Bigger isn't always better: Challenging assumptions about the associations between diapause, body weight, and overwintering survival.

ABSTRACT

During the winter, animals face limited food availability. Many animals enter dormancy to reduce their winter energy expenditure. Most insects spend the winter in diapause, a state of programmed dormancy. It is often assumed that diapausing insects need nutrient stores to fuel their many months of basal metabolism and must grow heavier than their non-diapause-programmed counterparts. However, the extent to which food limitation affects body weight during overwintering preparation as well as the likelihood and duration of diapause remains unclear. We limited the duration of the feeding period and thus the total quantity of food available to diapause-destined larvae of the pupal-diapausing flesh fly, Sarcophaga crassipalpis, to test how food limitation affects body weight in the context of diapause programming. We also tested the extent to which food deprivation and body weight affect the likelihood and duration of diapause. We hypothesized that diapause-destined larvae grow more quickly and pupariate at a heavier body weight than non-diapause larvae. We also hypothesized that body weight is more dramatically reduced by food limitations when a larva is programmed for diapause. Finally, we hypothesized that larvae with lighter body weight (i.e., food limited) are less likely to enter pupal diapause and also stay in diapause for a shorter duration than heavier, well-fed, individuals. Contrary to our hypotheses that diapausing insects are heavier than their non-diapausing counterparts, we found diapausing pupae weighed less than non-diapausing pupae, especially when larvae received limited food. We found light pupae did not abort their diapause program. In both diapausing and non-diapausing pupae, body weight was positively correlated with simulated winter survival. However, above a weight threshold, body weight no longer affected simulated winter survival in diapausing pupae. Contrary to our predictions and the general consensus in much of the diapause literature, we also found that lighter pupae stayed in diapause longer than heavier pupae. Overall, our results challenge the precept that body weight and diapause are positively associated. The relationship between body weight and diapause is complex and may be affected by the availability of food before and after winter, the availability of high-quality overwintering sites, and the life history of a particular insect.