Honey Bee Origins
Bees in the genus Apis, are primarily distinguished by their production and storage of honey and the construction of perennial, colonial nests out of wax. Currently, there are only seven recognized species of honey Bee with a total of 44 subspecies (Danforth 2006). Honey bees represent only a small fraction of the approximately 20,000 known species of bees. Some other types of related bees produce and store honey, but only members of the genus Apis are true honey bees.
Honey bees seem to have originated in south and south east asia. (Smith et al 2000) Apis melifera is estimated to be only about 1 million years old.
The first Apis bees appear in the fossil record at the Eocene–Oligocene (23-56 Mya) boundary, in European deposits. (Engel et al. 2009) The close relatives of modern honey bees, bumblebees and stingless bees, are also social to some degree, and social behavior seems a plesiomorphic trait that predates the origin of the genus.(Arias and Shepphard 2005)
Like many social animals, honey bees work together as a community to achieve the day-to-day goals of the colony. Honey bees display social behavior to such a degree that they are known as eusocial insects. Being eusocial is defined as there being a reproductive barrier as well as a social barrier within a social system. This means that there is generally one fertile female, known as the queen. These queens do all of the reproductive labor in the colony including producing a few thousand drones (fertile males) and a large number of sterile females who nurse the brood and gather pollen. These females are known as workers. (Gould and Gould 1995) These different classes are called castes.
Axis formation is a focus of study for several organisms with a majority of research being done on Drosophila, fruit flies, but insect axis formation is a rapidly evolving process. Honeybee axis formation displays unique characteristics indicating that the regulatory genes found in the honey bee interact differently. This also suggest that regulatory interactions differ within orders of insects. A study has also been done to investigate the localization of RNA in honeybee oocytes by examining the pattern of evolution.
Bees in both social and individual societies have a similar mating style. In most cases, the male bee only has the job of mating. In some species, the male bee’s do not have the configuration to support making honeycomb or carrying pollen. Therefore, in these species, the males will be forced from the hive prior to the winter season for lack of resources (Wilson, 2012).
Typically mating occurs in midair and in most cases only one time in the female bee’s life. She will mate with multiple male bees and collect all the sperm needed throughout her lifetime. This female is most often the queen. The other females, worker bees, do not have the duty of reproduction, but of hive maintenance and collection of resources.
Often times, the male will die after the mating ritual, as his endophallus will become lodged in the female’s body and this fatally injures the male bee. However, this is not the case for all honeybees. Males in some species can go on to multiple matings to increase their chances of producing offspring (as their sperm competes with sperm from other males the female has mated with).
Once the female is done mating, she will typically go back to the nest and lay eggs. The honeycomb, which the female worker bees produce, can either hold honey or one of the queen’s eggs, which will develop into another bee. These eggs go through a series of life stages (shown in the figure below).
In social bees, like Apis mellifera, queens lay thousands of eggs and has full control over whether the offspring are males or females. The females are diploid and the males are haploid. If she uses the sperm that was stored in the previous mating activities, then the offspring are female. After hatching, the larvae are raised by the worker bees. Initially, for all non-queen bees, they fed royal jelly and then pollen. The bees that are determined to be queens are fed royal jelly until she spins her cocoon.
Bee Life Cycle
Though each caste has different development length, different cell size, nutrition and genetic requirements, they all go through the same instars. There are seven total developmental stages, or instars, five are larval stages and two are pupal stages. It begins with the queen laying her eggs (fertilized or unfertilized) in horizontal cells or large vertical queen cells made by nurse bees. In the first two instars the nurses do no discriminate between the different larvae and all are fed royal jelly. The caste determining diet discrimination happens in the third instar (Mutti et al, 2011). During the first five instars the larvae eat as much as they can and grow rapidly. On the fifth instar the cells are sealed by the nurse bees and the first pupal stage begins. In the next two instars the larvae transform into prepupae and then into pupae, obtaining energy to grow only from their fat stores developed during their larval instars. When the pupae is ready, during the seventh instar it emerges from its cell a bee. While there is an average developmental time for each caste it is highly sensitive to the weather and temperature, (McKean, 2004).
Important nutrient sensing cascades for female caste development:
- IIS (insulin/insulin-like signaling), down regulation causes worker bee phenotype in larvae fed royal jelly (Wolschin, 2011)
- Egfr (epidermal growth factor), is induced by royalactin, which is only found in royal jelly (Kamakura, 2011)
- TOR (target of rapamycin), down regulation causes worker bee phenotype in larvae fed royal jelly (Patel, 2007)
These nutrient cascades effect the PI3K/Akt signaling pathway. PI3K/Akt is a proto-oncogene, a gene with the potential to become an oncogene, which has the potential to cause cancer through genetic mutations. This gene has important roles in many cellular processes like insulin metabolism, cell growth, and apoptosis regulation. Many studies have shown that this gene is important in developmental pathways in other model organisms, though its exact role is unknown. What is most understood is its role in cancer, where the gene becomes overactive caused by a defect in PTEN, a tumor suppressor gene. To better understand the mechanisms of this pathway watch this video.
A sterile female takes 21 days to fully develop. This female caste has two social stages, nurse and forager, (Denholm, 1999). Nurse bees take care of the hive, in their first days feeding the larvae, cleaning the hive and building combs, then progressing into storing nectar and pollen brought in by the foragers. The Foragers only task is to bring back nectar and pollen to the hive. Usually these stages are sequential, with the new bees starting as nurses and aging into foragers, though in cases where there are not enough older workers some nurses will leave the hive prematurely to become foragers (Mutti et al, 2011). This is often exploited by researchers in order to preform cohort studies.
Drones exist only to mate with queens from different colonies, (Denholm, 1999). Developing in 24 days they do not forage or help the hive in any other way when they emerge from their cell. When they mate with a queen they die immediately after, most of the time. Drones are completely fatherless, only getting half of the mother’s genome, which causes them to be haploid, (McKean, 2004).
Queens and have a very different life in comparison to their sisters, (Denholm, 1999). Instead of growing in small horizontal cells, potential queens are placed in larger vertical ones and develop for 16 days. It is believed by that the first queen to emerge will sting and kill the others before they can also emerge, but in most cases the workers tear down the other queen cells and kill those pre-queens, (McKean, 2004). Interestingly, there have been cases showing hives existing with two queens at once. The queen will spend most of her life in the hive, leaving when the hive space is too confined or to mate with drones. Queen development is triggered by three events:
- the queen leaves due to lack of hive space,
- the queen begins to weaken (or pheromones fade) and is killed by her hive or new queen
- the queen dies suddenly.
(The last two situations are called supersede and emergency supersede, respectively.)
Apis mellifera as a model organism
The honey bee, Apis mellifera, is one of several model organisms currently being used to achieve a comprehensive understanding of social life in molecular terms: how social life evolved, how it is governed, and how it influences all aspects of genome structure, genome activity, and organismal function (Whitfield et. al.). Honey bees offer complex but experimentally accessible social behavior, and a compact and well studied brain more than five orders of magnitude smaller than a human brain (Whitfield et. al.). Baylor College of Medicine has completed a sequenced genome of the honey bee that provides the foundation for ever-increasing genomic resources (BCM).
The honey bee is also used for studying several human health issues such as immunity, allergic reaction, antibiotic resistance, development, mental health, longevity, and diseases of the X chromosome (BCM).
Apis mellifera Communication: The Waggle Dance
The waggle dance is used for communication and information sharing between honey bees. It is used to communicate locations of resources, both direction and distance from the hive.
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