Reproductive Behaviour

Question 1

Intrasexual selection- male to male competition

Answer 1

Often more dramatic than mate choice, as typically involves some sort of direct competition between males

Question 2

Male-male competition by (in) direct fighting

Answer 2

There is strong selection pressure for males to accurately assess an opponent’s strength to avoid injury/death

As well as an honest indicator of size/fighting ability in male-male competition

Question 3

Male-male competition- roaring

Answer 3

Roaring was being used as the main indicator of strength and fighting ability

Roaring and associated activities were almost exclusively seen during the rut

Roaring can advance ovulation, so harem holding males can improve their mating success by regular calling

Question 4

Male-male competition- sexual selection

Answer 4

Sexual size dimorphism in pinnipeds is the product of an exclusively male response to sexual selection

Significant correlation between harem size and sexual size dimorphism- the larger the average harem size, the larger the relative size of males compared to females

Question 5

Three evolutionary developments in males

Answer 5

1. Size dimorphism (male-biased in mammals)
2. Aggressive behaviour
3. Armaments (e.g. horns, antlers, tusks)

Question 6

Male-mael competition by interference

Answer 6

There is an interesting subset within male-male competition, where a male interferes with another male while they attempt to mate with a female

In some cases, females appear to solicit males to remove a rival during a mating attempt

Question 7

What is sperm competition?

Answer 7

Direct competition between the sperm of different males to fertilise a femal’s eggs (i.e. Competition occurs after a female has mated with multiple males)

Females are not just “inert environments”- they can play an active role in sperm competition via cryptic choice (e.g. which sperm she selects for fertilisation)

Question 8

What is semelparity?

Answer 8

A reproductive strategy that is characterised by the die-off of one or both sexes after a single reproductive episode or season

Question 9

Sex-role reversal

Answer 9

Male pregnancy in seahorses etc. Predisposes males to limit female reproductive success- sexual selection may then operate more strongly on female and female sexual signals may evolve

In several species, males also evolve ornaments, female are “choosy” as well as being competitive, and males compete as well as choosing partners

Question 10

Endocrine mechanisms- testosterone

Answer 10

Essential for the male mating behaviour.

Low testosterone can lead to a reduction in both sexual motivation and performance, this can be reversed by testosterone treatment

Question 11

Testosterone and androstenedione

Answer 11

This can maintain mating behaviour in castrated rats

Both testosterone and androstenedione can be converted to estradiol and other estrogens, but DHT cannot

Question 12

Dinydrotestosterone and estradiol

Answer 12

Dihydrotestosterone does not prevent post-castration decline in mating behaviour

Estradoil is very effective in activating mating behaviour in castrated male rats

Question 13

What are chemosensory cues?

Answer 13

Chemical signals

Particularly olfaction is critical for reproductive behaviours

Question 14

Three regions of the brain that evokes the release of dopamine

Answer 14

1. Nigrostriatal tract
2. Mesolimbic tract
3. MPOA

Question 15

What is the nigrostriatal tract?

Answer 15

The largest dopaminergic system and mediates initiation of movement

e.g. Muscular movement associated with mounting females

Question 16

What is the mesolimbic tract?

Answer 16

Important in reward and appetitive behaviour

e.g. Sex and drugs

Question 17

What is the MPOA?

Answer 17

In the hypothalamus

Possesses receptors for sex steroid hormones

Question 18

What is the Coolidge effect?

Answer 18

A biological phenomenon whereby males exhibit renewed sexual interest whenever a new female is introduced even after previous mates are still available

le rat is placed in a box with an oestrus female, he will mate to satiation. However if a new female is introduced, the apparently satiated male will often immediately resume mating

Question 19

Intersexual selection (female mate choice)

Answer 19

One unifying theme across evolutionary models of mate choice is that the female’s choice of male is under some sort of genetic control

Learning also plays un important role in sexual selection

Question 20

Mate choice and direct benefits

Answer 20

Any female who has the tendency to choose males that provide her with some important resource will do better than her less choosy counterparts

Natural selection favours females who have a genetic predisposition to choose mates that provides them with tangible resources- above and beyond sperm - that increase their fecundity

Question 21

Mate choice and good genes

Answer 21

Females who choose the males with genes best suited to their particular environment receive indirect benefits, so their offspring receive genes associated with for example superior foraging or anti -predator skills

Question 22

What are honest indicator traits?

Answer 22

Generally ‘costly’ to produce- the costlier the trait, the more difficult to fake, so more likely that is a true indicator of good genes

Question 23

Examples of honest indicator traits

Answer 23

Bright colours and vigorus courtship rituals

Both energetically costly to maintain and perform

Question 24

Mate choice and sensory bias

Answer 24

Females initially refer male traits that elicit the greatest amount of stimulation from their sensory systems

Question 25

Example of sensory bias

Answer 25

For example, red berries are the most nutritious food source to a fruit, eating blue feathered bird species. Females who are best able to find these red berries will survive and reproduce better.

Natural selection will act on female neurobiology to make them more attuned to the colour red in the environment.

If red feathers should’ve suddenly appear in males these birds will be chosen as mates because the females nervous system is already designed to prefer red

Question 26

Make choice copying - social learning

Answer 26

When a female, my choice of preference is affected by the preference of other females in her population

Females were more interested in meeting with males who had already mated with other females on his territory, even if these were dummy females

Question 27

What is sexual imprinting?

Answer 27

Young individuals quickly learn amazing preferences from their interactions with adults. Typically, their parents

Question 28

Example of sexual imprinting - Japanese quails

Answer 28

The brown males raised with other Brown quails showed strong sexual preferences for brown females over blonde females

Phase 1 - the brown male was allowed to see a blonde female and meet with her
Phase 2 - the same Brown mail was allowed to see a brown female, but was never allowed physical contact with her

The males learn that the presence of a blonde female meant amazing opportunity 

Question 29

Two structures thought to most likely be producing hormones that influence oestrus behaviour

Answer 29

l. Follicles
2. Corpus luteum

Question 30

What is produced in the follicles?

Answer 30

The fluid within the mature follicles is rich in oestrogenic hormones, which are secreted into the circulatory system

Question 31

What is produced by the corpus luteum?

Answer 31

Progesterone produced, which works synergistically with oestrogen to induce behavioural oestrus

Question 32

What are the three female reproductive behaviours?

Answer 32

1. Attractivity
2. Proceptivity
3. Receptivity

Question 33

What is attractivity in female reproductive behaviour?

Answer 33

The stimulus value of a female for a given male

In nature, high blood estradiol concentrations correspond to the time of max fertility

Chemosensory queues emanate from the urinal and vagina secretions of a oestrus female, Mosul, often sniff or lick female external genitalia before mating

Question 34

What is proceptivity?

Answer 34

The extent to which a female initiates copulation

Question 35

What is receptivity?

Answer 35

The state of responsiveness to sexual initiation

Question 36

What does male mounting behaviour cause?

Answer 36

Activation of the cutaneous receptors in the female flanks-Axons from these receptors form a sensory nerve that projects to the dorsal root ganglion of the spine

Question 37

Where do the sensory signals travel to from the spinal cord?

Answer 37

They travel to the medulla reticular formation in the hindbrain midbrain central grey area

Question 38

Four parts to intrasexual selection summary

Answer 38

1. Direct fighting
2. Interference
3. Sperm competition
4. Neuroendocrine mechanisms for male reproductive behaviours

Question 39

Five parts to intersexual selection summary

Answer 39

1. Direct benefits
2. Good genes
3. Sensory bias
4. Mate choice copying and learning.
5. Neuro endocrine mechanisms for female reproductive behaviours