Abstract
Investigating patterns of among and within-individual trait variation in populations is essential to understanding how selection shapes phenotypes. Behavior is often the most flexible aspect of the phenotype, and to understand how it is affected by selection, we need to examine how consistent individuals are. However, it is not well understood whether among-individual differences tend to remain consistent over lifetimes, or whether the behavior of individuals relative to one another varies over time. We examined the dynamics of 4 behavioral traits (tendency to leave a refuge, shyness, activity, and exploration) in a wild population of field crickets (Gryllus campestris). We tagged individuals and then temporarily removed them from their natural environment and tested them under laboratory conditions. All 4 traits showed among-individual variance in mean levels of expression across the adult lifespan, but no significant differences in how rapidly expression changed with age. For all traits, among-individual variance increased as individuals got older. Our findings reveal seldom examined changes in variance components over the adult lifetime of wild individuals. Such changes will have important implications for the relationship between behavioral traits, life-histories, and fitness and the consequences of selection on wild individuals.
Highlights
Explaining variation in wild populations is crucial to the study of evolution
There was no evidence for selective disappearance, so crickets with longer adult lifespans did not have a different tendency to leave the tube to crickets with short adult lifespans
We do not think that the lack of amongindividual variation in slopes reflects a lack of power in our study, as the 95% credible intervals (CRIs) are narrow (Martin et al 2011)
Summary
Evolutionary and ecological studies have often considered behavioral variation among individuals in a single population to be noise surrounding adaptive peaks (Wilson 1998). Recent studies have emphasized that such among-individual behavioral variation is persistent and likely to be adaptive (Wilson 1998; Dall et al 2004; Smith and Blumstein 2008; Bell et al 2009). Consistent among-individual behavioral variation has classically been studied in traits such as boldness-shyness, exploration, aggressiveness, or activity. These traits, often referred to as “personality traits,” are thought to reflect underlying tendencies and are expected to influence other behaviors across contexts in a consistent way (Réale et al 2007). Adaptive explanations for the maintenance of consistent behavioral variation among individuals must deal with potential age-related behavioral variation within individuals (Dingemanse and Réale 2005; Schuett et al 2010; Kight et al 2013)
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