Lecture 11 Differential effects of intersexual and intrasexual selection in monogamousand polygynous mating systems

Question 1

what results in sperm competition?

Answer 1

In promiscuous mating systems, (common in many primates ie chimps, + many baboon species) females mate with many males over the course of the oestrous cycle.
SPERM COMPETITION RESULTS

Question 2

primate poly mating systems?

Answer 2

In polygynous mating systems, males monopolise access to several females, but in primates, mating incidents are low, as he guards relatively few females and these are usually rearing offspring and are in lactational anoestrous.

Question 3

what occurs in seasonally breeding poly species?

Answer 3

In seasonally breeding polygynous species, males indulge in scramble competition for access to females over a limited period (ie Antechinus see also last lecture). Sperm competition results

Question 4

what occurs in non seasonal primates with poly?

Answer 4

In non-seasonal primates with stable polygynous systems, female fertility is low and sperm competition reduced

Question 5

gorilla general description:

Answer 5

Silverback male has a harem of 3-4 females

Each adult female comes into oestrus once or twice every 4 years

For the remaining time, she is lactational anoestrous or is pregnant

Male may only get the opportunity to copulate once a year, since mating is confined to time that female is in oestrus

Male gorillas weigh 250Kg, yet testis are only 10g - small

Question 6

Chimpanzees general description:

Answer 6

Promiscuous or multi-male mating system

Several males mate with a single female while she is in oestrus

Sperm competition results
Dominant males may have relatively high copulation frequency.

Several adult females in the troop may come into oestrus at same time, favouring large testis size

If the female is to mate with many males, it pays her to advertise her receptive state with pronounced oestrous swelling at time of ovulation which can be seen as a badge by the males

Question 7

Orang-utan description:

Answer 7

Males are largely solitary
Occupy large defended territories

Females occupy overlapping ranges which They may share with their daughters

Prolonged period of offspring care and lactation
Means that they come into oestrus approximately once every 4 years.

Solitary non-promiscuous nature means that females do not advertise their ovulationwith overt oestrous swelling.

Question 8

Bonobo/West african pigmy chimp description:

Answer 8

Fission-fusion society – similar to E.African chimps

Male inherit social status from their mothers and often
remain in maternal area for life

Females have prolonged periods of oestrous swelling
well beyond period of fertility

Species is highly promiscuous

The only non-human primate species which
mates face to face

Question 9

homo sapiens

Answer 9

There is only one species of mammal in which all signs of ovulation
are suppressed

….so much so that the individual female is unaware of time of ovulation

This same species is the only species of mammal to mate over the entire ovarian cycle irrespective of fertility

This species has the longest period of post-natal care and greatest need to support the development of the offspring

Question 10

Kalahari !Kung people

Answer 10

Melvin Konner

decreased no of ovulations compared to western woman.

western better nutrition, less breastfeeding. smaller intervals between births

Question 11

hunter gatherer

Answer 11

Interval from menarche to 1st birth ca 3.5 years
Breast-feeding 4 times/h in 1st 2 years
Suckling stimulus blocks ovulation
Return to menses ca 24-36 months
Interval between births 3 years plus
Ovulations per lifetime = Age at menopause – Age at menarche, @ 13 ovulations per year = 403 possible
Of these, ca 215 cycles are anovulatory.
Add ca 30 cycles for post-menarche and pre-menopausal
Net Number is ca 160 cycles per lifetime

Question 12

western woman

Answer 12

Earlier menarche than hunter gatherers.
Interval from menarche to 1st birth over 14 years
Decrease in number of children reared
Decrease in prevalence of prolonged breast-feeding
Estimated life-time number of ovulations = 450

Question 13

examples of androgen action?

Answer 13

Mandrill - Facial & Rump colour.
testosterone increases and bright facial colours result, show dominance.
higher rank, brighter face/genitals/testis size. also change with rank/loss/gain

Brown howler monkey -Dimorphic colour & hyoid bone varies in size.
inverse to testis size, vocally mediated competition.

Question 14

Overt badges of fertility in female primates

Answer 14

Oestrous swelling in perineal region of chimpanzees and several baboon species

Oestrogen dependent

Females advertise their fertility

Oestrous swelling in female chimpanzees.
Female reproductive cycle is
36 days.
Females exhibit pronounced
swelling for ca 10 days.

Question 15

males mate most when

Answer 15

Alpha males focus most effort on times of maximal fertility

Question 16

Mating behaviour in chimps

Answer 16

Alpha males monopolise most mating at peak tumescence time
Alpha males show increased interest in females that show relative increases in tumescence size from cycle to cycle
Field data shows that increased tumescence from cycle to cycle is a reliable indicator of ability to conceive

Question 17

alpha males

Answer 17

Alpha males cannot monopolise access to all females or all mating. Female choice is important.
Alpha males focus time and energy on females in the group at their peak fertility times.
Alpha males are probably tracking the fertility of the resident females over successive oestrous cycles to the point of conception – perhaps by retaining a memory of previous tumescence sizes in individual females, since absolute size varies from female to female.

Question 18

spematoza

Answer 18

Mid-piece comprises densely packed
mitochondria and energy in the absence
of glycolytic support

Mitochondrial loading associated with
motility and flagellum activity

as spperm competition increases so does mid piece size.

Question 19

mating structure and mid piece size relationship

Answer 19

poly have increased testis size, ejac per hour, bigger mid piece