Fluid preservation causes minimal reduction of parasite detectability in fish specimens: A new approach for reconstructing parasite communities of the past?

Abstract

Long‐term datasets are needed to evaluate temporal patterns in wildlife disease burdens, but historical data on parasite abundance are extremely rare. For more than a century, natural history collections have been accumulating fluid‐preserved specimens, which should contain the parasites infecting the host at the time of its preservation. However, before this unique data source can be exploited, we must identify the artifacts that are introduced by the preservation process. Here, we experimentally address whether the preservation process alters the degree to which metazoan parasites are detectable in fluid‐preserved fish specimens when using visual parasite detection techniques. We randomly assigned fish of three species (Gadus chalcogrammus, Thaleichthys pacificus, and Parophrys vetulus) to two treatments. In the first treatment, fish were preserved according to the standard procedures used in ichthyological collections. Immediately after the fluid‐preservation process was complete, we performed parasitological dissection on those specimens. The second treatment was a control, in which fish were dissected without being subjected to the fluid‐preservation process. We compared parasite abundance between the two treatments. Across 298 fish individuals and 59 host–parasite pairs, we found few differences between treatments, with 24 of 27 host–parasite pairs equally abundant between the two treatments. Of these, one pair was significantly more abundant in the preservation treatment than in the control group, and two pairs were significantly less abundant in the preservation treatment than in the control group. Our data suggest that the fluid‐preservation process does not have a substantial effect on the detectability of metazoan parasites. This study addresses only the effects of the fixation and preservation process; long‐term experiments are needed to address whether parasite detectability remains unchanged in the months, years, and decades of storage following preservation. If so, ecologists will be able to reconstruct novel, long‐term datasets on parasite diversity and abundance over the past century or more using fluid‐preserved specimens from natural history collections.

Parasites of the past: 90 years of change in parasitism for English sole

“…For example, Black (1983) used museum specimens to demonstrate that lake trout (Salvelinus namaycush) in the North American Great Lakes lost a parasitic nematode (Cystidicola stigmatura) when the trout population crashed in 1925. Although this approach has been validated (Fiorenza et al 2020b), it has not been used to reconstruct a trajectory of change for a suite of parasite species -a missed opportunity to examine whether ecosystems are indeed facing a "rising tide" of marine disease.…”

“…Parasitological dissection of natural history specimens could fill this research gap (Harmon et al 2019). Such holdings contain millions of preserved fish collected over the past few centuries, and parasites that infected these fish in life are often also preserved with morphological integrity within their hosts (Fiorenza et al 2020b). For example, Black (1983) used museum specimens to demonstrate that lake trout (Salvelinus namaycush) in the North American Great Lakes lost a parasitic nematode (Cystidicola stigmatura) when the trout population crashed in 1925.…”

“…Although this approach has been validated (Fiorenza et al . 2020b), it has not been used to reconstruct a trajectory of change for a suite of parasite species – a missed opportunity to examine whether ecosystems are indeed facing a “rising tide” of marine disease.…”

Long-term change in the parasite burden of shore crabs ( Hemigrapsus oregonensis and Hemigrapsus nudus ) on the northwestern Pacific coast of North America

“…Few datasets are available to track change in parasite abundance across time [10,11,44], so historical datasets like the one documented here are extremely valuable for royalsocietypublishing.org/journal/rspb Proc. R. Soc.…”

Life history mediates the association between parasite abundance and geographic features

“…Estimates, errors, z scores and p values for all models are presented in Table S2 Model rank we used regression coefficients and standardized errors for the effect of island area and island isolation on the abundance of each parasite at >5% prevalence within each host from the individual parasite species GLMMs described above. We calculated a cumulative effect size across all host-parasite combinations using a fixed-effects model weighted by the inverse of the variance for each effect size in metafor (Fiorenza et al, 2020;Viechtbauer, 2010;Wood et al, 2018). Then, for each predictor, we ran meta-analytic fixed-effects general linear models using the moderator parasite taxonomic group (acanthocephalans, cestodes, copepods, monogeneans, nematodes and trematodes).…”