Within-individual canalization contributes to age-related increases in trait repeatability: a longitudinal experiment in red knots

Abstract

Age-related increases in the repeatable expression of labile phenotypic traits are often assumedto arise from an increase in among-individual variance due to differences in developmentalplasticity or by means of state-behavior feedbacks. However, age-related increases inrepeatability could also arise from a decrease in within-individual variance as a result ofstabilizing trait expression, i.e. canalization. Here we describe age-related changes in withinandamong-individual variance components in two correlated traits, gizzard mass andexploration behavior, in a medium-sized shorebird, the red knot (Calidris canutus). Increasedrepeatability of gizzard mass came about due to an increase in among-individual variance,unrelated to differences in developmental plasticity, together with decreases in withinindividualvariance, consistent with canalization. We also found canalization of exploration, butno age-related increase in overall repeatability, which suggests that showing predictableexpression of exploration behavior may be advantageous from a very young age onward.Contrasts between juveniles and adults in the first year after their capture provide support forthe idea that environmental conditions play a key role in generating among-individual variationin both gizzard mass and exploration behavior. Our study shows that stabilization of traitsoccurs under constant conditions: with increased exposure to predictable cues, individuals maybecome more certain in their assessment of the environment allowing traits to becomecanalized