Maternal manipulation of pollen provisions affects worker production in a small carpenter bee

Abstract

Mothers play a key role in determining the body size, behavior, and fitness of offspring. Mothers of the small carpenter bee, Ceratina calcarata, provide smaller pollen balls to their first female offspring resulting in the development of a smaller female. This smaller female, known as the dwarf eldest daughter, is coerced to stay at the nest to forage and feed siblings as a worker. In order to better understand how this maternal manipulation leads to the physiological and behavioral differences observed in dwarf eldest daughters, we characterized and compared the quality of the pollen balls fed to theses females vs. other offspring. Our results confirm earlier studies reporting that there is a female-biased sex allocation in the first brood cell position and these daughters received mass provisions significantly smaller than other daughters. In addition to the smaller quantities of pollen provisioned, we found evidence for maternal control of the quality of pollen invested in the dwarf eldest daughters. Late brood cells receive pollen balls with significantly less floral diversity than early brood cells. This difference in floral diversity affects the protein content of the pollen balls; in that, older offspring receive less protein than their younger siblings. These results reveal that C. calcarata mothers manipulate not only the quantity but also the quality of the provision provided to her first offspring to create a small worker she is able to coerce to remain at the nest to help raise her siblings. This overlapping of generations and division of labor between mother and dwarf eldest daughter may represent the first steps in the evolution of highly social groups. One of the major transitions to the formation of highly social groups is division of labor. By manipulating resource availability to offspring, parents can force offspring to remain at the nest to serve as a worker leading to a division of labor between parent and offspring. In the small carpenter bee, C. calcarata, mothers provide their eldest daughter with less food resulting in a smaller adult body size. This dwarf eldest daughter (DED) does not have the opportunity to reproduce and serves only as a worker for the colony. In addition to overall reduced investment, we found that mothers also provide a different variety of pollen to her DED. By exploring the factors and mechanisms that influence maternal manipulation in a non-eusocial bee, we can begin to understand one of the major transitions in social group formation.