[Plant-education] Re: Introductory Botany
David R. Hershey
dh321 at excite.com
Sun May 28 16:24:19 EST 2006
I was considering only the case of self-pollination of a completely
homozygous plant. That would fit the definition of cloning because the
offspring would be genetically identical to the parent.
You pose an interesting question about whether it would be more
advantageous for a plant that cannot cross-pollinate to put its
resources into self-pollinated seeds or vegetative reproduction. I
don't know any specific literature investigating that question but some
normally outcrossing plant species will resort to self-pollination when
cross-pollination does not occur (Dole 1990, Klips and Snow 1997). Do
you have a plant species in mind that may demonstrate that behavior?
If vegetative reproduction is the better choice, then shouldn't
dioecious species all have vegetative reproduction methods? Dioecious
species that fail to cross-pollinate cannot use self-pollination as a
backup. Many dioecious species do not seem to rely heavily on
One reason self-pollination may be better than vegetative cloning is
that seeds are superior to vegetative reproduction because of their
superior dispersal mechanisms and their ability to delay germination.
For example, if there was a major stress, such as a long dry period,
the parent and all the vegetative offspring might perish but some seeds
would probably survive. Vegetative cloning would probably not be an
option for most annual species either.
"Incest taboo" or dangers of inbreeding often seem to be exaggerated,
especially in people. In the U.S. over half the states have laws
against first cousins marrying. Few other countries have that
prohibition; first cousin marriages are very common and often
encouraged. Charles Darwin married his first cousin and produced some
outstanding children. It is somewhat ironic that Darwin promoted the
idea of the "evil which many plants suffer from self-fertilisation"
(Darwin 1876). Textbooks tend to forget that Darwin said "many" not
Wells (1979) tried to explain the paradox that "Self-fertilization is
prevalent and successful in many angiosperm taxa." Even some naturally
outcrossing plant species may not exhibit the expected inbreeding
depression (Hossaert-McKey and Bronstein, 2001). "Among the most common
evolutionary trends in flowering plants is the transition from
outcross- to self-pollination" (Fausto et al. 2001).
Would the term, geitenogamy, apply when a flower is self-pollinated by
a flower on another plant of the same clone? Or is there a separate
term for that? For example, peach cultivars are usually
self-compatible, so a pollinator could carry pollen from one 'Redhaven'
peach tree to another 'Redhaven' tree to provide self-pollination.
David R. Hershey
Darwin, C. 1876. The Effects of Cross and Self Fertilization in the
Vegetable Kingdom. John Murray, London.
Dole, J.A. 1990. Role of corolla abscission in delayed self-pollination
of Mimulus guttatus (Scrophulariaceae). American Journal of Botany 77:
Fausto, J.A. Jr., Eckhart, V.M. and Geber, M.A. 2001. Reproductive
assurance and the evolutionary ecology of self-pollination in Clarkia
xantiana (Onagraceae). American Journal of Botany 88: 1794-1800.
Hossaert-McKey, M. and Bronstein, J.L. 2001. Self-pollination and its
costs in a monoecious fig (Ficus aurea, Moraceae) in a highly seasonal
subtropical environment. American Journal of Botany 88: 685-692.
Klips, R.A. and Snow, A.A. 1997. Delayed autonomous self-pollination in
Hibiscus laevis (Malvaceae).
American Journal of Botany 84: 48-53.
Wells, H. 1979. Self-fertilization: Advantageous or deleterious?
Evolution 33: 252-255.
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