Biology Reference
In-Depth Information
We looked at ovariole number, an individual anatomical trait.
Strain explained about 40 percent of the variance, similar to the so-
cial trait of pollen hoarding. We also looked at individual foraging
traits. For example, we performed common-garden experiments (Fig-
ure 4.5) where we put marked high- and low-strain bees in common
wild-type colonies, collected returning foragers, measured their
loads, and partitioned the variance of the total, combined sample.
h e amount of variance explained by strain varied between 2 percent
and 16 percent.
h e combination of the phenotypic architecture and the reproductive-
ground-plan hypothesis suggests a hypothesis for the causal links be-
tween the pollen-hoarding genetic architecture and foraging behavior.
One can debate the degree to which we have been able to distinguish
between direct causal pathways and latent unknown variables af ect-
ing multiple factors, but this is our working hypothesis. h e pollen-
hoarding quantitative trait loci (QTLs) af ect ovary development, as is
demonstrated by dif erences in ovariole number between strains, which
in turn af ects vitellogenin levels in developing adult bees, which in
turn af ects response thresholds to sucrose throughout life. Sucrose re-
sponsiveness af ects the concentration of nectar collected, and the
amount of collected nectar af ects the amount of pollen collected. I
constructed the correlative relationships between the regulatory ele-
ments in the chain of hypothesized causal factors (Figure 9.2). Some
patterns are obvious.
1. Ge ne tic dif erences between highs and lows explain much more of
the phenotypic variance at the social phenotype level (stored pollen)
than at the individual foraging level. h is is the opposite of what I ex-
pected. I expected that the further we got from the more direct action
of the genes involved, the less genetic ef ect we would see. Stored pollen
is a consequence of many interacting features of the social and foraging
environment.
2. h e ge ne tic ef ects on ovariole number are strong, about equal to
the ef ects on stored pollen. I am not surprised, because I think that
ovary development is closer to the direct action of the genes than the
foraging behavior that they inl uence.
