Biology Reference
In-Depth Information
100
80
60
40
20
0
Control
Fleeing
Punishment
initial test
after teaching
Fig. 12.9 Punishment and the cleaner fish Labroides dimidiatus . The figure shows the
percentage of prawn items eaten from the Plexiglas plate by individuals during the
initial preference test (light blue columns) and after the experimental treatment (dark
blue columns). When the removal of prawns led to removal of the plate (to stimulate
fleeing) or chasing with the plate (to simulate punishment), the cleaner fish were more
likely to feed on the other food type, fish flakes. From Bshary and Grutter (2005). With
permission of the Royal Society. The photograph shows an individual feeding on an
experimental Plexiglas plate. Photo © Redouan Bshary.
level of individual nodules. They found that in all cases, when nitrogen fixation was
prevented, it led to a large and significant decrease in growth of the bacteria (Fig. 12.10).
Physiological monitoring showed that this was due to the plant reducing the supply of
oxygen to nodules where nitrogen was not being supplied. Each nodule tends to be
colonized by a single clonal bacterial lineage, and so the rhizobia are favoured to
cooperate for a mixture of direct and indirect benefits, to avoid resources being cut off
to both themselves and their clone-mates in the same nodule.
If rhizobia in a
root nodule do
not supply
nitrogen to their
host plant, then
the host cuts off
the supply of
resources to that
nodule
A case study - the Seychelles Warbler
In the above examples, we have often emphasized when cooperation leads to either a
direct or kin selected benefit. However, we have also pointed out that multiple factors may
play a role in a single species, sometimes in unexpected and even initially hidden ways.
In this section, we illustrate this with a discussion of research on the Seychelles warbler
( Acrocephalus sechellensis ) by Jan Komdeur and colleagues, where the accumulating
results of a long-term study have changed drastically the perception of why cooperation
occurs. This species is like the long-tailed tit in that helpers are not required for breeding
successfully, so only occur at some nests. When they do occur, the helpers aid in territory
defence, predator mobbing, nest-building, incubation and feeding young.
Early work by Komdeur (1992) suggested that helping behaviour is driven by kin
selection and a lack of vacant breeding territories. Helpers are offspring that were
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