Chapter 3- Hormones and neurobiology

Question 1

Martin house sparrow study

Answer 1

Glucocorticoid hormones like corticosterone have been linked to stress responses, so researchers hypothesized that birds in the most novel environments would show the strongest surge in corticosterone when exposed to a stressor. The data supported that birds in novel environments did have the strongest stress hormone response. Increased corticosterone likely leads to better memory of stressors, which gives individuals in novel environments an advantage

Question 2

Ultimate questions

Answer 2

Usually include “why” questions, concerned with evolutionary perspectives

Question 3

Proximate questions

Answer 3

Usually ask “what” or “how” questions. Concerned with factors that operate within the lifetime of an organism rather than phylogeny. Explanations include neurobiology, endocrinology, molecular genetics, and others

Question 4

House finch plumage coloration (Hill)

Answer 4

Male plumage is brighter than female plumage coloration. Researchers wanted to know what causes males and females to differ in coloration (proximate) and why color differences persist over evolutionary time (ultimate). Male plumage brightness in correlated with the amount of carotenoids in their diet. It was found that the same was true for females, and the differential availability of carotenoid pigments in food across populations appears to explain the difference in plumage coloration among females across populations. Differences in foraging behaviors between males and females in the same population also causes differences in plumage color. In ultimate analysis, it was found that males actively search for carotenoids because they receive benefits from these foods, while females do not.

Question 5

Evolutionarily, how do male house finches benefit from a high-carotenoid diet?

Answer 5

Males with bright plumage are more likely to obtain a mate in Hill’s study, where their plumage was experimentally brightened. Females are more likely to be attracted to males with brighter plumage because they are less likely to contract pathogens from these males. If disease resistance is heritable, then females that choose the more disease-resistant males as mates will produce offspring that are better able to resist disease. In addition, the number of times a male fed his chick was positively correlated with the intensity of his plumage coloration in some populations. Females probably prefer these males because they make better fathers. Finally, these males may be better foragers. The trait is not inherited, so the heritable trait is likely good foraging behavior, which leads to brighter plumage.

Question 6

Endocrine system

Answer 6

A communication network that is mostly composed of a group of ductless glands that secrete hormones directly into the bloodstream. Glands contain endocrine cells that synthesize and then secrete hormones.

Question 7

Major glands of the endocrine system (6)

Answer 7

Adrenal gland, pituitary gland, thyroid gland, pancreas, gonads, hypothalamus. Many glands can secrete more than one hormone, and different target cells can respond differently to the same hormone.

Question 8

Neurohormones

Answer 8

Hormones released into blood via neurons (usually within the brain). They are the exception to the rule that hormones are produced by ductless glands

Question 9

How are hormones secreted?

Answer 9

Enzymes in the Golgi apparatus process proteins into hormone molecules and package them inside secretory vesicles. The vesicles fuse with the cell membrane and release hormones into the bloodstream. The hormones circulate in the blood and reach the receptor sites of the target cells.

Question 10

Protein hormones

Answer 10

Made up of strings of amino acids- these make up most vertebrate hormones. These proteins can be stored in endocrine cells and do not have to be released immediately into the bloodstream. They are soluble in blood and water and are therefore considered hydrophilic- they don’t require any carrier molecules to travel in the blood.

Question 11

Peptide hormones

Answer 11

Protein hormones that are made of only a small number of amino acids. Prolactin is an example

Question 12

The larger a protein hormone, the greater

Answer 12

Its half life- the longer it takes for half of the hormone to be removed from the blood.

Question 13

Steroid hormones

Answer 13

Steroid hormones take much longer to be produced than protein hormones in response to a stimulus. These hormones can’t be stored in cells, so they’re immediately released to the bloodstream after they’re synthesized. They are hydrophobic and require a chaperone (usually a protein) to travel in the bloodstream

Question 14

How do hormones affect traits?

Answer 14

They affect traits both directly and indirectly through changes in cell metabolism and DNA expression. This includes behavioral traits

Question 15

How do hormones affect intracellular processes?

Answer 15

They can affect processes that promote cell division, cause ion channels involved in action potentials to open, cause muscle contractions, and trigger the synthesis of other hormones

Question 16

What does malfunctioning of the endocrine system cause?

