HB Lecture 7

Which organs are the primary sexual organs?

The gonads (testes and ovaries)

Secondary sexual characteristics (narrow definition) develop at what life stage?

During or after puberty

Name three narrow-sense secondary sexual characteristics that appear at puberty.

Any three: enlargement of genitalia, breast tissue, facial and pubic hair, muscle mass growth

Name four structures classed as secondary sex organs.

Any four: penis, scrotum, vulva, clitoris, fallopian tubes, prostate

Name the four wider (non-genital) categories of secondary sexual characteristics in this lecture.

Brain differentiation; pelage and feather dimorphism; weapons (teeth, antlers, horns, spurs); vocal traits (song, territorial calling)

Competition between members of the same sex for access to mates is called what?

Intrasexual selection

Choice of a partner by one sex, leading to adornments in the other sex, is called what?

Intersexual selection

In a monogamous system, how does intrasexual competition compare between the sexes?

It is equivalent in both sexes

In a polygynous system, which sex experiences huge intrasexual competition?

Males

Intrasexual selection in polygynous males drives which two traits?

Inter-male threat/aggression, and development of large body size and weapons

Define a promiscuous mating system.

Females mate with many males over the course of one oestrous cycle

Define a polygynous mating system.

Males monopolise access to several females

Why are mating incidents low in polygynous primates?

The male guards relatively few females, who are usually rearing offspring and are lactational anoestrous

Define sperm competition.

Competition between the sperm of different males when one female mates with several males within one ovulatory cycle

Sperm competition changes testis size in which direction?

Testis size increases

Sperm competition produces what form of competition between males?

Male-male competition for access of their sperm to the ova

Define cryptic female choice.

Sperm selection occurring deep in the female reproductive tract

Name three mechanisms of cryptic female choice listed in the lecture.

Reproductive tract contractions, the immune system, chemoattractants

Female promiscuity produces offspring of what paternity type?

Mixed paternity

Explain the maternal-paternal genome conflict.

A mother cares equally for all her offspring, but each offspring must compete with its half siblings

In the maternal-paternal genome conflict, which imprinted genes favour offspring growth?

Male imprinted genes

In the maternal-paternal genome conflict, which imprinted genes slow growth and conserve resources?

Female imprinted genes

Define scramble competition in seasonally breeding polygynous species (e.g. Antechinus).

Males share access to females over a limited period and compete in a frenzied scramble for them

In non-seasonal primates with stable polygynous systems, how do female fertility and sperm competition compare with promiscuous species?

Female fertility is low and sperm competition is reduced

Describe the gorilla social unit.

A silverback male with a harem of females

Why does a male gorilla rarely get to copulate?

Mating is confined to the time a female is in oestrus, which happens only once or twice every few years; otherwise she is lactational anoestrous or pregnant

Male gorillas are very heavy but have what testis size relative to body size?

Proportionately very small testes

What is the chimpanzee mating system?

Promiscuous (multimale); several males mate with a single female while she is in oestrus

Why does several adult female chimpanzees being in oestrus simultaneously favour large testis size?

It increases sperm competition between males

Why does a chimpanzee female mating with many males benefit from advertising her receptive state?

Pronounced oestrous swelling at ovulation acts as a badge signalling receptivity to males

What does the name orang-utan mean?

Person of the forest

Describe orang-utan male spacing.

Largely solitary, occupying large defended territories

Describe orang-utan female ranging.

Overlapping ranges, which may be shared with their daughters

How often do orang-utan females come into oestrus, and why?

Approximately once every 4 years, because of prolonged offspring care and lactation

Why do orang-utan females not advertise ovulation with overt oestrous swelling?

Their solitary, non-promiscuous nature

What type of society do bonobos have?

Fission-fusion (similar to East African chimps)

How do male bonobos acquire social status?

They inherit it from their mothers

Where do male bonobos often remain for life?

In their maternal area

How does the duration of female bonobo oestrous swelling compare with the fertile period?

Swelling is prolonged, well beyond the fertile period

Which non-human primate mates face to face?

The bonobo (the only one)

In bonobo paternity testing (Gerloff et al. 1999), who sired most infants?

Resident males

In bonobo paternity testing, which males together had the highest paternity success?

Two dominant males

In bonobo paternity testing, the highest-success males were sons of which type of female?

High-ranking females

What did the bonobo paternity findings suggest about mothers?

Mothers strongly influence the paternity success of their sons

Which mammal species suppresses all signs of ovulation, so females are unaware of ovulation time?

Humans (Homo sapiens)

Which mammal mates across the entire ovarian cycle irrespective of fertility?

Humans

Which primate species has the longest period of postnatal care?

Humans

In !Kung hunter-gatherers (Konner), what blocks ovulation during breastfeeding?

