There have been two studies, released within days of each other, regarding
Africanized bees in Calif. This is of great interest to us, and I was at
the Calif Bee Breeders Assoc meeting a week ago, where we are attempting to
exclude AHB's from being brought north to pollinate almonds. Anyway the
studies gave very different results, so I wrote the following for our local
monthly newsletter:
There have been a couple of scientific studies of interest regarding the
introgression of Africanized bee genetics northward in California. One
study
<http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0190604>
found that Africans have spread clear up to mid state and into Placer
County (Nevada County was not sampled). On the other hand, the second study
<https://academic.oup.com/gbe/advance-article-pdf/doi/10.1093/gbe/evy007/23511336/evy007.pdf>
found no Africans in Northern California, but plenty in SoCal.
Both studies were by researchers from U.C. Davis--how could they get such
different results? It was because the first study sampled *mitochondrial*
DNA (which codes for cellular energy processes), and indicates the
unbroken *maternal
line*. The second study sampled *nuclear *DNA—that which codes for bee
color, morphology, and behavior. Nuclear genes can be passed by either
queens or drones.
There are three main mitochondrial lines (*mitotypes*) in California:
- C line is central European, such as Italian and Carniolan
- M line is Western European, such as the German black bee
- A line is African and Africanized
Bee breeders select for characteristics associated with the C line. In
California, all three mitotypes are present in SoCal, but only the C and M
lines in Northern California.
Independent of the above mitotypes, there are the *nuclear* genes,
reflecting a mixture of all the races of bees that have been introduced
into California since the Gold Rush.
Here’s where it gets interesting. Just because a bee has an African
mitotype, doesn’t mean that it will be highly defensive. Nor vice
versa--the feral M-line dark bees that used to populate California back in
the day were often quite defensive.
But the mitotype can’t be transmitted by drones, since spermatozoa don’t
contain mitochondria. But the drones *do* transmit nuclear genes, so a
mating of a gentle Italian queen to an Africanized drone can result in hot
offspring. Thus, we would have expected to see Africanized nuclear genes
leading the way (due to drone matings) rather than mitochondrial DNA, which
must be carried by queens (by swarming or human transport).
This presents an interesting evolutionary question—why the heck are we
finding that the mitotypes are introgressing northward, rather than the
nuclear (*autosomal*) genes? It brings to mind a 2003 study
<https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwj7ncyMtvTYAhVPzWMKHX3zCeAQFgguMAE&url=https%3A%2F%2Fwww.apidologie.org%2Farticles%2Fapido%2Fpdf%2F2003%2F03%2FM3210.pdf&usg=AOvVaw0r0wCIEfi9sZ7drkOGzrRg>
from Peru, that found a similar introgression occurred at the African
mitotype worked its way in elevation up the Andes. I’m in the middle of
reading scientific papers on the subject regarding the evolution of other
invasive species—this looks to be a very interesting subject. I’ll let you
know what I find.
--
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com
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