what a species is, or isn't

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Karl K
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Re: what a species is, or isn't

Post: # 67763Post Karl K
Tue May 01, 2018 7:25 am

Don wrote:
Tue May 01, 2018 5:10 am
This article I pulled up through google seems to contradict that somewhat in saying that M. sylvestris is also present in the modern apple but my remembrance is that sieversii is the full founder of them all.
I read a similar article. It also discussed efforts to retrieve various threatened races of the species. Here is another:
http://hortsci.ashspublications.org/con ... /1440.full

Years ago, when I was reading about Michurin's extraordinary work, I became fascinated by Malus niedzwetzkyana. I hoped that I would someday get to see it. But then I learned that Hansen's 'Hopa Crabapple' was bred from M. baccata and M. niedzwetzkyana.

When I was just a youngster, a neighbor lady gave my mother a seedling, apparently from the Hopa. The fruit of this beautiful tree were too large to be 'Hopa', but just what would be expected in the F2 generation. The leaves appeared dark green because of the red pigment on the undersides. Purply-pink flowers and purple-red fruit. The tree is long gone (sad face), but was never bothered by Cedar-Apple rust that afflicted another apple tree growing about 30 feet away in a neighbors yard.
http://bulbnrose.x10.mx/Heredity/Niedzw ... a1904.html
http://bulbnrose.x10.mx/Heredity/Hansen ... brids.html

Also, apples bred for the far north often have the Siberian M. baccata in their background.
http://bulbnrose.x10.mx/Heredity/GideonApples1899.html

Karl K
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Re: what a species is, or isn't

Post: # 67764Post Karl K
Tue May 01, 2018 7:50 am

How much of the genome is required to distinguish species? I have some examples involving Rosa rugosa, or what passes for it in culture.

Hereditas 30:411-412 (1944)
The Constitution of the Rosa canina Complex
Åke Gustafsson
Institute of Genetics, Svalöf, Sweden
R. canina II x rugosa: 1934-4 — This series consists of two individuals. One is a monosomic plant showing almost no trace of the father but also being very unlike the mother. It is smaller and less vigorous than its sister-plant, having few and rather weak prickles, small purely white petals, a light-green colour on stem and leaves, and lacks anthocyanin. It is less winter-hardy than its sister-plant; during the cold winters 1941 and 1942 the superterrestrial parts were entirely killed. It cannot be a monosomic of the mother-plant since the meiotic behaviour is that typical of canina-rugosa hybrids. Therefore in this case the loss of one chromosome obliterates the characters brought in by the rugosa genome.

A Rose Odyssey (1937: p123-124)
J H Nicolas
In 1933 I had found a curious sport on Margaret McGredy. The foliage strongly resembled Rugosa but the plant characteristics also leaned toward R. cinnamomea. I mentioned this fact to Sam III [McGredy] when I visited him in 1934. Sam could not account for the sport. He had never used species in his breeding. His brother-in-law, Walter I. Johnston, spoke up, "Your father did much more work with species." We adjourned to the office, where complete hybridizing records from the early days of the firm are kept, one volume for each year, a valuable library. After several hours of research we traced the origin of Margaret McGredy to crosses of Rugosa and Cinnamomea. They were, of course, many generations back. But as these two species are in the blood stream of Margaret McGredy and all modern McGredy roses, the possibility of the sport was explained. It is an accepted fact that hybrids alone sport (pure species mutate, but rarely, if ever, sport) and can sport only within what is in them.*

Lately, the most unusual thing has happened to that sport. A sport is supposed to be a part of the hybrid compound which "took a walk". But this sport must have carried the whole pack as it has sported again a Hybrid Tea type with a magnificent bloom much more intensely colored than the original Margaret McGredy and is a distinctly a different rose. I am planning to name it "Margaret Second".

The first note clearly indicates that a single chromosome either carries the nearly all of the species-defining genes, or is the site of a regulatory network that controls genes in other chromosomes that contribute to the species distinctions.

The second example suggests that the hypothetical network control can be silenced without being entirely disrupted. Thus it can be released from silencing/suppression, and then silenced again.

Karl K
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Re: what a species is, or isn't

Post: # 67780Post Karl K
Thu May 03, 2018 10:41 am

And writing of regulatory mechanism, I got to thinking about Batesian mimicry in butterflies. One excellent example is Papilio dardanus, an African species that can mimic at least 11 distinct model species. Within a given population, however, it only manages (or needs) three forms.

The various forms of mimic (female only) involve multiple pigments in various patterns. And yet, the mimic-pattern is inherited as a "unit character", or nearly. As I recall, about 8 or 9% of females are imperfect in their mimicry. This is not an altogether bad thing, because this break-down allows the raw materials for building a new mimicry, when required.

This sort of modular control is found in other areas. And by a rather nifty coincidence I have been observing a break-down in regulatory control in a tall bearded iris.

The typical form of this variety is a very ordinary two-tone, with light blue-violet standards with darker and bearded falls.

