Theme 2

Interpret the costs and benefits of sexual reproduction and explain its consequences for the evolution of mating strategies, parental care and the battle of the sexes

❓ What is this learning goal really asking? Why do males and females often have different reproductive behaviours? 🧠 Intuitive explanation Sexual reproduction is costly (finding a mate, competition, disease risk), but it creates genetically diverse offspring that are better able to adapt. Females usually invest much more in each offspring (large egg, pregnancy, parental care), so they maximize fitness by choosing a high-quality mate. Males usually invest less per offspring (cheap sperm), so they maximize fitness by obtaining more mating opportunities. Because their optimal strategies differ, conflict can arise. For example, a male may benefit from mating with multiple females, whereas a female often benefits more if the male stays and helps care for the offspring. This conflict is called the battle of the sexes (sexual conflict). ⭐ Take-away Different parental investment → different mating strategies → possible sexual conflict. 🎯 Exam-ready answer Sexual reproduction increases genetic variation but is energetically costly. Because females generally invest more in each offspring than males, females tend to be more selective whereas males often compete for mating opportunities. These different reproductive interests drive the evolution of mating strategies, parental care and the battle of the sexes. 📍 Figure Lecture 3 – Sexual selection overview. 
Theme 2 – Extended Learning Outcomes (continued)

Analyse the behavioural endocrinology underlying sexual differentiation

❓ What is this learning goal really asking? How does an embryo develop into a male or female body, brain and behaviour? 🧠 Intuitive explanation Think of sexual differentiation as one continuous chain: Chromosomes → Gonads → Hormones → Brain & body → Behaviour An XY embryo contains the SRY gene, which activates SOX9. SOX9 causes the undifferentiated gonad to become a testis. The fetal testis then produces:

• AMH/MIH (Sertoli cells) → Müllerian ducts disappear.
• Testosterone (Leydig cells) → Wolffian ducts develop into epididymis, vas deferens and seminal vesicles.
• DHT (made from testosterone) → develops the penis, scrotum and prostate.
• In rodents, some testosterone is converted into oestradiol in the brain, which masculinizes and defeminizes neural circuits. In an XX embryo, there is no SRY. Together with Wnt4, the gonad develops into an ovary. No fetal AMH or high testosterone is produced, so Müllerian ducts develop into the female reproductive tract while Wolffian ducts regress. These hormones don't just build the reproductive organs—they also organize the brain, allowing adult male and female reproductive behaviours to develop later. ⭐ Take-away Genes decide the gonads, but gonadal hormones build both the reproductive organs and the reproductive brain. 🎯 Exam-ready answer Sexual differentiation begins with chromosomal sex. In XY embryos, SRY activates SOX9, resulting in testis development. Sertoli cells produce AMH, causing Müllerian duct regression, while Leydig cells produce testosterone, which stimulates Wolffian duct development and, via DHT, male external genitalia. In the absence of SRY/SOX9, Wnt4 promotes ovarian development and female differentiation. Gonadal hormones also organize sexually dimorphic brain circuits that later regulate reproductive behaviour. 📍 Figure Lecture 3 – SRY/SOX9 → Testis; Wnt4 → Ovary pathway.

Explain sex differences in male and female behaviour and parental care

❓ What is this learning goal really asking? Why do males and females often behave differently during reproduction? 🧠 Intuitive explanation The answer combines evolution and hormones. Because females usually invest much more in each offspring (egg, pregnancy, lactation and often parental care), they have relatively few reproductive opportunities. Therefore, they usually benefit from choosing a high-quality mate. Males often invest less per offspring (cheap sperm), so their reproductive success can increase by fertilizing more females. This often leads to greater competition between males. Hormones organize the brain during development and activate these sex-specific behaviours in adulthood. Example:

• Male birds often compete and sing to attract females.
• Female birds invest more in egg production and later parental care. ⭐ Take-away Different reproductive investment → different hormone-regulated behaviours. 🎯 Exam-ready answer Sex differences in behaviour result from interactions between hormones, brain organization and evolutionary selection. Differences in parental investment lead to different mating strategies and parental behaviours in males and females. 📍 Figure Lecture 3–5 (male vs female reproductive behaviour).

Integrate ultimate and proximate principles underlying sexual differentiation and sex differences in behaviour

❓ What is this learning goal really asking? Can you explain both how a behaviour happens and why it evolved? 🧠 Intuitive explanation Every reproductive behaviour has two explanations. Proximate = How does it work?
Genes, hormones, brain and physiology. Ultimate = Why did evolution favour it?
Because it increased reproductive success. Example: A male zebra finch sings because testosterone activates song circuits in the brain (proximate explanation). He sings because females prefer singing males, increasing his chance of reproducing (ultimate explanation). Good exam answers usually include both explanations. ⭐ Take-away Proximate explains the mechanism. Ultimate explains the evolutionary advantage. 🎯 Exam-ready answer Sex differences should be explained using both proximate mechanisms (genes, hormones, neural development) and ultimate explanations (selection and reproductive success). 📍 Figure Nelson Fig. 1.8 (Tinbergen's four questions).

Explain and interpret the organizational and activational effects of sex steroids and relate these effects to sexual behaviour

❓ What is this learning goal really asking? How do hormones affect behaviour during development compared with adulthood? 🧠 Intuitive explanation Sex steroids influence behaviour in two different ways. Organizational effects
occur during critical periods of development (before or shortly after birth). They permanently organize the brain. Activational effects
occur later in adulthood. Hormones temporarily activate the already organized brain to produce reproductive behaviour. Think of it like building a house. Organizational effects build the house. Activational effects turn the lights on. Example (Fig. 3.29): A female rat given testosterone shortly after birth develops a masculinized brain. As an adult, testosterone can activate mounting behaviour. Without that early exposure, adult testosterone cannot fully masculinize behaviour. ⭐ Take-away Organization builds the system. Activation uses the system. 🎯 Exam-ready answer Organizational effects permanently organize neural circuits during development, whereas activational effects reversibly activate these circuits during adulthood to produce reproductive behaviour. 📍 Figure Nelson Fig. 3.29. Lecture 3 – Organizational vs activational experiment.

