Exploratory Evidence of Sex-Dimorphic Associations of the Ulna-to-Fibula Ratio, a Potential Marker of Pubertal Sex Steroid Exposure, with the Implicit Need for Power

Relationships of the Ulna-to-fibula Ratio to Baseline and Reactive Steroid Hormone Levels: An Exploratory Study

Objective

Organizational hormone effects on the human brain and behavior are often retrospectively assessed via morphological markers of prenatal (e.g., 2D:4D digit ratio) or pubertal (e.g., facial width-to-height ratio, fWHR) hormone exposure. It has been argued that markers should relate to circulating hormones particularly in challenging, dominance/status-relevant situations. However, meta-analytic research indicates that fWHR, a frequently used pubertal marker, is neither reliably sex-dimorphic nor related to steroid hormones. This casts doubt on fWHR’s validity for reflecting hormone levels. Ulna-to-fibula ratio (UFR), an alternative, long-bone-length-based pubertal marker, is sex-dimorphic and associated with dominance motivation. However, its hormonal associations were never tested before. We therefore explored UFR’s relationships to baseline and reactive hormone levels.

Methods

We measured ulna and fibula length as well as shoulder/waist/hip circumference of 81 participants (49 women; after exclusions) via anthropometry. Salivary hormone levels (estradiol, testosterone) at baseline and after a gross-motor one-on-one balancing contest were measured via radioimmunoassay.

Results

We replicated UFR’s dimorphism, unrelatedness to height, and correlations to other putative markers of organizational hormone effects. On an exploratory basis, we found UFR to be related to overall baseline testosterone and to competition-induced reactive surges in steroid hormones (estradiol, testosterone) overall and in women.

Conclusions

Our results hint at UFR’s relationship to baseline testosterone and may indicate functional connections between outcomes of pubertal organizational hormone effects and contest-induced steroid reactivity. Pubertal organizational hormone effects may prepare the endocrine system for dominance and status contests. However, the small sample and the exploratory nature of our research demands replication.

Motives and Laterality: Exploring the Links

Objectives

We explored associations between the needs for power, achievement, and affiliation and functional cerebral asymmetries (FCAs), guided by three established hypotheses about the nature of these associations.

Methods

One-hundred-and-seven participants completed picture-story measures of dispositional motives and activity inhibition (AI), a frequent moderator of motive-behavior associations, tasks measuring FCAs (line bisection, chimeric emotional face judgments, turning bias, perceptual and response asymmetries on the Poffenberger task), self-reported laterality preferences (handedness, footedness, ear and eye preference), and interhemispheric interaction (crossed-uncrossed difference). They also completed an experiment manipulating hand contractions (left, right, both, neither) while they worked on a second picture-story motive measure.

Results

Dispositional power motivation was associated with stronger rightward asymmetry and less interhemispheric transfer in high-AI and stronger leftward asymmetry and more interhemispheric transfer in low-AI individuals. For the affiliation motive, findings were fewer and in the opposite direction of those for the power motive. These findings emerged for men, but not for women. Left- or right-hand contractions led to increases in power and achievement motivation, but not affiliation motivation. Only left-hand contractions led to decreased AI.

Conclusions

We discuss these findings in the context of sex-dimorphic organizing and activating effects of steroids on motives and laterality.