Biology Reference
In-Depth Information
h ere will always be susceptible and resistant genotypes in colonies.
Absolute resistance is not achieved. An increase in the numbers of
mates decreases the variance in disease load of colonies just as it de-
creases the variance in diploid males and brood inviability. If there is a
concave relationship between disease load and colony reproductive
output (successful queens and drones), then polyandry will be favored.
Or if there is a threshold ef ect where colonies below a certain disease
load die without reproducing, polyandry will be selected.
How plausible is this model for explaining polyandry in honey bees?
Genetic variation for disease resistance has been demonstrated repeat-
edly. However, there is little evidence for the gene-for-gene mechanisms.
Gene- for- gene re sis tance could be demonstrated if dif erent subfami-
lies within a colony showed dif erential infection from the same strain
of pathogen. Harry Laidlaw instrumentally inseminated a queen with
the semen of six dif erent males. h e queens were homozygous for two
visible recessive mutations, one that af ects integument color (cordovan,
cd
), the other eye color (snow,
s
). As discussed in Section 3.2, individu-
als homozygous for the recessive cordovan allele have a brown cuticle
where bees are normally black. h ere are three alleles for the snow
eye-color gene: wild type (+), snow
(s),
and tan
(s
t
). h e wild type is
dominant, so any individual with a wild-type allele will have black
eyes. Individuals homozygous (or hemizygous in the case of males) for
snow have white eyes, while individuals that get a white allele paired
with a tan allele have red eyes. Cordovan workers with red eyes are
striking in appearance. Homozygous workers or hemizygous males
with tan alleles have tan eyes. We used males that were either wild type
or cordovan for integument color and were wild-type, snow, or tan
eyed. Workers derived from the six combinations had either cordovan
or wild-type integument and wild-type, snow, or red eyes.
Queens were placed in colonies and began to lay eggs. h e experi-
ment was originally designed to study patterns of sperm use, another
look at sperm clumping and sperm competition, so emerging worker
samples were taken periodically over about three months. During the
sampling, one colony developed American foulbrood disease, a serious
disease of larvae caused by the bacterium
Paenibacillus larvae.
Associ-
