[paul.fr]

How did Asexual plants first evolve, and why?

[another_someone]

What do you mean by 'asexual reproduction'?  Are you talking about plants grown from cuttings (a little bit like the question elsewhere about the starfish tentacles), or are you talking about plants that can self pollinate?

http://en.wikipedia.org/wiki/Self-pollination

Self-pollination is a form of pollination that can occur when a flower has both stamens and a pistil in which the cultivar or species is self fertile and the stamens and the sticky stigma of the pistil contact each other to accomplish pollination. The term is inaccurately used in many cases where an outside pollinator is actually required; such plants are merely self fertile, or self pollenizing.

Few plants actually self pollinate. The mechanism is seen most often in some legumes such as peanuts. In another legume, Soybeans, the flowers open and remain receptive to insect cross pollination during the day; if this is not accomplished, the flowers self pollinate as they are closing.

Self pollination, or more generally self pollenizing, limits the variety of progeny and may depress plant vigor. However, self pollenizing can be advantageous, allowing plants to spread beyond the range of suitable pollinators or produce offspring in areas where pollinator populations have been greatly reduced or are naturally variable.

[paul.fr]

or are you talking about plants that can self pollinate?

That one.

[WylieE]

Hi Paul,

  Plants that can self fertilize have evolved many times.  How they do so really varies from plant to plant and depends on how the ancestor maintained a preference for not self-pollinating.  To prevent self-pollination, many plants have a mechanism to recognize and reject their own pollen- different species use different systems.  Mutations in these systems allow (or sometimes even require) self-pollination.

  I am wondering if your question is more about why a plant that can either self -pollinate or cross-pollinate would mostly seem to prefer self pollination.  This is again dependent on the plant, but it seems like a lot of the self-pollinating plants are mechanical issues. . .That is they are physically set up to prefer themselves over others (like frat boys?).  The most obvious example is when the flower doesn't open until after the plant is fertilized- this pretty much reduces the competition entirely. 

There are examples of plants that swing both ways. . for their first set of seeds in a year they have chasmogamous (open, cross-pollinating) Flowers and then their second set of flowers are cleistogamous, or completely closed and self- pollinating.  Talk about a self reliant back up system.

 It would be understandable for plants to want to keep the option of self-pollination.  While cross-pollination increases diversity it requires some mechanism of pollen transfer (wind, animal, . . )if these fail and the plant can't self pollinate it would be left without any chance of reproduction.  This can be seen in Hawaii where many of the animal pollinators have died and the plants are suffering the consequences.

Colleen

[paul.fr]

Thanks for the info, Colleen.

can some plants do both, cross polinate when there are insects etc around and then self polinate when...erm times get bad?

[WylieE]

Hi Paul,
 Yes, one example of a plant that can do both is a type of violet: V. pubescens.  In the early spring it has a normal flower that will cross pollinate.  Later, in the fall it will have a closed (cleistogamous) flower.

Colleen

[paul.fr]

Thanks, Colleen.

You learn something new every day. Thanks, Paul

[Karen W.]

OOOH that is interesting!

[JimBob]

Asexual reproduction is the most primitive type of reproduction know. All algae have an asexual phase and the most primitive of algae are totally asexual. Some algae have a haploid stage as well which is probably a later development. The term algae refers to the phylum of plants and bacteria (the blue-green algae are bacteria.) So, since blue-green have been around a LONG time, possibly 3+ billion years according to an Australian who has collected them from rocks that old (some dispute the rocks are younger - 2.5 billion) asexual is an odds on favorite for the first plant reproductive technique.

[another_someone]

asexual is an odds on favorite for the first plant reproductive technique.

Another biologist I know is of the opinion that sexual reproduction co-developed with the development of diploid chromosomes, and was the reason for diploid chromosomes (or multiples  of pairs, since some plants can have 4, 6, or 8 chromosomes; but an odd number of chromosomes cannot sexually reproduce).

Then again, what we are talking about here is arguable sexual reproduction, but self fertilisation - rather than truly asexual reproduction - although there is no new DNA enterinto the offspring, it still does allow the rearrangement of existing DNA, and thus does introduce some diversity, rather than merely creating clones of the parent.

[dkv]

Asexual lifestyle is the best to replicate genes.
Without incorporating desire to increase the pleasure.At best there should have been 50% chances finding asexual species.
which is not the case.
Whereas i state that the sexual reproductive system was a step towards sustainable pleasure under the given laws of physics.
Therefore asexuals are primitive species and are less likely to be found.
And sexual ones are more advance.
Can sombody give me a ratio between asexual and sexual species?

[Carol-A]

Self pollination is not asexual... it still needs a male and female gamete, but they both come from the same individual.

[dkv]

Yes . It is asexual .
Gamete is necessary and  it comes from same individual.
We can have a debate on this .
Cell division is also driven by same principle. Cell is not cut into halves. It is the interaction between Nucleus and Cytoplasm which produces the division.

[WylieE]

Carol and George are correct-

Self- pollination is NOT asexual reproduction.  Sorry I was a bit sloppy in the answer there, I was referring to self- pollination.  Thanks for catching that.

Colleen

[dkv]

Self -pollination is not asexual it takes another plant to reproduce sexually.