Meta-analytic insights into factors influencing the repeatability of hormone levels in agricultural, ecological, and medical fields

Abstract

Interest in individual variation in hormone concentrations is rapidly increasing, particularly with regard to the evolutionary and practical implications. A key aspect of studying individual variation in any labile trait is estimating the degree of within- versus among-individual variation, but at present, we do not have a broad consensus on the extent to which hormone levels are repeatable and what factors might influence repeatability. To address this knowledge gap, we conducted a comprehensive meta-analysis of hormone levels that included 1,132 estimates of repeatability from 368 studies across three fields of study: agriculture, ecology, and medicine. We assessed the influence of sex, age class, sample type, hormone family, type of hormone measure, assay type, number of subjects, number of samples per subject, and sampling interval on repeatability estimates. Overall mean repeatability was 0.58, but estimates differed substantially among study disciplines, being lowest in ecology (0.34), moderate in agriculture (0.52), and relatively high in medicine (0.68). In addition, repeatability decreased slightly as sampling interval increased, and also tended to be higher for peak hormone levels than baseline levels. Overall, hormone levels are moderately repeatable, suggesting that they can potentially be useful indicators of individual variation. However, estimates of repeatability are quite variable among fields, so caution should be used when relying on single samples to assess individual variation.

Repeatability of endocrine traits and dominance rank in female guinea pigs

“…Cortisol responsiveness was significantly repeatable at both sampling times (1 and 2 h after being placed in a novel environment), but baseline cortisol was not repeatable. Despite the low sample size of the current study (N = 12 individuals), this result is consistent with recent meta-analyses [ 28 , 30 , 31 ] as well as current research with male guinea pigs [ 29 , 37 ] that consistently find cortisol responsiveness to be more repeatable than baseline cortisol. Repeatability is calculated as the proportion of total phenotypic variance that is attributed to the between-individual component, and decomposing variance into the within- and between-individual components aids in understanding why measurements differ in repeatability [ 32 ].…”

“…Historically, female behavior has been dismissed as less stable due to the influence of reproductive state [ 25 ], although recent studies have shown that female behavior is at least as stable as male behavior [ 26 , 27 ]. Recent work has also demonstrated that hormonal patterns can be temporally stable [ 28 – 31 ]. Specifically, testosterone and cortisol responsiveness are repeatable, but results are inconclusive on the repeatability of baseline cortisol.…”

“…Specifically, testosterone and cortisol responsiveness are repeatable, but results are inconclusive on the repeatability of baseline cortisol. Baseline glucocorticoid levels fluctuate throughout the day with current activity, and meta-analyses have indicated that baseline cortisol is less repeatable than cortisol responsiveness [ 28 , 30 , 31 ]. Repeatability is calculated as the proportion of total phenotypic variance (between- and within-individual variance) that can be attributed to the between-individual component.…”

Social animal models for quantifying plasticity, assortment, and selection on interacting phenotypes

“…distinct trait‐specific SRN slopes). Such residual effects tend to be much larger than the repeatable component of measured phenotypes in both laboratory and field settings, particularly for labile traits such as behavior, cognitive performance or hormone levels (Bell et al., 2009; Cauchoix et al., 2018; Fanson & Biro, 2019). As a consequence, standard models using raw trait values to calculate will tend to bias the magnitude of SRN effects for measured traits, i.e.…”

Estimating Nonlinear Selection on Behavioral Reaction Norms

“…For labile phenotypes such as behavior, hormones, and cognition, the magnitude of repeatable betweenindividual variation in measurements is generally modest in comparison to the total phenotypic variation observed across space and time (Bell, Hankison, and Laskowski 2009;Cauchoix et al 2018;Fanson and Biro 2015). This is unsurprising, given that these traits are often the primary mechanisms by which organisms can flexibly respond to ephemeral and stochastic variation in their local environments, such as by up-regulating circulating testosterone in response to social challenges (Eisenegger, Haushofer, and Fehr 2011), or by temporarily inducing a fear state in response to odor cues of predation (Mathuru et al 2012).…”