Adaptation and evolutionary stasis across the North American range of gypsy moth (Lymantria dispar)

The advent and subsequent spread of gypsy moth in North America is perhaps the best-documented biological invasion worldwide.  Initially introduced near Boston, MA nearly 150 yrs. ago, its range now encompasses most of eastern North America from Quebec to North Carolina and west to Minnesota.  Across this distribution it encounters diverse climatic conditions and forest types. It has long been assumed that adaptation has played little role in the success of this species but this has only recently been empirically evaluated.  We compared a number of important life history traits (cold tolerance, egg size, phenology) among wild populations spanning the current latitudinal distribution as well as two standard laboratory populations.  All populations were standardized under common rearing conditions prior to life history trait evaluation.  We found that some traits such as cold tolerance and egg size were stable or did not exhibit any adaptive pattern while emergence phenology showed strong indication of selection.  This suggests that while some traits are evolutionary labile, other traits are relatively fixed, representing the limited variability and genetic constraints inherent to the founding population.