Wing lengths of three Arctic butterfly species decrease as summers warm in Alaska

Climate warming can cause arthropods to express plastic and/or evolved
changes in morphology. Previous studies have demonstrated that body sizes
of Arctic butterflies are influenced by the temperatures experienced as
larvae. To investigate whether this was occurring among Alaskan
butterflies, we analyzed temporal trends in the wing sizes of three
Holarctic species, Colias hecla, Boloria chariclea, and Boloria freija,
using museum specimens collected in Arctic tundra regions of Alaska
between 1971 and 1995. Wing length was compared to accumulated growing
degree days (GDD) during both the spring of the year collected and the
previous year’s summer during the normal period of larval development. We
used mixed-effects models to test if spring and summer temperatures
affected adult morphology. Results show that for every 1°C increase in
average seasonal temperature, wingspans decreased between 0.7 millimeters
and 5 millimeters, with B. freija the most strongly affected. Our results
suggest that the morphological sensitivity of Arctic butterflies to
warming is the outcome of interactions between life-history traits and
regional climate, with all species sensitive to warming the summer before
the flight year as well as warming the spring of the flight year. Boloria
freija, which overwinters as late instar larvae that do not feed before
pupation the following spring, was particularly strongly affected by
summer warming.