By: Kelsey DaSilva, Lauren Quintiliani, Cara Reynolds, and Mia Romano (Stonehill College, BIO323: Evolution, Spring 2020)
Welcome to the blog “What’s All the Buzz About,” serving you your daily buzz so prepare to be(e) amazed. This article examined honey bee queens of the species scientifically known as Apis mellifera. The common name for the species is western honey bee, and it is the most common honey bee species in the world. These bees are social insects, which means they exhibit a high level of societal organization. This is seen in their overlapping generations within a colony of adults, division of labor, and in the way broods, or groups of bees, work together. These characteristics make honey bees a model organism for studying social evolution. The article aimed to explore differences in observed egg size and the cause of egg size variation. Plasticity plays a large role here and is defined as the ability of an organism to be flexible and to change in various aspects based on factors in their environment. Plasticity occurs in organisms for evolutionary beneficial reasons. Understanding plasticity and variability in genes, specifically seen in the egg size of honey bees, is important because it serves as a model to understand life on earth, it can increase fitness, generate novelty, and facilitate evolution. This article helps to further understand evolution in a social context and provides a practical application of plasticity.
The authors of the article wanted to study the effects of genetic makeup, colony size, and colony nutrition. They predicted that egg size would differ due to genetic and environmental factors that influence the developmental success of these bees. To test the effects of the bees’ genetic background, young naturally mated queens were obtained from five different breeding areas within the United States: Minnesota Hygienic, USDA-POL, USDA-Russian, Hawaiians, and California Italian. The queen bees were placed into mating hives with maintained colony size. The results revealed that California Italian queens produced larger eggs, whereas the Hawaiian breeding queens produced smaller eggs. The other genetically different queens produced different egg sizes as well. From this, researchers concluded that egg size is significantly different among the genetically different bees that were studied under similar environmental conditions.
Next, to test the effect of colony size, the queen bees were maintained in three different colony sizes: small, medium, and large. Researchers found that queen bees in large colonies produced significantly smaller eggs than queen bees in small colonies. Specifically, researchers observed that when queens were initially placed in large colonies, they laid small eggs, and when transferred to a smaller colony, they produced larger eggs. Queen bees placed in medium-sized colonies produced intermediate-sized eggs. This led the researchers to strongly suggest that colony size does affect the size of the egg produced. The article stated that space in the hive is likely the reason behind this. The size of the colony affects the amount of space available in the hive and therefore a large colony producing smaller eggs is more beneficial to the colony as a whole.
Lastly, medium-sized colonies were used to examine the effects of the bees’ nutritional status. Three queens were used for each experimental group. The two experimental groups included colonies on a pollen-restricted diet and colonies that were overfed. Pollen-restricted colonies received a pollen trap that restricted incoming pollen and fed only on stored pollen from within. On the other hand, the overfed colonies could obtain pollen freely and were given one liter of sugar syrup every three days. The results of this showed that pollen-restricted colonies produced larger egg sizes than the overfed colonies, suggesting that nutritional status does have a significant influence on egg size. The healthier the queen bee, the healthier, larger offspring produced.
The researchers explored possible benefits to egg size variations and found evidence that larger eggs develop more successfully than smaller eggs. This benefit is adaptive, meaning larger eggs become more adjusted and are better suited to their environment. The results indicate that the queens adjust egg size according to the colonies, instead of variation in egg number. Ultimately, a trade-off between egg size and number of eggs produced does exist, and selection seems to have generated genetic variation and plasticity. In the future, researchers could improve and expand on this idea by including a larger sample size of bees. They could also try to relate the findings from this experiment to bumblebees or wasps to determine if they exhibit the same phenomenon as honey bees.
Article: Amiri, E., K. Le, C. Vega Melendez, M.K. Strand, D.R. Tarpy, and O. Rueppell. 2020. Egg‐size plasticity in Apis mellifera: Honey bee queens alter egg size in response to both genetic and environmental factors. Journal of Evolutionary Biology 33: 534–543.