Question

Imagine you are a nematode that infects Soay sheep. If you want to maximize the likelihood that you survive and reproduce, should you prefer a more resistant sheep host or more tolerant host? Why?

Answer 1

If I imagine myself to be a nematode that infects Soay sheep, I would prefer to infect a more tolerant host than a resistant sheep to maximize the likelihood that I survive and reproduce.

Tolerance indicates the ability of the host to minimize the damage caused by the nematode burden. It is the rate of decline in the health of host with increasing parasite burden.

Resistance, on the other hand, indicates the ability to ward off infection and recover from it while reducing parasite burden.

For example, if the infection of nematode causes weight loss in Soay sheep, then a less tolerant sheep will lose weight early with increasing parasite burden and a more tolerant will lose weight very slowly compared to the prior. A resistant sheep would avert the infection as soon as possible whereas a tolerant sheep would allow the increase in nematode number and might also reproduce.

Therefore, in favor of nematode a tolerant sheep will be more beneficial to survive and reproduce.