Analyse the cyclic organization of the female reproductive cycle at both the endocrine and behavioural level and explain their relationship with copulatory behaviour

❓ What is this learning goal really asking? How do hormone changes throughout the oestrous cycle explain female sexual behaviour? 🧠 Intuitive explanation Female behaviour changes because hormones change. During proestrus, follicles grow and produce increasing oestradiol (E2). E2 prepares the reproductive tract and brain for reproduction. High E2 triggers the LH surge, causing ovulation during estrus. This is when females become sexually receptive and copulation usually occurs. After ovulation, the follicle becomes the corpus luteum, which produces progesterone during diestrus to prepare the uterus for possible pregnancy. As hormone levels rise and fall, sexual motivation and receptivity also change. ⭐ Take-away Changing hormones create changing behaviour. 🎯 Exam-ready answer Fluctuations in oestradiol and progesterone regulate the oestrous cycle. High oestradiol induces the LH surge and behavioural oestrus, whereas progesterone dominates after ovulation and prepares the body for possible pregnancy. 📍 Figure Nelson Fig. 6.23. Lecture 5 – Oestrous cycle. 
Theme 2 – Extended Learning Outcomes (continued)

Explain the male reproductive cycle

❓ What is this learning goal really asking? How is male reproduction hormonally regulated, and why is it different from the female cycle? 🧠 Intuitive explanation Unlike females, males do not have a monthly reproductive cycle. Instead, sperm production is relatively continuous after puberty. The pathway is: Hypothalamus (GnRH) → Pituitary (LH & FSH) → Testis

• LH stimulates Leydig cells → produce testosterone.
• FSH stimulates Sertoli cells → support spermatogenesis.
• Sertoli cells also produce inhibin, which inhibits FSH release (negative feedback). Testosterone supports:
• sperm production
• libido (sexual motivation)
• male sexual behaviour
• development of male secondary sexual characteristics. ⭐ Take-away GnRH → LH/FSH → Testosterone + sperm production. 🎯 Exam-ready answer Male reproduction is continuously regulated by the HPG axis. GnRH stimulates LH and FSH release. LH stimulates Leydig cells to produce testosterone, whereas FSH stimulates Sertoli cells to support spermatogenesis. Testosterone and inhibin exert negative feedback on the hypothalamus and pituitary. 📍 Figure Lecture 2 – HPG axis & Testis histology.

Explain the relationship between hormones, brain structure and sexually dimorphic behaviour

❓ What is this learning goal really asking? How do hormones create different male and female brains, leading to different behaviours? 🧠 Intuitive explanation During development, sex steroids permanently organize several brain regions. These brain regions later control sex-specific behaviours. Examples:

• SDN-POA → larger in males → important for male sexual behaviour.
• AVPV → larger in females → contains many kisspeptin neurons and is important for the LH surge.
• Medial amygdala → processes pheromones and social odours.
• BNST → integrates reproductive and social information. Hormones shape these structures early in life, and adult hormones later activate them. ⭐ Take-away Hormones build the brain, and the brain produces sex-specific behaviour. 🎯 Exam-ready answer Sex steroids organize sexually dimorphic brain regions such as the SDN-POA, AVPV, BNST and medial amygdala. These structures contribute to differences in reproductive behaviour between males and females. 📍 Figure Lecture 3 – Sexually dimorphic brain regions.

Describe species differences in reproductive endocrinology in the context of different reproductive strategies

❓ What is this learning goal really asking? Why don't all animals use exactly the same reproductive hormones in the same way? 🧠 Intuitive explanation Evolution adapts endocrine systems to each species' reproductive strategy. Examples from the lectures:

• Seasonal breeders only activate reproduction during the breeding season.
• Continuous breeders reproduce throughout the year.
• Birds use progesterone to help trigger ovulation, whereas in mammals progesterone mainly maintains pregnancy.
• Birds have ZZ males and ZW females, unlike mammals (XY males, XX females). The hormones are often the same, but their timing and function differ. ⭐ Take-away Different reproductive strategies require different endocrine strategies. 🎯 Exam-ready answer Species differ in endocrine regulation because hormone systems have evolved to match different reproductive strategies. Examples include seasonal breeding, avian versus mammalian reproductive endocrinology, and different mechanisms of sex determination. 📍 Figure Lecture 3 & Lecture 5 (bird vs mammal examples).

Interpret the risks of asexual reproduction in vertebrates

❓ What is this learning goal really asking? If asexual reproduction seems easier, why don't most vertebrates use it? 🧠 Intuitive explanation Without mating, animals save time and energy. However, all offspring are genetically very similar. If the environment changes or a disease appears, the entire population may be vulnerable because there is little genetic variation. Sexual reproduction is more expensive, but it continuously creates new gene combinations that improve adaptation. ⭐ Take-away Asexual reproduction is efficient in the short term but risky in the long term. 🎯 Exam-ready answer Although asexual reproduction eliminates the costs of finding a mate, it greatly reduces genetic variation and adaptive potential, increasing vulnerability to environmental change and disease. 📍 Figure Lecture 3 – Costs and benefits of sexual reproduction.

Explain and apply the concepts of attractivity, proceptivity and receptivity

❓ What is this learning goal really asking? Can you distinguish the three different components of female sexual behaviour? 🧠 Intuitive explanation Female sexual behaviour is not one behaviour, but three separate components. Attractivity
→ How attractive the female is to the male (e.g. odour, pheromones). Proceptivity
→ The female actively encourages mating by approaching, hopping or darting. Receptivity
→ The female accepts mating (for rodents, this is shown by lordosis). A female can show one component without necessarily showing the others. ⭐ Take-away Attract → Encourage → Accept. 🎯 Exam-ready answer Attractivity reflects the female's attractiveness to the male, proceptivity reflects the female's active motivation to mate, and receptivity reflects acceptance of copulation. 📍 Figure Nelson Fig. 6.10. Lecture 5.