Answer 16

Hyposecretion or hypersecretion affects functions like growth, metabolism, reactions to stress, aggression, and reproduction.

Question 17

Hypothalamic-pituitary-adrenal (HPA) axis

Answer 17

1. Corticotropin-releasing hormone (CRH) is secreted from the hypothalamus
2. In response, the anterior pituitary gland secretes adrenocorticotropic hormone (ACTH)
3. This stimulates the adrenal glands to produce glucocorticoid hormones like cortisol

Question 18

Glucocorticoid hormones

Answer 18

Secreted by the adrenal glands, play a role in behavior like reduced aggression in the presence of dominant individuals

Question 19

Field endocrinology

Answer 19

Measuring hormone levels in natural populations

Question 20

Target cells

Answer 20

Cells with the receptor site for a specific hormone. The receptor site is usually located on the surface of a cell and works via a “lock and key” system. A hormone will not have an effect on a cell if it doesn’t have a receptor site for that hormone

Question 21

Hormone receptor complex

Answer 21

Hormones and receptor sites act as a lock and key system when they bind and form the complex. The receptor is not activated until it is bound by the correct hormone (the key). After the hormone binds, a series of interactions occurs that affects the expression of genes and the synthesis of proteins

Question 22

What hormones are released in male birds as breeding season approaches?

Answer 22

Many birds breed during the spring and summer. As the seasons change, the length of the day increases, which stimulates the release of testosterone and gonadotropin (stimulates sperm production) in male birds. Testosterone binds to receptors in the brain and results in behaviors related to mating and paternal care- aggression to competing males, guarding their mates, building nests, and defending their offspring.

Question 23

What might testosterone be converted to in birds?

Answer 23

Some testosterone is converted into estradiol or dihydrotestosterone. It binds to receptors and leads to behaviors linked to mating and paternal care.

Question 24

What happened to the hormones of male birds when day length increase was experimentally delayed?

Answer 24

The cues for breeding season were missing, so male testosterone levels remained low and the mating behaviors influenced by testosterone did not occur. Manipulation of day length can affect the hormone levels and the mating and breeding behavior of females as well.

Question 25

3 interactive systems in animals (feedback loop components)

Answer 25

1. An input system- senses like smell and sight
2. A central processor integrating and processing sensory information (like the brain)
3. Output systems (effectors) like muscles

Question 26

What effect do hormones have on the components of an animal’s feedback loops?

Answer 26

Hormones can change the probability that a specific sensory input leads to a specific output (behavior or response to a stimulus). Hormones can increase or decrease the frequency or duration of a behavior, trigger the onset or end of a behavior, or prime an animal to behave a certain way. Ex- testosterone primes an animal to act aggressively

Question 27

How do hormones affect the organization of behavior systems in mice?

Answer 27

Female mice gestate many fetuses simultaneously. If a male fetus is surrounded by female fetuses in utero, it will be exposed to lower levels of testosterone. In the future, these males will be less aggressive and less sexually active than males who were surrounded by other males in utero. Similarly, females surrounded by two males will exhibit more masculine behavior.

Question 28

What happens in the body when an individual senses a stressor?

Answer 28

The hypothalamus initiates a response- it can take one of two pathways. This depends on whether the hypothalamus initiates secretion of corticotropin releasing hormone or epinephrine.

Question 29

How does epinephrine affect the body?

Answer 29

Epinephrine is secreted from the adrenal glands and nerves in the CNS. It binds to smooth muscle receptors to constrict or dilate blood vessels depending on the receptor. Cardiopulmonary activity is increased. Blood sugar increases quickly and is delivered to vital organs (especially the heart, brain, and skeletal muscle) along with oxygen. Nonessential systems, like the reproductive and digestive systems, are shut down.

Question 30

How does corticotropin releasing hormone affect the body?

