Sexual selection lecture 8 part 1 Flashcards
What is Sexual selection?
Sexual selection equates to genetic selection acting via competition for mates (Not resources)
What is shaped by sexual selection?
Much that is fundamental about morphology, physiology and behaviour is shaped by sexual selection
Define intra-sexual selection
Selection within the sexes
Define inter-sexual selection
Selection between the sexes
What aspect do species have to have for sexual selection to be involved?
Sexual selection can only exist in species with sexual reproduction
What differs in male and female gametes?
The only universal criterion is that males have small, generally mobile gametes (sperm) and females have large, generally immobile gametes (Ova).
What are females choosy with?
Females are choosy in terms of looking for highest quality mates
What does discrimination not necessarily imply?
Discrimination does not necessarily imply more elaborate cognitive abilities, just an attraction for certain traits!
What is the difference between male and female sexual selection?
Females are choosy in terms of looking for highest quality mates
while
Males look to maximise matings and are likely to be less selective
What are the effects of female choice?
generate an important selection pressure for the evolution of male traits, whereas males do not have such an impact on selection pressure.
What does it mean by sexual selection is therefore rooted in the ability to access mating partners?
the advantages that certain individuals have over others in exclusive relation to reproduction.
What can sexual selection being rooted also explain?
It can be used to explain the evolution of secondary sexual traits both morphological and/or behavioral
What does sexual selection not relate to?
It does not relate to access to resources - just to mating partners
What does sexual selection generate?
It generates variation in reproductive success
The sexual selection of a certain trait, and its retention during evolution refers to a?
“heritable difference in mating success caused by competition for access to mating partners in expression of that trait”
Give an example of a sexual selection of a certain trait
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
How does Reproductive investment result in sexual selection?
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.
Define intra-sexual selection in relation to competition
Male-male competition
Define inter-sexual selection in relation to competition
female choice
What does intra-sexual selection involve?
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).
What are the odour signals in scent-marking in mandrills?
Odour signals sex, age, rank, identity and genetic quality (“opposites attract”) in mandrills.
What does inter-sexual selection involve?
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
How do courtship displays work?
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
What are the most colourful primates?
Mandrills are the most colourful primates
List different mating preferences and behavioural mechanisms?
Fisherian or Fisher’s runaway effect
Inter-sexual selection results from indicator mechanisms (Secondary sexual characteristics) and resultant mate choice.
Explain Fisher’s Runaway effect?
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.
Female preference for exaggerated ornamentation in mate selection should be enough to undermine?
natural selection (if the ornament under sexual selection is otherwise non-adaptive)
What does female preference result in?
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
Over subsequent generations this leads to the runaway selection via?
a positive feedback mechanism for males who possess the most exaggerated ornaments.
What is the result of females preferring long tails and mate with longer-tailed males?
Over time the population consists of long-tailed males and females with a long-tailed preference and therefore sexual dimorphism
What do other alternative hypothesis differ in?
Several alternative hypotheses use the Same genetic runaway (or positive feedback) mechanism But differ in the mechanisms of the initiation
What does the sexy sons hypothesis suggest?
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
What other hypothesis for the evolution of male ornamentation include?
The sensory bias hypothesis, the compatibility hypothesis And The handicap principle
What does indicator hypotheses suggest?
that females choose desirably ornamentedmales because the cost of producing the desirable ornaments is indicativeOf good genes by way of the individual’s vigour
What are the aspects of the Sexy son hypothesis?
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
What are the aspects of the Handicap Principle?
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!
What are the costs and benefits of exaggeration?
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
What is good gene hypothesis?
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).
What is the pluralist process?
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
How come Sexual selection mostly effect males?
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.
Define Sexual dimorphism
Sexual dimorphism is the discrepancy in various physiologies between the sexes observed in a number of animal species
What is Sexual dimorphism involved in?
Morphology and Signalling
Explain sexual dimorphism in morphology?
Body size, Canine size, Testes size, Other morphologies
How does sexual dimorphism differ in males and females?
In many animal species adult males are larger than adult females (body size), but also sexual dimorphism in size of canines and testes
Explain sexual dimorphism in signalling?
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
Explain the Sexual dimorphism effects on male morphology: Body size
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.
Explain the Sexual dimorphism effects on male morphology: Canine size
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
Post-copulatory sexual selection: Explain Cryptic female choice
“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”
Post-copulatory sexual selection: Explain sperm competition
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
Post-copulatory sexual selection: How are testes involved?
Sperm and testosterone production
Size variation correlates with body size and mating system
Post-copulatory sexual selection: When is Penis complexity greater?
Penis complexity is greater in systems such as MMMF and smaller in monogamous and polygamous societies
List this External morphology for female morphology?
Clitoris
Mammary glands
Sexual swellings
List the parts of sexual swellings
Signal probability of ovulation
Females favour more dominant males around ovulation
Mates compete more, so dominant males sire more
Swelling size = female quality
