Question for Hybridizers
 

I have been listening to Charles Darwin's Origin of Species. and I seem to be missing something. If hybrids are sterile, how is it that you are able to get a past the primary hybrid?

Hybrids aren't sterile normally to my knowledge.

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Hmmm! I think I've heard people say here that hybrids are for he most part sterile. thanks for the reply.

I don't really have any room to talk about this though lol...
I'm not exactly versed in this area.

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Most hybrids are not sterile but some are. When you cross orchids that are closely related they are usually fertile and can be used for further breeding. But some orchid hybrids wind up being sterile or others are just very difficult to breed.

Thanks Tucker, His book refers to variety's and different species. I need to re listen to that chapter. Maybe he was talking about in nature. or between unrelated species.

All living organisms on earth are related but they need to be closely related to breed and have fertile offspring. Some organisms are related closely enough to breed and have offspring but are far enough apart on the evolutionary tree that the offspring won't be fertile. A good example is a horse and a donkey. They're related and they can breed but the result is always a mule. A mule is bigger and stronger than either parent but is always sterile.

it's beginning to sink in. he also referred to the same cross and basically the same tree reference. Thanks again. I think I will still redo the chapter, I can be a little thick.

I didn't know he was still around! LOL :rofl:

LOL no he may not be around, but his work and finds still exist. The man was brilliant.

with orchids chromosome count determines whether the orchid is sterile or fertile ( all organisms ? ).
Essentially there are 2N, 3N, 4N, 4N+ orchids. The odd numbered ploidies are always/mostly infertile - so 3N x 3N will never propagate by seed. They can be cloned however - except for paphs which can't be cloned irrespective of ploidy. There may also be others, I am not trying to be exhaustive.....

Some breeders use chemicals to artificially change the ploidy of seeds when sown, hoping for progeny with better characteristics/vigour. 4N flowers for example are normally much larger/have better quality than 2N or 3N flowers of the same grex. Occasionally a 4N grex may arise in nature or a batch of seedlings spontaneously....

As can be expected, ploidy is complicated - and if you are interested there are articles online. Doing random crosses with any orchid without investigating ploidy compatibility/background is a primary reason for the failure of the pollination or for an infertile seed capsule.

Thanks, The basic's are complicated to me at this stage. I'm really only interested in the knowledge, I don't think I have the wherewithal to do it.

It all goes back to ploidy in animals also. There are species (such as in cichlid fish) that are fairly closely related AND have the same ploidy; they can interbreed (as long as they have not drifted far enough apart to make the act difficult or the participants unwilling) and produce fertile offspring. Even where the ploidy is different and the offspring normally sterile, there will very rarely be a fertile individual who arose from gametes that didn't segregate normally, resulting in an individual with the normal ploidy of one of the parent species. In the classic mule example, there have rarely been fertile mules- they breed as if they were horses.

Don't forget that darwin was writing in what, 1860? Things have advanced in the understanding of inheritance, since then, and Darwin was mostly dealing with animals in his book, which in most cases do produce sterile offspring.

With plants, species isolation does not necessarily require genetic barriers as geographic isolation and pollinator specificity are generally enough to keep the Sophronitis out of the woodpile, as it were. Why waste time and energy evolving genetic barriers when you can just evolve to utilize different pollinators, or have your pollen adhere to a different spot on the bee than others related to you?

Most things on the planet didn't see us coming, so they didn't bother evolving against great clumsy apes with toothpicks running about muddying the genes up.

-Ceci

---------- Post added at 07:08 AM ---------- Previous post was at 07:02 AM ----------

Hell, not only has understanding of inheritance changed in the last 100+ years, but understanding of how things actually relate to each other genetically, at all. Remember, when Darwin wrote The Various Contrivances by which Orchids are Fertilised by Insects, pretty much everything in the laeliinae except Cattleyas were Epidendrum. Darwin got it on the gist of things, but his inspiration must be considered with context. Hell, not just time, but Darwin's own perspective. After all, he wasn't even a scientist, in the strict sense. He was an inspired dilettante with an earth-shattering Idea and the patience to make the observances to back it up.

-Ceci

And of course increased understanding of things like epigenetics.

