Sexual selection lecture 8 part 1

Question 1

What is Sexual selection?

Answer 1

Sexual selection equates to genetic selection acting via competition for mates (Not resources)

Question 2

What is shaped by sexual selection?

Answer 2

Much that is fundamental about morphology, physiology and behaviour is shaped by sexual selection

Question 3

Define intra-sexual selection

Answer 3

Selection within the sexes

Question 4

Define inter-sexual selection

Answer 4

Selection between the sexes

Question 5

What aspect do species have to have for sexual selection to be involved?

Answer 5

Sexual selection can only exist in species with sexual reproduction

Question 6

What differs in male and female gametes?

Answer 6

The only universal criterion is that males have small, generally mobile gametes (sperm) and females have large, generally immobile gametes (Ova).

Question 7

What are females choosy with?

Answer 7

Females are choosy in terms of looking for highest quality mates

Question 8

What does discrimination not necessarily imply?

Answer 8

Discrimination does not necessarily imply more elaborate cognitive abilities, just an attraction for certain traits!

Question 9

What is the difference between male and female sexual selection?

Answer 9

Females are choosy in terms of looking for highest quality mates

while

Males look to maximise matings and are likely to be less selective

Question 10

What are the effects of female choice?

Answer 10

generate an important selection pressure for the evolution of male traits, whereas males do not have such an impact on selection pressure.

Question 11

What does it mean by sexual selection is therefore rooted in the ability to access mating partners?

Answer 11

the advantages that certain individuals have over others in exclusive relation to reproduction.

Question 12

What can sexual selection being rooted also explain?

Answer 12

It can be used to explain the evolution of secondary sexual traits both morphological and/or behavioral

Question 13

What does sexual selection not relate to?

Answer 13

It does not relate to access to resources - just to mating partners

Question 14

What does sexual selection generate?

Answer 14

It generates variation in reproductive success

Question 15

The sexual selection of a certain trait, and its retention during evolution refers to a?

Answer 15

“heritable difference in mating success caused by competition for access to mating partners in expression of that trait”

Question 16

Give an example of a sexual selection of a certain trait

Answer 16

individual may have some physiological trait that means it is less prone to disease - this will be passed on leading to better survival of offspring.

This generates variations in survival rate

Question 17

How does Reproductive investment result in sexual selection?

Answer 17

Differences in types of investments (I.e. various parental roles, different behavioural responses, groupings and territorial activities) put into reproduction, therefore results in sexual selection.

Question 18

Define intra-sexual selection in relation to competition

Answer 18

Male-male competition

Question 19

Define inter-sexual selection in relation to competition

Answer 19

female choice

Question 20

What does intra-sexual selection involve?

Answer 20

Males can acquire females directly by competing with other males using display, aggression or fighting

There is selective pressure to evolve features associated with this (e.g. the antlers and roaring - enlarged larynx - of a mature red deer stag, or the size and roaring of a mature fur seal bull)

Males can acquire females indirectly via the acquisition and defence of a territory.

Territory is defended using physical presence, scent marking or vocalisation also advertising the territory to females (e.g. scent glands for sternal gland marking by male mandrills).

Question 21

What are the odour signals in scent-marking in mandrills?

Answer 21

Odour signals sex, age, rank, identity and genetic quality (“opposites attract”) in mandrills.

Question 22

What does inter-sexual selection involve?

Answer 22

Females select males on the basis of courtship displays

In males there is selective pressure on the evolution of signals

• Bright colours and distinctive patterns
• Exaggerated ornamentation behaviours

Question 23

How do courtship displays work?

Answer 23

Displays are energetically costly - they are long and complex to reduce the opportunity for subordinate males to pretend to be fit.

Complex displays allow the female to identify fit males

Question 24

What are the most colourful primates?

Answer 24

Mandrills are the most colourful primates

Question 25

List different mating preferences and behavioural mechanisms?

Answer 25

Fisherian or Fisher’s runaway effect

Inter-sexual selection results from indicator mechanisms (Secondary sexual characteristics) and resultant mate choice.

Question 26

Explain Fisher’s Runaway effect?

Answer 26

Genetic, sexual selection mechanism for the evolution of exaggerated male ornamentation observed in numerous species which produce offspring through sexual reproduction; based upon female choice, the preference or attraction of females for ornamented male mates.

Question 27

Female preference for exaggerated ornamentation in mate selection should be enough to undermine?

Answer 27

natural selection (if the ornament under sexual selection is otherwise non-adaptive)

Question 28

What does female preference result in?

Answer 28

This results in the next generation’s male offspring being more likely to possess the ornament and female offspring more likely to possess the preference for the ornament than the previous generation

Question 29

Over subsequent generations this leads to the runaway selection via?

Answer 29

a positive feedback mechanism for males who possess the most exaggerated ornaments.

Question 30

What is the result of females preferring long tails and mate with longer-tailed males?

Answer 30

Over time the population consists of long-tailed males and females with a long-tailed preference and therefore sexual dimorphism

Question 31

What do other alternative hypothesis differ in?

Answer 31

Several alternative hypotheses use the Same genetic runaway (or positive feedback) mechanism But differ in the mechanisms of the initiation

Question 32

What does the sexy sons hypothesis suggest?

