1. The Comparative Approach
Comparing traits among species
Without phylogeny
Relate behavior to ecological factors across spp. or populations
E.g., Eggshell removal
Problems
Causation?
“Cherry picking” examples that support hypotheses
Confounds, like size, phylogeny

2. Allometry Body size is an important confound in comparative studies
Scaling one body part against another is tricky
Allometry is the study of the relationship between body measurements
log(Y)= b log (X) + log (a)
Slope (b) > 1 means Y increases faster than X
“positive allometry”
Comparing residuals is informative

3. Controlling for phylogeny
Phylogenetic inertia
Homology
Common descent
Homoplasy
Convergence
Determining ancestral characters
Maximum parsimony
Problem of equal parsimony

4. Method of Independent Contrasts
Looks for relationship between two continuous variables while controlling for phylogeny
Examples
Assumes random change, independent changes in different branches

5. Is evolution of x correlated with evolution of y (and if so, how)?

6. Method of Maximum Likelihood
Discrete variables
E.g., duetting and monogamy
1st model: State changes in two variables are independent (a)
2nd model: State changes are
interdependent (b)
Can find most likely
direction, order

7. Hormones and behavior

8. Hormones
Chemical messengers secreted in one part of an organism that affect a relatively distant part of that organism
Work in conjunction with neurotransmitters
Work in concert with nervous system to control behaviour
Relative to nervous system, slower and more general

9. Feedback mechanisms Negative feedback Positive feedback
Like a thermostat
The male hypothalamic-pituitary-gonadal (HPG) axis
Gonadotropin (GnRH) in hypothalamus  follicle-stimulating hormone (FSH) and leuteinizing hormone (LH) in pituitary  sperm and testosterone (T) in testes  rising T reduces output of GnRH
Positive feedback
Oxytocin release during labor
Pressure on cervix  Oxytocin release  Stronger contractions…

10. Transport and target cells
Transported in the blood
Affect remote cells by binding dynamically to receptor molecules
Protein hormones bind to surface receptors
Rapidly alter cellular behavior
Steroids (lipid hormones) pass through the membrane, bind to a receptor and affect transcription
Generally slow, but fast-acting steroids challenge model
Mountain chickadees and CORT

11. Modulating hormone activity
Hormone levels in blood
Binding protein concentration
Receptor density
Up- / down-regulation in response to concentration
Pulsatile hormone release limits receptor regulation
Hormone conversion by enzymes
T oestrodiol in brain by P450 aromatase
Chaperones that modify effects of hormones on receptors

12. Hormones & the brain
Radioactively labeled sex steroids accumulate at similar brain regions in rats, frogs, and chaffinches
Preoptic, limbic, & hypothalamus
Neural firing rates correspond to hormone presence
T injected directly into male mouse brains
Median preoptic area
+ vocalization
+ urine marking
+ mounting
Hypothalamus
Other regions
No increase in sexual behaviour

13. Behavior and environment affect hormone levels
Hormone secretion is dynamic
Responds to environmental cues
The “challenge hypothesis”
Male green tree frogs
Human males, coin flips, and T

14. Chromosomal sex determination
Gonads (testes and ovaries) develop from bipotential tissues
The gonads mediate further differentiation
In most mammals
XX  Female, XY  Male
SRY region on Y is major gene for sex determination
SRY product leads to a cascade that results in testes
Otherwise, ovaries
Other genes on Y involved in spermatogenesis
Snakes, birds, and some lizards and turtles
ZZ  Males, ZW  Females

15. Environmental sex determination
Incubation temperature influences the expression of cytochrome-P450
Cytochrome-P450 converts testosterone and androstenidone into oestrogen hormones
The amount oestrogens in the gonad directly influence differentiation

16. Establishment of the HPG
Critical regulatory pathway
Growth, stress, sexual behavior, etc.
Generally, cascade runs H  P  G
Develops in reverse
Lower levels control development of higher levels
Brains pretty well shuts down HPG in infancy
HPG kicks in at puberty

17. Organizational and Activational effects
As they relate to sex and the brain
Organizational effects of hormones in early life differentiate male and female brains
Activational effects later in life facilitate expression of sex-specific behaviours

18. Mammalian examples
SDN-POA in hypothalamus is up to 5 x larger in males
Lesions disrupt copulatory behavior in males
Lesions + female sex hormones cause males to exhibit lordosis
Dominant female hyenas pass more androgens to their offspring
Early androgens  aggression
Masculanization of females

19. Hormones affect developmental plasticity
Tree lizards exhibit permanent organizational effects and reversible activational effects
Males plain orange dewlap are non-territorial
Males with orange dewlap & blue spot are territorial
Higher T and progesterone as juveniles
Critical period
Adrenal origin suggests association with stress
Activational effects on spotless males
When stressed, they go nomadic
Low T, high Cort
When not stressed, they are sedentary
High T, low Cort
Can go back and forth

20. Hormones and maternal effects
Stress in rats
Daughters of mothers stressed during pregnancy secrete more Cort when stressed response relative to controls
Their HPA axis has been sensitized during development
Potentially adaptive maternal effects in birds
T helps male offspring grow faster

21. Hormones and sibling effects
Embryonic rats are exposed to their sibs hormones
Females b/t males mount more, have different genital structure
Males b/t females are more active, less sexual, and respond with less aggression to T injections in adulthood

22. Parental care in ring doves
T stimulates male to court
Interacting with female increases his T
Courtship stimulates female to release FSH, stimulating follicle development
Female’s own “coos” necessary
Interacting with the nest stimulates progesterone in females
Increasing LH stimulates female to lay
Progesterone maintains incubation in both sexes
Incubation stimulates secretion of prolactin
Inhibits FSH and LH
Stimulates crop milk production
Prolactin decreases while feeding young
Allows FSH and LH to rebound for next mating