Variation in chalkhill blues

[Susie]

I understand that there is quite a lot of variation in chalkhill blues and also that there are a great many aberrant forms, so my question is when does normal variation end and aberration begin?

I've viewed on line the NHM collection of abs but that only goes so far. Is there more info online, does anyone know?

Many thanks.

[MikeOxon]

when does normal variation end and aberration begin?

Why is it that simple questions can make familiar terms become suddenly difficult? I had a look at my copy of Russwurm "Aberrations of British Butterflies" to see if there was an answer to be found there. All I could see was "When an individual shows extreme variation from the type the term aberation is used. A factor which must be mentioned is that variation is inherited;..."

Several aberrations arise due to temperature or other environmental factors at the chrysalis stage and so are not inherited. A variation that is inherited would be expected to persist in a local population rather than being a 'one off' event.

That's all I can come up with but I'll be interested to hear the views of the experts.

Mike

[Susie]

Some of the chalkhills I saw the other day were browner than I would expect. Some had fainter spots. Others had spots which weren't circular, or were bigger or smaller than I would necessarily expect. Some had really faint markings on the underside of the forewings and on others the upperside the dark edging extended half way across the wing. Are these abs? Beggared if I know!

This little chap this morning has some spots missing near the rear end by the body I think. Is that "normal"?

[Pete Eeles]

I understand that there is quite a lot of variation in chalkhill blues and also that there are a great many aberrant forms, so my question is when does normal variation end and aberration begin?

Good question - the answer to which depends on terms such as "normal" and "extreme". Since both are subjective, I find the naming of aberrations somewhat subjective too. One end of the spectrum is an "aberration" such as Small Copper ab. caeruleopunctata, where this aberration can comprise a large proportion of a given population, and Small Copper ab. schmidtii (see Kipper's avatar) which is extremely rare.

I've viewed on line the NHM collection of abs but that only goes so far. Is there more info online, does anyone know?

I'm not aware of any better online reference. Of course, there are much more-detailed references such as Bright and Leeds' monograph of Chalkhill Blue aberrations, and the unpublished work of Goodson and Read (created when they worked in the Natural History Museum).

Cheers,

- Pete

[Pete Eeles]

when does normal variation end and aberration begin?

Why is it that simple questions can make familiar terms become suddenly difficult? I had a look at my copy of Russwurm "Aberrations of British Butterflies" to see if there was an answer to be found there. All I could see was "When an individual shows extreme variation from the type the term aberation is used. A factor which must be mentioned is that variation is inherited;..."

Several aberrations arise due to temperature or other environmental factors at the chrysalis stage and so are not inherited. A variation that is inherited would be expected to persist in a local population rather than being a 'one off' event.

That's all I can come up with but I'll be interested to hear the views of the experts.

Mike

Correct - variation is not inherited when it is caused by environmental factors.

Cheers,

- Pete

[Piers]

I'm not aware of any better on-line reference. Of course, there are much more-detailed references such as Bright and Leeds' monograph of Chalkhill Blue aberrations, and the unpublished work of Goodson and Read

Bright & Leeds is notorious for it's inaccuracies. H.A. Leeds almost appeared to just make it up as he went along; completely ignoring the work of his forebears and on occaisions describing and naming the same aberration twice, with different names!

The 'Cockayne' on-line data base provides some nice examples of aberrations of British species to give the layman a flavour of things, although it is by no means exhaustive and can not really be relied upon for successful and accurate identification, not least because some of the names are a little muddled up.

There are, as far as I am aware Susie, 446 named aberrations of coridon known to occur in Britain.

Piers.

[Susie]

Cheers Piers m'dears, as I said, a great many!

[Susie]

I should add that I am in awe of your knowledge of such matters, Piers.

[Wurzel]

Perhaps a way round this would be to rename the Chalkhill Blue as the Variable Blue?

As some areas seem to have unusual forms turning up more frequently could this be caused by a resticted gene pool, a bottle neck in genetic exchange in these populations? This off course is dependant on how strong a flier and how far Chalkhill's can range...that's the wonder of Science answer one question and 3 more arise...
Have a goodun

Wurzel

[Piers]

As some areas seem to have unusual forms turning up more frequently...

Really?

Aberrations (in all species, although this relates to the chalkhill blue) are far less frequntly found than in past decades, simply because populations are so much smaller. In addition, many of the great colonies which once 'put out' so many of the fine aberrations figured in literature are sadly long gone, most sacrificed to the plough during the 1940's when we lost so much of our chalk down-land.

Aberration in this species can be found, and some of the minor aberrations such as obsoleta very regularly indeed. However, the halcyon days of being able to expect to find extreme aberrations in this species merely through many hours field work and sheer determination are long gone.

