www.ukbutterflies.co.uk

I notice several books, including Jeremy Thomas & Richard Lewington Butterflies of Brittan and Ireland, suggest male Chalkhill wander from nearest breeding sites more than females.
Is this really so?

Why do the males wander more than females?

If it has anything to do with dispersal and colonising new sites, I think, this is a rather strange strategy. It would surly make more sense if females (preferably fertile ones) were to wander occasionally.

Or is it just because males are more numerous and easier to record that we think the males wander more?
I suspect there is more to it than strategies for dispersal.


Crispin

Great question Crispin! Just heading out the door and won't be back until the weekend, so will attempt an answer then.
Neil

I'm going to speculate on an answer and then see what the Kipper thinks of it when he gets back.

Outbreeding confers genetic strength. Butterflies that breed in relatively localised colonies will benefit from genetic exchange between nearby colonies. In principle, either males or females or both could wander from their birth colony in search of others in which to breed, but in practice females get mated early and are then egg-bound. Flying in search of another colony in which to lay her eggs (so the next generation would outbreed) would be energy intensive, because eggs are heavy to fly with. Thus, it makes more sense for the males to have this instinct built into them.

I would suggest, therefore, that males wander from their birth colony as part of Mother Nature's strategy for ensuring genetic exchange between nearby colonies in the larger regional population.

Dispersal obviously requires the females to move, so I suspect this particular fact is not dispersal-related.

Guy

EDIT : Thinking about it, the fact that males can ensure outbreeding in the same generation, while females can only ensure outbreeding for the subsequent generation (assuming they are mated soon after emergence) might be sufficient on its own to answer the question, without worrying about the energy expenditure of flying egg-bound.

I have been observing UK Butterflies ( and butterflies elsewhere ) for over sixty years... .

On more than two occasions, I have seen Chalkhill Blues far removed from their Upland Chalk. Even seen them in lowland Broadleaf Woodlands whilst looking for woodland Butterflies such as Apatura iris. Only a small sample over all those years but, on each occasion those observed far removed from the Chalk have been ... females. The Chalkhill Blue is a strong butterfly compared to most other Blue species of similar size. I suspect it is a stronger and more powerful flyer than the Large Blue based on my observations.

Whilst taking a breather eating my sandwiches sitting on a fallen tree in a wide woodland ride one hot day in late July, a female Chalkhill Blue settled briefly on some small flowers near my feet, feeding briefly for about ten seconds. Then was off again flying strongly along the ride just above ground level at a speed a migrating Clouded Yellow would find hard to match...

I have also observed a less strong flying British butterfly making its way along roadside hedges many miles away from its type habitat... That Butterfly being the Wood White... By an amazing coincidence, a Wood White making progress along the open plan front gardens where I live passed through my own garden. I had my net handy at the time so netted it to confirm identity ~ after all, it could have been a slighly undersized weak flying Small or Green Viened White... such individual specimens being misleading unless positively identified... My son was a pre-school lad then so that must have been over twenty years ago. I then knew of no locality for the Wood White in my area within a twenty mile radius and I know most quite well over fifty years plus observations.

However, the woodland about seven miles away from where I currently live ~ as the Crow or Wood white flies ~ now has this charming butterfly present. I almost lived in that wood as a schoolboy in the 1950s and saw many fine woodland species there ... including the Greyling. Howver, never saw a Wood White there where now it breeds... saw females egg-laying on low vetches...

It's freak one-off or two-off observations like these which give us a better idea of the way these things work.
..
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In the 1950s, I caught a male CHB at Shirley, near Bimingham. None had been recorded anywhere near there before.

Tony M.

Guy said:

I would suggest, therefore, that males wander from their birth colony as part of Mother Nature's strategy for ensuring genetic exchange between nearby colonies in the larger regional population.

Probably the chief reason why males of any order wander. An important part of natural selection too. Think back lads, did you go for the girl next door?

padfield wrote: Outbreeding confers genetic strength. Butterflies that breed in relatively localised colonies will benefit from genetic exchange between nearby colonies. In principle, either males or females or both could wander from their birth colony in search of others in which to breed, but in practice females get mated early and are then egg-bound. Flying in search of another colony in which to lay her eggs (so the next generation would outbreed) would be energy intensive, because eggs are heavy to fly with. Thus, it makes more sense for the males to have this instinct built into them.

Yer, I think your right there and that is sort of what I thought after I had posted.

padfield wrote:EDIT : Thinking about it, the fact that males can ensure outbreeding in the same generation, while females can only ensure outbreeding for the subsequent generation (assuming they are mated soon after emergence) might be sufficient on its own to answer the question, without worrying about the energy expenditure of flying egg-bound.

So, male "A" mates with female "A" who stays at the site. Male "A" moves to a new site and mates with female "B" resulting in genetic exchange and outbreeding.

IF I have interpreted this right, it possibly suggests the females are not moving - or very little amusing conditions and the site are suitable. So, that it begs the question about colonising new sites. I would expect there is some movement in the females possibly caused by environmental change and certain genetic triggers. I remember something about that with saprophytic beetles when they run out of dead wood to feed on.
It also makes me think about the maximum carrying capacity or threshold of a site and at what point does a site or patch become over crowded - resulting in dispersal(?). I don't expect answers, these are just thoughts that are going though my mind.

The fact females get mated early raises another thought:
Would an un-mated female, say from a site where there are few males, be more likely or able to disperse and fly further in search of males?
Something tells me she probably wouldn't bother.
That then comes on to the size of the thorax or wing muscles. Have females got larger thorax or wing muscles, therefor they have the potential to fly further - I think so.

Crispin

Hanski's study of the Glanville fritillary found that emigration rate is increased by small patch size and by low density of conspecifics (p.232) and that females tended to disperse more often than males (p.220).

http://books.google.co.uk/books?id=jsk4 ... &q&f=false

It would seem likely that the recent colonisation of Warham Camp in North Norfolk (to southeast of Wells) is entirely natural; a few wandering females from a strong colony (eg Devils Dyke near Newmarket) drifted off with the southwest wind. This combined with their apparent in-built desire to find new less-crowded areas offers an easy explanation – no need to suggest human introductions.

I have observed in the past that population densities of new colonists (eg, the Comma in the Yorkshire Moors) can be very high. The Horse Chestnut Leaf Miner is another example. The accepted theory, as recently explained on Autumn Watch (can’t actually stand the programme but it happened to be on) is that natural control, the parasatoids, don’t follow the colonists until some while later with the result that initially the population explodes.

I read in the Norfolk Branch newsletter that the Chalkhill Blues at Warham are doing very well. Doubtless, the population will plummet once the parasites arrive over the next few years.

Jack

Females of all species clearly do wander, or else there would be no colonisation of new areas. But in blues in particular the males are the ones you see considerable distances from their home colonies. Marking experiments in the Rhône Valley in Switzerland have shown that male iolas blues may cruise many kilometres along the valley in a day and are often seen nowhere near their foodplant, bladder senna, though when they do find it they stop and nectar. In other species of blue males also travel great distances to mineral sites, while females do this much less readily. In blues, unlike most groups of butterflies, the male is typically the bigger insect - this is especially noticeable in some of the smaller species, like little blue and short-tailed blue. In short, my experience is that in blues, the male is the flighty one, who is most likely to be found at random far from home and who is most likely to provide channels for genetic exchange between different parts of a large population.

The situation may well be quite different for other groups.

Guy