Biology Reference
In-Depth Information
the amount one male produces, to i ll her spermatheca. However, she
stores only roughly the amount produced by one male, so why is she so
inei cient in acquiring sperm? She has what appear to be clear ana-
tomical adaptations to be inei cient. (As a queen l ies through the air,
each of her mates deposits his semen into the median oviduct [see Fig-
ure 3.1]. Each load of semen pushes the previous deposits back into the
lateral oviducts, which are l uted and capable of expanding like large
balloons. At er returning to the nest, the queen sits around for up to 24
hours pulsating her abdomen, squeezing the oviducts like toothpaste
tubes, and sending the sperm back past the spermathecal duct and into
the vaginal orii ce, where it is then expelled in thin threads that the
workers remove. h e spermatozoa of each male have access to the sper-
matheca only while they sit at the opening of the spermathecal duct,
where they can then actively swim up the duct and into the sperma-
theca. By regulating the process of passing sperm back, the queen regu-
lates the mixing of the sperm of her many mates.) And why don't males
make more sperm, enough to i ll the spermatheca? Another explana-
tion was that queens simply cannot resist the mating attempts of males
as they l y through the drone congregating areas. Multiple mating is
just a matter of convenience; the ef ort for queens to resist the males is
too costly. h en why do they make additional mating l ights at er they
have mated with enough males to i ll their spermatheca?
h ere have been many hypotheses about the evolution of polyandry
in honey bees and other social insects since the publication of the i rst
detailed model of polyandry in 1980. Currently, there are at least 14 rec-
ognized hypotheses, which fall into two categories: those that are about
genetic heterogeneity and those that are not. h e sperm-need and
mating-convenience hypotheses discussed in the preceding paragraph
are not about genetic heterogeneity and are not supported by critical
analyses. Most reviews of polyandry models consider that only three of
the remaining genetic-heterogeneity hypotheses warrant further study:
sex determination, parasites and pathogens, and division of labor. I will
discuss them in Sections 4.2, 4.3, and 4.4. In my view, the evolution of
polyandry is really a two-part problem, and a sui cient model must ad-
dress both. First is the question of what maintains genetic variation in
