The Colour of Honeybees

[little john]

I hope the following will prove of interest to other people - it was an explanation I wrote about a year ago, but never got around to posting, due to more pressing matters in the apiary ...


The Colour of Honeybees

In a recent discussion on a beekeeping forum I commented that when a honey bee colony begins to mongrelise it gradually turns black, regardless of it's initial starting colour, thus indicating that the colour black must be dominant over any other colour.

However, one person asserted the opposite view - that yellow is dominant over black, and cited Woyke (1977) as the source for that assertion.

I found this quite an extraordinary claim, for if yellow was truly dominant over black, then one would expect mongrelised honey bee colonies to be essentially yellow, with perhaps just the occasional dash of a darker colour - but this is not what is observed in practice.

So - my first step was to check the Woyke (1977) reference, and indeed he does make such an assertion in his paper: Differences in Body Colour Expression Between European and Asian Honeybees, in which he writes:-
"A cross between yellow Italian queen (gene Y/Y) and black European drone (gene ybl) results in yellow hybrid workers (Y/ybl). This occurs because yellow colour is dominant over black."

So what is going on here ?  Can it really be the case that someone of Woyke's standing has made such an elementary mistake when, unless there is another explanation - black is very obviously the dominant colour in our everyday experience of mongrelised colonies ?

And so it was, that I was motivated to find some explanation for this apparent contradiction, which required me to return to some very basic considerations - and - just in case this might be of interest to others, I am outlining my findings here. But - bearing in mind that not everyone is well versed in the language which will follow, here is a list of the more unusual words which will be encountered:

Code Select Expand

TERMINOLOGY:
chromosome long chains of DNA
gene hereditary unit within a chromosome
locus position of the gene on a chromosome
allele alternative forms of a gene occurring at a locus
diploid having two sets of chromosomes
haploid having one set of chromosomes
homozygous an allele pair being identical
heterozygous an allele pair being dissimilar
hemizygous having only one allele (as with a haploid drone)
dominant one allele masking the expression of another
recessive an allele having it's expression masked
phenotype that which physically results from genetic coding
integument the 'skin' covering the bee's abdomen
sclerotization converting chitin into a hard, horn-like substance
poikilothermic cold-blooded: the environment determining body temperature


Perhaps the first question to be asked is "why are bees coloured anyway ?" - that is, what evolutionary advantage can there possibly be for honey bees to sport so many various coloured liveries ? - for in the natural world, subtle colours are invariably associated with camouflage; bright colours with the deterring of predators; and specific colours being associated with mating cues and species identification. But - none of these roles seem to apply to honey bees, who appear to be quite oblivious to any variation in colour marking.

I think it might be useful at this point to remind ourselves that bees are poikilothermic (cold-blooded), and although for much of the time they happily operate within the protection of a nice warm bee-hive, when a bee leaves that hive in order to forage, it then becomes subject to the vagaries of the elements.

Tucker (in Bee Genetics and Breeding, edited by Thomas E. Rinderer, 2013) - an author I will be quoting from extensively - writes:
"The original distribution of the honey bee was in general, with some exceptions, with the darker body colors common at higher latitudes, higher altitudes, and cooler climates, and with the yellow body colors at lower latitudes, lower altitudes, and warmer climates."

This then gives one possible explanation for colour: a black body giving an advantage in cooler climates by the absorption of warmth from the sun's rays and, conversely, a lighter colour helping to reflect the sun's rays in order to avoid over-heating.

The next question to be asked perhaps, is "how are the colours of the honey bee created ?"

Tucker again:
"A tentative explanation of body color in honey bees in terms of biochemical genetics can be attempted ...
The first assumption is that the chemical likely to account for all of the honey bee's body colors is melanin. The colors for melanin solutions of increasing concentrations are yellow, brown and black (Needham, 1978), precisely those colors of the honey bee's integument. Thus considered, the difference between yellow and black is quantitative, rather than qualitative, as has been previously supposed (e.g. Laidlaw and el-Banby, 1962). Thus, in the descriptions above, black could be considered as most melanin, brown as less melanin, and yellow as least melanin."

This is a very persuasive explanation, and exposes a serious flaw in some theories of colour dominance in honey bees. Gregor Mendel was extremely fortunate in selecting peas for his ground-breaking 19th Century experiments in genetics, as pea flowers are either purple or white - that is, those colours are absolute. Intermediate colours (i.e. shades of purple) never appear in the offspring of cross-pollinated pea plants - it's always a case of either 100% purple OR 100% white, but never an in-between colour ... as can be observed with the varying colours of the honey bee.

