The ghost of hosts past: impacts of host extinction on parasite specificity

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The incidence of zoonotic diseases is increasing worldwide, which makes identifying parasites likely to become zoonotic and hosts likely to harbour zoonotic parasites a critical concern. Prior work indicates that there is a higher risk of zoonotic spillover accruing from closely related hosts and from hosts that are infected with a high phylogenetic diversity of parasites. This suggests that host and parasite evolutionary history may be important drivers of spillover, but identifying whether host–parasite associations are more strongly structured by the host, parasite or both requires co-phylogenetic analyses that combine host–parasite association data with host and parasite phylogenies. Here, we use host–parasite datasets containing associations between helminth taxa and free-range mammals in combination with phylogenetic models to explore whether host, parasite, or both host and parasite evolutionary history influences host–parasite associations. We find that host phylogenetic history is most important for driving patterns of helminth-mammal association, indicating that zoonoses are most likely to come from a host's close relatives. More broadly, our results suggest that co-phylogenetic analyses across broad taxonomic scales can provide a novel perspective for surveying potential emerging infectious diseases. This article is part of the theme issue ‘Infectious disease macroecology: parasite diversity and dynamics across the globe’.

Section: Discussionmentioning

confidence: 99%

Identifying co-phylogenetic hotspots for zoonotic disease

Pfenning-Butterworth

Davies

Cressler

2021

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“…Two hosts may share a given parasite even if they do not currently co-occur, P(H i )P(H j ) = 0, as a legacy from past sympatry or geographic bridging by extinct hosts (see [69] this issue, among others). Nevertheless, for simplicity, we assume here that host i and j must have a non-zero probability of co-occurrence, P(H i )P(H j ) > 0, such that the probability that they share a parasite is given by P(D x , H i , H j ) ¼ Sh Dx ij P(H i )P(H j ): ð2:8Þ Importantly, P(H i )P(H j ) may vary depending on whether current or future host distributions are considered.…”

Section: (B) Step 2: Probabilistic Conceptualization For Parasite Sharing Interactionsmentioning

confidence: 99%

Forecasting parasite sharing under climate change

Morales‐Castilla

Pappalardo

Farrell

et al. 2021

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Species are shifting their distributions in response to climate change. This geographic reshuffling may result in novel co-occurrences among species, which could lead to unseen biotic interactions, including the exchange of parasites between previously isolated hosts. Identifying potential new host–parasite interactions would improve forecasting of disease emergence and inform proactive disease surveillance. However, accurate predictions of future cross-species disease transmission have been hampered by the lack of a generalized approach and data availability. Here, we propose a framework to predict novel host–parasite interactions based on a combination of niche modelling of future host distributions and parasite sharing models. Using the North American ungulates as a proof of concept, we show this approach has high cross-validation accuracy in over 85% of modelled parasites and find that more than 34% of the host–parasite associations forecasted by our models have already been recorded in the literature. We discuss potential sources of uncertainty and bias that may affect our results and similar forecasting approaches, and propose pathways to generate increasingly accurate predictions. Our results indicate that forecasting parasite sharing in response to shifts in host geographic distributions allow for the identification of regions and taxa most susceptible to emergent pathogens under climate change. This article is part of the theme issue ‘Infectious disease macroecology: parasite diversity and dynamics across the globe’.

“…This would also be consistent with the positive correlation with origination rates (tables 1 and 3). However, there is also support for the extinction of specialized parasite-host associations in the past [69,115,154,168] and it has been argued that co-extinction with hosts might be an important driver of extinction for parasites and symbionts more generally [169][170][171][172][173]. An important role of diversity loss has also been postulated for the modern dilution effect hypothesis [58].…”

Section: (I) Evidence For the Amplification Hypothesismentioning

confidence: 99%

Phanerozoic parasitism and marine metazoan diversity: dilution versus amplification

Baets

Huntley

Scarponi

et al. 2021

Growing evidence suggests that biodiversity mediates parasite prevalence. We have compiled the first global database on occurrences and prevalence of marine parasitism throughout the Phanerozoic and assess the relationship with biodiversity to test if there is support for amplification or dilution of parasitism at the macroevolutionary scale. Median prevalence values by era are 5% for the Paleozoic, 4% for the Mesozoic, and a significant increase to 10% for the Cenozoic. We calculated period-level shareholder quorum sub-sampled (SQS) estimates of mean sampled diversity, three-timer (3T) origination rates, and 3T extinction rates for the most abundant host clades in the Paleobiology Database to compare to both occurrences of parasitism and the more informative parasite prevalence values. Generalized linear models (GLMs) of parasite occurrences and SQS diversity measures support both the amplification (all taxa pooled, crinoids and blastoids, and molluscs) and dilution hypotheses (arthropods, cnidarians, and bivalves). GLMs of prevalence and SQS diversity measures support the amplification hypothesis (all taxa pooled and molluscs). Though likely scale-dependent, parasitism has increased through the Phanerozoic and clear patterns primarily support the amplification of parasitism with biodiversity in the history of life. This article is part of the theme issue ‘Infectious disease macroecology: parasite diversity and dynamics across the globe’.