Biology Reference
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of mates af ects the distribution of alleles and brood viability in the
population. But to have a complete model, I need to show how brood
viability af ects the i tness of queens that mate with dif erent numbers
of males. Imagine that colonies survive and reproduce in proportion to
the viability of their brood. In that case, queens that mate one time will
have on average a i tness of 0.80 relative to the maximum of 1.00. Queens
that mate a very large number of times will also have a relative i tness of
0.80, so there is no advantage for any genotypes that af ect number of
mates. However, what if only colonies with more than 75 percent viable
brood are able to produce worker populations that are sui cient to
maintain the colony, survive, and produce successful new queens and
drones? In that case queens that mate just one time will have a 20 percent
chance of failing, while those that mate a very large number of times will
be successful, a clear advantage for genotypes that result in polyandrous
mating. h is model can be developed more completely to show dif erent
kinds of relationships between the relative i tness of mating number
genotypes and brood viability, but the example just shown is sui cient
(Figure 4.4). In general, as long as the relationship between i tness
(including survival and reproduction) and brood viability is concave,
multiple mating will be selected.
Dave Tarpy, a former graduate student of mine, tested the sex-
determination model for the evolution of polyandry. He instrumentally
inseminated 31 queens, each with the semen of three dif erent drones
that were brothers of the queens. h e expected result of the inbreeding
was that the matings would produce an average of 25 percent diploid
progeny, or a brood viability of 75 percent. h e actual median for the 31
queens was 72 percent. Each male produces a dif erent amount of sperm,
and because brother drones were selected as fathers at random, there was
a continuous distribution of brood viability between about 50 percent
and 100 percent (Figure 4.4). Colonies were allowed to develop through-
out the season and to acquire resources necessary for surviving the
winter. All colonies with at least the median of 72 percent viable brood
survived the winter and built back up in the spring, while 63 percent of
the colonies with less than the median viable brood perished. He also
estimated worker populations in the colonies, the most important de-
