Biology Reference
In-Depth Information
The mechanisms of sex ratio conflict
Sundström's results suggest that workers firstly can count how many times their queen
has mated, and secondly can then manipulate the sex ratio. How could they do this? One
possibility is that they could estimate the queen mating frequency by some phenotypic
cue of genetic diversity in the colony, with lots of variation suggesting multiple mating
and low variation suggesting single mating. Koos Boomsma and colleagues investigated
whether scent was the cue in
F. truncorum
, analogous to how the scent from oral and
dorsal glands is used as a cue of relatedness in ground squirrels (Chapter 11). The 'smell'
of an ant is largely determined by the organic compounds in the wax layer on its cuticle,
which are termed hydrocarbons. Boomsma
et al
. (2003) hypothesized that if queens
were singly mated then all the workers would have a very similar hydocarbon profile,
and hence smell the same. In contrast, if queens mated multiply, the workers would
have more variable hydrocarbon profiles and would smell differently. Consequently, by
examining variation across other workers in smell, a worker would be able to estimate
whether or not its queen had mated multiply. Boomsma
et al
. found support for their
hypothesis, with the sex ratio produced in colonies with multiply mated queens showing
a strong correlation with variation in hydrocarbon profile (Fig. 13.12).
As well as showing how workers can assess queen mating frequency, Boomsma
et al
.'s
results were able to explain when workers got it wrong. In cases where queens mated
Workers can
count how many
times their queen
has mated …
… by the variance
in the smell of
other workers
1.0
0.8
0.6
0.4
0.2
0
0
0.1
0.2
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Variation in hydrocarbon profile
Fig. 13.12
Hydrocarbons and sex ratios in the wood ant
F. truncorum
. Across colonies
with multiple mated queens, the proportion of females in the reproductive brood was
negatively correlated with the variance in the cuticular hydrocarbon profile of the
workers. Open circles and solid line are colonies sampled in 1994. Solid circles and
dashed line are colonies sampled in 2000. Curves are logistic regression lines. From
Boomsma
et al
. (2003).
