Biology Reference
In-Depth Information
We recommend 'ESS thinking' throughout the topic, because evolution is the outcome
of competitive games. In Chapter 1, for example, we argued that restricting the birth
rate for the good of the group was not stable because selfish mutants, which optimized
their production of young, would invade and spread. Later in the topic we will use ESS
thinking to consider whether optimal group sizes are stable, the honesty of signalling
systems, the evolution of sex ratios and many other problems.
ESS thinking:
Could a mutant
strategy do
better? What is
the stable
outcome of
competition?
Animal personalities
We are all familiar with differences in human personalities; for example, some
individuals are bolder, more sociable or more aggressive than others. These differences
have a genetic basis and they have consequences for our health, social relationships and
sexual behaviour (Carere & Eens, 2005). In this chapter, we have seen that animals, too,
often differ in their behaviour, with individual differences in tactics or strategies arising
as an evolutionary outcome of competition for resources. Sometimes these differences
are discrete, for example caller versus satellite behaviour in toads, horned versus
hornless beetles or orange, blue and yellow-throated lizards. Sometimes the differences
are continuous, for example waiting times in dung flies. Recent studies have begun to
investigate continuous differences in more detail and have shown that they often involve
suites of correlated traits. For example, in birds, rodents and fish, individuals that are
relatively aggressive to conspecifics are also often bolder in their approach to predators
and quicker to explore novel environments. Such consistent differences in behaviour,
both over time and across different situations, are comparable to those in humans and
are now being referred to with the same terminology, namely animal personalities,
temperaments, coping styles or behavioural syndromes. Personalities are being
recognized not only in vertebrates but even in insects and spiders. (Sih
et al
., 2004;
Dingemanse & Réale, 2005; Réale
et al
., 2007).
Studies in The Netherlands have shown that great tit personalities can be assessed
by a remarkably simple technique. In one four-year study (Dingemanse
et al
., 2002),
1342 wild great tits from a nest-box population were caught and kept overnight in
aviaries, where they were housed individually. The following morning, before they
were released back into the wild, their exploratory behaviour was measured by
placing each bird individually in a small room with five artificial trees. The total
number of flights and hops within the first two minutes was used as an index of their
exploratory behaviour. This measure was repeatable (individuals were consistent
when re-tested) and heritable (offspring scores correlated with those of their parents).
In another study, great tits were bred in aviaries and two selection lines were created:
one breeding from juveniles who had the highest exploration scores and one from
those with the lowest scores. Over four generations, there were strong responses to
selection in both lines showing that there is a genetic basis to exploratory behaviour
(Drent
et al
., 2003).
The index of exploratory behaviour was correlated with various behavioural traits.
More exploratory individuals were more aggressive towards conspecifics, bolder in their
approach of novel objects, more likely to scrounge food from others and showed lower
physiological signs of stress when handled (Dingemanse & Réale, 2005).
Suites of
correlated
behavioural traits
and consistent
individual
differences