On April 24, while walking my dog in the park, I saw a freak flower with six horizontal, bearded falls. I have seen pictures of this sort of flower (e.g. 'Clementina'), but had never seen one in person. The next day I saw two more of these odd flowers, but on a different plant of the same variety. Clearly these were not the result of a mutation.

Looking more closely, and taking more pictures, I saw that some of the later blooms were imperfectly modified. Some of the organs that should have been standards were only partially bearded, and the tepal was streaked with darker pigment over the lighter.

Photographing one yesterday I saw a stamen sticking out where it should not be. Looking closer, I pulled up a style-arm and found three more stamens where there should have been only one.
http://bulbnrose.x10.mx/Heredity/Freaky ... owers.html

It appears that the initial function of this regulatory network was to distinguish the inner tepals from the outer. This provided a basis for further differentiation: form and disposition (standard or fall), beard, colors, etc.

The relevance, here, is that some aspects of species distinction are in large clumps that tend to hand together. Hurst discussed these groups of traits at great length, but his critics thought he was being silly for not spending more time considering such pressing matters as the quantity and distribution of pubescence on the underside of the leaves. /s

I am suggesting that these large sets of traits are analogous to the mimicry patterns of the African butterfly, and to the regulatory control of standard/fall differentiation in the tall bearded iris. The contrary position would be to assume that all Rosa species are merely collections of coincidentally associated unit characters.

Karl K
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Re: what a species is, or isn't

Post: # 67808Post Karl K
Wed May 09, 2018 9:12 am

Getting back to the point I was trying to make about Papilio dardanus:

Within a given population, something more than 90% of the females will mimic three model species (one mimicry per female). And it is not coincidental that the pattern of dominance among the mimic patterns parallels the relative abundance of the model species. I.e., Where model species A is most common of the three, and C is the least, the mimicry dominance is a>b>c.

However, in a different population, the model species may be D, B and C, where D is the most common, A the least.

The first point to note is that the dominance is not based on the individual dominance of all the various genes involved in the mimicry pattern. Dominance is a quality of the regulator.

Now, if a P. dardanus female of the (c) mimicry pattern is mated with a male with the (c) genotype from the second species, the female offspring should duplicate mimicry of species C fairly well. But if a female (d) mimic or male with (d) genotype is mated to any member of the first population, the (d) pattern breaks down.

Something similar appears to be going on in roses. In the cases of both Rosa laevigata and R. bracteata, the distinctive characteristics of the species can be entirely lost in F1 hybrids or their progeny.

Penzance pollinated various HPs by R. laevigata, but few of the progeny showed even vague hints of the paternity. Maybe he was sloppy in his technique. But Van Fleet got the same results using R. laevigata as the seed parent.
http://bulbnrose.x10.mx/Roses/breeding/ ... e1896.html
http://bulbnrose.x10.mx/Roses/breeding/ ... e1908.html

'Mermaid' is an obvious hybrid of Rosa bracteata, but its progeny may show little of the species.
History of the Rose - Page 90 (1954)
Roy E. Shepherd
This beautiful pillar rose, introduced in 1918, was created by W. Paul by crossing R. bracteata with an unknown yellow Tea Rose. Mermaid is not dependably hardy in the North, but the freedom with which it produces its large, single, pale sulphur-yellow flowers and the attractive foliage make it a very desirable rose and worthy of any protection it may require in the colder parts of our country. With its many desirable attributes, including fertility, it seems strange that there are but few progeny of Mermaid worthy of mention, and these are much inferior to the parent. SEA FOAM (Paul, 1919) bears small, double, white flowers and partakes more of its Polyantha parent than it does of Mermaid. LEIPSIG (Kordes, 1939) is the result of crossing Eva with Mermaid, but the influence of the latter is again very slight. Apparently the characters of Mermaid are suppressed by those of the variety with which it is crossed, as Leipsig is a 3- to 4-foot shrub rose that bears semidouble, orange-scarlet blossoms in clusters and is recurrent in its bloom.

'Pearl Drift' is reported to be Mermaid x New Dawn, though there seems to be some dispute. It looks like something that might come from 'New Dawn' without outside help. But I have only seen pictures.

Karl K
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Re: what a species is, or isn't

Post: # 67966Post Karl K
Sun Jun 10, 2018 10:39 pm

Here is an example of what a species is NOT.
Journal of Horticultural Science & Biotechnology (2010) 
Genetic diversity and genetic similarities between Iranian rose species
By L. SAMIEI, et al.
The authors go into some detail explaining how DNA evidence revealed little to distinguish Rosa canina and R. iberica, They offered the polite suggestion that the two species were hybridizing. But what are the external differences?
The morphological differences between these two species are very slight. According to Rechinger (1982), the presence of hairs on the hip and a somewhat more-rounded hip distinguishes R. iberica from R. canina. Moreover, these morphological traits are environment-dependent.
That's it? Hairy hips, most likely inherited as a unit character, was enough for someone to raise a mere "form" to species rank.

I'm not buying it.

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