Answer 32

suggests that females that choose desirably ornamented males will have desirably ornamented (or sexy) sons, and that the effect of that behaviour on spreading the female’s genes through subsequent generations may outweigh other factors such as the level of parental investment by the father

Question 33

What other hypothesis for the evolution of male ornamentation include?

Answer 33

The sensory bias hypothesis, the compatibility hypothesis And The handicap principle

Question 34

What does indicator hypotheses suggest?

Answer 34

that females choose desirably ornamentedmales because the cost of producing the desirable ornaments is indicativeOf good genes by way of the individual’s vigour

Question 35

What are the aspects of the Sexy son hypothesis?

Answer 35

Females acquire a preference for a particular shape, size and colour

Males are preferentially selected by females on the basis of exaggerating these traits

The male offspring of a ‘sexy’ father will inherit his sexy genes

The male offspring will therefore in turn be more likely to acquire mates

Question 36

What are the aspects of the Handicap Principle?

Answer 36

Females acquire a preference for a particular shape, size and colour and males are preferentially selected by females on the basis of exaggerating these traits

These traits slow the animal down (i.e. size) or make the animal high visible to predators (i.ie colour).

Only the fittest males can survive under these handicaps

Exaggerated characteristics in a survivor are therefore a measure of the high genetic quality of a potential mate or luck!

Question 37

What are the costs and benefits of exaggeration?

Answer 37

With both the Sexy Son Hypothesis and the Handicap principle there is directional evolutionary pressure for males to continue exaggerating their morphology and behaviour until costs outweigh benefits.

There is therefore a “ceiling on exaggeration

Question 38

What is good gene hypothesis?

Answer 38

Some of the genes which enable males to develop impressive ornaments or fighting ability may be correlated with fitness markers (e.g. disease resistance or more efficient metabolism).

Question 39

What is the pluralist process?

Answer 39

Range of views on the development of inter-sexual selection

Non longer seen as a unique process - various processes acting in combination in the evolution of traits and preferences

Question 40

How come Sexual selection mostly effect males?

Answer 40

Females: Limited number of offspring, Only conceive when not pregnant or lactating, plenty of males around to mate with

Males: Almost no limit, Can mate any time, compete for access to limited chances to sire offspring.

Question 41

Define Sexual dimorphism

Answer 41

Sexual dimorphism is the discrepancy in various physiologies between the sexes observed in a number of animal species

Question 42

What is Sexual dimorphism involved in?

Answer 42

Morphology and Signalling

Question 43

Explain sexual dimorphism in morphology?

Answer 43

Body size, Canine size, Testes size, Other morphologies

Question 44

How does sexual dimorphism differ in males and females?

Answer 44

In many animal species adult males are larger than adult females (body size), but also sexual dimorphism in size of canines and testes

Question 45

Explain sexual dimorphism in signalling?

Answer 45

Pelage and skin colour, Glands, Vocalisation

Signalling may include pelage and skin colouration, scent making and vocalisations

• Signals are thought to indicate dominance rank, and possibly condition of the individual
• They are used in male-male competition and mate competition

Question 46

Explain the Sexual dimorphism effects on male morphology: Body size

Answer 46

Species that exhibit the most extreme body size dimorphism = species that live in polygynous and MMMF groups.
-Male-male competition for either monopoly over females, or greater access to females, is thought to females, is thought to have selected for this dimorphism

Human males are -20% larger than females, which in addition to testes size, suggests we may have evolved in MMMF groups.

Question 47

Explain the Sexual dimorphism effects on male morphology: Canine size

Answer 47

Sexual dimorphism in canine size varies widely across primate species

Mating systems have important implications

• Yet constraints on this relationship exist
• Importance may vary within species

The role of other influences

• Primate diet
• Predator defence
• Allometric link to body size

Question 48

Post-copulatory sexual selection: Explain Cryptic female choice

Answer 48

“Females store sperm, they eject sperm, they destroy sperm and they carefully and precisely select the most genetically compatible sperm for them[selves] with their amazing genitalia”

Question 49

Post-copulatory sexual selection: Explain sperm competition

Answer 49

Females have a range of possibilities enabling them to choose between received sperm (Cryptic female choice)

• Ejecting sperm after mating
• Sperm choice in the female genital tract
• Choice by egg (involving spontaneous abortion and resorption or early-stage embryonic growth)
• Selective infanticide
• After mating numerous sperm compete inside the female genital tract for fertilisation

Male adaptations:

• Sperm proteins that outcompete the sperm of other males
• Copulatory organs shaped by sperm competition

Question 50

Post-copulatory sexual selection: How are testes involved?

Answer 50

Sperm and testosterone production

Size variation correlates with body size and mating system

Question 51

Post-copulatory sexual selection: When is Penis complexity greater?

Answer 51

Penis complexity is greater in systems such as MMMF and smaller in monogamous and polygamous societies

Question 52

List this External morphology for female morphology?

Answer 52

Clitoris
Mammary glands
Sexual swellings

Question 53

List the parts of sexual swellings

Answer 53

Signal probability of ovulation

Females favour more dominant males around ovulation

Mates compete more, so dominant males sire more

Swelling size = female quality