Selective Breeding for a Behavioral Trait Changes Digit Ratio

The ratio of the length of the second digit (index finger) divided by the fourth digit (ring finger) tends to be lower in men than in women. This 2D∶4D digit ratio is often used as a proxy for prenatal androgen exposure in studies of human health and behavior. For example, 2D∶4D ratio is lower (i.e. more “masculinized”) in both men and women of greater physical fitness and/or sporting ability. Lab mice have also shown variation in 2D∶4D as a function of uterine environment, and mouse digit ratios seem also to correlate with behavioral traits, including daily activity levels. Selective breeding for increased rates of voluntary exercise (wheel running) in four lines of mice has caused correlated increases in aerobic exercise capacity, circulating corticosterone level, and predatory aggression. Here, we show that this selection regime has also increased 2D∶4D. This apparent “feminization” in mice is opposite to the relationship seen between 2D∶4D and physical fitness in human beings. The present results are difficult to reconcile with the notion that 2D∶4D is an effective proxy for prenatal androgen exposure; instead, it may more accurately reflect effects of glucocorticoids, or other factors that regulate any of many genes

Callous-unemotional traits moderate the relation between prenatal testosterone (2D:4D) and externalising behaviours in children

Children who exhibit callous-unemotional (CU) traits are identified as developing particularly severe forms of externalising behaviours (EB). A number of risk factors have been identified in the development of CU traits, including biological, physiological, and genetic factors. However, prenatal testosterone (PT) remains un-investigated, yet could signal fetal programming of a combination of CU/EB. Using the 2D:4D digit ratio, the current study examined whether CU traits moderated the relationship between PT and EB. Hand scans were obtained from 79 children aged between 5 and 6 years old whose parents completed the parent report ICU (Inventory of Callous Unemotional Traits) and SDQ (Strengths and Difficulties Questionnaire). CU traits were found to moderate the relationship between PT and EB so that children who were exposed to increased PT and were higher in CU traits exhibited more EB. Findings emphasize the importance of recognising that vulnerability for EB that is accompanied by callousness may arise before birth

Foetal and postnatal exposure to high temperatures alter growth pattern but do not modify reproductive function in male rabbits

Purpose: The foetal origin hypothesis postulates that a number of organ structures and associated functions undergo programming during embryonic and foetal life and the neonatal period, which determines the set point of physiological and metabolic responses that carry into adulthood. We evaluate the relationship between high environmental temperatures and the reproductive function of male offspring to determine whether pregnant mammals and their infants are potentially vulnerable to the effects of climate change. Methods: Rabbit pups were exposed to high temperatures during gestation and lactation. Results: Foetal and postnatal exposure to high temperatures did not alter semen characteristics and was associated with a similar fertility rate and number of pups born. Moreover, males showed reduced rate of maturing and carcass traits at adulthood. Conclusion: Our findings suggest that male exposure during the foetal period to high temperatures did not affect sperm quality but permitted an adaptive phenotypic plasticity of growth in adulthood.This work was supported by the Spanish Research Projects AGL2008-03274 and AGL2011-30170-C02-01 (CICYT) and funding from the Generalitat Valenciana Research Programme (Prometeo 2009/125). Estrella Jimenez-Trigos and Carmen Naturil-Alfonso were supported by a research grant from the Education Ministry of the Valencian Regional Government (programme VALi+d. ACIF/2010/262 and ACIF/2013/296, respectively). The English text version was revised by N. Macowan English Language Service. The authors declare they have no actual or potential competing financial interests. The authors alone are responsible for the content and writing of the paper.Marco Jiménez, F.; Naturil Alfonso, C.; Jiménez Trigos, ME.; García Diego, FJ.; Lavara García, R.; Vicente Antón, JS. (2014). Foetal and postnatal exposure to high temperatures alter growth pattern but do not modify reproductive function in male rabbits. International Journal of Hyperthermia. 2(30):86-95. https://doi.org/10.3109/02656736.2013.878042S869523