Geographic variation in wing melanism of the butterfly Parnassius phoebus F. (Lepidoptera: Papilionidae)

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Abstract
Butterflies from higher elevations and latitudes are often darker than populations from low elevations and latitudes. This "alpine melanism" may be an adaptation to colder environments and may be correlated with smaller size. I quantified geographic patterns of variation in wing melanism and size for the butterfly Parnassius phoebus to determine if individuals from populations living at higher elevations and latitudes are smaller and more melanic. The ratio of black to white scales in the basal area of the hind wings is well correlated with the elevation, latitude, and mean air temperature of a population. This suggests that variation in that component of wing melanism is the result of adaptation to different thermal environments. The width of the predominantly black patch in the basal area of the hind wings of males is correlated with elevation, latitude, and air temperature, suggesting that variation in this character may also have a thermoregulatory significance. In the distal area of the front wings, wing transparency and the extent of black scaling are correlated with elevation on individual mountains, but are not correlated with elevation when populations from many mountains are considered together. Other environmental factors correlated with elevation, such as predation, may be more important than thermal effects in determining variation in melanism of the distal area of the wings of P. phoebus. The positive correlation between size and mean air temperature during the flight period is significantly weaker than the negative correlation between size and elevation, suggesting that thermoregulatory considerations can not account for variation in size between populations.