Melanin is a substance which is produced from the amino acid tyrosine, and the biochemical pathway from tyrosine-to-melanin contains approximately 6 steps.

Tucker tells us that "Woyke (1977) estimated six or seven polygenes, and postulated that the segregation of three pairs of polygenes is adequate to explain the observed variation. Each polygenic locus would have a yellow or black alternative, with the increments of yellowness or blackness cumulative between polygenes."

Although we are, of necessity, still in the realm of conjecture here - the story is firming-up of a colourant, the biochemical generation of which has 6 or so steps, and which has 6 or so genes (the 'polygenes') associated with it's production.
It also appears that yellow is not a 'true' selected colour, but rather that the colour 'yellow' is that which results from the absence of melanin, in exactly the same way as human blonde hair and blue eyes result from their lack of pigment. And of course, neither blonde hair nor blue eyes are dominant human characteristics.

But - the story is far from over - for in addition to these 6 'polygenes', there is also another single gene (termed 'bl') involved which operates independently of the polygenes, and which codes for black in a true 'absolute' Mendelian way.

Tucker again: "The body color of honey bees seems to be due to the joint action of two independently segregating genic systems: major factor alleles at the black locus modified by a number of polygenes (Woyke, 1977)."

"For diploids (workers, queens and diploid drones), Woyke (1977) suggested a dominance of black over yellow at each of the three polygenic loci, then a sum of the expressions of the three pairs of polygenes as they modify whatever 'bl' gene is present."

Either this is poorly worded, or these guys have got the cart before the horse - for it is obvious to me that it must be the 'bl' gene which is overriding the result of the polygenes, and not the polygenes modifying the 'bl' gene.

Laidlaw illustrates this with - an event which was thought at the time to be - a rather curious occurrence:
"Watson reported that a German black queen was artificially inseminated with a yellow drone, which produced all black offspring." (From: Inhibition of Yellow Body Color in the Honey Bee, Laidlaw 1962)

And, from: The influence of temperature on cuticular color of honeybee (Apis mellifera L) queens, DeGrandi-Hoffman, Spivak, Martin, 1993:
"The inheritance of abdomen color in honeybees is controlled by genes on at least 7 different loci (Roberts and Mackensen, 1951). There is also an inhibitor gene that when homozygous prevents the development of yellow body color in worker bees, and when hemizygous prevents the production of yellow males (Laidlaw and El-Banby, 1962)."

So - we have a situation in which, whenever the polygenes code for 100% black, a black phenotype will always result regardless of whatever the status of the 'bl' gene happens to be.

And, whenever the polygenes code for 50% black, then either brown (50% black) will result (if the 'bl' gene is hemizygous) or 100% black will result should the 'bl' gene be homozygous.

However, if the polygenes should code for 0% black (i.e. yellow), then either yellow (0% black) will result if the 'bl' gene is hemizygous or 100% black if the 'bl' gene is homozygous.

"The gene 'bl' is most easily identified if it is maintained in "golden" stock (four- to five-banded workers). Then, this gene can be seen to behave as a Mendelian recessive with black phenotypes always distinct from the yellow (Laidlaw and el-Banby, 1962). [...] In golden stock, 'bl' can be studied as a marker and employed in genetic tests along with mutant genes (Laidlaw et al 1965a; Tucker, 1980)."

And so we have finally reached a tentative conclusion: that the operation of the 'bl' gene - when considered in isolation - may be viewed as a Mendelian recessive gene, in which yellow is dominant over black, and which may thus be used as a genetic tool. This would appear to be the case which Woyke was referring to: a yellow queen being inseminated with a black drone which resulted in yellow offspring. But this only occurred because, a) the 'bl' gene was/is recessive, and b) the polygenes of that yellow queen would already have been coding for 0% black. QED.


Hopefully, at least somebody will find the above of interest ... ?

Regards,
LJ

[iddee]

I did... VERY interesting. Thank You.

[BeeMaster2]

Good post. Thanks.
JIm

[GSF]

I knew that (lol)

[Wombat2]

Interesting - thanks

[jalentour]

I would think the the black would be dominant.
What are the characteristics of the black bees as opposed to the yellow bees?

[Michael Bush]

>What are the characteristics of the black bees as opposed to the yellow bees?

In my experience they are more frugal, fly in colder weather, winter in smaller clusters, shut down in dearths... but those are generalizations.

In my experience (here in the US) most feral bees are a mixture of leather color and black.  It is very seldom one sees an all black colony and when we do they tend towards AMM characteristics (more propolis, runnier, more defensive, more frugal...)