What is the Blackberry That Ate The Pacific Northwest?

It's a member of the European Blackberry Complex, which includes R. fruticosa, R. armeniaca, R. bifrons, R. ulmifolia, and others. There's a basic, biological problem with members of this complex. (This explanation is somewhat simplified.)

Most species reproduce sexually. A very common, widely used definition of the species is a group of organisms that breed with one another, producing fertile offspring. Even if they looks a bit different, they're the same species if they breed together. Consider variation within the species humans, or mallard ducks, or dogs, etc. We can tell where the species boundaries are by who breeds with whom (producing fertile offspring). Within sexually reproducing species, genes get mixed up, so you can have blonds with blue eyes, blonds with brown eyes, brunettes with brown eyes, brunettes with blue eyes, etc.

Some species don't have sex; they are asexual. Many of these reproduce by bulbs, rhizomes, or other obviously asexual means, but some plants are apomictic, producing seeds without sex. In asexual species, the genes don't get mixed up, so you might get only blue-eyed blondes and brown-eyed brunettes, no other combinations, for example. Mutations introduce some variation to asexual species. To accommodate that variation, we tend to use broad species concepts for completely asexual species, though not all biologists agree.

Members of the European Blackberry Complex reproduce in a way that really messes with our species concepts. They mostly set seed asexually. What seem to be distinct individuals are actually clones, and a single clone might cover a whole county or more. However, blackberries also have sex. They may have sex even with distantly related members of the complex. The offspring of such crosses can look a bit different from the blackberry clones that were already spreading around the area. Are these clonal populations best thought of as different species or just different genetic individuals? Should every slightly different type be called a species? (Some people would argue yes, which is why you have 2000 named dandelion species in Europe.) If not, how much difference is necessary to name a species? This really messes with biologists minds. We don't agree. We probably will never agree.

Meanwhile, the blackberries go their merry way, spreading asexually through their stems (canes), asexually through seeds, and occasionally through sexually produced seeds. They do not care about our human need for neat, mutually exclusive names for talking about the kinds of blackberries.

This is why when people disagree about the species concepts of Rubus bifrons, R. armeniacus, and R. ulmifolius, I Don't Care. Call it what you want. I'll try to follow the herd when/if there is evidence of agreement about what species names we will arbitrarily apply to these plants that don't have species concepts the way we wish they would.

Publicado por sedgequeen sedgequeen, 10 de julio de 2021

Comentarios

So one question about this: I have heard that one of the major benefits of sexual reproduction is that it increases genetic diversity, so that a single parasite or disease can't spread too quickly, because it needs to adjust itself to organisms being slightly different.

So if all of the plants in our local area are actually genetically identical clones, is it a situation where a disease or parasite might attack them sometime soon? It is especially interesting because, in general, all of that complex seems to be very hardy, and unlike some other trees, I have never seen, say, aphid infestation on them. Or galls, for that matter.

Publicado por mnharris hace más de 1 año (Marca)

As a side note: It could be mentioned that one of the reasons of success of this Blackberry complex, is as a result of deforestation. Acting as a "pioneer" species, these are perfect to take opportunity of the newly sunlit environs.

Publicado por benjaminleo hace más de 1 año (Marca)

@mharris -- Yes, genetic variation and thus the ability to escape pathogens is a major reason sexual reproduction is favored evolutionarily. Rubus get the benefits of both sexual and asexual reproduction. Fast reproduction of well-adapted genotypes, without worrying about pollinators, weather, etc., through asexual reproduction. Genetic variation from the occasional sex. Perhaps a disease will wipe out one clone or several related clones, but there are other clones around to fill in.

There is evidence that one of these blackberry "species" introduced to Oregon is susceptible to a rust fungus that has recently been introduced. The others aren't, though.

Publicado por sedgequeen hace más de 1 año (Marca)

@benjaminleo -- True. We've worked hard to create lots of Rubus habitat!

Publicado por sedgequeen hace más de 1 año (Marca)

Thanks for the post, Barb! It was a fun (and funny) read. :)

Publicado por quercusboletus hace más de 1 año (Marca)

Glad you liked it, Kevin!

Publicado por sedgequeen hace más de 1 año (Marca)

Do you know offhand which groups this happens in? Hieracium for sure, but what about Rosa? I do a lot of looking at the impact of introduced species (in Cape Breton Nova Scotia), and R. multiflora is a huge problem. I find plants with many of the same behavioural characteristics (climbing and killing trees) that are, for example, thornless, or don't have the bearded petiole we usually see.

It seems to me, that with the rapid introduction of many genera by humans to each other that we are "speeding up" the evolutionary process with unpredictable results. Should we be "circling the wagons" around native plant species that support most of our animals? (no rush on an answer BTW, I am just excited to find someone with your depth of knowledge and experience.

Publicado por marianwhit hace 8 meses (Marca)

I know this happens in Rubus, Crataegus, Taraxacum, and Hieracium. Probably happens in many others that I don't know.

--Barbara

Publicado por sedgequeen hace 8 meses (Marca)

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