Biology 363/563 Ornithology
Dr. David Swanson, Office: CL 180
** ENDOCRINE SYSTEM **
- In general, similar hormones (and actions) to mammals.
ENDOCRINE GLANDS = ductless glands; secretion diffuses directly into blood vessels which are closely associated with secretory units of the gland.
Secretion = hormones - act in small amounts, usually at a site different from the site of origin.
1. Pituitary = located at base of brain, connected to the hypothalamus region of the brain by a stalk (infundibular stalk). Divided into two lobes.
- A) Anterior Pituitary secretes:
- (1) Gonadotropic Hormones (FSH, LH) = regulate growth of gonads and production of gonadal hormones; also regulates production of gametes.
- (2) Adrenocorticotropic Hormone (ACTH) = controls function of adrenal cortex
- (3) Thyrotropic Hormone = stimulates activity of thyroid gland
- (4) Prolactin = inhibits gonadal activity, increases fat storage, possibly induces brooding behavior.
- (5) Growth Hormone (GH) = stimulates growth; also stimulates lipolysis and glycogen sparing.
- (1) Gonadotropic Hormones (FSH, LH) = regulate growth of gonads and production of gonadal hormones; also regulates production of gametes.
- B) Posterior Pituitary secretes (Hormones are actually produced by cell bodies in the hypothalamus, but they are released from axon terminals in the posterior pituitary):
- (1) Arginine Vasotocin (AVT) = regulates blood pressure by serving as vasoconstrictor; antidiuretic mechanism - decreases glomerular filtration rate by constricting arterioles leading to glomerulus and increases reabsorption of water from collecting ducts of mammalian type nephrons in kidney.
- (2) Oxytocin = stimulates expulsion of eggs from oviduct.
- A) Interrenal = regulates carbohydrate and lipid metabolism, salt metabolism, regulates gonadotropins.
- B) Chromaffin = secretes norepinephrine and epinephrine, regulate blood pressure and heart rate.
4. Parathyroid = closely associated with thyroid; secretes parathyroid hormone which acts to mobilize Calcium ions from bone.
5. Ultimobranchial Bodies = located posterior to parathyroids; secrete calcitonin which inhibits release of calcium ions from bone. Homologue to C-cells of mammal thyroid.
6. Pancreas = secretes:
- A) Insulin = promotes cellular uptake of glucose, decreases blood glucose.
- B) Glucagon = promotes glycogenolysis, lipolysis, increases blood glucose.
- A) Androgens = in males; promotes development of secondary sex characteristics, general growth, courtship behavior.
- B) Estrogens = in females; promotes development of secondary sex characteristics, breeding behavior, stimulates substrate mobilization for egg production.
PHOTOPERIODISM
- Photoperiod regulates activity state of gonads so that birds can:
- 1) predict optimal time for reproduction
- 2) accommodate annual variations in weather
- 3) synchronize reproductive function in males and females
- 4) terminate reproductive function after the breeding season
- Subsequent research has shown that:
- 1) Sexual cycle initiated by daylength: GnRH (hypothalamus) --> FSH, LH (anterior pituitary) --> stimulates gonad development
- 2) Eyes are not essential for photoperiodic response. Eyeless birds respond to changing photoperiod in the same fashion as untreated birds. Response appears to be mediated by hypothalamic receptors.
- 3) Endogenous circannual rhythms may control breeding cycle; reset (synchronized) in some fashion by long days.
- 1) In some manner, gonadotropins from anterior pituitary are blocked.
- 2) Prolactin may be involved.
- 3) Short days of winter somehow act to reset photostimulatory phase.
- Photoperiod probably also regulates other seasonal cycles as well (e.g., migration, winter fattening).
POSSIBLE MECHANISMS (of Photoperiod Sensitivity)
I. Circadian Cycles exist in different hormones (e.g., prolactin, corticosterone, melatonin [from pineal, important to circadian rhythms]).
- Phases of circadian hormone cycles relative to other hormone cycles may influence sensitivity to photoperiod (e.g., prolactin injections give differing results depending on the phase of corticosterone).
II. Circadian Cycles in photosensitivity relative to the amount of daylength present may also be important.
- With longer days there is an increased chance of the photostimulatory period occurring during the day + a longer duration of overlap between the photostimulatory phase and daylight.
