In disease ecology and parasitology, we often talk about a host’s ability to resist or tolerate parasites. What’s the difference? Resistance is a measure of a host’s ability to reduce parasite establishment. For instance, imagine that two hosts are each exposed to 10 parasites. In the first host, 8 of those parasites manage to evade the host’s immune system and successfully establish, and in the second host, only 2 of the parasites successfully establish. The second host is more resistant to infection. Tolerance is a measure of a host’s ability to “deal with” a given parasite load. Now imagine that two hosts each have 5 parasites. Those parasites hardly affect the first host’s ability to survive or reproduce, but the same number of parasites causes a huge reduction in the second host’s ability to survive and reproduce. The first host is more tolerant. (A really great figure from Raberg et al. (2007) sums this up.)
What determines a host’s ability to resist or tolerate parasites? Good question! This is a hot topic for research. Body condition (i.e., overall health) likely has something to do with resistance and tolerance. And then there is that ever-present explainer of all the things: genetics (Raberg et al. 2007). But today, I want to talk about something else. Do paternal effects influence resistance and tolerance?
In a recent, awesome, open access study, Kaufmann et al. (2014) exposed three-spined stickleback “sires” (fathers/dads/sperm-makers) to nematodes. Then they used sperm from either these exposed sires or unexposed sires to fertilize strickleback eggs. Here’s what they found: when the sires were exposed to parasites, the eggs were less likely to develop and the juveniles were less likely to survive. But if they took surviving offspring from both exposed and unexposed sires, and then exposed some of those offspring to nematodes, the offspring from exposed sires had higher tolerance to parasites. Specifically, parasites had a big effect on the body condition of offspring from unexposed sires, but no effect on offspring from exposed sires. Neat! Surprisingly, parental effects didn’t influence offspring resistance to parasites. Unsurprisingly, genetics also played a role in both resistance and tolerance.
Raberg, L., D. Sim, and A.F. Read. 2007. Disentangling Genetic Variation for Resistance and Tolerance to Infectious Diseases in Animals. Science 318(5851): 812-814.
Kaufmann, J., T.L. Lenz, M. Milinski, and C. Eizaguirre. 2014. Experimental parasite infection reveals costs and benefits of paternal effects. Ecology Letters. (Open access.)