Freethought & Rationalism Archive

Shpongle · 03-30-2003, 08:51 PM

1) What type of genetic variation is required to "create" a new species from an existing species? I guess what I'm trying to ask, is what functional differences have to exist between two organisms so they can no longer successfully interbreed.

2) How much of a genetic difference (%) is required between two organisms to be considered difference species? What's the minimum genetic difference before they'll become two different species?

3) In controlled experiments, what's the greatest amount of genetic variation between organisms when producing new species from existing species?

Utnapishtim · 03-30-2003, 09:07 PM

If we use the biological species concept, then any functional difference that prevents a viable offspring is good enough. You could have physical incompatibility (size or shape of the genitals, for example) or genetic differences. The genetic differences needed would depend on how the sexes are differentiated in a given species. This could be differing number of chromosomes, chromosomes that don't match up correctly during meiosis, DNA doesn't match up during copulation, etc. The differences can be small; there are two different species of ant which apparently only differ by a pheromone they produce. That appears to be the only thing that prevents mating between the species.

There isn't really a minimum amount of genetic difference needed. Theoretically, a difference in one gene could produce an incompatibility. Now most organisms have a small but noticeable difference between themselves and closely related species, but if one gene altered chromosome shape, physical size or genital structure, that would be enough.

As for your third question I don't know.

Secular Pinoy · 03-31-2003, 02:17 AM

From here:

Quote:

Reproductive behaviour is the primary criterion of defining species in nature and the sexual signalling of those species whose communication signals are detectable by human senses or technology are invaluable for this purpose. Paterson (1985) therefore introduced a species concept based upon the recognition of appropriate mating partners. In the recognition concept a species is bound by its own particular specific mate recognition system (SMRS). The SMRS is the series of steps in mate signalling that result in mating, fertilisation and syngamy if both sexes recognise one another�s signals. If any of the steps in the system fail or do not prompt a response in the opposite sex, then reproduction will not occur. There are a number of possible reasons for termination in the mating system. A female cicada may not recognise the call of a signalling male cicada and therefore, she does not respond. Both sexes may have engaged in copulation pose, but genitalia coupling mechanisms may not be compatible.

This means that if the SMRS of two individuals of opposite sex (or populations) is so different that they can no longer recognize each other as a potential mate, then they are two species (or at the very least, they are on the way to become separate species).

ps418 · 03-31-2003, 10:50 AM

Just to reiterate Utnapishtim said, there is no set degree of genetic difference that defines a species boundary. For instance, there are seperate species (biological species) of Drosophila that are as genetically close to each others as are members within other species (crappy phrasing!).

Patrick

Monkey · 04-01-2003, 06:25 AM

Quote:

Originally posted by Pete Harcoff
1) What type of genetic variation is required to "create" a new species from an existing species? I guess what I'm trying to ask, is what functional differences have to exist between two organisms so they can no longer successfully interbreed.

2) How much of a genetic difference (%) is required between two organisms to be considered difference species? What's the minimum genetic difference before they'll become two different species?

3) In controlled experiments, what's the greatest amount of genetic variation between organisms when producing new species from existing species?

Biology textbooks should give you a reasonable understanding of speciation.

As you picked up, reproductive isolation is the key to speciaition. Reproductive isolation occurs in pre and post zygotic forms both of which influence the type of speciation that occurs, ie sympatric, allopatric or parapatric isolation.

There's Ecological, Temporal, Ethological, Mechanical and Gametic pre-zygotic mechanisms and if species manage to get past these barriers, hybrids are inviable, sterile or further hybrid breakdown occurs.

There's plenty of good info and examples in textbooks and journals. Try Bioscience and Evolution.

KC · 04-01-2003, 06:35 AM

Jim Mallet, at University College, London has an excellent webpage. He is interested in issues with speciation, and has some very good links:

Speciation Issues

Enjoy!

KC

03-30-2003, 08:51 PM	#1
Shpongle Veteran Member Join Date: Jan 2003 Location: Frozen North Posts: 9,920	Speciation questions 1) What type of genetic variation is required to "create" a new species from an existing species? I guess what I'm trying to ask, is what functional differences have to exist between two organisms so they can no longer successfully interbreed. 2) How much of a genetic difference (%) is required between two organisms to be considered difference species? What's the minimum genetic difference before they'll become two different species? 3) In controlled experiments, what's the greatest amount of genetic variation between organisms when producing new species from existing species?

04-01-2003, 06:35 AM	#6
KC Senior Member Join Date: Mar 2002 Location: San Narcisco, RRR Posts: 527	Speciation Questions Jim Mallet, at University College, London has an excellent webpage. He is interested in issues with speciation, and has some very good links: Speciation Issues Enjoy! KC

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03-30-2003, 09:07 PM	#2
Utnapishtim Regular Member Join Date: Feb 2002 Location: Vancouver, BC Posts: 330	If we use the biological species concept, then any functional difference that prevents a viable offspring is good enough. You could have physical incompatibility (size or shape of the genitals, for example) or genetic differences. The genetic differences needed would depend on how the sexes are differentiated in a given species. This could be differing number of chromosomes, chromosomes that don't match up correctly during meiosis, DNA doesn't match up during copulation, etc. The differences can be small; there are two different species of ant which apparently only differ by a pheromone they produce. That appears to be the only thing that prevents mating between the species. There isn't really a minimum amount of genetic difference needed. Theoretically, a difference in one gene could produce an incompatibility. Now most organisms have a small but noticeable difference between themselves and closely related species, but if one gene altered chromosome shape, physical size or genital structure, that would be enough. As for your third question I don't know.

03-31-2003, 10:50 AM	#4
ps418 Veteran Member Join Date: Mar 2001 Location: Louisville, KY, USA Posts: 1,840	Just to reiterate Utnapishtim said, there is no set degree of genetic difference that defines a species boundary. For instance, there are seperate species (biological species) of Drosophila that are as genetically close to each others as are members within other species (crappy phrasing!). Patrick

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