Hix said:All of a sudden this thread got really interesting (for me anyway).
Sdaji said:...Bynoe's geckoes, which are hybrids, as the result of one hybridisation event between two species, then a back cross, and then no more hybridisation for over 100,000 years...The grasshoppers I've been working on for about 18 months are hybrids, from hybridisation which occurred around 100,000 years ago..
I'm curious how you know it was a hybridisation event that spawned these tow species, and not the usual evolution for selected adaptations. And what do you mean by "back cross" in this context - back cross to what? If they were two dfifferent species spawning a hybrid, how can that be a back cross?
Hix
(Note: Re my first statement - I'm not suggesting the discussion of Maculosa is not interesting, just that Sdaji's statements I found really interesting.)
In the case of the geckoes, it's very easy (well, easy for me to understand now that other people have done the hard work ). To avoid typing for two or three pages, I'll give the 'nutshell sized' version. They are triploid, two sets of chromosomes coming from one species of Heteronotia, one from another. There has been no recombination between the 'odd' set of chromosomes and the other two. With this information, and knowing that the species is an obligate parthenogen, reproducing clonally, we can deduce that there must be an intermediate form, a parthenogenetic diploid hybrid. This hybrid backcrossed to one of the parental (sexual) species (obviously a diploid hybrid parthenogen with a 'normal' sexual male of one parental species), creating a triploid parthenogen. We can work out which species was male and female by looking at the mitochondria, which is clonally carried through from the original sexual female to the diploid parthenogen and then to the triploid back cross. We can work out which species the back cross male was, by looking at which species' DNA is represented twice in the triploid genome. We can work out how long ago this happened using molecular clocks in the mtDNA.
As for the grasshoppers, they're diploid, so it's even easier. A lot of the work was done a few decades ago and was cutting edge at the time. The parthenogenetic species (Warramamba virgo) is a hybrid between W. P169 and W. P196 (soon to be given 'proper' names). Phenotypically, P169 and P196 are extremely different, so much that at first, the guy who proved that virgo was a hybrid between the two wouldn't even accept that P169 was part of the phylogenetic group at all. It was discovered that virgo was a parthenogen when someone was out collecting morabine grasshoppers and noticed that all of this species was female. The grasshoppers (virgo) look just like W. P196, so it was assumed it was just a parthenogenetic form, back then they couldn't do fancy genotyping, just crude karyotyping. Don't ask me how, but another researcher came up with the hypothesis that virgo was a hybrid between P169 and P196, Michael White thought that was absurd, as he didn't even think P169 was remotely related to either. To attempt to disprove his critic, Michael White kept P169 and P196 together, to show that hybrids couldn't be produced, but he ended up proving his critic right, as he did produce hybrids and they were parthenogens! More recently, more advanced genetic testing (which I've had the privelage of watching the process of and then sharing the excitement of the fresh results) have confirmed the hybrid findings. Again, by looking at the mtDNA, we can determine which of the sexual species supplied sperm and which supplied eggs. The recent testing has also shown that there are many, many more clones than were initially thought, and also that these clones arrose from different populations which were genetically and phenotypically quite distinct (the sexual species/populations are still around and we can still go and collect them for comparisons). Again, 'molecular clocks' in the mtDNA are used to estimate how long ago the hybridisation events occurred.
Does that answer your questions? I can ramble on a bit more if it doesn't Parthenogens are lots of fun