Distribution & Evolution
Before domestication, around 5000 years ago, the silk worm was abundant throughout Asian regions. Now days the silk worm relies solely on humans to survive and reproduce. This allows us to manipulate specific mutations within the silk worms’ genome. One such specific mutation results from the inbreeding specific races from China, Japan, Korea and Europe with the best qualities (Takeda 2009). Scientists identify key traits that increase silk worm productivity and mate these with worms with similar traits to create strains with better silk production, faster growth rate, and better silk quality. Mapping the silk worm genetics allows scientists to identify where key traits were inherited and use them to their advantage (Abe et al. 2005). This also gives us an insight into where, how and why the silk worm came to evolve such specific traits, such as the silk cocoon.
Some evidence suggests that the silk worm evolved from the Chinese silk worm, Bombyx mandarina however it is not known exactly where and when the silk worm became a creature that relies solely on humans. A study conducted by (wang et al. 2009) sequenced 40 domesticated and 11 wild (B.mandarina) silk worms to identify the possibility that B.mori evolved as a domesticated B.mandarina. They found a clear genetic separation between the two species with little gene flow, suggesting a "unique domestication event". However they also found that although domestic worms are genetically different they share around 83% of variation in the wild type (wang et al. 2009). This suggests that there would have been a large amount of worms being domesticated at one single time, or many domesticated in different places at the same time. However due to voltinism they could not identify actual locations where the first domestication of this worm began (wang et al. 2009).
As a result of such domestication silk worms have lost almost all of their mechanisms of defence. Most adults are incapable of flight and have slowly lost their entire colour resulting in a flightless, pure white insect (Takeda 2009).
Some evidence suggests that the silk worm evolved from the Chinese silk worm, Bombyx mandarina however it is not known exactly where and when the silk worm became a creature that relies solely on humans. A study conducted by (wang et al. 2009) sequenced 40 domesticated and 11 wild (B.mandarina) silk worms to identify the possibility that B.mori evolved as a domesticated B.mandarina. They found a clear genetic separation between the two species with little gene flow, suggesting a "unique domestication event". However they also found that although domestic worms are genetically different they share around 83% of variation in the wild type (wang et al. 2009). This suggests that there would have been a large amount of worms being domesticated at one single time, or many domesticated in different places at the same time. However due to voltinism they could not identify actual locations where the first domestication of this worm began (wang et al. 2009).
As a result of such domestication silk worms have lost almost all of their mechanisms of defence. Most adults are incapable of flight and have slowly lost their entire colour resulting in a flightless, pure white insect (Takeda 2009).