Piers.

[Susie]

We cann still live in hope of finding something interesting though

[Wurzel]

You are correct Piers - Whilst historically there may have been much more variation I was merely referring to the extant populations now - and even if there is less variation from the norm now than historically it appears that some sites (Denbies for instance)have more than there fair share - hence the basis for my question...

So to reiterate - could variations within a population be caused by a resticted gene pool, a bottle neck of genetic flow?

Jeez you didn't even comment on the suggested name change
Cheers

Wurzel

[Piers]

So to reiterate - could variations within a population be caused by a resticted gene pool, a bottle neck of genetic flow?

Yes, in a way...There are some instances (when the gene or genes responsible are present) where homozygotes are produced on an annual basis in small and isolated colonies. There are a couple of tiny populations of small copper on the Dorset chalk that produce ab schmidtii almost every year, and a tiny population of lulworth skipper on the coast which produces a beautiful silver-blue form, again pretty much annually.

This happens because the colonies are so small and isolated, were they larger then the gene could become buried within the colony or meta population.

However, with the chalkhill blue, some of the largest colonies were the ones producing the most aberrations. It does depend upon which aberration we are discussing though. In addition, sometimes simply because of the laws of chance you need a big colony to maximise your chances of success; if the aberration you are searching for occurs at a ratio of roughly 1:10000 then a colony where 100000 or so fly together at peak would be a good place to start, rather than the one at the local abandoned quarry where no more that a dozen are ever seen at any one time.

you didn't even comment on the suggested name change

As it happens I am very relaxed about common names, I am still a 'small mountain ringlet', 'wall brown', and 'duke of Burgundy fritillary' man myself. I'd quite like to see the return of 'hog' to displace 'skipper'. That would be nice, but irrelevant in the grand scheme of things; I don't really care what people use as common names for butterflies as long as each individual is consistent.

Piers.

[Matsukaze]

Hi Piers,

To reply to a question of yours from a week or so back, the Chalkhill Blue still survives at Stoke Camp but not in very good numbers - a decline in population of the foodplant which has become distinctly scarce is probably the issue. There are still plenty of Chalkhills across the road at Draycott Sleights and along the ridge at Westbury Beacon. For Small Blue the situation is reversed with Stoke Camp being the strongest colony on the Mendips if not the whole of Somerset, and the slopes there being carpeted in the foodplant. The trick is going to be to improve the site for the Chalkhills without risking the Small Blue population.

Were the Mendip Chalkhills ever known for their aberrations?

[Piers]

Hi Matsukaze,

Many thanks for the information.

I remember when Dolebury Warren was the site on the Mendip Hills for small blue, and I also recall my distress in the late 1970's or early 1980's when upon visiting the hill I discovered that a host of grazing sheep had eaten off all of the kidney vetch flower heads which should have been harbouring ova and developing larvae. Am I correct in thinking that the colony went extinct but has subsequently been reintroduced or has recolonised..?

I'm pleased to hear that the small blue is doing well at Stoke Camp, even if the chalkhills are not. It certainly illustrates the conundrums that can be faced by conservation organisations when managing a relatively small territory; often the success of one species shall be at the detriment of another.

With regard to chalkhill blue aberrations on Mendip; certainly a number of minor aberrations could be found year after year (as would be expected in any colony really) and the beautiful aberration fowleri (where the black border is replaced with white) was also known from the area. Having said that, we rely of course in the main upon records and specimens from the collectors who lived in the region in the early to mid 20th century, and the majority of these gentlemen would have journeyed to the well known and productive colonies in Wiltshire, Buckinghamshire, and Hertfordshire in their hunt for aberrations rather than risk 'wasting time' working smaller colonies closer to home that were not known for producing good numbers of extreme aberrant forms.

The only other chalkhill record of note that springs to mind for the Mendip Hills was of a small colony centred around an "abandoned quarry somewhere near Priddy" where the majority of the males were of the beautiful silver hue similar to those that were once found on the eastern Dorset coast. This vague record comes from the late 1980's/early 1990's so who knows, it could still be extant, although I know of nowhere in the area that fits this description.

Additionally of course (regarding aberrant forms generally) the collectors of old would devote many hundreds of hours searching for that prize specimen, often returning day after day to known sites and working through thousands and thousands of butterflies, netting and examining each one in turn, in the hope of finding just one 'prize' specimen. Few of us have the time, inclination, or patience to do this nowadays; and indeed, without netting and examining every specimen that you see it would be impossible to be as thorough as our spiritual antecedents (and I caveat this by stating that I do not advocate a return to such methods either). Therefore it could be argued that even if such large and productive colonies remained today, we would probably not be recording the quantity of aberrant forms that were recorded a century ago.

Piers.