what a species is, or isn't

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what a species is, or isn't

Postby Peter Harris » Thu Nov 02, 2017 11:34 am

When I began spreading pollen on roses in 1972, I didn't even think about rose species. But gradually I learned about [i]R. spinosissima[/i] and other species. And I learned (incorrectly) that species are unchangeable things.

But since that concept did not account for obvious differences in how they grew and in their flowers and their ease of breeding with other roses (etc), my concept of "species" became less strict.

Anyone who examines a group or population of plants that are supposedly of the same species will see considerable variation within the population, just as we see within the species [i]Homo sapiens[/i]. After all, the concept of species is a human construct, something that people have created to help them simplify reality by classifying/grouping the phenomena they encounter. Maybe our efforts with roses are not as crude as the generalization that all people with red hair have hot tempers, but they surely are over-generalizations.

Today I came across an article its (URL is below) that deals with concepts of species. I think you'll learn something valuable by reading it.

[url]https://www.sciencenews.org/article/defining-species-fuzzy-art[/url]

Peter
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Re: what a species is, or isn't

Postby david mears » Thu Nov 02, 2017 3:10 pm

Thanks Peter, that is a great article, simple for the layperson to read.
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Re: what a species is, or isn't

Postby jbergeson » Thu Nov 02, 2017 6:20 pm

Thanks, Peter. I agree that variability within a species is an important concept to remember when breeding. Significant differences between plants of the same species can occur. On top of that are the possibilities for interbreeding within a particular supplier's seed plots, as well as the potential for mislabeling or misidentifying at any stage.

My R. carolina and R. virginiana both came from Lawyer Nurseries in MT. I ordered a bundle of 25 or 50 of each, because those were the minimums, and selected the five least thorny plants from each to plant out. The differences between the two species in my field are subtle at best, although the R. carolina seem a little healthier overall. I wonder if Lawyer might have a patch of R. carolina and R. virginiana in their field from which they collect seed every year. Are the two patches close enough together for bees to be flying freely between them? Who identified the species to begin with when they acquired them?

I have started masses of R. carolina and R. virginiana in outdoor seed plots and selected at the end of one season those plants that seemed the healthiest and/or had the fewest thorns. In this way I hope to ensure that the species genetics that I incorporate with modern roses are contributing the best possible genes from their species.
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Re: what a species is, or isn't

Postby Jwindha » Thu Nov 02, 2017 10:37 pm

I've pondered this question for a while now and this thread seems like an appropriate place to ask for a general consensus:

How many generations removed from a full-species can a hybrid be before we no longer label it a hybrid of that species? For example, if I have a 5th generation plant descended from R. palustris, with no backcrossing or other species crosses in its lineage, can I really refer to it as a "hybrid palustris"?

My personal opinion is 3 generations.

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Re: what a species is, or isn't

Postby david mears » Fri Nov 03, 2017 12:40 am

Hi Jonathan, may I ask what crosses from the "original" R. palustris have been made, this might determine the class the third/fourth/fifth generation could be called. I am no expert just asking what comes into my head at the time.
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Re: what a species is, or isn't

Postby Jwindha » Fri Nov 03, 2017 10:48 am

David,

No specific crosses, I meant in general. If you continue to "dilute" a species with genes from modern roses like the hybrid teas.
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Re: what a species is, or isn't

Postby Karl K » Sat Nov 04, 2017 1:05 pm

Jwindha wrote:How many generations removed from a full-species can a hybrid be before we no longer label it a hybrid of that species? For example, if I have a 5th generation plant descended from R. palustris, with no backcrossing or other species crosses in its lineage, can I really refer to it as a "hybrid palustris"?
-Jonathan

Jonathan,
Much depends on the species involved, and whether a particularly obvious trait is strongly associated with the species, and is present in the later progeny. This is particularly true of "Rugosas" that are far removed from Rosa rugosa, but still have the rugose leaves.

The real R. rugosa Thnbg. Is a once-bloomer bearing solitary blooms (rarely pairs). The leaves are small (leaflets scarcely more than one inch long). But the rugose character is expressed in some progeny, despite many generations of "dilution". In this case one of the most distinctive traits of the original species happens to be transmitted as a unit character.

If the closely allied R. nitida were used instead, the story would be very different because the leaves are not so distinctive.
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Re: what a species is, or isn't

Postby Don » Fri Nov 10, 2017 2:35 am

>> My R. carolina and R. virginiana both came from Lawyer Nurseries in MT. I ordered a bundle of 25 or 50 of each, because those were the minimums, and selected the five least thorny plants from each to plant out. The differences between the two species in my field are subtle at best, although the R. carolina seem a little healthier overall.