Explain the concepts of alternative and conditional mating strategies and illustrate these concepts with examples

❓ What is this learning goal really asking? Why don't all individuals reproduce using the same strategy? 🧠 Intuitive explanation Different strategies can lead to the same evolutionary success. Alternative strategies
are genetically fixed. Example:
One male morph always defends territories, another always sneaks matings. Conditional strategies
depend on circumstances. Example:
A large male may defend a territory, while a smaller male adopts a sneaking strategy because he cannot win fights. Both strategies increase reproductive success under different conditions. ⭐ Take-away Alternative = genetically fixed. Conditional = depends on condition or environment. 🎯 Exam-ready answer Alternative mating strategies are genetically determined, whereas conditional mating strategies depend on environmental or individual conditions. Both strategies can maximize reproductive success. 📍 Figure Lecture 3 – Alternative reproductive tactics.

Interpret the extent in which selection pressure has shaped sexual differentiation and mating strategies

❓ What is this learning goal really asking? How has evolution produced the reproductive behaviours we see today? 🧠 Intuitive explanation Individuals that left more surviving offspring passed on more genes. Over thousands of generations, this selected for:

• sex differences,
• mating systems,
• parental care,
• hormone systems,
• sexually dimorphic brain structures. Everything you've learned in Theme 2 can ultimately be explained as traits that improved reproductive success. ⭐ Take-away Selection shapes hormones, brains and behaviour to maximize fitness. 🎯 Exam-ready answer Natural and sexual selection have shaped sexual differentiation, sexually dimorphic behaviour and mating strategies by favouring traits that maximize reproductive success and fitness. 📍 Figure Lecture 3 – Sexual selection examples.

Chromosomal sex, gonadal sex, gametic sex, hormonal sex, morphological sex, behavioural sex

❓ What is this really asking? What does "sex" actually mean? 🧠 Intuitive explanation Sex develops in stages: Chromosomes → Gonads → Hormones → Body → Behaviour

• Chromosomal = XX/XY (or ZZ/ZW)
• Gonadal = ovaries/testes
• Gametic = eggs/sperm
• Hormonal = E2/P4 or testosterone
• Morphological = reproductive anatomy
• Behavioural = reproductive behaviour ⭐ Take-away Sex is a chain, not one characteristic. 🎯 Exam-ready answer Sex can be defined at several levels: chromosomal, gonadal, gametic, hormonal, morphological and behavioural. These usually align but may differ in atypical sexual development. 📍 Figure Lecture 3 – Sexual differentiation overview.

Gender identity, gender role

❓ What is this really asking? How is gender different from biological sex? 🧠 Intuitive explanation

• Gender identity = how someone experiences their own gender.
• Gender role = behaviours and expectations society associates with gender. These are mainly human concepts and differ from biological sex. ⭐ Take-away Biological sex ≠ gender. 🎯 Exam-ready answer Gender identity refers to an individual's internal experience of gender, whereas gender role refers to socially influenced gender behaviours. 📍 Figure Lecture 3.

Sexual orientation, sexual preference

❓ What is this really asking? Who is someone attracted to? 🧠 Intuitive explanation

• Sexual orientation = the sex toward which someone is attracted.
• Sexual preference = which partner or characteristics someone prefers. ⭐ Take-away Orientation = who. Preference = which. 🎯 Exam-ready answer Sexual orientation describes attraction to a particular sex, whereas sexual preference refers to preferred partners or partner characteristics. 📍 Figure Lecture 3.

Asexual reproduction

❓ What is this really asking? Why isn't asexual reproduction common in vertebrates? 🧠 Intuitive explanation No mate is needed, so reproduction is fast. However, offspring are genetically almost identical, making populations less adaptable to disease or environmental change. ⭐ Take-away Fast reproduction, little variation. 🎯 Exam-ready answer Asexual reproduction avoids mating costs but greatly reduces genetic diversity and adaptive potential. 📍 Figure Lecture 3.

Monogamous and polygynous species

❓ What is this really asking? How does the mating system influence parental care? 🧠 Intuitive explanation Monogamous: one breeding pair → both parents often care for offspring. Polygynous: one male mates with several females → males compete more, females usually provide most parental care. ⭐ Take-away Monogamy → shared care. Polygyny → male competition. 🎯 Exam-ready answer Monogamous species often show biparental care, whereas polygynous species typically show greater male competition and reduced paternal care. 📍 Figure Lecture 3.

Organizational/activational hypothesis

❓ What is this really asking? Why can the same hormone have different effects? 🧠 Intuitive explanation Organizational: during development, hormones permanently organize the brain. Activational: in adulthood, hormones activate those circuits. Think: build the house → turn the lights on. ⭐ Take-away Organization builds. Activation uses. 🎯 Exam-ready answer Organizational effects permanently shape neural circuits during development, whereas activational effects temporarily activate these circuits in adulthood. 📍 Figure Nelson Fig. 3.29.

Mammalian sexual differentiation

sex determination at fertilization - expression SRY and SOX9 leads to testis development; absence of SRY and SOX9 expression and presence of Wnt4 expression leads to ovarian development
: ❓ What is this really asking? How does an embryo become male or female? 🧠 Intuitive explanation XY:
SRY → SOX9 → Testis ↓ AMH → Müllerian ducts regress Testosterone → Wolffian ducts develop DHT → male external genitalia XX: No SRY/SOX9 + Wnt4 ↓ Ovary ↓ Female reproductive tract develops. ⭐ Take-away SRY starts the pathway; gonadal hormones finish it. 🎯 Exam-ready answer SRY activates SOX9, causing testis development. Testes produce AMH, testosterone and DHT to masculinize the reproductive tract. Without SRY/SOX9, Wnt4 promotes ovarian development and female differentiation. 📍 Figure Lecture 3 – SRY/SOX9 vs Wnt4.