- The amount of overlap may allow measurement of daylength. SEE PG. 271, GILL.
** ENERGETICS **
I. DEFINITIONS AND MEASUREMENT
Metabolism = sum total of biochemical reactions occurring within an organism, serves to provide energy in a usable form (ATP). Energy is obtained from the oxidation of foodstuffs (carbohydrates, fats, and proteins).
Metabolic Rate = rate at which energy (ATP) is produced and used (because very little ATP is stored) from ingested or stored substrates.
- Usually measured (in the laboratory) as oxygen consumption, because direct measurement of heat production (energy use) is very difficult. Oxygen consumption works because the amount of oxygen used to produce a given amount of heat is relatively constant regardless of the substrate being utilized (maximum difference is 10%, usually less because a combination of substrates are being oxidized).
- Metabolic rate can also be estimated (in the field) by two different techniques.
1) Doubly Labeled Water (D2O18, D = deuterium [H3]). Procedure = Inject doubly labeled water
--> Allow to equilibrate with general pool of body water (1 hour) --> Take initial blood sample --> Release bird to environment --> Recapture after about 24-48 hours --> Take final blood sample
- a) As doubly labeled water equilibrates with general body pool, you get H2O18, D2O, and CO218 within the body.
- b) Deuterium is lost only via water loss.
- c) O18 is lost both through water and CO2
- d) Difference between isotope turnover ratios (after second capture) allows an estimate of CO2-production, which estimates metabolic rate (because CO2 is produced as O2 is consumed during aerobic metabolism).
- Provides a ballpark (+ 10%) estimate of field metabolic rate.
2) Time-Activity Budgets
- a) Measure cost of certain activities (resting, hopping, flying, etc.) in the lab by oxygen consumption.
- b) Measure time spent in different activities in the field.
- Again, gives ballpark estimate of FMR (usually in fairly close agreement (+ 10%) with doubly labeled water measurement, but requires careful measurement of metabolic rates in lab and careful and extended observation in the field.
II. THERMOREGULATION
1) Rate of Heat Loss from body can be described by:
H = C(Tb - Ta)
where H is heat loss (heat loss = heat gain because Tb is constant); C is thermal conductance = a net measure of heat transfer via radiation, conduction, convection, and evaporation (equivalent to the inverse of insulation); Tb is body temperature; and Ta is ambient or environmental temperature.
2) To maintain Tb, birds can respond by:
- a) modifying conductance, thereby influencing heat loss
- (i) plumage or postural adjustments
- (ii) peripheral circulation adjustments
- (i) plumage or postural adjustments
- b) a change in Tb (modifies gradient for heat exchange with the environment)
- c) changing heat production to offset changes in heat loss
3) General Metabolic Response to Temperature (for Endotherms) (SEE HANDOUT AND PG. 131, GILL)
4) BMR in Birds - influenced by many factors
- a) Body Size - Total metabolic rate (per bird) increases with size, but at a slower rate:
MR ~ Mass0.75 (not 1:1);
- - This means that mass-specific MR (per gram of tissue) decreases with increasing body size (i.e., small birds have relatively higher MR than large birds).
- b) Phylogeny - different taxa may show different metabolic levels (e.g., shorebirds appear to have relatively high BMR, passerines may be higher than nonpasserines - SEE PG. 125, GILL).
- c) Other Effectors
- (i) Circadian Phase = higher MR during active phase than during resting phase (20% in small birds).
- (ii) Digestive State - specific dynamic action = energy needed to digest a meal, contributes to higher MR with food in digestive tract than in empty condition.
- (iii) Environment - BMR may vary with habitat (e.g., tropical birds with lower BMR than those from higher latitudes).
- (iv) Life History - Food habits may influence BMR (e.g., frugivores typically have lower MR than carnivores).
- (v) Sex - some species show sexual dimorphism in MR.
- (i) Circadian Phase = higher MR during active phase than during resting phase (20% in small birds).
- (1) Arginine Vasotocin (AVT) = regulates blood pressure by serving as vasoconstrictor; antidiuretic mechanism - decreases glomerular filtration rate by constricting arterioles leading to glomerulus and increases reabsorption of water from collecting ducts of mammalian type nephrons in kidney.
