.