Accessory sex organs

❓ What is this really asking? Which reproductive organs develop after the gonads? 🧠 Intuitive explanation The gonads (testes/ovaries) produce the gametes. The accessory sex organs help transport, nourish or receive gametes. Male: epididymis, vas deferens, seminal vesicles, prostate, penis. Female: oviducts (fallopian tubes), uterus, cervix, vagina. ⭐ Take-away Gonads make gametes; accessory organs help reproduction. 🎯 Exam-ready answer Accessory sex organs are the reproductive structures other than the gonads that transport, support or receive gametes and enable reproduction. 📍 Figure Lecture 3 – Male and female reproductive anatomy.

Müllerian and Wolffian duct system

❓ What is this really asking? How do male and female reproductive tracts develop? 🧠 Intuitive explanation Every embryo starts with both duct systems. XY (testis):

• AMH → Müllerian ducts disappear.
• Testosterone → Wolffian ducts develop into epididymis, vas deferens and seminal vesicles. XX (ovary):
• No AMH → Müllerian ducts develop into oviducts, uterus and upper vagina.
• No testosterone → Wolffian ducts regress. ⭐ Take-away AMH removes Müllerian ducts; testosterone saves Wolffian ducts. 🎯 Exam-ready answer All embryos initially possess Müllerian and Wolffian ducts. AMH causes Müllerian duct regression, while testosterone stimulates Wolffian duct development. Without these hormones, the female reproductive tract develops. 📍 Figure Lecture 3 – Müllerian/Wolffian ducts.

Müllerian inhibiting hormone (MIH)/anti-Müllerian hormone (AMH)

❓ What is this really asking? What is the job of AMH? 🧠 Intuitive explanation AMH is produced by Sertoli cells in the fetal testis. Its only major developmental job is to remove the female reproductive ducts. Without AMH, Müllerian ducts develop into the uterus and oviducts. 🧠 Memory trick AMH = Abolishes Müllerian ducts. ⭐ Take-away AMH prevents development of the female reproductive tract. 🎯 Exam-ready answer AMH (MIH) is secreted by fetal Sertoli cells and causes regression of the Müllerian ducts during male sexual differentiation. 📍 Figure Lecture 3 – Sexual differentiation pathway.

Testis histology and function (see also Lecture 5)

❓ What is this really asking? Which cells are in the testis, and what does each do? 🧠 Intuitive explanation Remember only two important cell types. Leydig cells
→ make testosterone (stimulated by LH). Sertoli cells
→ support sperm production (stimulated by FSH), nourish developing sperm and produce AMH (fetus) and inhibin(adult). ⭐ Take-away Leydig = Testosterone. Sertoli = Support sperm. 🎯 Exam-ready answer Leydig cells produce testosterone in response to LH. Sertoli cells support spermatogenesis in response to FSH and secrete AMH during fetal life and inhibin in adulthood. 📍 Figure Lecture 2 – Testis histology.

(De)masculinization, (de)feminization: role of androgens and oestrogens in development of external genitalia

❓ What is this really asking? How do hormones determine whether male or female external genitalia develop? 🧠 Intuitive explanation External genitalia are initially the same in every embryo. DHT (made from testosterone) masculinizes them into a penis and scrotum. Without DHT, female external genitalia develop by default. In the brain (especially in rodents), testosterone is converted into oestradiol, which helps masculinize the brain and suppress female neural circuits (defeminization). ⭐ Take-away DHT masculinizes the body; oestradiol masculinizes the rodent brain. 🎯 Exam-ready answer DHT is responsible for masculinization of the external genitalia. In rodents, testosterone is converted into oestradiol in the brain, contributing to masculinization and defeminization of neural circuits. 📍 Figure Lecture 3 – External genitalia development.

Androgens, Testosterone (T), 5α-dihydrotestosterone (DHT)

❓ What is this really asking? Why do males need both testosterone and DHT? 🧠 Intuitive explanation Think: Testosterone
= internal male development + sperm production + male behaviour. DHT
= stronger version of testosterone that mainly develops external male genitalia and the prostate. DHT is made from testosterone by the enzyme 5α-reductase. ⭐ Take-away Testosterone = inside. DHT = outside. 🎯 Exam-ready answer Testosterone promotes development of the internal male reproductive tract and male reproductive behaviour. DHT, produced from testosterone by 5α-reductase, is essential for masculinization of the external genitalia. 📍 Figure Lecture 3 – Testosterone → DHT pathway.

Birds: female heterogametic sex (ZW), male homogametic sex (ZZ)

❓ What is this really asking? How is sex determination in birds different from mammals? 🧠 Intuitive explanation Mammals Female = XX Male = XY The male (Y chromosome) determines sex. Birds Female = ZW Male = ZZ Now the female (W chromosome) determines sex. The chromosomes are reversed, but the result is still male or female development. ⭐ Take-away Mammals: male heterogametic (XY). Birds: female heterogametic (ZW). 🎯 Exam-ready answer Unlike mammals, birds have female heterogametic sex determination (ZW) and male homogametic sex determination (ZZ). 📍 Figure Lecture 3 – Bird sexual differentiation.

Determining organizational versus activational effects of androgens on sexual behaviour in rodents – Fig. 3.29

❓ What is this really asking? How do we know organizational and activational effects are different? 🧠 Intuitive explanation Researchers exposed newborn female rats to testosterone. As adults:

• without testosterone → little male behaviour.
• with testosterone → they showed mounting behaviour. This proves that early testosterone permanently organized the brain, while adult testosterone later activated that organization. If testosterone was only given in adulthood (without neonatal exposure), male behaviour was much weaker. ⭐ Take-away Early hormones build the brain. Adult hormones activate it. 🎯 Exam-ready answer Figure 3.29 demonstrates that neonatal androgen exposure permanently organizes neural circuits, whereas adult testosterone activates these circuits to produce male sexual behaviour. 📍 Figure Nelson Fig. 3.29.