Among several papers on the exact subject of the relationship of American species including virginiana and carolina this is maybe the most relevant though there are a couple other papers as well:

Delimiting Species Boundaries in Rosa Sect. Cinnamomeae (Rosaceae) in Eastern North America

https://www.webdepot.umontreal.ca/Usage ... ystBot.pdf

The take-away is what Peter has said, these species exist in a phenotypic and geneotypic continuum with large overlaps in range and genetics. Ploidy plays a role in genetic isolation as well.

Earlenson also had quite a collection of American species early on and addressed the topic too, possibly Karl King can dredge up something on it.

>> I have started masses of R. carolina and R. virginiana in outdoor seed plots...I hope to ensure that the species genetics that I incorporate with modern roses are contributing the best possible genes from their species.

Hopefully the patches are surrounded by concrete walls to a depth of twelve feet with incendiary fail-safe devices all around.
What doesn't kill them makes them stronger.
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Re: what a species is, or isn't

Postby Karl K » Thu Dec 14, 2017 12:43 pm

Peter Harris wrote:When I began spreading pollen on roses in 1972, I didn't even think about rose species. But gradually I learned about R. spinosissima and other species. And I learned (incorrectly) that species are unchangeable things.
Peter

Peter,
My notion of species changed in the late 1970s. The goldenrods were in bloom, and as I walked among them I saw some very distinct differences. One type in particular had a thicker stalk, and was stiffly erect. I visited a library to find a book on local plants, hoping to learn about the Solidago species. The author wrote that goldenrods hybridize so freely that the lines between the species have become blurred.

Hmm. This statement made me understand that the "species" is largely a matter of faith. Species cannot be precisely delineated because the (assumed) lines of delineation have become blurred. Why should I accept such an assumption? If species evolve by natural selection of the "fittest", how does it happen that various types of goldenrod can co-exist in the same field?

Well, others have had similar thoughts long before me. Bateson (1912) observed Veronica spp. that co-existed as peacefully as the goldenrods.
http://bulbnrose.x10.mx/Heredity/Bateso ... ilure.html

Speciation does not require that a new-and-improve type kill-off all its relatives. And a population can become divided into different "species" while interbreeding. In fact, interbreeding actually hastens the process.
http://bulbnrose.x10.mx/Heredity/mimulus/mimulus.html
http://bulbnrose.x10.mx/Heredity/mimulu ... s2013.html
https://books.google.com/books?id=zpLJd ... &q&f=false

Regarding American roses, it may be useful to consider the American Butterflyweed (Asclepias tuberosa) studied by Woodson (1947, 1953). The 1947 paper has two very instructive maps: I shows the current distribution of three subspecies, and map II shows how the high sea-levels during the Cretaceous, and the ice sheet of the Pleistocene, separated Appalachia from Ozarkia (Ozark plateau plus the Llano uplift in central Texas) and from Orange Island. The modern distribution of the subspecies suggests that subspeciation occurred in these regions.

It is instructive (I think) to compare the distributions of RR. palustris, foliolosis and floridana with those of the A. tuberosa subspecies. A. t. interior has certainly spread further north than R. foliolosa, but the distribution of R. floridana seems more closely parallel, though less southerly, to that of A. t. Rolfsii.

Dr. Erlanson Macfarlane (1966) discussed some of the difficulties in recognizing Rosa spp. She wrote, among other things, "Dr. Boulenger told me that Francois Crepin studied the rose species of the world for thirty years 'and then went mad.' Certainly he was never able to publish any revision of the Genus Rosa."
http://bulbnrose.x10.mx/Roses/breeding/ ... s1966.html

"Boulenger also stressed the importance of the width of the disc at the base of the stamens and the width of the orifice through which the styles and stigmas emerge. These characters of the flower have been largely ignored by rhodologists, chiefly because they are difficult or impossible to study on dried herbarium specimens."

I can only wonder whether pollinators distinguish among rose blossoms based on the relative proportions of disc and orifice. The bees I've observed among my roses do not seem to distinguish much of anything.
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Re: what a species is, or isn't

Postby Don » Thu Dec 14, 2017 3:17 pm

Evolutionary theory has advanced a lot since since we old fossils sat through Biology 101.

The concept of hierarchical species is pretty much obsolete. The DNA is showing us we should be thinking in terms of hybridization networks in which each individual is related to all other individuals to varying degrees.

Hybridization networks are really just an abstract way to quantify and visualize a fitness landscape: https://en.wikipedia.org/wiki/Fitness_landscape. The seminal publications on fitness landscapes would be Stuart Kauffman's works especially "The Origins of Order: Self Organization and Selection in Evolution":

https://books.google.com/books?id=lZcSp ... -5&f=false

and another titled "At home in the universe" which got a lot of press at the time (1996):

https://www.amazon.com/At-Home-Universe ... 0195111303

I've tried to come up with a phrase that condenses the concepts of hybridization networks and fitness landscapes in the way that 'survival of the fittest' describes evolutionary theory but so far I've got nothing. Maybe some of our learned colleagues can help with this?
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