The suckling stimulus

How does breastfeeding intensity differ in Western women compared with !Kung hunter-gatherers?

Prolonged breastfeeding is less prevalent

How does menarche timing differ in Western women compared with hunter-gatherers?

Menarche is earlier

Do Western women or hunter-gatherer women have more lifetime ovulations?

Western women

What unique breast feature do humans have among primates?

Permanent enlargement after puberty

Which author wrote The Naked Ape?

Desmond Morris

Who first suggested (1976) that the human breast is a dimorphic signal?

Frank Beach

What chimpanzee structure did Beach propose the human breast is homologous in function to?

Perineal swelling

Beach linked the human breast signal to the evolution of which locomotion?

Bipedalism

Bonobo females have what breast state until pregnant?

Flat chested

In the Maslin comparison, what does a large genitalia/testis or breast size ratio indicate?

Mating strategy

Which structure is present in all primates except humans?

The os penis (baculum), a bone within the penis

Primates with simple penises tend to have which two mating systems?

Monogamous or polygynous

Why can primates with simple penises be monogamous or polygynous?

There is no sperm competition

Name two primates with simple penises from the lecture.

Cotton top tamarin and gorilla

How does complex penis structure aid reproduction?

It allows longer coitus, delivering more sperm

Name three primate groups with complex penises (multi-male to multi-female mating).

Chimpanzees, brown lemurs, macaques

Which hormone class drives facial and rump colour in mandrills?

Androgens

Name five androgen-driven traits shown in the lecture.

Mandrill facial/rump colour; howler dimorphic colour and hyoid bone; orang-utan large dewlap; gorilla nucal crest and coat colour; chimp male pattern baldness

What is the howler monkey hyoid bone's function?

A hollow resonance box for vocalisation

What causes greater hyoid development in male howler monkeys?

Testosterone

Howler species with single-male groups have which hyoid and testis sizes?

Large hyoids and small testes

As males per group increase across howler species, what happens to testis volume?

It increases

As males per group increase across howler species, what happens to hyoid volume?

It decreases

Larger howler hyoids produce what change in formant frequencies?

Lower formant frequencies

What acoustic impression do lower formant frequencies give?

Larger male body size

What evolutionary trade-off do howler monkeys show (Dunn et al.)?

Between investment in pre-copulatory vocal traits (hyoid) and post-copulatory sperm production (testes)

How does howler monkey call frequency compare with that predicted by body mass?

Exceptionally low

What does sperm production correlate closely with?

Testicular size

Most expansion of the testis in high sperm producers is in which tissue?

Tubular structure and germ cell production

Which testis cells make testosterone and occupy relatively little space?

Leydig cells

Primates are unusual among mammals in which feature?

They are the most colourful

Primate colour illustrates the key role of which sense, at the expense of which other?

Vision at the expense of olfaction

In mandrills, what two body regions show colour linked to dominance?

Face and rump

When a mandrill gains alpha rank, which of these increases: testosterone, testis volume, genital red colour?

All three increase

What happens to testis volume and sternal gland score when a mandrill loses alpha rank?

Both decrease

What does the mandrill sternal gland secrete?

A scent

After defeat of an alpha mandrill, what happens to most subordinate males' skin colouration?

Some increase, then three regress, while one takes over alpha status with the highest colouration

What is the oestrous swelling site in chimpanzees and several baboon species?

The perineal region

Oestrous swelling is dependent on which hormone?

Oestrogen

How long is the chimpanzee female reproductive cycle?

36 days

For roughly how long do female chimpanzees show pronounced swelling?

About 10 days

Define the periovulatory period (POP) in chimpanzees.

The day of ovulation plus the three preceding days

Define pre-POP and post-POP in chimpanzee swelling.

Pre-POP: period of maximum tumescence before the POP; post-POP: period of maximum tumescence after the POP

How long before conception do wild chimpanzee females typically show cycling with tumescence and mating?

About 3 years

When do cycles of tumescence begin in a young chimpanzee female relative to menarche?

Irregular cycles begin before the first menstrual bleed

When do alpha male chimpanzees focus mating effort?

At times of maximal fertility (peak tumescence)

Which chimpanzee males monopolise most mating at peak tumescence?

Alpha males

What swelling change attracts increased alpha male interest?

A relative increase in tumescence size from cycle to cycle

Increasing tumescence from cycle to cycle indicates what?

Ability to conceive

Why do males need to track individual female swelling over cycles rather than use absolute size?

Absolute swelling size varies from female to female

Why can alpha males not monopolise all matings in a promiscuous system?

They cannot monopolise all females, so choice of female matters

Name the five labelled parts of a spermatozoon.

Acrosome, membrane, nucleus, mid-piece, tail