The influence of sex hormones on brain lateralisation

Brain lateralization is the phenomenon that both hemispheres of the brain are specialised in different functions. Lateralization differs in strength and direction between individuals and among tasks within individuals, potentially affecting cognitive performance. There is debate to what extent individual differences in lateralization are due to early or later exposure to sex hormones. We use unique data sets to test this: (1) Existing data on prenatal hormone exposure, obtained from amniotic fluid during pregnancy of the mothers, will be correlated with brain lateralization and cognitive performance in a group of healthy adolescents of 13-15 years old (30 boys, 30 girls). (2) Current testosterone and progesterone levels are measured in saliva and will be correlated with brain lateralization and cognitive performance of the same individuals. Brain lateralization of verbal fluency, mental rotation and facial emotion processing is measured with functional transcranial Doppler s! onograph

Unravelling the many facets of human cooperation in an experimental study

Humans readily cooperate, even with strangers and without prospects of reciprocation. Despite thousands of studies, this finding is not well understood. Most studies focussed on a single aspect of cooperation and were conducted under anonymous conditions. However, cooperation is a multi-faceted phenomenon, involving generosity, readiness to share, fairness, trust, trustworthiness, and willingness to take cooperative risks. Here, we report findings of an experiment where subjects had to make decisions in ten situations representing different aspects of cooperation, both under anonymous and ‘personalised’ conditions. In an anonymous setting, we found considerable individual variation in each decision situation, while individuals were consistent both within and across situations. Prosocial tendencies such as generosity, trust, and trustworthiness were positively correlated, constituting a ‘cooperativeness syndrome’, but the tendency to punish non-cooperative individuals is not part of this syndrome. In a personalised setting, information on the appearance of the interaction partner systematically affected cooperation-related behaviour. Subjects were more cooperative toward interaction partners whose facial photographs were judged ‘generous’, ‘trustworthy’, ‘not greedy’, ‘happy’, ‘attractive’, and ‘not angry’ by a separate panel. However, individuals eliciting more cooperation were not more cooperative themselves in our experiment. Our study shows that a multi-faceted approach can reveal general behavioural tendencies underlying cooperation, but it also uncovers new puzzling features of human cooperation

Maternally‐transferred thyroid hormones and life‐history variation in birds

This is the final version. Available on open access from Wiley via the DOI in this recordThe data and the R code used to produce the results of this study are available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.547d7wmb5.1. In vertebrates, thyroid hormones (THs) play an important role in the regulation of growth, development, metabolism, photoperiodic responses and migration. Maternally transferred THs are important for normal early-phase embryonic development when embryos are not able to produce endogenous THs. Previous studies have shown that variation in maternal THs within the physiological range can influence offspring phenotype. 2. Given the essential functions of maternal THs in development and metabolism, THs may be a mediator of life-history variation across species. 3. We tested the hypothesis that differences in life histories are associated with differences in maternal TH transfer across species. Using birds as a model, we specifically tested whether maternally transferred yolk THs co-vary with migratory status, developmental mode, and traits related to pace-of-life (e.g. basal metabolic rate, maximum lifespan). 4. We collected un-incubated eggs (n = 1-21 eggs per species, median = 7) from 34 wild and captive bird species across 17 families and 6 orders to measure yolk THs (both triiodothyronine, T3 and thyroxine, T4), compiled life-history trait data from the literature, and used Bayesian phylogenetic mixed models to test our hypotheses. 5. Our models indicated that both concentrations and total amounts of the two main forms of THs (T3 and T4) were higher in the eggs of migratory species compared to resident species, and total amounts were higher in the eggs of precocial species, which have longer prenatal developmental periods, than in those of altricial species. However, maternal yolk THs did not show clear associations with pace-of-life related traits, such as fecundity, basal metabolic rate, or maximum lifespan. 6. We quantified interspecific variation in maternal yolk THs in birds and our findings suggest higher maternal TH transfer is associated with the precocial mode of development and migratory status. Whether maternal THs represent a part of the mechanism underlying the evolution of precocial development and migration or a consequence of such life histories is currently unclear. We therefore encourage further studies to explore the physiological mechanisms and evolutionary processes underlying these patterns.Academy of FinlandAcademy of FinlandCape Horn International Center, Chil

On the ontogeny of display behaviour in the black-headed gull : (Larus ridibundus)

In dit proefschrift wordt onderzocht op welke wijze de vorm en het gebruik van stereotiepe en soort-specifieke signaalhoudingen en geluiden zich ontwikkelen in het opgroeiende individu. Deze motorpatronen vervullen een belangrijke rol in de communicatie tussen soortgenoten, en worden displays genoemd. Kennis over de ontogenese van displays kan inzicht verschaffen in principes die aan de ontwikkeling van sociaal gedrag ten grondslag lisgen en kan tevens tot een beter begrip leiden van de organisatie-struktuur van sociaal gedrag in volwassen dieren. Als studieobject werden de displays van de kokmeeuw gekozen: deze vogels bezitten een uitgebreid display-repertoire en laten zich goed bestuderen in het veld alsook onder laboratorium omstandigheden. ... Zie: Samenvatting