Biology Reference
In-Depth Information
pean foulbrood (a bacterial disease), but did show a signii cance dif er-
ence in disease intensity for chalkbrood (a fungal disease).
From the combined studies just described we can conclude that there
is selectable genetic variation for many dif erent mechanisms of resis-
tance to disease. Selection in the case of American foulbrood resulted
in changes in a suite of traits involving behavior, anatomy, and physiol-
ogy. Genetic-diversity studies have shown that multiple mating de-
creases disease prevalence for American foulbrood, but the mechanism
is unclear. h e prevalance of chalkbrood disease is reduced at some
times but not at others, and the variance is lower when colonies have
more genotypic diversity (more drone fathers). Multiple mating re-
duces the variance among colonies in hygienic behavior, a behavioral
mechanism with broad ef ects on disease resistance. Hygienic behavior
reduces chalkbrood prevalence.
Although there is little support for the Red Queen hypothesis, and
equivocal support for the general-resistance hypothesis, there is clear
support for hygienic behavior as a mechanism to reduce disease by
eliminating the sources of inoculum, dead larvae and pupae. So why is
hygienic behavior rare? I assume that there must be a cost to the behav-
ior that outweighs its benei t for disease resistance, but I can only spec-
ulate what that cost might be (Section 4.4.2). h e ef ect of the cost is to
make alleles for the behavior relatively rare and ef ective in low doses in
colonies. In this case, polyandry could increase the chance that a queen
mates with a few males, not too many, that carry the alleles for hygienic
behavior. With behavioral dominance, the colony could be hygienic
with a small percentage of workers engaged at a reduced cost—a
genotypic- diversity hypothesis.
4.4 Genotypic Diversity and Division of Labor
Division-of-labor hypotheses for the evolution of polyandry come in
two forms:
ge ne tic specialists
(genotypic variation results in more
specialists and higher-performing colonies) and
colony stability
(ge-
notypic variation buf ers colonies from the ef ects of changes in the
environment).
