On Thu, 25 Mar 2004 16:49:05 +0000 (UTC), crognum{at}yahoo.com (crognum)
wrote:

>Greetings,
>
>I am interested in learning of any occurences in nature where two
>related species (or subspecies) both derived from the same parent
>species, display a difference in their propensity for parasitism.
>
>I know there are species of wasp that are parasitic and species of
>wasp that are non-parasitic, but is there a case, for example, where a
>wasp species has given rise to wasp species Y and Z, where X is
>parasitic and Y is not?
>
>Also, I know that there are certain birds that sometimes lay their
>eggs in the nests of other members of their own species to increase
>their own brood at the expense of fellow birds (I believe this is
>called non-obligate brood parasitism), but I am unsure if there are
>any cases where this activity occurs between related species or
>subspecies.
>
>Ideas anyone?

How close do you need a relationship do you need?  There are numerous
groups with both parasitic and non-parasitic forms: leeches, copepods,
nematodes, just about every group in fact.  Parasitic plants like
mistletoe have closely related non-parasitic relatives.  Many soil
bacteria seem extremely closely related to virulent forms.

In general, though, parasitism is usually a fairly specialized life
style and is not the type of thing that easily arises in one quick
step -- one sibling species is parasitic but the parent and the other
siblings are not.
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