Answer 30

CRH stimulates the anterior pituitary gland to increase the production of ACTH, which stimulates the adrenal gland to secrete cortisol. The cascade of hormones causes noncarbohydrates to be converted into sugars to provide energy. The adrenal glands will also produce more aldosterone, which increases water retention and reduces bleeding if an animal is injured

Question 31

Mating and parental care in male gerbils (Clark)

Answer 31

*Goal- to determine whether testosterone differences in males in utero would affect male reproductive behavior (both mating and parental care).
*Background- circulating testosterone levels in 2M males were significantly higher than in 2F males, probably due to being surrounded by 2 males in utero. 2M males were hypothesized to provide less parental care.
*Methods- a male was housed with a female, and time it took before sexually mounting the female, and time between mounting and ejaculation were measured. Males were also housed with pregnant females until they gave birth. Male behavior toward pups was examined.
*Results- 2M males mounted and ejaculated more quickly and sired more offspring. 2M males also spent less time in contact with pups than 2F males
*Explanation- results suggest causal link between testosterone and parental care

Question 32

In gerbils, how are 2M females affected by the excess testosterone?

Answer 32

These females are less preferred as mates because they are more aggressive than other females. They have fewer litters and begin reproducing later. In addition, 2M females have preoptic metabolic activity resembling that of males more than that of 2F females.

Question 33

Preoptic area of the hypothalamus

Answer 33

Controls copulatory behavior in gerbils. Males and females show different activity patterns

Question 34

Vasopressin function in prairie voles and meadow voles

Answer 34

The number of vasopressin receptors in the brain is responsible for differences in male social behavior between prairie voles and meadow voles. Vasopressin stimulates mate guarding and parental care in male prairie voles, but not in meadow voles- these voles lack the receptors to bind extra vasopressin. However, behavior may be able to be modified if the number of receptors could be experimentally increased.

Question 35

Where are vasopressin receptors located?

Answer 35

The ventral pallidum, in the basal ganglia

Question 36

Sullivan honeybee forager study

Answer 36

*Goal- examining the effect of JH 3 hormone on forager behavior and hive activities
*Background- at 21 days of age, some bees leave their nest to forage. This shift in behavior is associated with JH3.
*Methods- surgically removed the bees’ corpus allatum (gland where JH3 is produced) and compared with control groups
*Results- both experimental and control groups eventually became foragers, but the bees in the experimental group began foraging significantly later than control group bees. These bees returned to the nest less often and had problems with environmental navigation. The only behavior changes were related to foraging
*Explanation- JH3 is likely causal in foraging behavior, behavior returns to normal when JH3 is experimentally increased

Question 37

Octopamine in honeybees

Answer 37

A neurohormone associated with increased foraging activity in honeybees. It’s the honeybee version of noradrenaline. It’s responsible for learning, memory, and senses like vision, smell, and taste. Forager bees have higher concentrations of octopamine than bees that stay at their hive, and concentration peaks when a bee switches to foraging activities. Its role in foraging is supported by experimental evidence- octopamine increased flight activity related to foraging not not other flight related behavior. Also, when bees treated with octopamine were exposed to other hormones associated with a new brood of offspring, they increased foraging behavior but not other activities related to caring for offspring.

Question 38

Plainfin midshipman fish study (Bass)

Answer 38

*Goal- examining the role of the endocrine system in communication in midshipman fish. It was expected that there would be higher levels of circulating KT and lower levels of circulating cortisol in type 1 than type 2 males during reproduction
*Background- there are 2 types of male fish. Type 1 males are larger, have a higher gonad to body size ratio, and produce specific sounds when competing with other males and when courting females. When type 1 males mate with females, the male remains on the nest after a female lays her eggs there. Type 2 males don’t build nests, but they hang around type 1 male nests to shed sperm and attempt to fertilize the nesting female. These males don’t make sounds. Hormones KT and cortisol are linked to the differences in sound produced by type 1 and 2 males
*Results- Type 1 males had higher levels of KT in plasma samples and in their testes than type 2 males. Type 2 males had higher plasma cortisol levels.

Question 39

Neuroethology

Answer 39

The neurobiological basis of behavior in animals

Question 40

Axons

Answer 40

Nerve fibers that transmit electrical information from one cell to another. They can vary widely in length and diameter. The thicker the diameter of an axon, the faster the nerve impulse travels along it.

Question 41

Sections of an axon

Answer 41

The first section is called the axon hillock, the last section consists of axon terminals (where information leaves the neuron).

