Biology Reference
In-Depth Information
hormones that act on the fat body and stimulate Vg production. h e
causal chain in this case is clear: ovary
behavior. If this is true,
then we should observe this correlative structure in wild-type bees.
Jennifer Tsuruda asked this question as part of her doctoral disserta-
tion. She sampled 6-7-day-old wild-type workers from the brood
combs of a colony and tested them for a relationship among ovary size,
vg
mRNA, and responsiveness to sugar, using the proboscis extension
rel ex (PER) test (Figure 2.7). Sucrose response correlates with the other
behavioral traits in the pollen-hoarding syndrome (Chapter 5). She
found that bees with more ovarioles had higher titers of
vg
mRNA and
were more responsive to lower concentrations of sugar, like high-strain
bees. h us the ef ects of the ovary were directly linked to a key compo-
nent of the pollen-hoarding syndrome—sugar sensitivity.
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Vg
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7.5.2 Vg Knockdown and Foraging Behavior
Another approach is to reduce vitellogenin circulating in the blood and
look at ef ects on behavior. h e prediction from the double-repressor
and the reproductive-ground-plan models is that reduced Vg will result
in an earlier onset of foraging because of earlier loss of circulating Vg
and earlier increase in JH, and a nectar-foraging bias due to reduced
Vg, as found in low-strain bees (Figure 7.5). Mindy Nelson and Kate
Ihle tested this hypothesis by reducing the amount of circulating Vg in
bees by RNA interference (Figure 7.6). Small pieces of double-stranded
RNA (dsRNA) can inhibit the production of the protein encoded by the
RNA. h ey injected
vg
dsRNA into the abdomen of newly emerged
bees, the dsRNA was taken up by fat-body cells, and Vg production was
greatly reduced. Control bees were injected with dsRNA for a gene that
is not expressed in honey bees to test the ef ects of the injection minus
the knockdown. Bees that had reduced Vg foraged earlier in life and
demonstrated a bias for collecting nectar, as predicted.
7.5.3 Vg Knockdown and Sensitivity to Sugar
We were able to tie vitellogenin titers to foraging onset and foraging bias
(specialization), but what about sensory sensitivity? Sucrose sensitivity
