Behavioral Genetics Friday Lecture Series

Behavioral Genetics Friday Lecture Series

Part 1

Presented by:

Allie Bailey

allie@ualberta.ca

Why are some individuals more aggressive than others?

Activational vs. Organizational Testosterone

Activational: short-term effects of hormones which trigger behavior

Organizational: long-term effects of exposure to hormones during development

Activational Effects of Hormones

Testosterone Aggressive Behavior

The Reciprocal Model

A cyclical relationship exists between aggressive behavior and activational testosterone

Aggressive Behavior Testosterone

The Reciprocal Model

The Reciprocal Model

The Reciprocal Model

Organizational Effects of Testosterone on Aggression

• Animal Models– Mice (vom Saal & Bronson, 1980)– Lizards (polymorphic throat badges)

Organizational Effects of Testosterone on Aggression

• Humans– high risk spontaneous

abortions (treated with progestins & estrogens)

– Congenital Adrenal Hyperplasia (CAH)

Digit Ratio: an indicator of natural variations in prenatal

testosterone Fact or Fiction?

Outline

•What is digit ratio (2D:4D)?

•History of digit ratio

•Sexually dimorphic and stable (humans & other species)

•Indirect evidence of digit ratio as an indicator of prenatal testosterone

•CAH studies

•Hox genes

•Androgen receptor gene

•fetal testosterone study

What is digit ratio (2D:4D)?

Basal Crease

Finger Tip2D4D

Males and Females Differ

•Digit Ratio is a sexually dimorphic trait

Female Male

History of digit patterns

First year U of A students’ 2D:4D

Digit ratio is stable

-by 13th week of development hand bone proportions are stable

- digit ratio not affected by age (but see Buck et al., 2003)

Sexual dimorphism in digit ratio

• Larger on the right than the left side (humans, mice, & zebra finches)

• Suggested that androgenization affects the right more than the left

• Stronger effects on the right hand when digit ratio has been correlated with psychological factors

• Not due to bones in hand

• 2D:4D most sexually dimorphic of all ratio combinations

Ethnicity plays a role in 2D:4D

2D:4D and Other Species

How do you measure 2D:4D in mice?

Brown et al. (2003) method

Bailey et al. (in press) method

2D:4D is sexually dimorphic in laboratory mice

But not in inbred strains...

Digit ratio differs between strains, but not between sexes within a strain (Bailey & Hurd, in press)

Digit ratio is sexually dimorphic in zebra finches (Burley & Foster, 2004)

•Female digit ratio was lower than male digit ratio (similar to pattern seen in human toes- McFadden & Schubel, 2002)

•Digit ratio positively correlated with egg order in both males and females (decreasing androgen allocation as egg order increases).

Congenital Adrenal Hyperplasia (CAH)

•Autosomal recessive condition

•Results in abnormally high androgen concentrations

•Diagnosed and treated after birth typically (reflects organizational rather than activational testosterone influence).

CAH and 2D:4D (Brown et al., 2002)

CAH and 2D:4D (Buck et al., 2003)

Hox genes

•are highly conserved across species

•38 genes organized in 4 families (Hoxa- Hoxd)

•Hoxa and Hoxd control the patterning of the appendicular skeleton

Hox genes and 2D:4D

Androgen receptor gene (Manning et al, 2003)

X-linked gene that codes for a receptor protein (3 domains)

terminal domain encodes variable length of glutamine repeats (range: 11-30)

determines sensitivity to testosterone

Increased numbers of CAG repeats increased androgen insensitivity

2D:4D and the Androgen Receptor Gene

Fetal testosterone/estradiol and 2D:4D (Lutchmaya et al., 2004)

The BIG Idea (Austin et al., 2002)

•Males and females consistently differ for a number of cognitive & personality traits

•Some of these traits have been theoretically or empirically linked to sex hormones

•If there is a hormonal basis for the sexual dimorphism seen in such traits then there should be an association between 2D:4D and these traits

Hypothesis

Testosterone organizes human aggressive behavior and therefore, 2D:4D will correlate with adult

aggressive behavior.

Methods

•298 Introductory Psychology Students

•Questionnaire•Aggression Questionnaire (Buss & Perry, 1992)

•Hostility (Cognitive)•Anger (Emotional)•Verbal (Instrumental)•Physical (Instrumental)

•Paulhus Deception Scale (PDS)

Methods

Digital Imaging of Hands

Results

Men had smaller digit ratios than women on both their right (p< 0.001) and left (p< 0.001) hands.

Males Females tMean Right 2D:4D 0.946 0.965 -5.35Mean Left 2D:4D 0.951 0.966 -4.28

ResultsPhysical aggression is the most sexually dimorphic aggression subscale therefore, of the 4 subscales it should most strongly correlate with digit ratio.

Results

Physical aggression was the only subscale to correlate with digit ratio

Results

Males with lower 2D:4D had higher physical aggression scores

Conclusions•Prenatal testosterone (as assayed by 2D:4D) predicts male physical aggression

- physical aggression was the most sexually dimorphic trait

•No relationship found between activational testosterone and aggression questionnaire (Archer et al., 1998)

Conclusions

•Our organizational effect of testosterone on physical aggression (rpartial= -0.21, r= -0.17) was larger than average activational relationship (r= 0.14) reported in meta-analyses (Archer et al., 1998; Book et al., 2001).

-different methodologies across studies-testosterone fluctuates daily & seasonally-small unrepresentative samples

Future Research

2D:4D and physical aggression in hockey players

Do aggressive penalty minutes correlate with digit ratio?

Any Questions?