Data from: Using museum specimens to track morphological shifts through climate change

Museum specimens offer a largely untapped resource for detecting
morphological shifts in response to climate change. However, morphological
shifts can be obscured by shifts in phenology or distribution or sampling
biases. Additionally, interpreting phenotypic shifts requires
distinguishing whether they result from plastic or genetic changes.
Previous studies using collections have documented consistent historical
size changes, but the limited studies of other morphological traits have
often failed to support, or even test, hypotheses. We explore the
potential of collections by investigating shifts in the
functionally-significant coloration of a montane butterfly, Colias meadii,
over the past 60 years within three North American geographic regions. We
find declines in ventral wing melanism, which correspond to reduced
absorption of solar radiation and thus reduced risk of overheating, in two
regions. However, contrary to expected responses to climate warming, we
find melanism increases in the most thoroughly sampled region.
Relationships among temperature, phenology, and morphology vary across
years and complicate the distinction between plastic and genetic
responses. Differences in these relationships may account for the
differing morphological shifts among regions. Our findings highlight the
promise of using museum specimens to test mechanistic hypotheses for
shifts in functional traits, which is essential for deciphering
interacting responses to climate change.