Here, extra legs and here Scientific American, page 2 mentions parasites other causes are noted.
It takes no great leap to find potential for attribution here, well outside of aberrantly rapid evolution. Isolated populations will be exposed to different environmental factors, including vegetation, chemicals (natural and manmade, the latter in precipitation or runoff) and quite possibly different pathogens. One population exposed to a chemical (natural or manmade) or a pathogen, be it viral, bacterial, fungal, or parasitic, will naturally successfully breed only those who can adapt to or are resistant to that pathogen or chemical and still produce viable young.
That change could handily occur in just a few generations, not even 8000 years.
The other population, not exposed, might not fare as well if the pathogen or traces of the chemical are transferred in the act of breeding and that population has little or no natural resistance to the pathogen.
Here, extra legs and here Scientific American, page 2 mentions parasites other causes are noted.
It takes no great leap to find potential for attribution here, well outside of aberrantly rapid evolution. Isolated populations will be exposed to different environmental factors, including vegetation, chemicals (natural and manmade, the latter in precipitation or runoff) and quite possibly different pathogens. One population exposed to a chemical (natural or manmade) or a pathogen, be it viral, bacterial, fungal, or parasitic, will naturally successfully breed only those who can adapt to or are resistant to that pathogen or chemical and still produce viable young.
That change could handily occur in just a few generations, not even 8000 years.
The other population, not exposed, might not fare as well if the pathogen or traces of the chemical are transferred in the act of breeding and that population has little or no natural resistance to the pathogen.
A significant difference between the case you are citing and the frogs in the article is that your case is about a phenomenon that appeared within a single community of frogs and the article's case is about a split group that only exhibits the defect when interbred. However, your suggestion that exposure of one group to a pathogenic or parasitic environmental agent might have happened. In that case, it would have contributed to the environmental pressures that, through natural selection, favored genetic drift that was successful at overcoming this change to the environment.
However, while an infected parent might pass along a pathological infection to its offspring, it is unlikely that this would become a heritable entity. Especially if the infectious pathogen prevents viability.
In short, a pathogenic infection is more likely to have been a factor responsible for the genetic drift of one group than to have become a heritable trait itself.
I won't add much to what Antonello said, other than you seem to be ignoring my statements that since the problem occurs with in vitro frogs, it's not an ecological factor, but rather a heritable one.
The developmental problems in the offspring between the northern and southern strains are based on genomic incompatibilities, not ecological factors. As Antonello said, a pathogen could easily be the driving force (in just a few generations, by your own words) to create genomic divergence.
Do you have reason to doubt this? Have you read the research article in enough depth to criticize their methodology and see evidence for your competing hypothesis?