Joanae ancestors

[Kenelm Philip]

> ...about 15000 years ago virtually all of machaon's current range
> was covered with ICE - where was "machaon" at then?

_P. machaon_'s current range includes Interior Alaska and the Seward
Peninsula. These areas were ice-free during the last glaciation, as were
adjacent regions in NE Russia where _machaon_ also flies.

> Basically - dark taxa inhabit the north - colorful taxa the tropics.

We have a fair number of Pieridae in Alaska--and _Pterourus canadensis_
is not darker than _P. glaucus_. Nor are our Lycaenids darker than the
same species at lower latitudes (and _L. phlaeas feildeni_ is, if anything,
lighter than more southerly forms).

	I would agree that northern butterflies are less colorful than
tropical ones, on the whole (although our Arctiidae are pretty gaudy).
And the large number of _Erebia_ species certainly gives the Alaskan
fauna a higher proportion of dark species. But I see melanism as occurring
primarily in two situations:

1. Rockslide/scree species. Here we have an assemblage of very dark species,
both butterflies (_Erebia mackinleyensis_, _E. occulta_) and moths (various
_Sympistis_, _Acsala anomala_, etc.) which live in rockslides. The rock
may be dark, or white (dolomite/limestone)--so this is not protective
coloration. There is also a dark race of _B. distincta_ on the western
North Slope--another scree species.

	My guess is that these species are using the relative warmth of
the rockslides (compared to the surrounding tundra) to exist north of
their expected limits of range--and their darkness allows them to profit
from every available bit of heat. But that's no more than a guess...

2. 'Arctic melanism'. This shows up in the Arctic Coastal Plain in Alaska,
and in the Canadian Arctic Archipelago. There is a dramatic increase in
melanism for some species as you move from Interior Alaska to the north
coast and the arctic islands. _Boloria improba_ from Melville Island
have to be seen to be believed! Female _Colias hecla_ from the Beaufort
Lagoon area in Alaska, or from Banks Island, are darker than those from
Eagle Summit. (However, specimens from Ellesmere Island are not particu-
larly dark, so the situation is more complex than one might think.)

	Melville Island is very near the limit of any species of butter-
fly's ability to exist in the north, owing to the cool cloudy summers in
the western arctic islands--so it's not surprising that melanism would
be extreme there.

	But I would not say that most Alaskan butterflies are darker than
the same species from warmer climes. The larger proportion of dark species
is due mainly to the richness of _Erebia_ here.

							Ken Philip
fnkwp at uaf.edu




 
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