Adult nutrition and reproductive physiology: a stable isotope analysis in a eusocial paper wasp (Mischocyttarus mastigophorus, Hymenoptera: Vespidae)

Division of labor in social groups can be influenced by differential nutrition. Consumption of more food or higher-quality food often affects individuals' capacities for reproduction. In social insects, nutrients consumed during immature (e.g., larval) stages often affect adult reproductive capacity, but adult nutrition may also impact reproductive status. This study tested whether ovary development, an indicator of reproductive status, corresponded to higher trophic-level feeding for adults in the primitively eusocial paper wasp Mischocyttarus mastigophorus. Our main prediction was that females' ovary development would correlate positively with evidence of feeding at higher trophic levels, as indicated by stable isotope ratios of nitrogen (delta 15N) and carbon (delta 13C). We first asked whether isotope ratios of mature females co-varied with ovary development. delta 15N values were higher for mature females with better-developed ovaries, as expected if they fed on a diet richer in animal tissue. There was a negative relationship of delta 13C with ovary development in mature females, as would be expected if females with developed ovaries had higher body lipid stores. To test for evidence of nutritional biasing of caste during immature development, we measured changes in isotope ratios across pupal development leading up to early adulthood (i.e., immediately before and after adult eclosion). The delta 15N and delta 13C values for mature pupae were similar to those of newly emerged adults and to those of mature adults lacking developed ovaries. In contrast, mature females with developed ovaries showed N-isotope signatures of a more prey-based diet and C-isotope signatures of elevated lipid content. We conclude the N and C isotopic signatures of ovary-developed mature females diverged from their levels at the end of immature development. The findings suggest reproductive caste status was associated with differences in nutrient acquisition and reflects differences in consumption of animal-derived versus plant-based foods during adulthood. Significance statement Pre-adult nutrition is known to affect caste development, and thereby influence division of labor, in diverse insect societies. In temperate independent-founding (IF) paper wasps, the effects of larval nutrition on adult caste may reflect adaptations for overwintering and diapause by reproductive females. We asked whether adult nutritional content showed caste-related trophic differences in the Neotropical IF paper wasp Mischocyttarus mastigophorus. Previous studies suggested interactions among adult nest-mates affected food sharing and caused biased nutrient flow within colonies. Our data suggest adult nutrition affected reproductive physiology. We propose this pattern may be widespread in tropical IF paper wasps, where opportunities for adult reproductive plasticity are favored by long colony cycles and relatively aseasonal nest founding.