Hybrid speciation in the USA

[NickB]

My son posted me this link on speciation - The Appalachian tiger swallowtail, Papilio appalachiensis—that evolved from mixing between the Eastern tiger swallowtail, P. glaucus, and the Canadian tiger swallowtail, P. Canadensis
Interesting stuff...
http://www.futurity.org/science-technol ... dium=email
N

[Paul Wetton]

Very interesting Nick

Makes me wonder if the wierd Heath Fritillaries we saw in Switzerland that had traits of both False Heath and Heath Fritillary could possibly be hybrids. I guess the only way to know for certain would be to perform some gene sequencing and compare DNA.

[Padfield]

Hybridisation is surprisingly common, but it should be remembered that false heath frit and heath frit are not quite so close as their appearance sometimes suggests.

See http://tolweb.org/Melitaea/70305

Guy

[David M]

Do the butterflies have to belong to the same genus in order to interbreed?

[Padfield]

Not necessarily, in principle (because the definition of 'genus' allows these taxa to be arbitrarily large or small); but because animals don't exhibit polyploidy (unlike plants) there is a requirement for quite good matching of gene sites on the chromosomes if any offspring are to be viable. This becomes increasingly improbable with genetic distance. Given the current trend for rather large, umbrella genera, I would expect viable hybrids between individuals of different genera to be extremely rare.

Their rarity will be increased by the physical and ecological barriers to interbreeding that evolution usually generates.

Guy

[NickB]

Thanks Guy; it appears as we learn more about the genetic make-up of our butterflies, many of the seemingly similar species, which were named and classified before DNA sampling gave us the very specific details, appear much further removed from each other than those names might imply.
As Guy alluded before, in the light these recent developments, maybe Linnaean taxonomy has had it's day...? The question is, how should it be replaced?

[Padfield]

I see a possible way forward, but I propose it more as a speculative prediction of what might happen than a suggestion of what should happen.

The science has moved from being essentially qualitative, giving names to discrete taxa, to being largely quantitative. Species, in particular, can no longer be thought of as discrete partitions of the living world - the situation is far more fluid than a system of discrete names permits. The binomial system of naming can no longer represent the scientific picture with anything approaching completeness or accuracy. I therefore suggest that nomenclature and quantitative science should be allowed to drift apart, to maximise the usefulness of each in their appropriate domains. I would let the system of nomenclature describe actual breeding communities, without obliging it to reflect the various theoretical relationships between disjunctive communities that no longer have any actual contact. The quantitative science can deal with all that. For example: The Swiss and Spanish populations of Zephyr blue are entirely discrete and have perfect taxonomic integrity. The question of whether they are 'the same species' is a purely theoretical one, better answered in terms of numbers than in terms of 'yes' or 'no'. The same applies to all those island graylings. In practice, there are discrete populations on different islands. It is taxonomically valid to name each population. The further question of the precise relationship between them is far better represented by numbers than by names.

In short, my proposal is this:

Name the actual breeding populations. That is a useful exercise, especially for the field naturalist.
Express the more precise relationship between breeding populations by quantitative analysis and multidimensional graphs of evolutionary relationships.

There are lots of objections to this, but I can see something like it happening.

Guy

[NickB]

As Roger said to me, "Let's face it, does that butterfly care whether it is a Rosy Grizzled or a Grizzled or an Oberthur's?
It is perfectly happy just being".

Naming and classifying it is our obsession however, so the genetic tree and distinction of the various populations by their physical characteristics and geographies does seem a more valid way to go, even if it has to lead to more headaches for traditional taxonomy. P. pylaon helvetica.....P.pylaon iberica ...etc. perhaps.