Day 13 correct (without images)

Slide 1 – Behavioural endocrinology

Behavioural endocrinology studies the two-way relationship between hormones and behaviour. Hormones influence behaviour, but behaviour can also change hormone secretion. Throughout this lecture, remember that hormones make behaviours more or less likely rather than directly causing them.

📸 Figure: Whole title slide.

⭐ Remember: Hormones ↔ Behaviour.

Slide 2 – Social interactions

Social interactions are behaviours between individuals that affect fitness (survival and reproduction). The four-box figure classifies interactions based on whether the actor (donor) and recipient each gain (+) or lose (−) fitness. Cooperation (+/+): both benefit. Selfishness (+/−): actor benefits, recipient loses. Altruism (−/+): actor pays a cost, recipient benefits. Spitefulness (−/−): both lose. All later examples fit into one of these four categories.

📸 Figure: Four-quadrant diagram (whole figure).

⭐ Remember: First ask "Does the actor benefit?", then "Does the recipient benefit?"

Slide 3 – Cooperation

Cooperation means both individuals benefit (+/+). The elephant experiment shows this perfectly. Food could only be obtained if both elephants pulled the ropes together. Some elephants even waited until their partner arrived before pulling, showing they understood cooperation was necessary rather than simply pulling randomly. You do not need to memorize the graph values—only the conclusion.

📸 Figure: Rope-pulling apparatus + bottom graph.

⭐ Remember: 🐘 + 🐘 = 🍌

Slide 4 – Altruism

Altruism means the actor pays a fitness cost while another individual benefits (−/+). Honeybees protect the colony even if this costs them energy or their own life. The thermal image shows bees clustering together to generate heat against a hornet. The key idea is that the individual sacrifices itself for the benefit of the colony.

📸 Figure: Thermal image + honeybee swarm.

⭐ Remember: 🐝 sacrifices itself → colony survives.

Slide 5 – Selfishness

Selfish behaviour benefits the actor while harming the recipient (+/−). The praying mantis is the classic example: after mating, the female may eat the male. She gains nutrients that improve reproduction, while the male pays the ultimate cost. Evolution only "cares" about reproductive success, not fairness.

📸 Figure: Praying mantis photographs.

⭐ Remember: I win, you lose.

Slide 6 – Spitefulness

Spitefulness means both the actor and the recipient pay a fitness cost (−/−). The lecture uses bonobo "aunting to death" as an example, where both individuals waste time and energy. Notice that lion infanticide is crossed out because it is NOT spitefulness: the male actually benefits by bringing females back into oestrus sooner, making it an example of selfishness instead.

📸 Figure: Bonobo photo + lion photo with red cross.

⭐ Remember: Lion infanticide = selfishness, NOT spitefulness.

Slide 7 – Territoriality

Territoriality is defending an area against other individuals because it contains valuable resources such as food, shelter, nesting sites or mates. Animals defend the resources within the territory, not the land itself. Territorial behaviour is an important form of social interaction because it often leads to competition and aggression.

📸 Figure: Title/transition slide.

⭐ Remember: Defend resources, not land.

Slide 8 – Sociality: benefits and costs

Living in groups has advantages and disadvantages. Benefits include increased mating opportunities, better foraging efficiency, the dilution effect (lower individual predation risk), and social affiliation (e.g. grooming and bonding). Costs include disease transmission, competition, conspicuousness to predators and increased aggression. Whether animals live socially depends on whether the benefits outweigh the costs.

📸 Figure: Benefits vs Costs overview.

⭐ Remember: Sociality evolves only if Benefits > Costs.

Slide 9 – Solitary versus social species

Species differ in how social they are. Wolverines are mostly solitary and only meet to mate, reducing competition and disease spread. Elephants live in stable family groups, benefiting from cooperation, protection and social learning. Neither strategy is "better"; the optimal strategy depends on ecology and environment.

📸 Figure: Wolverine (left) + elephant herd (right).

⭐ Remember: Sociality exists on a continuum.

Slide 10 – Flexible sociality

Social behaviour is flexible rather than fixed. Meadow voles are solitary during summer because females defend separate territories, but become much more social during winter when territories overlap and they share nests to conserve heat. This shows that environmental conditions and hormones interact to change behaviour.

📸 Figure: Meadow vole territory maps (summer vs winter).

⭐ Remember: Same animal, different season → different social behaviour.

Slide 11 – Hormonal regulation of sociality

Hormones regulate social behaviour. The lecture highlights especially testosterone (androgens) and estrogens. These hormones influence behaviours such as aggression, territoriality, dominance and mating. Hormones do not directly determine behaviour but change the likelihood that a behaviour occurs in a particular context.

