Biology Reference
In-Depth Information
Personalities in
great tits are
heritable
Two interesting questions arise from these and other studies of animal personalities.
Firstly, what maintains the genetic variation in exploration, or other personality traits?
One possibility is that there is frequency dependent selection, and the outcome is a
stable mixture of traits, for example various degrees of exploratory behaviour. For
example, fast explorers do best in a population of slow explorers and vice versa, leading
to a stable mixture of the two (see the example of 'rover' and 'sitter'
Drosophila
larvae in
Chapter 1). This has been a familiar theme throughout this chapter. Another possibility
is that different personalities do better under different circumstances (e.g. different
ecological or social environments) and that a varying environment in space and time
leads to persistence of the different traits because of fluctuating selection pressures.
Studies of great tits support this last possibility but the link between personality and
fitness is complex (Dingemanse
et al
., 2004). In years with high winter food supplies
(beech nuts), relaxed competition for food led to better survival for slow exploring
females (no benefit to fast explorers from seeking out novel feeding sites). However, the
resulting high survival of the tits led to more intense male competition for breeding
sites, in which fast exploring males did best. By contrast, in years with low winter food
supplies, fast exploring females survived better (they found novel food sources more
quickly) but, curiously, among the males it was the slow explorers who did best. The
causes of these differences are not yet fully understood, but the message is that long-
term studies are needed to elucidate their effects.
The second question is: why are different behavioural traits often correlated to form
personality types? One possibility is that they are controlled by the same hormones or
genes and so the traits are constrained to occur together, boldness towards predators with
risk taking in foraging and aggressiveness towards conspecifics, for example. If traits were
not independent then there might be trade-offs, where one behaviour can be optimized
only at the expense of another. Therefore, to understand the evolution of correlated
behaviours we could not study their costs and benefits in isolation (Sih
et al
., 2004).
While different behaviours may sometimes be constrained to occur together because
of common proximate control, in three-spined sticklebacks (
Gasterosteus aculeatus
) the
correlation between intraspecific aggressiveness and exploratory behaviour or boldness
towards predators differs between populations, suggesting that these can evolve as
separate traits (Bell, 2005; Dingemanse
et al
., 2007). The more likely possibility,
therefore, is that personality traits form suites of adaptive traits which are selected to go
together. For example, a slow life history, which favours investment in adult survival
and breeding over many seasons, may select for less risk taking across several contexts
(foraging, approaching predators) than a fast life history, which favours increased
investment in the current brood at the expense of adult survival (Wolf
et al
., 2007; Biro
& Stamps, 2008). Consistent with this view is the finding that in a number of species
bolder individuals tend to have higher reproductive success but lower survival than
shyer conspecifics (Smith & Blumstein, 2008).
In great tits,
different
personality types
do better under
different
ecological
conditions
Why are different
behavioural traits
correlated? ... A
constraint?
... or adaptation?
Summary
When individuals compete for scarce resources, such as food or mates, their best options
will be influenced by what their competitors are doing. In these cases, we need to
consider what is the stable outcome of competition, namely the evolutionarily stable
