A reconstruction of parasite burden reveals one century of climate-associated parasite decline

Abstract

Long-term data allow ecologists to assess trajectories of population abundance. Without this context, it is impossible to know whether a taxon is thriving or declining to extinction. For parasites of wildlife, there are few long-term data—a gap that creates an impediment to managing parasite biodiversity and infectious threats in a changing world. We produced a century-scale time series of metazoan parasite abundance and used it to test whether parasitism is changing in Puget Sound, United States, and, if so, why. We performed parasitological dissection of fluid-preserved specimens held in natural history collections for eight fish species collected between 1880 and 2019. We found that parasite taxa using three or more obligately required host species—a group that comprised 52% of the parasite taxa we detected—declined in abundance at a rate of 10.9% per decade, whereas no change in abundance was detected for parasites using one or two obligately required host species. We tested several potential mechanisms for the decline in 3+-host parasites and found that parasite abundance was negatively correlated with sea surface temperature, diminishing at a rate of 38% for every 1 °C increase. Although the temperature effect was strong, it did not explain all variability in parasite burden, suggesting that other factors may also have contributed to the long-term declines we observed. These data document one century of climate-associated parasite decline in Puget Sound—a massive loss of biodiversity, undetected until now.

Major drivers of biodiversity loss and their impacts on helminth parasite populations and communities

“…Interestingly, using an innovative approach involving the examination of preserved hosts held in natural history collections, Wood et al (2023) revealed a decline in parasite abundance in fishes from Puget Sound, Washington, United States, over a 100-year period. Declines in numerous species were correlated with an increase in temperature over the same period.…”

Is the world wormier than it used to be? We'll never know without natural history collections

“…Parasite taxonomic identifications should be as highly resolved as possible and—because most of these specimens have been fixed in formalin—we often cannot rely on sequencing to achieve this. In the ‘parasites of the past’ project, we stained, mounted and cleared parasites to better visualize diagnostic features and we partnered with a parasite taxonomist to achieve high taxonomic resolution through strictly morphological identification (Welicky et al, 2021; Wood et al, in review). Derivative specimens (e.g.…”

Extreme heat reduces host and parasite performance in a butterfly–parasite interaction

“…Past work shows that insect and parasite traits relevant to infection, such as immune defence, development rate and survival, can respond to temperature in different ways [4,14,[18][19][20][21][22]. In some cases, heat stress experienced by hosts could exacerbate susceptibility to and impacts of infection; in other cases, hosts might benefit from reduced parasite replication at very high temperatures [23][24][25][26]. Insect innate immunity includes cellular defences (executed by haemocytes responsible for encapsulation, phagocytosis and secretion of molecules involved in lysis and melanization [27,28]) and humoral immunity, which relies on the circulation of immune peptides and phenoloxidases (PO), enzymes vital for melanin production [28,29].…”