📸 Figure: Hormones! (testosterone & estrogens).

⭐ Remember: Hormones change probability, not destiny.

Slide 12 – Sociality and personality

Hormones, the brain and behaviour continuously influence each other. Hormones affect perception, motivation and cognition, which influence behaviour. Behaviour then changes social interactions, which feed back to alter hormone levels. This feedback loop helps explain why individuals of the same species can have different personalities, such as being more aggressive, bold or social.

📸 Figure: Feedback-loop diagram.

⭐ Remember: Hormones → Behaviour → Hormones.

Slide 13 – Agonistic behaviour

Agonistic behaviour includes all behaviours occurring during conflicts between individuals, not only aggression. It includes attacking, threatening, defending, retreating and submitting. Submission is also agonistic behaviour because it is part of resolving conflict and reduces the risk of injury. Aggression is therefore only one part of agonistic behaviour.

📸 Figure: Agonistic behaviour overview.

⭐ Remember: Aggression ⊂ Agonistic behaviour.

Slide 14 – Reactive versus proactive aggression

Aggression is behaviour that causes harm to another organism. Reactive aggression is impulsive, emotional and occurs in response to a threat ("I react because I feel threatened"). Proactive (instrumental) aggression is planned and goal-directed ("I attack to obtain something"). Knowing the difference helps explain why not all aggression has the same hormonal regulation.

📸 Figure: Reactive vs Instrumental/Proactive aggression comparison.

⭐ Remember: Reactive = emotional response. Proactive/instrumental = planned strategy

Slide 15 – Offensive versus defensive aggression

Offensive aggression is used to obtain resources, such as territory, food or mates. Defensive aggression is used for protection, for example when an animal protects itself or its offspring. The key difference is motivation: offensive = trying to gain something; defensive = trying not to lose something. 📸 Figure: Left deer fight = offensive aggression; right elephant protecting itself/young = defensive aggression.

⭐ Remember: Offensive = obtain. Defensive = protect.

Slide 16 – Costs of testosterone

Testosterone can increase competitive behaviour, but it also has costs. The graphs show that higher testosterone can reduce normal responsiveness in some contexts and increase sensitivity to social/sexual cues in others. So testosterone is not simply "more = better"; it changes priorities and can create trade-offs. 📸 Figure: Left graph with implants + right testosterone-response curve + bird photo.

here it seems left that more testosterone = worse immune system.
however, right it seems more testosterone, better immune system. this is confounded bc those birds w high testosterone have blue colours early in winter but they can afford it bc they are fit enough. therefore they are the exception, but as these are the ones that survive/we can see, it seems like higher testosterone = better immunity = confounded. it was just that their immunity baseline level was higher, therefore still being able to survive winter despite loosing energy on their colours (not representative for birds that had a worse immune system and died as a response of high testosterone).

⭐ Remember: Testosterone helps competition, but it comes with costs.

Slide 17 – Multiple costs of testosterone

High testosterone can reduce parental care, shorten longevity, increase energy use, increase predation risk, increase injury risk and may have oncogenic effects. This explains why animals do not keep testosterone maximally high all the time.

📸 Figure: Whole slide with cost list + mouse/lizard graphs.

⭐ Remember: Testosterone is useful, but expensive.

Slide 18 – How much testosterone?

Fitness is highest at an intermediate testosterone level. Too little testosterone can reduce reproductive success because the animal cannot compete well. Too much testosterone can reduce survival by suppressing immunity, increasing aggression, energy use and risk-taking. Natural selection favours the optimal level, not the highest level.

📸 Figure: Central inverted-U graph + junco image.

⭐ Remember: Optimal testosterone ≠ maximum testosterone.

Slide 19 – Benefits of hormone regulation of sociality

Hormones allow flexible regulation of social behaviour. Testosterone can rise during social challenges, support dominance signalling and then drop again to avoid long-term costs.

The left figures show the Challenge Hypothesis; the right graph shows that social stimuli can change testosterone in participants and observers. 📸 Figure: Challenge Hypothesis graphs on the left + dominance signalling graph on the right. ⭐ Remember: Hormones help animals respond only when needed.

Slide 20 – Challenge Hypothesis across species

The Challenge Hypothesis predicts that testosterone rises during periods of social/reproductive competition and falls during parental care. Different bird species show different testosterone patterns depending on their breeding system. Species with repeated sexual challenges show repeated testosterone peaks.

📸 Figure: Multi-species testosterone curves across pre-breeding, sexual and parental phases.

