Biology Reference
In-Depth Information
7.6 Dii culties with the Vitellogenin Foraging Model
Like most models in biology, ours cannot explain all the observed re-
sults. h at is why I call it a heuristic model. It serves as a framework on
which to hang data and thoughts and for the generation of new ques-
tions. Ours is certainly false, but where and how? First, Vg and JH must
be working together. Joseph Sullivan and colleagues showed that JH is
not necessary for the onset of foraging by removing the JH-producing
corpora allata from bees—they foraged anyway. We assume that be-
cause JH inhibits Vg production, the allatectomized bees had higher
titers of Vg but foraged at about the same time as the undisturbed con-
trols. h ere must be a JH-independent pathway, but there also must be
a Vg-independent pathway. We showed that knocking down Vg in low-
strain bees does not increase JH, but the knockdown bees still forage at
the same age as the controls, in which case neither Vg nor JH has an ef-
fect. h e ways in which JH and Vg interact to af ect foraging onset need
to be resolved.
High-strain bees have higher levels of Vg in the blood over the i rst
10 days of adult life. h e double-repressor hypothesis, in its original
form, suggested that blood titers in nurse bees decrease as they feed
brood. h e fat-body cells are still producing Vg, but the rate of produc-
tion is less than the rate of transfer of Vg through the brood food
glands to developing larvae. High-strain bees forage earlier in life, so
their blood titers of Vg must fall very rapidly compared with low-
strain bees. h erefore, we can assume that high-strain bees feed more
larvae.
Adam Siegel looked at the nurse behavior of high-strain bees. He
uniquely marked 600 high-strain and 600 low-strain bees and placed
300 of each in two observation hives. For behavioral studies, we ot en
tag workers with plastic disks that are numbered. h e disks are glued to
the thoraces of bees and usually remain throughout life. Observation
hives are also a common tool for behavioral research. h ey typically
consist of two to four frames with combs stacked vertically and have
glass sides so that the activities of the bees can be observed (Figure 7.8).
Siegel observed the marked cohorts for about 30 days, through the nor-
