Fusion_power
Field Bee
- Joined
- Jan 13, 2016
- Messages
- 774
- Reaction score
- 82
- Location
- Hamilton, AL U.S.A.
- Hive Type
- Other
- Number of Hives
- 24
I thought it might be worth posting a thread about the differences between mass selection and individual selection. These are two very different genetic tools that have significantly different outcomes. As beekeepers, we tend to focus most on individual selection, i.e. picking out the best performer in a group to propagate the next generation of queens. Individual selection is an incredibly effective method of improving honeybees by picking outstanding colonies to produce drones and queens. It has one huge weakness which can negate most of the benefits. Individual selection strongly favors inbreeding. Picking 1 in 1000 or even higher ratios of selection invariably result in inbreeding at some stage. Avoiding inbreeding has therefore been a targeted goal of most breeding programs. This can be done via artificial insemination (AI) by choosing several hundred drones representing hundreds of colonies, collecting semen, then mixing it thoroughly before using it to inseminate queens. This method and other similar selection programs keep inbreeding at a minimum but at the same time limit the amount of genetic gain that can be made in the breeding population. Takeaway is that individual selection either produces high levels of inbreeding or else limit genetic gain.
Mass selection is a different approach that is implemented by choosing a very large population to start with, applying a strong selective pressure, then breeding from the survivors. This selection method is highly effective when breeding for disease or pest resistance. A good historical example is selection for trachea mite tolerance. When trachea mites began to decimate honeybees 100 years ago, beekeepers quickly realized that a few colonies were tolerant. There were no chemical treatments therefore beekeepers had no choice except to breed from the survivors. Notice the element of mass selection at work. There was a large population, a strong selective pressure was exerted, the survivors were used to produce the next generation. The result of mass selection was the entire population becoming resistant to trachea mites in just a few generations.
Think through the methods being used in breeding for varroa tolerance. Instead of applying the principles of mass selection, the breeding efforts are focused on individual selection with associated inherent weaknesses. The example of trachea mites clearly shows the path forward. Choose a large population, apply a strong selective pressure, and breed from the survivors. When survivors are clearly identified and the genetics have stabilized, they can be used to breed the survivor traits into susceptible lines that have other desirable traits such as high honey production, gentleness, winter survival in adverse climates, etc.
Now switch to the events that played out here in the Southeastern U.S. beginning about 1990. There was a huge population of feral colonies with A.M.Mellifera, A.M.Ligustica, and A.M.Carnica background genetics along with some novel genetics including A.M. Lamarckii from Egypt. Varroa were found and rapidly spread throughout the country. By 1993, most feral colonies were infested and began to die in late fall and early winter. Between 1994 and 2004, there were so few feral colonies that they were almost undetectable, but a few survived. In 2004, a few swarms started showing up that originated from feral colonies and had measurable levels of varroa tolerance. All the elements of mass selection were present except beekeeper selection. There was a huge starting population, very strong selection pressure was applied, and the survivors breed and reproduced.
What did beekeepers do during these years? They treated their bees to keep them alive. I used Apistan for the first time in 1994 after losing all but one colony to varroa over the winter of 1993/1994. I had split my one remaining colony into 3 using purchased queens. All beekeepers treated for mites, if they did not treat, their bees died. What was the effect of these managed colonies on decimated feral populations? They reversed the gene flow such that feral colonies mated with susceptible drones wiping out the ferals because their weak mite tolerance had been compromised. But there were some areas that had few to no beekeepers and therefore the only bees around were the ferals. These feral colonies were able to survive and over 10 years concentrated enough small effect genes to express some mite tolerance. In 2004, I caught a feral swarm and found that they had significant levels of mite tolerance. I was able to purchase some queens from Purvis Apiaries that had been highly selected for varroa tolerance. Their heritage was from the Primorski bees brought into the U.S. a few years earlier. I used the Purvis queens to produce drones and raised queens from my feral swarm queen to mate with the drones. For the last 11 years, I have bred from the survivors. The net result is that I have bees with high levels of varroa tolerance. They are the result of mass selection here in Alabama, and in the Primorski region.
Do you see the difference in the effect of mass selection vs individual selection? With mass selection, an entire population shifts to a new genetic combination while keeping inbreeding at a very low level.
Mass selection is a different approach that is implemented by choosing a very large population to start with, applying a strong selective pressure, then breeding from the survivors. This selection method is highly effective when breeding for disease or pest resistance. A good historical example is selection for trachea mite tolerance. When trachea mites began to decimate honeybees 100 years ago, beekeepers quickly realized that a few colonies were tolerant. There were no chemical treatments therefore beekeepers had no choice except to breed from the survivors. Notice the element of mass selection at work. There was a large population, a strong selective pressure was exerted, the survivors were used to produce the next generation. The result of mass selection was the entire population becoming resistant to trachea mites in just a few generations.
Think through the methods being used in breeding for varroa tolerance. Instead of applying the principles of mass selection, the breeding efforts are focused on individual selection with associated inherent weaknesses. The example of trachea mites clearly shows the path forward. Choose a large population, apply a strong selective pressure, and breed from the survivors. When survivors are clearly identified and the genetics have stabilized, they can be used to breed the survivor traits into susceptible lines that have other desirable traits such as high honey production, gentleness, winter survival in adverse climates, etc.
Now switch to the events that played out here in the Southeastern U.S. beginning about 1990. There was a huge population of feral colonies with A.M.Mellifera, A.M.Ligustica, and A.M.Carnica background genetics along with some novel genetics including A.M. Lamarckii from Egypt. Varroa were found and rapidly spread throughout the country. By 1993, most feral colonies were infested and began to die in late fall and early winter. Between 1994 and 2004, there were so few feral colonies that they were almost undetectable, but a few survived. In 2004, a few swarms started showing up that originated from feral colonies and had measurable levels of varroa tolerance. All the elements of mass selection were present except beekeeper selection. There was a huge starting population, very strong selection pressure was applied, and the survivors breed and reproduced.
What did beekeepers do during these years? They treated their bees to keep them alive. I used Apistan for the first time in 1994 after losing all but one colony to varroa over the winter of 1993/1994. I had split my one remaining colony into 3 using purchased queens. All beekeepers treated for mites, if they did not treat, their bees died. What was the effect of these managed colonies on decimated feral populations? They reversed the gene flow such that feral colonies mated with susceptible drones wiping out the ferals because their weak mite tolerance had been compromised. But there were some areas that had few to no beekeepers and therefore the only bees around were the ferals. These feral colonies were able to survive and over 10 years concentrated enough small effect genes to express some mite tolerance. In 2004, I caught a feral swarm and found that they had significant levels of mite tolerance. I was able to purchase some queens from Purvis Apiaries that had been highly selected for varroa tolerance. Their heritage was from the Primorski bees brought into the U.S. a few years earlier. I used the Purvis queens to produce drones and raised queens from my feral swarm queen to mate with the drones. For the last 11 years, I have bred from the survivors. The net result is that I have bees with high levels of varroa tolerance. They are the result of mass selection here in Alabama, and in the Primorski region.
Do you see the difference in the effect of mass selection vs individual selection? With mass selection, an entire population shifts to a new genetic combination while keeping inbreeding at a very low level.