⭐ Remember: Testosterone peaks when competition is high.

Slide 21 – Challenge Hypothesis in humans

Testosterone is also linked to human social status and competition. The left graph shows that relationship/parental status is associated with different testosterone levels: unpaired men tend to have higher testosterone than married fathers. The right graph suggests testosterone may increase preference for status-related products.

📸 Figure: Left salivary testosterone graph + right product preference graph.

⭐ Remember: Testosterone relates to competition/status, not only aggression.

Slide 22 – Testosterone and status signalling

This slide illustrates that testosterone can influence status-related choices. The luxury car images show that testosterone may increase preference for products associated with status rather than simply quality or power. This is an example of dominance/status signalling in humans.

📸 Figure: Car images + product liking graph.

⭐ Remember: Testosterone can promote status signalling.

Slide 23 – Dominance signalling in football fans

Social victories can affect testosterone even in observers. After the 1994 World Cup final, Brazilian fans showed increased testosterone after Brazil won, while Italian fans showed decreased testosterone after Italy lost. This shows that identifying with a winner or loser can change hormones.

📸 Figure: Football fan testosterone graph, Italy vs Brazil.

⭐ Remember: Winning team → fans’ testosterone up; losing team → down.

Slide 24 – Dominance signalling in football fans II

Watching an important match can activate hormonal responses in fans. In the Netherlands vs Spain final, testosterone and cortisol patterns differed between match viewers and controls. This shows that social competition can influence hormones even when people are not physically competing.

📸 Figure: Testosterone graphs for men/women + cortisol graph.

⭐ Remember: Social competition can affect hormones in the audience too.

Slide 25 – Benefits of hormone regulation repeated

This slide repeats the key message: hormone regulation allows flexible social responses. Testosterone can rise during challenges and dominance situations, but does not need to stay high all the time. This flexibility gives the benefits of competitiveness while limiting long-term costs.

📸 Figure: Same Challenge Hypothesis + dominance signalling overview as Slide 19.

⭐ Remember: Flexible hormones = benefits without constant costs.

The Challenge Hypothesis states that a male animal's testosterone levels are driven by social challenges, such as competing with rival males, rather than just the change in seasons.

It explains that keeping testosterone permanently high is harmful because it lowers immunity and stops males from caring for their offspring. Therefore, testosterone only spikes when a male is actively challenged.

1. The Three Hormone Levels (Top-Right Diagram)

• Level A (Constitutive baseline): The standard level during the non-breeding season. It keeps basic body functions running.

• Level B (Breeding baseline): The elevated level needed automatically for the breeding season. It triggers singing and territory setup.

• Level C (Physiological max): The maximum possible hormonal spike. It is only triggered by social challenges like a rival male showing up.

Slide 27 – Sociality, distancing and hormones

Meadow voles show that sociality can change with season. In summer, female territories are separate, meaning they are more solitary. In winter, territories overlap, meaning they tolerate each other and become more social. Hormones and environmental conditions help regulate this social spacing.

📸 Figure: Meadow vole photo + female territory maps in summer vs winter.

⭐ Remember: Summer = separate; winter = overlap.

Slide 28 – Aggression and testosterone

Testosterone is especially important when male-male competition is high. Polygynous species often show higher daily male-male competition and stronger androgen regulation than monogamous species. The graphs compare baseline and maximum androgen responses across mating systems.

📸 Figure: Left androgen-level model + right bar graphs comparing mating systems.

⭐ Remember: More male-male competition → stronger testosterone involvement.

Slide 29 – Testosterone and winning

Winning can increase testosterone. In the sports example, winners show a stronger post-match testosterone increase than losers. Cortisol does not show the same clear winner-loser pattern here. This supports the idea that testosterone is linked to dominance and competitive success.

📸 Figure: Winner vs loser testosterone graph + soccer photo.

⭐ Remember: Winning can boost testosterone.

Slide 30 – Winner effect and testosterone

Prior winning plus testosterone can increase future aggression and dominance. In the mouse experiment, animals with testosterone and a previous win were more likely to win again, attacked faster and attacked more often. This shows how hormones and social experience reinforce each other.

📸 Figure: Bar graphs showing resident winners, attack latency and number of attacks + mouse photo.

⭐ Remember: Testosterone + winning experience = stronger future aggressi

Slide 31 – Aggression and Testosterone

Testosterone promotes aggression, but the effect depends on context.
• Higher testosterone → generally more aggression
• Testosterone mainly increases the motivation to compete, not aggression all the time.
• Environment and social situation still determine behaviour.