Masculinization in rodents caused by testosterone converted into oestradiol in the brain

❓ What is this really asking? How can oestrogen make a male brain? 🧠 Intuitive explanation In rodents, testosterone enters the brain and is converted by aromatase into oestradiol. Surprisingly, it is this oestradiol that masculinizes and defeminizes the developing brain. Females are protected because α-fetoprotein binds circulating oestrogens, preventing them from entering the brain. ⭐ Take-away Rodent brain: Testosterone → Oestradiol → Masculinization. 🎯 Exam-ready answer In rodents, testosterone is aromatized into oestradiol within the brain. Oestradiol organizes male neural circuits during development, whereas α-fetoprotein protects the female brain by binding circulating oestrogens. 📍 Figure Lecture 3 – Aromatization pathway.

Oestrogen receptor α knockout (αERKO), oestrogen receptor β knockout (βERKO) and androgen receptor knockout (ARKO) mice and male/female reproductive behaviour

❓ What is this really asking? How do we know which hormone receptor controls reproductive behaviour? 🧠 Intuitive explanation Researchers "knocked out" one receptor at a time.

• αERKO: severe reproductive and sexual behaviour deficits → ERα is most important.
• βERKO: relatively mild effects.
• ARKO: males cannot respond properly to testosterone, so male sexual behaviour is greatly reduced. These mice show that hormones only work if their receptors are present. ⭐ Take-away No receptor = hormone cannot act. ERα has the largest behavioural role. 🎯 Exam-ready answer Knockout mice demonstrate that hormone receptors are essential for reproductive behaviour. ERα has a major role in both sexes, whereas AR is required for normal male sexual behaviour. 📍 Figure Lecture 3 – Knockout mouse experiments.

Intrauterine foetus positioning and interfemale aggressiveness

❓ What is this really asking? Can neighbouring fetuses influence each other's behaviour before birth? 🧠 Intuitive explanation Yes. A female fetus developing between two males (2M female) is exposed to more testosterone before birth. As an adult she is often:

• more aggressive,
• less sexually receptive,
• slightly more masculinized. A female between two females (2F) develops with much less testosterone exposure. ⭐ Take-away Prenatal hormones can come from neighbouring fetuses. 🎯 Exam-ready answer In rodents, females positioned between two male fetuses are exposed to higher prenatal androgen levels, resulting in increased aggressiveness and partial masculinization of adult behaviour. 📍 Figure Lecture 3 – Intrauterine position experiment.

Examples of sexually dimorphic areas in the brain: SDN-POA, medial amygdala, BNST, AVPV

❓ What is this really asking? Which brain regions differ between males and females, and why? 🧠 Intuitive explanation Hormones permanently organize several brain regions. SDN-POA
→ larger in males
→ controls male sexual behaviour. Medial amygdala
→ processes pheromones and social odours important for reproduction. BNST
→ integrates reproductive, hormonal and social information. AVPV
→ larger in females
→ contains many kisspeptin neurons that generate the LH surge before ovulation. ⭐ Take-away SDN = male sexual behaviour. AVPV = female LH surge. Amygdala & BNST = process reproductive information. 🎯 Exam-ready answer Sex steroids organize sexually dimorphic brain regions including the SDN-POA, medial amygdala, BNST and AVPV. These regions contribute to sex-specific reproductive physiology and behaviour. 📍 Figure Lecture 3 – Sexually dimorphic brain regions.

Examples of neuronal basis of sexual dimorphic behaviour: bird song; urinary posture in canines; rough and tumble play in primates (including humans)

❓ What is this really asking? How can differences in the brain produce different male and female behaviours? 🧠 Intuitive explanation Hormones organize neural circuits during development. Examples:

• Bird song: males develop larger song-control nuclei and sing more.
• Dogs: males usually lift one leg to urinate, females usually squat.
• Primates: males generally show more rough-and-tumble play than females. These behaviours arise because hormones organized the brain differently during development. ⭐ Take-away Different brains → different behaviours. 🎯 Exam-ready answer Sexually dimorphic behaviours arise because developmental hormones organize different neural circuits in males and females. Examples include bird song, urinary posture and rough-and-tumble play. 📍 Figure Lecture 3 – Behavioural examples.

Role of hormones in development of bird song (zebra finch)

❓ What is this really asking? Why do male zebra finches sing but females usually do not? 🧠 Intuitive explanation During development, testosterone (and its metabolites) organizes the song-control nuclei in the male brain. As adults, testosterone activates these circuits, allowing males to sing complex courtship songs. Females have much smaller song nuclei and usually do not sing. This nicely demonstrates organizational + activational effects in one example. ⭐ Take-away Hormones build the song system first, then activate it later. 🎯 Exam-ready answer In zebra finches, developmental sex steroids organize the song-control nuclei, while adult testosterone activates these neural circuits to produce male courtship song. 📍 Figure Lecture 3 – Zebra finch song system.

Masculinization in rodents caused by testosterone converted into oestradiol in the brain

❓ What is this really asking? How can oestrogen make a male brain? 🧠 Intuitive explanation In rodents, testosterone enters the brain and is converted by aromatase into oestradiol. Surprisingly, it is this oestradiol that masculinizes and defeminizes the developing brain. Females are protected because α-fetoprotein binds circulating oestrogens, preventing them from entering the brain. ⭐ Take-away Rodent brain: Testosterone → Oestradiol → Masculinization. 🎯 Exam-ready answer In rodents, testosterone is aromatized into oestradiol within the brain. Oestradiol organizes male neural circuits during development, whereas α-fetoprotein protects the female brain by binding circulating oestrogens. 📍 Figure Lecture 3 – Aromatization pathway.

