Chapter 3: Hormones & Neurobiology
Ultimate and Proximate Perspectives:
oHOW a behaviour is expressed in terms of genetic &
physiological mechanisms. Studies the immediate cause and
effect of behaviour (“WHAT”)
oWhat causes differences in plumage colouration between male
and female finches? Differences in foraging between genders.
Males actively search for and ingest carotenoid-based foods.
Females eat carotenoid-based foods, but do not actively search
oWHY a behaviour exists
oWhy do males, but not females, actively search for carotenoid-
based foods? Because females are attracted to makes with
bright plumage as potential mates
oWhy do females prefer males with bright plumage? Males
appear to be better able to fight off pathogens. Bright males
feed chicks more than twice as often as drabber males.
Brighter males forage better and this trait may be passed to
Hormones and Proximate Causation:
•Endocrine system is composed of
ductless glands that secrete
hormones in to the bloodstream (in
vertebrates) or fluids into the
surrounding tissue (invertebrates- no
•Major glands of invertebrates:
adrenal, pituitary, thyroid, pancreas,
•Ductless glands means that neurohormones can be released by
neurons into the blood
•There are messengers that affect target cells
•Protein hormones are strings of amino acids
oSmall number of amino acids= peptide hormones
oHydrophilic (soluble in water and blood- “water
loving”) – can carry themselves through blood
oIncreased size = increased half-life
•Steroid hormones (i.e. testosterone)
oLag time between stimulus and production
oCant be stored in cells- released right away
oHydrophobic (“water-fearing”) and fat soluble
oNeed protein carrier
•Hyposecretion: diminished secretion
•Hypersecretion: excessive secretion
•Hypothalamic-Pituitary Axis (HPA): changes behaviour, i.e.
how a subordinate animal interacts with a dominant animal in
oSubordinate animal: hypothalamus releases
corticotropin-releasing hormone (CRH), anterior
pituitary secretes adrenocorticotropic hormone
(ATCH), adrenal glands secretes glucocorticoid = reduced aggression towards
•Need proper receptor site for target cell- on surface of cell. Like a lock and key
system/hormone receptor complex. Enzymes in golgi apparatus of endocrine cells
process proteins into hormones then put them into vesicles, which fuse with cell
membrane and release hormones into blood. They bond at receptor site.
How the Endocrine System Integrates Sensory Input and Output:
•The Hormone changes can modify behaviour by increasing or decreasing the frequency
of that behaviour, or they might trigger the onset or end of a behaviour. Hormones might
prime animals so that they are more or less likely to behave in a specific way (i.e. when
testosterone levels are high, males are primed for aggression).
The Longer-Term Effect of In Utero Exposure to Hormones:
•A developing male fetus surrounded by female fetuses (2F) is
exposed to lower levels of circulating testosterone. When males
mature, they are less aggressive and less sexually active than males
surrounded by male fetuses.
•2M males have 2x the level of circulating testosterone, sire more
offspring and show less parental care
•2M females have high levels or circulating testosterone and lower
levels for circulating estradiol.
•2M females are less attracted to males, reproduce later than other
females and have fewer litters