Sexual Behaviour Flashcards
What is important to know when studying reproductive biology?
When studying reproductive biology it’s important to know that due to each sexes respective differences in biology the reproductive interests of males and females are often at odds
What are the usual sex ratios in species?
Usually at any given time there are more males available than females
What does the sex ratio depend on?
This depends on the species
What is the main biological difference between males and females
The key biological difference between males and females is that game production varies greatly between the sexes
For males gametogenesis is energetically cheap and usually continuos in males
Males also do no/little for the offspring usually
For females gametogenesis is energetically costly and rare in females
Caring of offspring is usually a key aspect of female reproductive behaviour
What is the difference between the sexes in terms of offspring production?
Females are genetically limited in how many offspring they can produce and nurture compared to males
What determines what an animal needs to do to gain sexual access to conspecifics?
Mating systems determine what an animal needs to do to gain sexual access to conspecifics
Species differences in background, biology and social systems affect an individual’s chances of mating
In vertebrates with only 2 sexes there’s 4 different mating systems they could use, what are they?
1) Promiscuity
2) Polygyny
3) Polyandry
4) Monogamy
In vertebrates with only 2 sexes there’s 4 different mating systems they could use, what are they?
1) Promiscuity
2) Polygyny
3) Polyandry
4) Monogamy
What determines which mating systems a species will use?
Which mating system is used depends on how many sexual partners each of the sexes may have
Describe the promiscuity mating system
The promiscuity mating system is used when there are a lot of females and a lot of males available
There are no stable pair bonds
Every individual mates with multiple partners regardless of their sex
In terms of behaviour either 1 or both sexes will search for mates
Females are generally more picky than males in most species
Give examples of what kinds of animals use promiscuity mating systems
Carnivores
Rodents
Primates
Give an example of an exception to the rule that carnivores use the promiscuity mating system
Wolves are an example of an exception to the promiscuity system as wolves use the Polygyny mating system
Describe the monogamy mating system
This is where strong pair bonds form between individuals
Monogamy is rare
Monogamy is a mating system where parental care and paternal care are the most common
Monogamy is a mating system where both sexes are very choosy about who they pair with
Give some examples of monogamy
Some rodents species
Some humans
Many bird species
What is social monogamy?
Social monogamy refers to a male and female’s social living arrangement without inferring any sexual interactions or reproductive patterns
What kind of animals are the exception to monogamous mating systems?
Harm holders are examples of exceptions to the monogamy mating system
Describe the Polygyny mating system
Polygyny is a mating system that creates a harem consisting of 1 male and multiple females
Males get access to females by defeating other males
Females can still choose their mates however it’s less direct than in monogamous and promiscuous mating systems
Give examples of animals that use the Polygyny mating system
Wolves
Ungulates
Most domesticated species use Polygyny as a mating system
Describe Polyandry
Polyandry is a mating system that creates a harem consisting of 1 female and multiple males
Polyandry is a rare form of mating system with only a few species using it
Sexual behaviour is linked to what 2 phases?
1) Appetitive phase
2) Consummatory phase
What does the appetitive phase focus on?
The appetitive phase focuses on all the behaviours associated with gaining access to the other sex
What does the consummatory phase focus on?
The consummatory phase focuses on all the behaviours during the actual mating
The appetitive phase can be broken down into 3 sub-phases, what are they?
1) Mate search
2) Attraction
3) Proceptive behaviour
Mate search is a sub-phases of the appetitive phase and is only seen in what kinds of animals?
Mate search is an extra phase seen in species that are solitary and/or promiscuous
Describe what happens in the appetitive sub-phase, attraction
Attraction focused on any behaviours where the individual emits a stimuli and performance behaviour to attract any individual of the opposite sex
These are species specific behaviours
What are the the kinds of behaviours seen in the appetitive sub-phase Proceptive behaviour?
Proceptive behaviours are behaviours done in the context of sexual behaviour known as courtship behaviour
Where are courtship displays done?
Courtship behaviours are given/done to a specific individual in their immediate vicinity
What do proceptive behaviours do?
Proceptive behaviours will:
- promote sexual interactions
- advertise readiness to mate
Are Proceptive behaviours species specific?
Proceptive behaviours are usually species specific
True or false
Some species have sensory modalities that are capable of sending proceptive behaviour signals over vast distances and to detect them
True
Scent marking and pheromones are examples of this in certain situations
Proceptive behaviours that are courtship behaviours are behaviours between what?
Proceptive behaviours that are courtship behaviours are behaviours between a pair of individuals from opposite sexes
Give examples of Proceptive behaviours that are courtship behaviours between a pair of individuals from opposite sexes
They’re typically seen in species where females choose their partners
Proceptive behaviours that are courtship behaviours tend to be vocalisations or another display of readiness to mate and why they’re the best option
Many examples can be seen in birds like in the birds of paradise
In rodents females will perform an ear wiggle to keep a male nearby and release pheromones
Some mice also sing to females, serenading them in ultrasound with specific songs that are only used in courtship displays
In polygynous species the courtship behaviour can be more subtle
During the consummatory phase of sexual behaviour there will be receptive behaviours
What are receptive behaviours?