Oestrogen receptor α knockout (αERKO), oestrogen receptor β knockout (βERKO) and androgen receptor knockout (ARKO) mice and male/female reproductive behaviour

❓ What is this really asking? How do we know which hormone receptor controls reproductive behaviour? 🧠 Intuitive explanation Researchers "knocked out" one receptor at a time.

• αERKO: severe reproductive and sexual behaviour deficits → ERα is most important.
• βERKO: relatively mild effects.
• ARKO: males cannot respond properly to testosterone, so male sexual behaviour is greatly reduced. These mice show that hormones only work if their receptors are present. ⭐ Take-away No receptor = hormone cannot act. ERα has the largest behavioural role. 🎯 Exam-ready answer Knockout mice demonstrate that hormone receptors are essential for reproductive behaviour. ERα has a major role in both sexes, whereas AR is required for normal male sexual behaviour. 📍 Figure Lecture 3 – Knockout mouse experiments.

Intrauterine foetus positioning and interfemale aggressiveness

❓ What is this really asking? Can neighbouring fetuses influence each other's behaviour before birth? 🧠 Intuitive explanation Yes. A female fetus developing between two males (2M female) is exposed to more testosterone before birth. As an adult she is often:

• more aggressive,
• less sexually receptive,
• slightly more masculinized. A female between two females (2F) develops with much less testosterone exposure. ⭐ Take-away Prenatal hormones can come from neighbouring fetuses. 🎯 Exam-ready answer In rodents, females positioned between two male fetuses are exposed to higher prenatal androgen levels, resulting in increased aggressiveness and partial masculinization of adult behaviour. 📍 Figure Lecture 3 – Intrauterine position experiment.

Examples of sexually dimorphic areas in the brain: SDN-POA, medial amygdala, BNST, AVPV

❓ What is this really asking? Which brain regions differ between males and females, and why? 🧠 Intuitive explanation Hormones permanently organize several brain regions. SDN-POA
→ larger in males
→ controls male sexual behaviour. Medial amygdala
→ processes pheromones and social odours important for reproduction. BNST
→ integrates reproductive, hormonal and social information. AVPV
→ larger in females
→ contains many kisspeptin neurons that generate the LH surge before ovulation. ⭐ Take-away SDN = male sexual behaviour. AVPV = female LH surge. Amygdala & BNST = process reproductive information. 🎯 Exam-ready answer Sex steroids organize sexually dimorphic brain regions including the SDN-POA, medial amygdala, BNST and AVPV. These regions contribute to sex-specific reproductive physiology and behaviour. 📍 Figure Lecture 3 – Sexually dimorphic brain regions.

Examples of neuronal basis of sexual dimorphic behaviour: bird song; urinary posture in canines; rough and tumble play in primates (including humans)

❓ What is this really asking? How can differences in the brain produce different male and female behaviours? 🧠 Intuitive explanation Hormones organize neural circuits during development. Examples:

• Bird song: males develop larger song-control nuclei and sing more.
• Dogs: males usually lift one leg to urinate, females usually squat.
• Primates: males generally show more rough-and-tumble play than females. These behaviours arise because hormones organized the brain differently during development. ⭐ Take-away Different brains → different behaviours. 🎯 Exam-ready answer Sexually dimorphic behaviours arise because developmental hormones organize different neural circuits in males and females. Examples include bird song, urinary posture and rough-and-tumble play. 📍 Figure Lecture 3 – Behavioural examples.

Role of hormones in development of bird song (zebra finch)

❓ What is this really asking? Why do male zebra finches sing but females usually do not? 🧠 Intuitive explanation During development, testosterone (and its metabolites) organizes the song-control nuclei in the male brain. As adults, testosterone activates these circuits, allowing males to sing complex courtship songs. Females have much smaller song nuclei and usually do not sing. This nicely demonstrates organizational + activational effects in one example. ⭐ Take-away Hormones build the song system first, then activate it later. 🎯 Exam-ready answer In zebra finches, developmental sex steroids organize the song-control nuclei, while adult testosterone activates these neural circuits to produce male courtship song. 📍 Figure Lecture 3 – Zebra finch song system.

Oestrus, anoestrus, role of oestradiol (oestrogen)

❓ What is this really asking When is a female sexually receptive, and what hormone causes this? 🧠 Intuitive explanation Oestrus = the female is sexually receptive ("in heat"). Anoestrus = reproductively inactive; she is not receptive. As follicles grow, oestradiol (E2) rises. E2 prepares the reproductive tract, stimulates the brain and triggers the LH surge, leading to ovulation and behavioural oestrus. ⭐ Take-away High E2 → oestrus → ovulation → mating. 🎯 Exam-ready answer Oestradiol produced by developing follicles induces behavioural oestrus, prepares the reproductive tract and triggers the LH surge leading to ovulation. During anoestrus, females are reproductively inactive. 📍 Figure Lecture 5 – Oestrous cycle.

Components of female sexual behaviour; courtship, mating, ovulation (Chapter 6), pregnancy, parturition, lactation (Chapter 7)

❓ What is this really asking? What are the main stages of female reproduction? 🧠 Intuitive explanation Think of one continuous timeline: Courtship ↓ Mating ↓ Ovulation ↓ Pregnancy ↓ Parturition (birth) ↓ Lactation Each stage is controlled by different hormones, but together they form one reproductive sequence. ⭐ Take-away Reproduction is one continuous hormonal timeline. 🎯 Exam-ready answer Female reproductive behaviour progresses from courtship and mating to ovulation, pregnancy, parturition and lactation, with each stage regulated by specific endocrine changes. 📍 Figure Lecture 5 & Chapter 6 overview.

