A mother eastern small carpenter bee (Ceratina calcarata) (right) and a dwarf eldest daughter (left). Photo credit: Sandra Rehan.
A mother eastern small carpenter bee (Ceratina calcarata) (right) and a dwarf eldest daughter (left). Photo credit: Sandra Rehan.
From the moment they emerge in late summer, the fate of each young eastern small carpenter bee (Ceratina calcarata) is already determined. Some are destined to found new colonies the following year, having survived winter, but the first youngsters that emerge from the nest – known as dwarf eldest daughters – are small and go on to serve their younger siblings, foraging to feed them, leaving themselves unprepared to survive into the following season; ‘[This is] true worker-like altruism to take care of your siblings for their survival and future reproductive success’, says Sandra Rehan from York University, Canada. But why do some bees from each generation develop into colony founders, while others are destined for servitude, although they are all offspring of the same mother? Knowing that the dwarf eldest daughters are significantly smaller than their more robust regular sisters, Rehan and Jesse Huisken (York University) wondered whether food deprivation might seal the small eldest daughter's fate.
To find out, the duo had to collect some eastern small carpenter bee nests complete with their mother at just the right moment, ready to intervene in the amount of pollen provided to the developing larvae. The duo removed some of the pollen feast from some of these larvae – to deprive future small and regular siblings of food – while the stolen pollen was passed on to other bees in the nest to supplement their diet, to ensure that they were well nourished regardless of which role they were destined to fulfil. Then, the duo waited until the youngsters emerged as young adults in late summer, recording that seven of the newly emerged adults were small daughters destined for servitude, 11 were regular daughters that could go on to found colonies, 14 were better nourished small daughters and six were regular daughters that had been deprived of food. Finally, the duo collected samples of the bees’ brains to identify the genes that were active when the youngsters emerged as adults, to try to get to the bottom of how much of a role nutrition has in their future.
However, the insects’ diet didn't affect the activity of genes that could lead them to become servers or larger bees that survived to next season. The developing bees’ diet did not determine their fate. Yet when Huisken and Rehan compared the gene activity patterns between the larger regular bees and their smaller siblings, they were impressed to find differences in 540 genes that were active in the brain, with 258 genes activated differently in the larger bees, while 282 genes were activated differently in the smaller bees. And when the duo took a closer look at the genes, they could begin to piece together how some of the genes might be contributing to the bees’ status, including a gene called hexamerin – which drives social insects, such as some orchid bees, to become more dominant and determines which role other insects assume within their colony. In contrast, genes that regulate the activity of other genes were more active in the brains of the smaller elder sisters, some of which are likely to drive the smaller bees’ determination to forage for their siblings.
The duo suspects that the social experiences and environment experienced by the first borns has more of an impact on their destiny than their diet or order of birth, driving the small elder daughters to make the ultimate sacrifice, ensuring the success of their younger siblings after their demise.
