Plasticity of response in development in an invasive mosquito: Does degree of environmental variability play a role?

Background/Question/Methods

Some insects display sexually dimorphic trade-offs in development time versus mass at eclosion, with males sacrificing mass for shorter development times and females maximizing mass but taking longer to develop.  In mosquitoes, this dichotomy between the sexes may have evolved as the result of selection on different fitness criteria within each sex.  Aedes albopictus (Asian Tiger mosquito) is an important invasive species and vector of several arboviruses.  Aedes albopictus overwinters as diapausing eggs, so larvae or adults that experience unfavorable conditions (e.g., freezing) will die.  Thus, larvae might be expected to show developmental plasticity, accelerating development in response to a seasonal constraint of approaching winter.  This plasticity is expected to be more pronounced where winters are more severe;  degree of severity is correlated with photoperiod across latitudes.  Repeated studies have documented sex-specific trade-offs in development time and mass in A. albopictus under a variety of conditions.  It is unknown if larvae show adaptive plasticity in the sex-specific mass-development trade-off in response to seasonal constraints indicated by photoperiod, and whether this plastic response varies with latitude.  We conducted a laboratory experiment wherein we compared mass and development time of four populations of A. albopictus under three photoperiods (long, short stable, and short declining).  Populations were obtained from along a latitudinal gradient predicted to correlate with winter severity (Florida, North Carolina, Virginia, and New Jersey).  We hypothesized that the mass-development trade-off is affected by winter severity that is reflected in variation of photoperiod.  We predicted that individuals from mild climates relatively free of winter freezing (Florida) would exhibit relatively low plasticity in response to simulated seasonal photoperiods, whereas individuals from areas with high winter severity (New Jersey) would show strong plastic responses. 

Results/Conclusions
Contrary to our predications, males and females displayed no differences among populations in response to photoperiods, although females from all locations were larger and took longer to develop under long versus short or declining photoperiods.  In general, individuals from northern populations were larger and developed more slowly, and male mass displayed the largest interpopulation variation in these traits.  Although there were no differences among populations in their response to photoperiods, New Jersey and North Carolina populations had lower overall survival, and sex ratios for both populations were skewed toward females.  Mass-development trade-offs in A. albopictus are thus flexible in response to photoperiod, but populations do not appear to vary as a function of winter severity.