> >Is it known how the queen stores the sperm from different drones?.
Essentially no, and this needs further research to clarify it, but it
is likely to be random mixing in the spermatheca (her sperm storage
organ). The queen will mate with some 17-34 drones per mating
flight (gary 1963; Adams et al. 1977) and may take up to 5 mating
flights (Roberts 1944; Gary 1971). The level of sperm she acrues is
likely to be excess of her needs for worker production (fertilised
eggs) over the year [A. mellifersa sperm is long lived..over two
years viability in the queen spermatheca]. Indeed she is often seen
to exude sperm after the/ each mating flight (e.g. Woyke 1960;
Rattner et al. 1973). This later point suggests sperm mixing in her
spermatheca and so it simplistically would be expected that all
drones will have a random chance of parternity...... However, it is
not certain that this has to be or indeed is the case. Firstly
different drones may allocate different amounts of sperm, or
different proportions of sperm (fertilising versus non-fertilising
but defending sperm; known as pyrene and apyrene) to the queen and so
would not have equal paternity chances under a random mixing model.
Secondly, there may be sperm competiition between the sperm of
different drones and consequently different drones would have
different probabilities of paternity. Thirdly, first male mating may
place the sperm so far up the spermatheca that it is both mixed with
sperm from subsequent matings less as it is not displaced as much,
and / or it is exuded less compared to say the last drone's
contribution. Thios would bais the queens allocation more to the
first male she mated with. Lastly, it is not impossible that the
female may somehow discriminate against sperm from some males(but
there is no evidence for this in Hymenoptera (bees, ants wasps and
sawflies) let alone honey bees and is not viewed as that likely as it
is more likely she would evolve discrimination against copulation
with the "inferior" drone than to select against his sperm usage
after multiple mating.
Genetic studies of the queens progeny using minisatellite dna
fingerprinting, as John Burgess has pointed out , and more
recently using microsatellite analysis (a more sensitive form of
genetic dna fingerprinting), has confirmed that the fertilised eggs
(workers) are derived from at least 10-17different drones (e.g. Adams
et al. 1997; Estoup et al. 1994) so late drones do still get
paternity. They do not however address the above points. That is
sperm may not be randomly mixed etc., and this interesting question
awaits resolving. For example is the first male sperm used (mainly)
first and then subsequent drones sperm used after this has been
exhausted? If so, it would depend upon the colony size (number of
fertilised eggs laid) as to how much paternity late mating drones
recieved, for example. This requires a temporal analysis of the
queens diploid progeny (workers) after her mating flights over the
whole year, as opposed to the studies to date on the whole colony at
a single time point.
By the way, any thoughts on why queens are so polyandrous (multiply
mate so many times) if she isnt sperm limited and discards a large
proportion of the acquired sperm (remember mating has both an
energetic cost, increased vulnerability to predators and risk of
sexually transmitted deseases and so is a risky buisness)?
Ok because honey bees have complimentary sex determination
(Inbrreding leads to up to 50% of the workers actually developing
as sterile diploid MALES and not females (workers) the queen ,
assuming she cannot discriminate against sex-allele related males
and avoid mating with them, will need to multiply mate to sample the
genetic pool and reduce the number of sex-allele related sperm she
acquires on average (OK diploid males are killed in the cells, but
this translates as a 50% sterile queen, prevent rapid colony growth
and challenging the viability of the hive to survive). However,
theoretical analysis predicts that to minimise the cost of sex alle
related matings, assuming all sex alleles are at equal frequency in
the population, she will only need to mate with 5-7 drones (Page
1980; Ratnieks 1990) .
Therefore why the excess, that is 17-37 drone copulations per mating
flight and up to 5 mating flights?
Cheers
Rob
Robert Butcher,
Evolutionary and Ecological Entomology Unit,
Department of Biological Sciences,
Dundee University,
Dundee, DD1 4HN,
Tayside, Scotland,
UK.
Work Phone:- 01382-344291 (Office), 01382-344756 (Lab).
Fax:- 01382-344864
e-mail:- [log in to unmask]
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