In Darwin's day, they didn't really understand inheritance at all (at least not in anything we'd consider today to be "detail"); once we'd worked out what DNA was (and how it was responsible for inheritance, a surprisingly recent finding; for a long time, protein was suspected to be behind inheritance, as people couldn't imagine how just 4 bases could "code" for so much complexity) things started making a lot more sense.

Mendel was the first person to recognised that inheritance followed distinct "packets" of inheritance (we call these genes or alleles now). If you're not familiar with this part of the history of science (DNA as the molecule of inheritance) DNA and Molecular Genetics gives a nice overview.

Ploidy isn't the only barrier; chromosome number can also play a role. (Ploidy = the numbers of copies of a chromosome you have in a cell). Humans are diploid, their gametes, haploid. Chromosome number in humans is 46 (23 pairs). Having extra copies of a particular chromosome can cause severe problems, most of which are called "death" (most commonly of early stage embryos), but a few go on to produce conditions like Downs Syndrome and intersex (e.g. XXY).

Unequal chromosome numbers cause difficulties when cells divide; this is one of the major reasons mules are usually sterile. Similarly, look at the table on the second page of http://aob.oxfordjournals.org/content/82/2/189.full.pdf You'll see lots of "intergeneric" hybrids between Laelias and Cattleyas (n=40) and Vanda, Rhychostylis, Neofinetia and Phalaenopsis (n=38), but I don't recall any hybrids between those two. Indeed, to a large extent, the "alliance" concept tends to group together plants with similar chromosome numbers which tend to hybridise fairly freely, even between genera. This is not particularly surprising, as Alliances tend to also more or less follow taxonomic groupings (families and the like) too, although I suppose some are probably para- or poly- phyletic (I haven't looked at this in detail).

I'm not sure if this is a factor in orchids, but you do also get a barrier called "Cytoplasmic Incompatibility" - Cytoplasmic incompatibility - Wikipedia, the free encyclopedia

---------- Post added at 03:26 PM ---------- Previous post was at 03:05 PM ----------

Flhiker - not sure if this discussion has clarified the topic to you at all?

The key is perhaps to realise that not all hybrids are sterile. The orchids are a relatively young group that doesn't seem to have as many barriers to hybridisation as some others may. In addition, humans with toothpicks and the like then surmount many natural "barriers" to interbreeding such a geography, pollinator specificity and even seasonality of blooming.

Many orchid hybrids are indeed sterile "dead ends" with regards to future breeding (like many triploids), but with meristem culture, and repeated crossing of the parents, you can get lots of those plants anyway (just like you can get lots of mules by repeatedly mating horses and donkeys).

You may find it useful to know about the various "species concepts" in biology, knowing that not a single one of them is globally applicable across all groups, nor accepted by all biologists (a species is an artificial construct used by humans to make more sense of the world). https://en.wikipedia.org/wiki/Species_problem

Also, of course, until Darwin (and his contemporaries) most people thought of species as fixed; they didn't think that they could change through time (evolution), and it wasn't obvious to all that there were distinct lineages of things which were derived from common ancestors. Once you take on board the Modern evolutionary synthesis - Wikipedia, the free encyclopedia and the further developments to it, the biological world starts to make a lot more sense.

Hope this helps!

The orchid family is somewhat unique in that not only can you cross different species, but also different but related genera and get fertile offspring.

To put this into a different perspective:

Most animal species have a genetic barrier to inter-species breeding. Some that are very close (horse x donkey = mule) can produce off-spring, but the hybrids are usually sterile. There are some cat breeding programs, using various wild species (and also lion x tiger). While their off-spring are not sterile, they are 'low fertility'.

Orchids do not breed the way animals do. They rely on a pollinator, whether it be an insect, bird, reptile or whatever. Since the flowers have evolved together with their species specific pollinator, there has been less of a need to evolve genetic barriers to cross pollination with other species. As a result, breeding is possible within broad groups of orchids such as:
Abt 1000 Vandaceous species
Abt 1000 Cattleya family species

From time to time we run into hybrids, which are infertile, but more often than not it is because the plant is triploid (3N) and not 2N (std) or 4N (rarer, but normally fertile).

In some cases the infertility can be traced to incompatible number of chromosomes. For example, the 2N number in Paphiopedilum varies considerably from species to species.