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

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

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

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

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

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

Hormones and behavior

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

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…

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

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

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

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

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

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

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

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

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 http://www.eurekalert.org/multimedia/pub/web/716_web.jpg

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

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

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

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