Correlation vaginal cytology collates closely with changes in ovarian function/structure

❓ What is this really asking? Why do researchers examine vaginal smears? 🧠 Intuitive explanation Cells in the vagina change throughout the oestrous cycle. By examining a vaginal smear, researchers can determine:

• which stage of the cycle the female is in,
• what the ovaries are doing,
• which hormones are dominant. It is an indirect measure of ovarian activity. ⭐ Take-away Vaginal cells reflect ovarian hormones. 🎯 Exam-ready answer Changes in vaginal cytology closely reflect ovarian activity and hormone levels, allowing researchers to determine the stage of the oestrous cycle. 📍 Figure Lecture 5 – Vaginal cytology.

Behavioural oestrous: species specific role of oestrogen and progesterone

❓ What is this really asking? How do oestrogen and progesterone control female sexual behaviour? 🧠 Intuitive explanation Oestrogen prepares the female for mating by increasing sexual motivation and receptivity. In many species, progesterone acts after oestrogen and further facilitates sexual behaviour. The exact roles differ between species, which is why the study guide emphasizes species specific. ⭐ Take-away E2 prepares; progesterone fine-tunes. 🎯 Exam-ready answer Behavioural oestrus is primarily induced by oestrogen, while progesterone further modulates sexual behaviour. Their relative importance differs between species. 📍 Figure Lecture 5 – Behavioural oestrus.

Biphasic effects progesterone on female oestrus behaviour

❓ What is this really asking? Why can progesterone both stimulate and inhibit sexual behaviour? 🧠 Intuitive explanation Progesterone has two phases. Immediately after E2, a small rise in progesterone enhances receptivity. Later, sustained high progesterone suppresses sexual behaviour because the female has already ovulated and may be pregnant. ⭐ Take-away Early progesterone stimulates. Late progesterone inhibits. 🎯 Exam-ready answer Progesterone has biphasic effects: shortly after oestrogen it facilitates female sexual behaviour, whereas prolonged elevated progesterone suppresses receptivity. 📍 Figure Lecture 5 – Behavioural effects of progesterone.

Components of female rodent sexual behaviour: Figures 6.5, 6.6, 6.7

❓ What is this really asking? How does a female rodent actively control mating? 🧠 Intuitive explanation Female rodents are active participants. They:

• approach the male,
• investigate him,
• hop and dart,
• show lordosis when receptive,
• pace the interaction by leaving and returning. This allows them to control mating frequency. ⭐ Take-away Females control mating more than you might think. 🎯 Exam-ready answer Female rodent sexual behaviour includes approach behaviour, hopping, darting, pacing and lordosis, allowing females to actively regulate mating interactions. 📍 Figure Nelson Figs. 6.5–6.7.

Attractivity, proceptivity, receptivity (example Figure 6.10)

❓ What is this really asking? Can you distinguish the three components of female sexual behaviour? 🧠 Intuitive explanation Think of three consecutive steps. Attractivity
→ the male finds the female attractive. Proceptivity
→ the female actively encourages mating. Receptivity
→ the female accepts copulation (lordosis). These are separate behaviours and can occur independently. ⭐ Take-away Attract → Encourage → Accept. 🎯 Exam-ready answer Attractivity reflects attractiveness to the male, proceptivity reflects the female's motivation to mate, and receptivity reflects acceptance of copulation. 📍 Figure Nelson Fig. 6.10.

Role of females in initiating sexual interaction with males: laboratory versus social reality

❓ What is this really asking? Who actually starts mating? 🧠 Intuitive explanation Early laboratory studies suggested males initiate mating. However, in more natural settings, females often initiate and control sexual interactions by approaching, pacing and deciding when mating occurs. The lecture's message is that female behaviour was historically underestimated. ⭐ Take-away Females are active decision-makers. 🎯 Exam-ready answer Although laboratory studies traditionally emphasized male initiation, naturalistic studies show that females actively initiate and regulate many sexual interactions. 📍 Figure Lecture 5 – Laboratory versus social reality. 

Theme 2 – Concepts (Part 6 – Final)

Oestrous cycle: follicular phase, luteal phase (Figure 6.23)

❓ What is this really asking? What are the two major phases of the female reproductive cycle? 🧠 Intuitive explanation Follicular phase
→ follicles grow → E2 increases → female becomes receptive → LH surge → ovulation. Luteal phase
→ corpus luteum forms → progesterone increases → uterus prepared for pregnancy → receptivity decreases. ⭐ Take-away Follicular = E2 + ovulation. Luteal = progesterone + pregnancy preparation. 🎯 Exam-ready answer The follicular phase is dominated by follicle growth and oestradiol production leading to ovulation, whereas the luteal phase is dominated by progesterone production from the corpus luteum, preparing the uterus for pregnancy. 📍 Figure Nelson Fig. 6.23.

Ovarian histology and function (see also lecture 5)

❓ What is this really asking? Which ovarian structures produce the hormones? 🧠 Intuitive explanation Growing follicles contain:

• Theca cells → make androgens.
• Granulosa cells → convert androgens into oestradiol (aromatase). After ovulation: ↓ Corpus luteum ↓ Produces progesterone. ⭐ Take-away Follicle = E2. Corpus luteum = progesterone. 🎯 Exam-ready answer Growing follicles produce oestradiol through cooperation between theca and granulosa cells. After ovulation, the corpus luteum becomes the main source of progesterone. 📍 Figure Lecture 5 – Ovarian histology.

Parental behaviour, maternal behaviour, paternal behaviour

❓ What is this really asking? What is the difference between these forms of care? 🧠 Intuitive explanation Parental behaviour
= any behaviour increasing offspring survival. Maternal behaviour
= care by the mother. Paternal behaviour
= care by the father. The amount of maternal and paternal care differs greatly between species. ⭐ Take-away Parental = both parents. Maternal = mother. Paternal = father. 🎯 Exam-ready answer Parental behaviour includes all care directed towards offspring. Maternal and paternal behaviour refer specifically to care provided by the mother or father. 📍 Figure Lecture 6 – Parental behaviour.

