Charlie, here's an excerpt from my article What's Happening with the Bees
Part 4:
Unlike humans, in which maleness is determined by the inheritance of a
sex-determining Y chromosome, in bees (which have no sex chromosome) the
default development of any fertilized egg is to become a male (yes,
fertilized eggs can develop into viable diploid drones [[i] <#_edn1>]). The
egg will become a female only if it inherited two different variants of the
“sex allele” at one specific gene locus on chromosome 8 (the complementary
sex determiner (csd) gene). Haploid (unfertilized) eggs would of course
have only have one sex allele, since they’d have only a single set of
chromosomes, and thus always become males. Surprisingly, the csd gene is
not even directly involved in the feminization process—the presence of two
different alleles at this “sex locus” is merely a trigger for the cell to
epigenetically activate another gene (called *feminize*) [[ii] <#_edn2>],
which *then* starts the process of feminization.
My point is that since the csd gene doesn’t code for any proteins involved
in actually growing the bee, that means that for all intents and purposes a
worker, queen, or drone are genetically identical, and it is only the
epigenetic regulation that makes them develop differently. In the female
castes, this regulation is based upon what the larvae are fed by the nurses
(who choose whether a larva will become a worker or a queen) [[iii] <#_edn3>
].
In other words, the bee is akin to the stem cells in your body—it can
develop into any number of forms. Such an organism is said to exhibit
*phenotypic
plasticity. * And the honey bee exhibits such plasticity at both the
individual and at the colony level. As observed by Weiner and Toth [[iv]
<#_edn4>]:
*Phenotypic plasticity is an important biological phenomenon that allows
organisms with the same genotype to respond adaptively to variable biotic
and abiotic environments.*
End of quote (citations below). Charlie, please let me know if you wish
for further elaboration.
------------------------------
[i] <#_ednref1> Polaczek, B, et al (2000)A new, simple method for rearing
diploid drones in the honeybee (*Apis mellifera *L.). Apidologie 31:
525–530. *Small colonies will naturally rear to adulthood diploid drones
in fall.*
Herrmann M1, Trenzcek T, Fahrenhorst H, Engels W. (2005) Characters that
differ between diploid and haploid honey bee (Apis mellifera) drones. Genet
Mol Res. 2005 Dec 30;4(4):624-41.
[ii] <#_ednref2> Gempe, T and M Beye (2009) Sex determination in
honeybees. *Nature
Education* 2(2):1
http://www.nature.com/scitable/topicpage/sex-determination-in-honeybees-2591764#
<http://www.nature.com/scitable/topicpage/sex-determination-in-honeybees-2591764>
[iii] <#_ednref3> Kucharski R, et al (2008) Nutritional control of
reproductive status in honeybees via DNA methylation. Science 319:
1827–1830. http://www.sciencemag.org/content/319/5871/1827.full
Kamakura, M (2011) Royalactin induces queen differentiation in
honeybees. Nature 473(7348):478–483). *Open access.*
Guo X, et al. (2013) Recipe for a busy bee: MicroRNAs in honey bee caste
determination. PLoS ONE 8(12): e81661. *Open access.*
[iv] <#_ednref4> Weiner, SA and AL Toth (2012) Epigenetics in social
insects: a new direction for understanding the evolution of castes. Genetics
Research International http://www.hindawi.com/journals/gri/2012/609810/
--
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com
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