Genetic Variation and Parthenogenic Beasties

[Anonymous]

If an animal reproduces by parthenogenesis, does this make them an evolutioanry dead end, or is there a mechanisim to create genetic diversity?

Aphids and Stick Insects reproduce this way, and I've never seen any work on how they can evolve, or how the process itself can evolve without it setting in stone, as it were, the body form of the animal.

Thoughts?

 

[marion]

A dividing cell can itself mutate, even if it is supposed to make an exact copy of itself it can mess up, aphids and stick insects could still develop variations, some of which might be more beneficial than the original leading to later generations from this particular animal surviving where originals wouldn't.

 

[_schnor]

Shit, lost a post AGAIN

IIRC Parthenogenesis occurs in species with a higher gene count, so when mitosis occurs there is a greater diversity after the second cell split

I suppose there does come a point of reaching diminishing returns, but I'd guess as there would be a quadrillion different outcomes, it'd take a time for the species cease becoming fecund

 

[Anonymous]

Hmmm,interesting post...afraid I don't know too much about the subject though.
There are lizards which are parthenogenic as well.
It does seem they might be at a disadvantage for genetic diversity but as Schnor mentions perhaps the organism has enough potential variation within itself to carry on in the face of environmental pressures.
Are these species soley parthenogenic or do they occasionally reproduce sexually when mates become available or when a need is sensed to diversify.
I have read in abook by Stephen J. Gould that warm blooded species for instance maintain their species status for no more than about 5 million years,then that particular species has either split into other evolutionary lines or dead ended.
Either way the species does in fact become extinct as it's particular form expires. It must evolve into a new species if its genes are to carry on.
Darwin's finches of the Galapogos evolved from a single species but diversified into new forms to the point where they became distinct new species.
If these finches were parthenogenic I would think their plasticity of form would have been seriously handicapped. They may not have filled out so many niches thereby limiting the potential survival of the finch at all.

 

[mendhak]

There's always radiation too, which gives you a higher chance of mutation in there.

Perhaps if anyone is to gain from the loss of the ozone layer/magnetic field, it's the parthenogenic creatures?

(More thoughts?)

 

[stonedog3]

Is there anything that does both - sex when there's an opposite available and DIY when there isn't?

Kath

 

[Bosbaba]

In Green Stick Insects (also known as laboratory stick insects or the Great Indian stick insect) the females reproduce by parthenogenesis for up to 20 generations. At this point a male is required, after which they can again reproduce for up to 20 generations.

There is diversity even with asexually produced offspring. The stick insects I have vary both in colour and size, though some lines are nearing the end of successful asexual reproduction and are producing thinner, paler insects that are far more fragile than the norm.

I am unaware of a species of stick insect that is completely parthenogenic, all that are commonly kept in captivity at least do produce males, though on an average ratio of 1 male to 3000 females.

From what I can gather, this alternate form of reproduction is more a survival mechanism than the standard by which the species regenerates itself. If males are scarce, at least the species can continue, given the average lifespan of a stick insect is a year to a year and a half, this gives them 30 years for a male to make his appearance and save the day, so to speak.

 

[Anonymous]

And Aphids? do they only reporduce asexually, or are there sport male ones?

 

[Bosbaba]

And Aphids? do they only reporduce asexually, or are there sport male ones?

Don't know much about aphids. At school we were told they were all female, but personally don't know if that is the case or if they are actually hermaphrodite. My main field of study over the past few months has been leaf and stick insects, and we will be moving on to mantids soon, so feel I can comment (even only as a layman) on these critters' habits, but I would be lying if I said I knew anything about aphids.

 

[Anonymous]

Thanks to you all

At school they always hedged on such thing in my day...

 

[OneWingedBird]

Parthinogenesis has the advantages that:

a) The species can reproduce twice as fast because all members can bear offspring, and

b) If you have a very good set of genes they all get passed on to the offspring without having to be mixed with those of a genetically poorer mate.

So in an environment where there is little change and little need for the organism to evolve, parthinogenesis is useful for outcompeting the opposition.

As soon as things start to change, then genetic diversity is a far greater advantage.


Edit: Someone else had said what I was going to say already...

 

[mendhak]

Is there anything that does both - sex when there's an opposite available and DIY when there isn't?

Kath

The Nematode worm. (And the stick insect as pointed out) I suppose they use the males only when required.

>>Link<<

 

[Anonymous]

And Aphids? do they only reporduce asexually, or are there sport male ones?

Aphids in cold climates reproduce sexually at the end of summer, and lay eggs which survive the winter when the aphids themselves die off. Parthenogenesis is their main form of reproduction in the summer.

By the way, the adjective is 'parthenogenetic', not 'parthenogenic'.

 

[Anonymous]

Is there anything that does both - sex when there's an opposite available and DIY when there isn't?

Kath

Some protozoa. Usually they reproduce asexually - e.g. by binary fission, which means the protozoan divides into two complete, equal organisms. But there are protozoa that can directly exchange DNA with other single-cell organisms of the same kind. Usually they go back to asexual reproduction after that though, so I guess protozoan sex life can't be all too exciting

And insects. Apparently for some insectoid species there seems to be a big advantage in facultative parthenogenesis.
While asexual reproduction allows them to quickly build up populations and colonies, the occasional round of mating will ensure genetic diversity.

Parthenogenesis and other forms of asexual reproduction will enable single individuals to produce a vast number of identical offspring. While this may mean that whole populations could be easily wiped out just because of an unfavorable genotype, it will mean that other populations will survive and multiply because of their genetical fitness.
Still, new genotypes in such species are only created through mutation.

 

[Anonymous]

Aphids in cold climates reproduce sexually at the end of summer, and lay eggs which survive the winter when the aphids themselves die off. Parthenogenesis is their main form of reproduction in the summer.

By the way, the adjective is 'parthenogenetic', not 'parthenogenic'.

Thanks for clearing up the aphids thing...

The adjectives, in all the materials I've looked at, seem to be interchangeable, some study papers making references to 'parthenogenic species', others to 'parthenogenetic speicies'. I would say the latter is more decriptively accurate, but there doesn't appear to be one convention on the subject, unless, like the introduction of the Pin Yin system for the transliteration of Chinese into the Roman alphabet, its a very recent thing.

 

[Anonymous]

The adjectives, in all the materials I've looked at, seem to be interchangeable, some study papers making references to 'parthenogenic species', others to 'parthenogenetic speicies'.

I suspect it's becoming gradually accepted as an alternate spelling- certainly older dictionaries list 'parthenogenetic' but not 'parthenogenic'.

 

[Anonymous]

Only unlike me, they can spell the word 'species'. I get the feeling that its an Americanism that is being adopted, rather like the definition of billion as a thousand million, rather than the more logical million million...

 

[lemonpie3]

You know what, that american billion never ceases to annoy me! I just don't know where I am after 900 million.