December 10, 2012
Queen Sweat Bees Control The Size Of Their Offspring
Brett Smith for redOrbit.com - Your Universe Online
According to new research from a pair of Swiss researchers, queen sweat bees influence the adult size of their daughters based on which brood they are born into.
During the initial observation period of the study, the researchers noted that first brood females were always smaller than second brood females, but first brood males are sometimes the same size as males from the second brood.
The queen bees were found regulating the amount of food they provide for their developing female larvae to determine whether the daughter becomes a smaller-sized worker or a potential new queen, the researchers wrote in their report that appeared in the latest edition of the journal Frontiers in Zoology.
In the study, the biologists from the University of Lausanne, Switzerland, explored the possibility of queen bees restricting the food supply to their first brood to ensure that they become workers, which are small sized, easier to dominate, and therefore, less likely to reproduce. These worker bees could then assist with the raising of the next brood of larvae.
The biologists compared adult body size, weight and fat content of sweat bee foundresses, or mated females, that have overwintered. They also examined the physical aspects of first and second brood females.
To determine if the mothers control the food supply to their offspring in an attempt to influence their adult body size, the team also compared the pollen and nectar provisions provided to the first and second brood.
The researchers also checked to see if body size was correlated with the ability to survive the winter.
Their findings showed that the total amount of pollen and nectar given to the first brood was about 1.4 times less than that to the second brood. The biologists also found that the amount of sugar provided to the two broods was approximately the same. This suggests that the second brood was intentionally given more pollen.
"Although it is hard to distinguish parental manipulation from resource availability and resource acquisition, which are influenced by vegetation, weather, seasonal variation, numbers of foragers and more, the fact that we were able to see that first brood female body size remained constant despite pronounced differences in weather strengthens our argument that the foundresses restrict the food of their daughters to drive them into the worker role,” said co-author Michel Chapuisat, from the university´s Department of Ecology and Evolution.
Sweat bees, also known as Halictus scabiosae, were chosen for the study because they are a primitive eusocial insect. Eusocial insect populations are organized into a hierarchical society with a division of labor between the reproductive queens and males, and their worker counterparts, despite the fact that all the adults are able to reproduce.
“In Switzerland, H. scabiosae forms annual colonies in which females raise two broods that are well-separated in time,” the report said. “The foundresses raise a first brood (B1) that is female-biased and emerge from the nests in June and July.”
“The B2 (second brood) females and males emerge from the nest in August and September,” the report added.