Paul Wetton wrote:Hi Neil
Some interesting information there. This just backs up my argument in that the genetic mingling you refer to would have been perfectly natural and wholly acceptable.
The Swallowtail was just an example of a possibility that was brought up by Jack.
My worry is where the gene pool of a very small population of native butterflies may be adversely affected by the introduction of a different race of individuals. This is all theoretical and I guess that a large influx of genetic material may be required to totally overwrite that which is already present.
The problem is it is not as simple as that. Take the Swallowtails that used to exist at Wicken Fen until the 1950s.
They had been isolated for about 100 years or more and eventually succumbed to changes in the habitat caused by the fen drying out a bit. They were measurably different from Norfolk Swallowtails and had changed over time. Their thoraxes were smaller and this is probably due to negative selection for vigorous dispersing flight.
So that population may have been more sensitive to "bad" or different genes.
Take the Marsh Fritillary for example. It is possible with detailed study to identify the location at which a photograph was taken by examining the differences in the markings on the wings of the butterfly. Some years ago I was tested at this by a colleague at a BC meeting and placed every one of his photos correctly. I doubt I could do it now because I don't have the time to see all our Marsh Frit colonies in the summer. Back then I knew all of them.
Why do they vary like this? We don't know. We don't know why butterflies have the patterns they have on their wings.
There is an interesting book by a chap called Nijhoot on this but it doesn't explain everything. One interesting piece of information suggests that parasitism and melanin production might be linked. It is a complex matter.
One of the American species related to the Marsh Fritillary has actually been shown to be able to tell plants from its habitat apart from the identical looking plants from another site where the butterfly also occurs.