Jason Cosens Walsman

Journal article Journal of the Royal Society, Interface · February 2026 Individual heterogeneity, in number of parasites, size, etc., interacts critically with population dynamics. We tease this out in a model case study of microparasite load with empirically supported assumptions to investigate how variance in load interacts ... Full text Cite

Wildlife Provisioning Selects for Higher Pathogen Virulence in Hosts with Incomplete Immunity.

Journal article The American naturalist · February 2026 AbstractHumans provide massive inputs of food to wildlife, with profound ecological and evolutionary consequences. By potentially altering wildlife host immunity, density, and behavior, provisioning can influence transmission of wildlife pathogens and thus ... Full text Cite

Integrating infection intensity and aggregation into the dynamics of pathogens with within-host replication

Journal article Journal of Animal Ecology · January 1, 2026 Disease outcomes depend heavily on infection intensity which is often heterogeneous across and within host populations. Most individuals carry low pathogen loads and a few carry high loads, a pattern known as aggregation. Although well characterized in mac ... Full text Cite

Evolution of pathogen tolerance and reproductive trade-off implications.

Journal article Journal of mathematical biology · April 2025 We develop an epidemic model that accounts explicitly for the pathogen pool and incorporates population variations in host defense strategy, measured in disease tolerance that is assumed to be perfectly inherited by offspring. Although the proposed model i ... Full text Cite

Do fungi look like macroparasites? Quantifying the patterns and mechanisms of aggregation for host-fungal parasite relationships.

Journal article Proceedings. Biological sciences · March 2025 Most hosts contain few parasites, whereas few hosts contain many. This pattern, known as aggregation, is well-documented in macroparasites where parasite intensity distribution among hosts affects host-parasite dynamics. Infection intensity also drives fun ... Full text Cite

Diverse Relationships between Batrachochytrium Infections and Antimicrobial Peptide Defenses Across Leopard Frog Populations.

Conference Integrative and comparative biology · September 2024 Antimicrobial peptides (AMPs) play a fundamental role in the innate defense against microbial pathogens, as well as other immune and non-immune functions. Their role in amphibian skin defense against the pathogenic fungus Batrachochytrium dendrobatidis (Bd ... Full text Cite

Associating with kin selects for disease resistance and against tolerance.

Journal article Proceedings. Biological sciences · May 2024 Behavioural and physiological resistance are key to slowing epidemic spread. We explore the evolutionary and epidemic consequences of their different costs for the evolution of tolerance that trades off with resistance. Behavioural resistance affects socia ... Full text Cite

"Resistance Is Futile": Weaker Selection for Resistance by Abundant Parasites Increases Prevalence and Depresses Host Density.

Journal article The American naturalist · June 2023 AbstractTheory often predicts that host populations should evolve greater resistance when parasites become abundant. Furthermore, that evolutionary response could ameliorate declines in host populations during epidemics. Here, we argue for an update: when ... Full text Cite

A paradox of parasite resistance: disease-driven trophic cascades increase the cost of resistance, selecting for lower resistance with parasites than without them

Journal article Evolutionary Ecology · February 1, 2023 Most evolutionary theory predicts that, during epidemics, hosts will evolve higher resistance to parasites that kill them. Here, we provide an alternative to that typical expectation, with an explanation centered on resource feedbacks. When resistance is c ... Full text Cite

Predation shifts coevolution toward higher host contact rate and parasite virulence.

Journal article Proceedings. Biological sciences · July 2022 Hosts can avoid parasites (and pathogens) by reducing social contact, but such isolation may carry costs, e.g. increased vulnerability to predators. Thus, many predator-host-parasite systems confront hosts with a trade-off between predation and parasitism. ... Full text Cite

Shoaling guppies evade predation but have deadlier parasites.

Journal article Nature ecology & evolution · July 2022 Parasites exploit hosts to replicate and transmit, but overexploitation kills both host and parasite. Predators may shift this cost-benefit balance by consuming infected hosts or changing host behaviour, but the strength of these effects remains unclear. H ... Full text Cite

Parasite-driven cascades or hydra effects: Susceptibility and foraging depression shape parasite–host–resource interactions

Journal article Functional Ecology · May 1, 2022 Parasites kill hosts but also can indirectly increase the abundance of their resources. Given this resource feedback, how much will parasites decrease host density? Can they increase host density? Seeking answers, we integrate trait measurements, a resourc ... Full text Cite