Ellstrand and Schierenbeck, 2000. Hybridization as a stimulus for the evolution of invasiveness in p

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Ellstrand and Schierenbeck, 2000. Hybridization
as a stimulus for the evolution of invasiveness
in plants?
Invasiveness might be a trait that has evolved
after establishment, rather than a
pre-adaptation. This might explain the time lag
between establishment and invasion the lag would
be the time necessary for the selection of
invasiveness. (couldnt the lag be explained by
some simpler population dynamics features??)
Hybridization could then catalyze the evolution
of invasiveness This would explain why invasion
often result from multiple introductions.
28 well supported examples of invasive species
that are hybridized and which parent species are
not invasive. Herbaceous, perennial, species
predominates apart from that, no obvious pattern!
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Species A
Species B
F1
recombination
segregation
chromosome doubling
translocation recombination
translocation


Increased variation
Evolutionary novelty
Purge of genetic load
Fixed heterosis
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Increased variation high genetic variation could
confer better evolutionary survival, but... -
this is a group selection argument, - the only
data supporting this view is that some invasive
populations are more diverse than their parent
populations.
Evolutionary novelty new genotypes arise that
allow adaptation to a new niche... - new
genotypes arise by recombination, translocation
(exchange of genetic material between no
homologous chromosomes)
Purge of genetic load deleterious mutations that
were fixed in the parent species segregate after
recombination, so that selection can play
Fixed heterosis hybrids have higher fitness than
parent species - a possible cause (found in
maize and rice) is that deleterious mutations
that were fixed in the parent species are at an
heterozygous state in the hybrids, - a mechanism
that would fix this heterosis (such has
chromosome doubling, or clonal reproduction that
prevents recombination) would confer a
permanent superiority of the hybrid.
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Human activity and hybridization rate
Human activity brings together species that have
never been sympatric, suppresses geographic
barriers between allopatric species
Human activity creates disturbed habitat were
fast growing generalists might be best fit.
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Hybridization within a species
The mechanism that have been described for
between species hybridization could apply as well
to within species hybridization.
parent populations are too close (hybridization
cannot bring novelty)
parent populations are too distant (recombination
will be harmful)