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only sugar solution or only pollen, even when the feeders are side by
side.
Adam Siegel studied nectar loading. His hypothesis was that the
ovary af ects sucrose sensitivity, which af ects nectar loading, which in
turn af ects pollen load size. He started with the knowledge that (1)
nectar loading negatively af ects pollen loading, (2) sucrose responsive-
ness correlates with nectar and pollen loads, and (3) ovary size af ects
sucrose responsiveness and foraging load. He set up a foraging cage
and had bees forage at an artii cial feeder that mimicked a l ower and
controlled the rate of delivery of sucrose solution. He of ered bees solu-
tions of dif erent concentrations, determined the quantity of solution
they collected and their responsiveness to sucrose using the proboscis
extension response (PER) assay, and dissected their ovaries to deter-
mine the number of ovarioles. He found that sucrose responsiveness
correlated with the concentration of solution the bees would collect,
the concentration af ected the amount of solution collected, and the
number of ovarioles correlated with the relationship between the
amount of solution collected and the concentration. h e ovary appar-
ently tuned the loading algorithm.
9.2 Heritability of the Pollen-Hoarding Syndrome
How much of the phenotypic architecture of the traits associated with
pollen hoarding do we explain by the genetic architecture? h e answer
is “a lot and very little.” Each generation, we measured the amount of
pollen stored by high- and low-strain colonies. Each generation, we
calculated the proportion of the total variance of the pooled colonies
(high- and low-strain colonies together) that was a consequence of be-
ing from the high or low strain. h is is a measure of the genetic separa-
tion of the strains (heritability or genetic determination; see Section
5.2.1). h e average proportion was 0.41; in other words, the genetic dif-
ferences between the strains determined 41 percent of the total vari-
ance (Figure 9.2). h is value is very high and shows a very strong re-
sponse to our selection.
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