Question 42

Threshold

Answer 42

The voltage across a neuron’s membrane must change by a specific amount. If it doesn’t, the nerve cell won’t fire. All nerve cells fire the same way when the threshold is reached, regardless of the strength of the stimulus

Question 43

How are organisms able to gauge the strength of a stimulus? (2)

Answer 43

1. The number of times a neuron fires increases with the strength of the stimulus
2. The number of neurons that fire in response to a stimulus increases as the strength of the stimulus increases

Question 44

What happens when an action potential reaches the end of an axon terminal?

Answer 44

A neurotransmitter is usually released. Sometimes, an electrical impulse can jump across the synaptic cleft

Question 45

Evolutionary trends in the nervous system (3)

Answer 45

1. Nerve cells that controlled specific functions became clustered
2. Nervous systems became centralized, and a longitudinal nerve cord became a major path for action potentials to travel
3. The front end of the longitudinal nerve cord became dominant, leading to the evolution of the brain

Question 46

What questions can fMRI help answer?

Answer 46

fMRI allows researchers to measure neuronal activity across large sections of the brain in high resolution. This data can be used to determine how stimuli translate into neural activity, how brain activity patterns occur during a behavior and whether the patterns change in different contexts, how behaviors associated with a positive reward impact brain activity, and others.

Question 47

Mushroom bodies

Answer 47

A cluster of small neurons located at the front of the brain in invertebrates. It is linked to spatial navigation skills. Foraging bees use visual and olfactory cues to search for food, and mushroom bodies help with this.

Question 48

Orientation flight

Answer 48

Foraging bees turn toward their nest and hover up and down for a few minutes. This orients the foragers to the relative position of their nest in the environment

Question 49

Honeybee task mushroom bodies study (Withers)

Answer 49

*Goal- examine bees to determine whether the relative size of their mushroom bodies differed as a function of task allocation.
*Methods- formed a new colony using one day old bees (eliminating age as a confound). This induced early foraging behavior
*Results- mushroom bodies of foragers were 14.8% larger than those of the other groups they measured. Only mushroom bodies increased in size- the sizes of other cell clusters did not change relative to brain size. Bees in the experimental treatment began foraging early, at 4-7 days of age. Their mushroom bodies represented those of normal aged foragers.
*Explanation- suggests a link between mushroom bodies and foraging. Also suggests that activities related to foraging trigger neuronal based changes in mushroom body volume- an example of neural plasticity.

Question 50

Neurobiological basis of how type 1 and 2 midshipman fish communicate

Answer 50

Both type 1 and 2 males have sonic muscles (their vocal organ). Type 1 males have larger sonic muscles with more muscle fibers, which impacts sound production. The sonic muscles are innervated by pacemaker neurons that generate impulses in a cyclic pattern. The pacemaker neurons in type 1 males fire at a rate higher than that of type 2 males, which also causes differences in vocalization.

Question 51

Brain size and problem solving study (Holekamp)

Answer 51

*Goal- to test the hypothesis that carnivores with large brains for their body mass are better at solving foraging related problems
*Methods- used a puzzle box paradigm- a locked puzzle box with food inside of it. The animals were tested on their ability to open the box and get the food.
*Results- individuals from group living species were no better at solving the problem than those from social living species. Both absolute brain size and brain size scaled to body size were positively correlated with ability to open the box- only brain size scaled to body size was significant.

Question 52

Association between neurobiological and endocrinological approaches to sound production in male midshipman fish

Answer 52

Arginine vasotocin (AVT) inhibits activity in neurobiological circuitry associated with production of sound in type 1 males, but not type 2 males. Isotocin (IT) has the opposite effect- inhibits activity for type 2 males, but not type 1.

Question 53

Sleep and antipredator behavior in mallard ducks (Ratternborg and Lima)

Answer 53

*Goal- examine the proximate basis of antipredator behavior
*Background- mallards utilize unihemispheric sleep- they sleep with half of their brain awake.
*Methods- used a sleeping apparatus to record eye state and electrophysiology of the ducks
*Results- mallards can sleep with one eye open, and mallards on the periphery of the group rely on unihemispheric sleep more than mallards at the center of the group. They sleep facing outward to remain aware of predation.

Question 54

How does unihemispheric sleep work in mallard ducks?

