Regarding abilities used to survive predators and parasites, are they subjected more to directional selection or frequency-dependent selection?

It's usually that host-parasite coevolution is represented to be characterized by frequency-dependent selection, such that rare traits in hosts select for traits in parasites subject. That would make the phenomenon of female choice for "good genes" males surprising because one might instead expect healthy males to be more likely to yield sickly offspring or grandoffspring. Is this a simplification and are there some aspects of host immunity subject to directional selection? If so, which?

Same with anti-predator defense traits: only frequency-dependent selection or some substantial percentage subjected to directional selection?

Thank you for your time.

  • 2
    $\begingroup$ Both. These are sometimes called "arms race" or "trench warfare" (directional) and "Red Queen" (freq-dependent). $\endgroup$
    – Ben Bolker
    Mar 4, 2022 at 20:04
  • $\begingroup$ Would you be able to offer more, such as what sorts of characteristics are selected on directional vs freq-dependent? $\endgroup$
    – sterid
    Mar 5, 2022 at 21:15


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