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Validity of the theory of sex in relation to parasites.

Brian Jones jbj at frc.maf.govt.nz
Wed Dec 9 15:23:43 EST 1992

In article <1992Dec6.232615.6426 at u.washington.edu> xia at darwin.genetics.washington.edu (Xia) writes:
>In article <Byt9vv.Jw8 at usenet.ucs.indiana.edu> adpeters at sunflower.bio.indiana.edu (Andy Peters) writes:
>>In article <1992Dec5.195711.22967 at u.washington.edu> xia at darwin.genetics.washington.edu (Xia) writes:
>>>No, it does not make sense, because it applies only to specialised
>>>host-parasite pairs. When the host is harbouring many different species
>>>of parasites, a recombination to avoid one species of parasite would 
>>>send the host to the mercy of other species of paes.
>>I disagree.  No matter how many parasites are coevolving with the
>>host, each parasite population will be tracking the most common
>>host genotype.  By "tracking," I mean that the parasite populations
>>will constantly be evolving to mimic some feature of the host (not
>>necessarily the same feature for each parasite).  Hence, recombining
>>and producing rare offspring allows the host a chance to escape from
>>any number of parasites.
>Are there many people agreeing with Andy? If there are, then I will
>post responses, otherwise I will communicate with Andy only.
>Xuhua Xia
>Department of Genetics
>U of Washington

Yes I've been following the discussion. As a parasitologist, rather than
a geneticist, I find the arguments quaint.

Most parasites I know of rely on sex just as much as the host. However they
have two problems. 1) to find a host animal to infect 2) once in/on the host,
to establish themselves.

For 1) sex seems to be almost essential in providing the diversity necessary
to cope with minute changes in the host genotype, but more frequently changes 
in the environment. 

Once a parasite has found a host, rapid duplication of the successful
genetic material is accomplished by asexual means.


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