asexuality in pathogens

Una Smith smith-una at yale.edu
Tue Dec 8 19:38:57 EST 1992

Kathie Hodge <kh11 at cornell.edu> writes:

>Why do pathogens tend to reproduce asexually?

I am reminded that we used to believe most rare tropical trees (rareness
and high diversity go hand in hand) would be potential or even obligate
self-crossers.  The idea was that if your chances of finding the right
mate (conspecific and of the opposite sex) are too low, then you're
better off selfing, or at least becoming monecious (single-sexed), so
that reproduction is assured.  Taken to an extreme, you get parthenogenic
or asexual species.

It has been shown that the tendency toward dioecy (male and female
trees) seems to correlate with rareness.  You want references?  All
I have are unpublished numbers from various botanists met in the
field.  But there's a large literature on breeding systems in trees.

[details about fungi with obligate insect hosts deleted]

>Wouldn't pathogens benefit by the production of rare offspring[...]

I think it depends on how the spores are dispersed.  If contagion is
wind-borne, then the fungus might be better off producing rare offspring,
but if transmission is from host to host by some more direct method,
then it becomes important not to mess with fungal genetics too much,
lest the ability to modify, for example, insect behavior (a
common stragegy used by fungal pathogens of insects) is lost.


      Una Smith      Biology Department       smith-una at yale.edu
                     Yale University
                     New Haven, CT  06511

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