📸 Figure to use

Left graph: testosterone treatment increases aggressive behaviour.
Right graph: aggression rises with increasing testosterone concentration.
⭐ Remember
Testosterone facilitates aggression rather than directly causing it.

Slide 32 – Sociality (Bonding) and Hormones

Hormones can change how social animals are by changing territorial behaviour.

• Example: meadow voles
• Summer: females keep separate territories → less social.
• Winter: territories overlap → animals become more social.
• Hormones help regulate this seasonal shift.

📸 Figure to use

Meadow vole.
Territory maps: summer (little overlap) vs winter (large overlap).
⭐ Remember
Hormones regulate when animals live alone or together.

Slide 33 – Oxytocin

Oxytocin is the major hormone promoting social bonding and trust. • Produced in the hypothalamus. • Released by the posterior pituitary. • Promotes:

Bonding

Trust

Social affiliation

Maternal behaviour

• Often called the "cuddle hormone." 📸 Figure to use Human bonding picture. Oxytocin molecule/pathway figure. ⭐ Remember Oxytocin strengthens positive social relationships.

Slide 34 – Oxytocin and Coupling

Higher oxytocin is associated with stronger pair bonding.

• Individuals with higher oxytocin generally show:

stronger attachment
more partner-directed behaviour
• Oxytocin helps maintain long-term relationships.
📸 Figure to use
Scatterplot showing positive relationship.
Couple image.
⭐ Remember
Oxytocin supports pair bond maintenance.

Slide 35 – Oxytocin and Mating Systems

Different mating systems are associated with different oxytocin receptor distributions.

• Monogamous species

stronger pair bonds
more oxytocin receptor activity
• Polygamous species
weaker pair bonds
different receptor distribution
📸 Figure to use
Prairie vole vs meadow vole.
Central receptor distribution graph.
⭐ Remember
Bond strength depends more on receptor distribution than on oxytocin levels alone.

Slide 36 – Oxytocin and Coupling

Changing oxytocin signalling changes pair-bond behaviour. • Increasing oxytocin signalling → stronger bonding (female = oxytocin. male = vasopressin). • Blocking oxytocin signalling → weaker bonding. • Demonstrates a causal role of oxytocin. 📸 Figure to use Left behavioural graph. Upper-right receptor graph. Meadow vole picture. ⭐ Remember Oxytocin is necessary for normal pair bonding.

Slide 37 – Oxytocin and Conflict

Oxytocin does not simply make animals "nice."

• Can reduce aggression towards partners.
• Can increase defence of the social group.
• Promotes in-group cooperation, but sometimes out-group conflict.

📸 Figure to use

Behaviour graph.
Conflict illustration.
⭐ Remember
Oxytocin promotes social behaviour, not universal kindness.

Slide 38 – Oxytocin and Grouping

Oxytocin increases social grouping.

• Animals spend more time together.
• Social interactions become more frequent.
• Group cohesion increases.

📸 Figure to use

Arena/grouping experiment.
Bar graph.
Animal photograph.
⭐ Remember
Oxytocin promotes living together in groups.

Slide 39 – Oxytocin and Parental Care

Oxytocin stimulates parental behaviour.

• More oxytocin →

increased parental care
increased grooming
increased nursing
• Important for successful offspring development.
📸 Figure to use
Monogamous vs polygamous rodents.
Two bar graphs.
⭐ Remember
Oxytocin promotes caring for offspring.

Slide 40 – Oxytocin and Parental Care

Oxytocin increases maternal behaviour after birth.

• Mothers with more oxytocin show:

more licking/grooming
more nursing
more offspring care
📸 Figure to use
Human/maternal hormone bar graph.
⭐ Remember
Oxytocin supports maternal behaviour immediately after birth.

Slide 41 – Opioids and Comfort

Endogenous opioids create feelings of comfort during social contact.

• Social touch releases endorphins (opioids).
• Produces:

comfort
relaxation
reduced stress
• Blocking opioid receptors reduces the rewarding feeling of social contact.
📸 Figure to use
Hand holding chick.
Bar graph on opioid manipulation.
⭐ Remember
Oxytocin promotes bonding; opioids make bonding feel rewarding.

Slide 42 – End of Lecture

Main take-home messages

• Testosterone

regulates aggression
regulates dominance
has benefits and costs
• Oxytocin
promotes bonding
sociality
parental care
• Hormones do not directly determine behaviour; they change the probability that behaviours occur depending on the social context.
📸 Figure to use
Final title slide with turtles.
⭐ Remember
Behaviour = hormones × brain × environment × social contex