Cooperation between unrelated individuals has attracted a
lot of research interest for two main reasons. First, it presents
a challenge for evolutionary theory: why do individuals perform
a behaviour that increases the fitness of another individual?
Second, it has been proposed that the ecological need to
perform complex social behaviours like cooperation selects
for an increase in cognitive abilities.
The aim of my PhD is to integrate these two main research
questions in a project on the cleaner wrasse Labroides
dimidiatus. This mutualism between cleaners and their client
reef fish has been studied in quite some detail, which allows
me to develop quite fine-tuned hypotheses concerning cooperation
and the selective pressures on the cleaners' interspecific social
I have completed experiments on the first major part of my thesis,
which has focused on a more detailed understanding of image
scoring in a communication network and resulting audience effects.
I found that cleaners flexibly adjust service quality to the relative
value of current clients versus bystander. Thus, their behaviour is
very much fine-tuned and not a fixed action pattern. Moreover, they
are even capable of refraining completely from feeding providing
tactile stimulation instead if this allows them to access a more
attractive client. The results show that the behaviour and performance
of the cleaner fish Labroides dimidiatus becomes more cooperative
in the presence of a bystander.
The major aim of the second part of my PhD thesis is to test
how important interspecific social competence is for the foraging
success of cleaners. The 'Machiavellian intelligence' hypothesis
proposes that the evolution of brain size and distinctive cognitive
abilities have evolved via intense social behaviour including
cooperation and defection. However, the knowledge about cognitive
mechanisms underlying social competence remains insufficient. In
recent years, several studies on cognitive abilities show that these
aptitudes are not only found in primates but in other animal taxa as
well. Thus, the basic assumption behind the ecological approach to
the evolution of cognitive abilities is that any species should be
understood according to its specific ecological challenges under
natural conditions rather than by its evolutionary proximity to humans
or brain size. In this context, it appears clear that the main selective
force on cleaner wrasses is to maximise the food intake over their
2000 interactions per day and hence on their ability to cooperate,
manipulate and exploit clients.