Review: Jeyaprakash et al. (2009). Apidologie, 40: 178-183

Written: April 27, 2009

Posted: 05/04/09

Word count: 833

Question: What causes Cape bee workers to lay queen eggs?

Answer: An oddity in genetics, but also possibly a bacterial symbiont

Arches National Park in Moab, Utah, is among the most popular and highly visited in the nation, largely because their famous rock formations are so rare, elaborate, and sensational. To a hardened geologist, however, the sandstone formations are fairly uninteresting simply because they are so rare. The biological analogy is finding a two-headed snake; yes, it does happen, but it is so rare and quirky that it doesn’t really represent “real” snakes. To a scientist, though, sometimes understanding such “mistakes” in nature can tell us a great deal about normal things—understand how a snake grows two heads and you can better understand the complexities of how most snakes only grow one head.

It is for this reason that many honey bee researchers investigate the oddities of honey bees, since the more we understand the exception to the rule, the more we understand the rule. And honey bees definitely have many exceptions! Colonies are “supposed” to have only one queen, but every once in a blue moon one of our colonies can have mother and daughter queen laying in the same brood nest. Bees aren’t supposed to swarm in the fall, as it doesn’t give them enough time to store enough honey to survive the winter, but sometimes their wires get crossed during supersedure and split in two rather than simply replace the queen. If we can understand why their wires get crossed in these instances, it might prove quite beneficial to beekeepers (imagine being able to consistently keep multiple queens in your colonies!).

One of the foremost oddities in bee biology has to be thelytoky (pronounced “theh-LET-eh-toe-key”). Odd indeed, as this is the technical genetic term for when unmated sterile workers can actually lay female eggs that can develop into queens. While it may not be surprising that workers can lay eggs (since many of us have experienced a queenless colony turning anarchistic where workers start laying lots of eggs), most of us have also been taught that those eggs—since they are not fertilized—can only develop into males. While true in the vast majority of cases, there are times when something weird happens and the egg, in essence, fertilizes itself. The result is female (rather than male) genetics, and those individuals can be raised as either workers or queens. Thus even hopelessly queenless workers can be resurrected by thelytoky.

While our bees in North America express thelytoky only very rarely (say, in 1 out of 1,000,000 worker-laid eggs), in other parts of the world it isn’t all that rare. In fact, the Cape bee, Apis mellifera capensis of the southern horn of Africa, is famous for their workers being able to lay female eggs fairly regularly. How they are able to do it can therefore tell us a lot about how—normally—workers don’t. Much like in all biological traits, it can be the result of either nature (genetics) or nurture (environment). While most geneticists believe that thelytoky is merely a genetic quirk, others have investigated non-genetic factors.

It is this latter possibility that a trans-Atlantic research team recently investigated to be behind thelytoky in the Cape bee. While they do not dismiss a genetic component behind the trait, they believe that there may be a prominent environmental factor to the high prevalence of worker requeening in the subspecies. Specifically, they investigated the potential role of an intracellular bacterial symbiont in bees that might “drive” their ability for their eggs to self-fertilize. This endosymbiont, Wolbachia, is actually incredibly common and widespread throughout insects, and it is known to cause reproductive changes in its host (such as altering the sex ratio by preventing males from being born). Think of them not as a disease, but rather a hitchhiker that sometimes compels its host to do its bidding. In the case of the Cape bee, if Wolbachia are only passed on in female offspring and not in the males, then it might be in the best interests of both bacteria and bee to enable workers to lay fertilized eggs.

Wolbachia has been found in bees before, and as far as we know they don’t really do anything to affect the bees (for better or for worse). But Ayyamperumal Jeyaprakash from the University of Florida and his colleagues recently found that A. m. capensis has a different Wolbachia strain than its nearest cousin, A. m. scutellata (also known as the African bee). This finding opens the door for additional investigations into the potential role of the Wolbachia symbionts into thelytoky and other bee oddities. In doing so, it is important to remember how the exceptions to the rule can help us understand the rule.

Reference

Jeyaprakash, A., M. A. Hoy, and M. H. Allsopp. (2009). Multiple Wolbachia strains in Apis mellifera capensis from South Africa. Apidologie, 40: 178-183.