Hi,
perhaps (i.e. IMHO, not scientific accepted fact) really you are
getting at the question why did arrhenotoky (unfertilised eggs as
haploid males, fertilised eggs as diploid females) evolve? For
example aside of Hymenoptera, arrhenotoky has stabily evolved from
diploid-diploid sex chromosome systems in some seven other occasions
including the ambrosia/ scotylid beetles which are highly inbreeding
as well.
So is the correlation between inbreeding and arrhenotoky real? Pass.
However things to think about are, if your ecological niche means
that you have to inbreed often or always such as limited foundress
colonisation like mites and many hymenoptera, large dispersal
distances etc.
(1) Under arrhenotoky the exposure of rare recessive lethals is rare
and so inbreeding has less of an immediate fitness cost. This may be
because each generation you "cleanse" nearly all the recessive
lethals through exposure in the haploid male (of course any genes
involved only in female behaviour or morphology will not be selected
against). thus inbreeding does not expose as many lethals because the
genome is purged of them.
(2) under this system a lone virgin female foundress is not committed
to extinction as long as she lives long enough to mate with her son
and then lay the next generation. Standard diplo-diploid virgin
females would of course die without reproduction and so could not
colonise such niches.

there are several  other hypotheses, but im not sure the answer is
known. Just something to strat you thinking.
 It has been claimed that the low genetic diversity often reported in
Hymenoptera is due to the arrhenotokous system. this isnt
substantiated, but doesnt appear to change much between inbreeding
and outbreeding Hymenoptera species anyway. A possible case of rare
outbreeding is enough? just as rare sex is enough for those
thelytokous species perhaps. If so, colonise as a single or limited
founfdress number and expand (committed inbreeding but with the above
mentioned purging of your gene pool) and then await the rare
immigrant with different genes to arrive..the reinforcements if you
like, and so you stabilise your position!.

By the way, dont get the comparsions between varroa and honey bees
genetic diversity clouded. The outbreeding honeybee doesnt have a
great deal of genetic diversity either...relative to say a relatively
outbreeding Drosophila melanogaster ..but does say compared to an
obligatory asexual wasp like Venturia canescens. The question is
whether if they have sufficient genetic diversity to cope with
changes in their local niches relative to competing species. They
both survive at this point in time quiet well, so at present the
answer is maybe, as does the drosophila. In another million years,
after we are all dead and gone (as a species, not individuals)...who
knows.
 Rob
Robert Butcher,
Evolutionary and Ecological Entomology Unit,
Department of Biological Sciences,
Dundee University,
Dundee, DD1 4HN,
Tayside, Scotland,
UK.
Work Phone:- 01382-344291 (Office), 01382-344756 (Lab).
Fax:- 01382-344864
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