Trade-offs in defence to pathogen species revealed in expanding nematode populations.

Many host organisms live in polymicrobial environments and must respond to a diversity of pathogens. The degree to which host defences towards one pathogen species affect susceptibility to others is unclear. We used a panel of Caenorhabditis elegans nematode isolates to test for natural genetic variation in fitness costs of immune upregulation and pathogen damage, as well as for trade-offs in defence against two pathogen species, Staphylococcus aureus and Pseudomonas aeruginosa.

Reproductive consequences of transient pathogen exposure across host genotypes and generations.

To maximize fitness upon pathogenic infection, host organisms might reallocate energy and resources among life-history traits, such as reproduction and defense. The fitness costs of infection can result from both immune upregulation and direct pathogen exploitation. The extent to which these costs, separately and together, vary by host genotype and across generations is unknown.

Microbial protection favors parasite tolerance and alters host-parasite coevolutionary dynamics.

Coevolution between hosts and parasites is a major driver of rapid evolutionary change and diversification. However, direct antagonistic interactions between hosts and parasites could be disrupted when host microbiota form a line of defense, a phenomenon widespread across animal and plant species. By suppressing parasite infection, protective microbiota could reduce the need for host-based defenses and favor host support for microbiota colonization, raising the possibility that the microbiota can alter host-parasite coevolutionary patterns and processes.

Tripartite interactions: how immunity, microbiota and pathogens interact and affect pathogen virulence evolution.

The bipartite interactions between insect hosts and their bacterial gut microbiota, or their bacterial pathogens, are empirically and theoretically well-explored. However, direct, and indirect tripartite interactions will also likely occur inside a host. These interactions will almost certainly affect the trajectory of pathogen virulence evolution, an area that is currently under researched.

Sex Matters: Effects of Sex and Mating in the Presence and Absence of a Protective Microbe.

In most animals, female investment in offspring production is greater than for males. Lifetime reproductive success (LRS) is predicted to be optimized in females through extended lifespans to maximize reproductive events by increased investment in immunity. Males, however, maximize lifetime reproductive success by obtaining as many matings as possible.

Fecundity compensation is dependent on the generalized stress response in a nematode host.

Background: Fecundity compensation, increased offspring output following parasite exposure, is widely reported, but the underlying mechanisms remain unclear. General stress responses are linked to other indirect defenses against parasites, and therefore may be responsible. We challenged strains of (wild type and mutants with compromised or strengthened stress responses) with .

Host genetic diversity limits parasite success beyond agricultural systems: a meta-analysis.

There is evidence that human activities are reducing the population genetic diversity of species worldwide. Given the prediction that parasites better exploit genetically homogeneous host populations, many species could be vulnerable to disease outbreaks. While agricultural studies have shown the devastating effects of infectious disease in crop monocultures, the widespread nature of this diversity-disease relationship remains unclear in natural systems.

The relationship between parasite virulence and environmental persistence: a meta-analysis.

Why some parasites evolve and maintain extreme levels of virulence is a question that remains largely unanswered. A body of theory predicts that parasites that form long-lived spores able to persist in the environment evolve higher virulence, known as the sit and wait hypothesis. Such parasites can obliterate their local host population and wait in the environment for further hosts to arrive, reducing some of the costs of high virulence.

Mutual fitness benefits arise during coevolution in a nematode-defensive microbe model.

Species interactions can shift along the parasitism-mutualism continuum. However, the consequences of these transitions for coevolutionary interactions remain unclear. We experimentally coevolved a novel species interaction between hosts and a mildly parasitic bacterium, , with host-protective properties against virulent .

Cross-Resistance: A Consequence of Bi-partite Host-Parasite Coevolution.

Host-parasite coevolution can influence interactions of the host and parasite with the wider ecological community. One way that this may manifest is in cross-resistance towards other parasites, which has been observed to occur in some host-parasite evolution experiments. In this paper, we test for cross-resistance towards and in the red flour beetle , which was previously allowed to coevolve with the generalist entomopathogenic fungus .

Cryptic changes in immune response and fitness in Tribolium castaneum as a consequence of coevolution with Beauveria bassiana.

Immunity is a key trait in host defence against parasites and is thus likely to be under selection during host-parasite coevolution. Broadly, the immune system consists of several lines of defence including physiological innate immunity, physical barriers such as the cuticle, avoidance behaviours and in some cases antimicrobial secretions. The defence conferring the highest fitness benefit may be situation specific and depend on the taxon and infection route of the parasite.