Answer 54

The hemisphere of the brain that is active during sleep is put into slow wave sleep. Slow wave sleep allows a quick response to predators without interfering with the sleeping half of the brain, unless danger is present

Question 55

Other than ducks, which species use unihemispheric sleep?

Answer 55

Aquatic mammals like dolphins, whales, seals, and sea lions use unihemispheric sleep so they can swim to the surface of the water and breathe during sleep. EEG studies in dolphins showed that the left hemisphere of the parietooccipital cortex is asleep, with high amplitude waves. The right hemisphere is awake

Question 56

Proximate causes of behavior

Answer 56

Includes hormones, genes, development, and neurobiology. We need to understand the role that each can play individually before understanding their interaction

Question 57

Hypothalamic-pituitary-gonadal (HPG) axis

Answer 57

The hypothalamus releases gonadotropin-releasing hormone (GnRH). When GnRH reaches the anterior pituitary, it causes the anterior pituitary to release luteinizing hormone (LH) and follicle stimulating hormone (FSH). FSH and LH act on either the ovaries or testes so they will produce estradiol (estrogen) or testosterone. FSH and LH are responsible for the maturation of sperm and egg cells after puberty.

Question 58

How might hormones affect behavior?

Answer 58

In certain birds (zebra finches), testosterone is needed for the male to sing, and therefore mate. Testosterone may affect the sensory system capacity by making the bird more aware of females or of males surrounding him, influence the neuronal architecture and the motivation to sing, and influence the effector organs (muscle). Absence of testosterone will inhibit these behaviors

Question 59

How can behavior affect testosterone levels?

Answer 59

Can be reduced by defeat in humans, mice and monkeys. In humans, testosterone is reduced in male soccer fans of
the losing team

Question 60

In mice, how are 2M females affected by intrauterine positioning? (4)

Answer 60

Females placed between males show:
1. More aggressive behaviors
2. Are less attractive to males
3. Longer ovarian cycles
4. Longer ano-genital distance (masculinized genitalia)

Question 61

Proximal causes of species differences in IUP effects (3)

Answer 61

1. Direction of blood flow in uterine horns- in mice it’s bidirectional, in rats it’s unidirectional, caudal to distal
2. Number of offspring
3. Mating system and the behaviors controlled by T,
   prolactin

Question 62

Freemartins

Answer 62

Sterile female twin of a male found in cattle, sheep,
goats and pigs. They have an XX genotype and female external genitalia, but variable development of
internal genital tracts- gonads are atrophic but resemble testes. Possibly caused by the transfer of a factor through
a common artery

Question 63

Role of oxytocin in prairie voles

Answer 63

In the females, oxytocin (OT) facilitates formation of partner preference, increase social contact after cohabitation even in the absence of mating. High densities of OT receptors in the brain areas involved in the reward system and play a role in conditioned learning. OT in these area may reinforce the association between the rewarding effects of brain activation and the male she just mated with. In contrast, montane voles have no OT receptors in their reward system

Question 64

Social experience and song development in birds

Answer 64

When a young white-crowned sparrow is listening to the
song of an adult, later it will be integrated in his songs. When captive female starlings are given the choice between
perching next to nest boxes where a long versus short song
is played, they spend more time perching next to the box of
long song- females may prefer males who produce longer songs

Question 65

Nuclei involved in song production in birds

Answer 65

Include the robust nucleus of arcopallium (RA),
anterior nidopallium (IMAN),high vocal center (HVC), caudomedial neostriatum (NCM)

Question 66

RA nucleus

Answer 66

Responsible for song control in birds (starling). RA nucleus can respond to a social environment. RA is the only song control nucleus that grows substantially in males exposed to high-quality (long) songs of other males.

Question 67

Plasticity

Answer 67

Structural changes such as number of synapses and strength of chemical synapses between neurons. Synaptic connections in the brain are dynamic in part due to formation and elimination of dendritic spines

Question 68

Dendritic spines and learning in mice

Answer 68

Mice learn to walk on a rotorod that can vary in speed during two days of training. It measures the ability to stay on the rod. Young mice learned better than old mice. Performance was associated with the number of dendritic
spines (branches off dendrites) that a mouse had