Climate-related geographic variation in performance traits across the invasion front of a widespread nonnative insect

Aim: Invasive species are an ideal system for testing geographic
differences in performance traits and measuring evolutionary responses as
a species spreads across divergent climates and habitats. The European
gypsy moth, Lymantria dispar dispar L. (Lepidoptera: Erebidae), is a
generalist forest defoliator introduced to Medford, Massachusetts, USA in
1869. Currently, the invasion front extends from Minnesota to North
Carolina and the ability of gypsy moth populations to adapt to local
climate may contribute to its continuing spread. We evaluate the
performance of gypsy moth from populations along the climatic gradient of
the invasion front to test for a relationship between climate and
ecologically important performance traits. Methods: Gypsy moth from 14
populations across the US invasion front and the interior of the invasive
range were reared from hatch to adult emergence in six constant
temperature treatments. The responses of survival, pupal mass, and larval
development time were analyzed as a function of source climate (annual
mean normal temperature), rearing temperature, and their interaction.
Results: With the exception of female development time, there were no
significant interactions between source climate and rearing temperature,
indicating little divergence in the shape of thermal reaction norms among
populations. Source population and rearing temperature were significant
predictors of survival and pupal mass. Independent of rearing temperature,
populations from warmer climates had lower survival than those from colder
climates, but attained larger body size despite similar development times.
Larval development time was dependent on rearing temperature, but there
were not consistent relationships with source climate. Main Conclusions:
Thermal adaptation may be an important factor in shaping the spread of
invasive species, particularly in the context of climate change. Our
results suggest that gypsy moth is highly plastic, but has undergone
climate-related adaptation in thermal performance and life history traits
as it spread across North America.