Altricial, precocious young

❓ What is this really asking? How developed are offspring at birth? 🧠 Intuitive explanation Altricial
→ born helpless. Examples:
mouse, rat, cat. Need extensive parental care. Precocial
→ born well developed. Examples:
horse, sheep. Can walk soon after birth. ⭐ Take-away Altricial = helpless. Precocial = independent. 🎯 Exam-ready answer Altricial offspring are poorly developed and highly dependent at birth, whereas precocial offspring are relatively mature and capable of independent movement shortly after birth. 📍 Figure Lecture 6.

Parental investment

❓ What is this really asking? Why do parents care for offspring? 🧠 Intuitive explanation Parental investment is any investment that increases offspring survival but costs the parent. Examples:

• feeding,
• protection,
• incubation,
• carrying young. The more parents invest in one offspring, the fewer resources remain for future offspring. ⭐ Take-away Helping offspring always has a cost. 🎯 Exam-ready answer Parental investment is any parental effort that increases offspring survival while reducing the parent's ability to invest in other offspring. 📍 Figure Lecture 6.

Alloparental behaviour

❓ What is this really asking? Can individuals care for offspring that are not their own? 🧠 Intuitive explanation Yes. Alloparental behaviour is care provided by individuals other than the biological parents. Examples:

• older siblings,
• grandparents,
• helpers at the nest. ⭐ Take-away Parents aren't always the caregivers. 🎯 Exam-ready answer Alloparental behaviour refers to parental care provided by individuals other than the biological mother or father. 📍 Figure Lecture 6.

Avian maternal behaviour, role of prolactin, oestrogens and progesterone

❓ What is this really asking? How do hormones prepare a female bird for reproduction and parenting? 🧠 Intuitive explanation Oestrogen
→ follicle growth and reproductive behaviour. Progesterone
→ helps trigger the LH surge and ovulation in birds. Prolactin
→ incubation and chick care. ⭐ Take-away E2 prepares. Progesterone ovulates. Prolactin parents. 🎯 Exam-ready answer In birds, oestrogen stimulates reproductive development, progesterone contributes to ovulation, and prolactin promotes incubation and parental care. 📍 Figure Lecture 6 – Avian parental behaviour.

Avian paternal behaviour, role of androgens and prolactin

❓ What is this really asking? How does a male bird switch from mating to parenting? 🧠 Intuitive explanation Before breeding: ↑ Testosterone ↓ Courtship and territorial behaviour. After chicks hatch: ↓ Testosterone ↑ Prolactin ↓ Feeding and caring for chicks. ⭐ Take-away Testosterone gets the mate. Prolactin raises the chicks. 🎯 Exam-ready answer Androgens promote male reproductive behaviour before breeding, whereas prolactin promotes paternal care after offspring hatch. 📍 Figure Lecture 6 – Avian paternal behaviour.

Vasoactive intestinal peptide (VIP, neuropeptide): implicated in social and possibly nesting behaviour in birds

❓ What is this really asking? Why is VIP important in birds? 🧠 Intuitive explanation VIP is a brain neuropeptide. It stimulates prolactin release, helping switch birds from reproduction to parental behaviour. It is associated with incubation, nesting and chick care. ⭐ Take-away VIP helps activate parenting. 🎯 Exam-ready answer VIP stimulates prolactin release and is implicated in nesting and parental behaviour in birds. 📍 Figure Lecture 6.

Marsupials, monotremes, eutherian

❓ What is this really asking What are the three major mammal groups? 🧠 Intuitive explanation Monotremes
→ lay eggs. Marsupials
→ short pregnancy, development continues in pouch. Eutherians
→ placental mammals; most development occurs before birth. ⭐ Take-away Egg → Pouch → Placenta. 🎯 Exam-ready answer Monotremes lay eggs, marsupials complete much of development in a pouch, and eutherians are placental mammals whose offspring develop mainly before birth. 📍 Figure Lecture 6.

Eutherian mammalian maternal care: (1) altricial young; (2) precocial young; (3) semi-precocial young

❓ What is this really asking? How does offspring development determine maternal care? 🧠 Intuitive explanation Altricial
→ mother provides almost everything. Semi-precocial
→ mother often carries or nests the young. Precocial
→ offspring can move early, so the mother mainly protects and nurses. The less developed the offspring, the more care is needed. ⭐ Take-away Less developed offspring = more maternal care. 🎯 Exam-ready answer Eutherian maternal care depends on offspring development: altricial young require extensive care, semi-precocial young show intermediate dependence, and precocial young are relatively independent after birth. 📍 Figure Lecture 6.

Endocrine correlates maternal behaviour: oestrogens, progesterone, prolactin, oxytocin

❓ What is this really asking? How do hormones transform a female into a mother? 🧠 Intuitive explanation Oestrogen
→ prepares the maternal brain. Progesterone
→ maintains pregnancy. Oxytocin
→ contractions, milk let-down and bonding. Prolactin
→ milk production and maternal care. ⭐ Take-away Prepare → Pregnancy → Birth → Care. 🎯 Exam-ready answer Maternal behaviour is regulated by coordinated actions of oestrogen, progesterone, oxytocin and prolactin, which prepare the female for pregnancy, birth, lactation and offspring care. 📍 Figure Lecture 6 – Maternal hormones.

Concaveation

❓ What is this really asking? Can maternal behaviour occur without pregnancy? 🧠 Intuitive explanation Yes. Researchers can induce maternal behaviour in non-mothers by giving hormones and/or repeatedly exposing them to pups. This demonstrates that maternal behaviour is hormonally and neurally regulated. ⭐ Take-away Motherhood can be experimentally induced. 🎯 Exam-ready answer Concaveation is the experimental induction of maternal behaviour in animals that have not been pregnant, demonstrating the hormonal and neural basis of maternal care. 📍 Figure Lecture 6.