Receptive behaviours are specific postures and signals letting the other individual know that they’re ready to mate
In species with internal fertilisation what follows after the receptive behaviours of the consummatory phase of sexual behaviour?
In species with internal fertilisation there will also be male intromission (penetration) and ejaculation
This is typically followed by a refractory period of low sexual motivation
There sometimes needs to be a lot of coordination between male and female to safely and successfully copulate
What is the motivational state underlying the consummatory behaviours called?
Libido
What 2 internal factors are causal explanations of sexual behaviour?
1) Hormones
2) Neurotransmitters
What 2 external factors are causal explanations of sexual behaviour?
1) Things that affect general abilities to become sexually motivated
2) Things that are necessary to trigger bouts of courtship and mating
An internal causal factor is the activational effects of testosterone may be needed for males of some species
Explain how this works?
Testosterone is needed in some species for the male to display the sexual behaviour
Activational effects are things that tend to either increase or decrease the probability of a behaviour being expressed
Give examples of neurotransmitters that act as internal causal factors for sexual behaviour
Oxytocin
Vasopressin
There are also ‘enabling’ internal causal factors, explain what they are
The enabling internal factors are not by themselves essential for sexual behaviour but they contribute to sexual behaviour occurring
Enabling internal factors are general factors that allow the individual to become sexually motivated
Give 3 examples of enabling internal causal factors
1) Good health
- Health problems can cause pain that reduces sexual motivation
2) Low adiposity
- Excess or insufficient fat often reduces:
- sex hormones
- sexual motivation
- fertility
3) Low stress
- Acute and chronic stress reduces sexual motivation in both sexes
- Stress can interfere with testosterone release
- Stress can interfere with normal female menstral cycling
Give examples of external factors affecting general abilities of an individual to become sexually motivated
1) Season
2) Social environment
3) sensory perception cues
How is season an external causal factor affecting general abilities of an individual to become sexually motivated?
Many species only mate once a year
When they mate is timed for optimal infant survival
In some species seasonal effects are reduced due to domestication
Seasonal cue examples are altered photoperiods
Photoperiod = the period of time each day during which an organism receives illumination; day length
How is social environment an external causal factor?
The social environment is where cues from the other sex elicit the sexual motivation
Specific cues from the other sex induce sexual motivation
Examples of this are:
Courtship behaviours
Whitten effect
What is the Whitten effect?
The Whitten effect is where the mere presence of a male induces estrous in females
Give some example of sensory perceptive cues that act as external causal factors
Olfactory cues
Pheromones
Auditory cues
Specific vocalisations
Tactile cues
In many species genital contact between male and female is necessary to elicit receptive postures
Visual cues
Some species have visual signals associated with estrous and also specific postures
Social environment is another example
Novelty effects
These are new things that may trigger sexual behaviour
A new individual can also do this
Explain how puberty effects sexual behaviour
In both sexes hormonal changes at puberty result in the onset of sexual behaviour
The hormonal changes cause activational effects
The hormonal changes during puberty lead to morphological and behavioural changes happening after hormonal changes
The timing of these changes will vary between species
The timing of these changes depends on many factors, both social and asocial
Give examples of morphological and behavioural changes following hormonal changes in puberty
Development of secondary sex characteristics so they become more attractive to the opposite sex
Changes in olfactory cues
Changes in social and sexual behaviour
In adulthood animal preferences for mate selection change and are usually what?
Males often prefer younger females
Females often prefer older males
There are also changes in sexual behaviour in late adulthood, what are they?
Both sexes show a decline in sexual behaviours with age, which is associated with the reduction in sex hormones
Females generally decline in sexual activity earlier than males
True or false
Only mammals show a true menopause
False
Only humans show a true menopause
Menopause = the ceasing of menstration
This means that only humans have a set time where females completely stop producing ova
In other animals reproductive function works but declined with age
Effects of early experiences on later adult sexual behaviour can be seen in what 3 types of changes?
1) Organizational effects of hormones
2) Lasting effects of early stress and/or malnutrition
Suffering from stress or malnutrition in early life can compromise later on adult sexual behaviour
3) Imprinting and socialisation
Imprinting and socialisation is done via learning about conspecifics in infancy
Give some examples of how lasting effects of early stress and/or malnutrition can affect sexual behaviour
Prenatal stress can interfere with prenatal and neonatal testosterone surges and demasculinize males
In birds the stress can affect male bird early brain development
Some birds have a specific structure in their brains called the song nuclei which is devoted to singing
Some negative developmental effects can compromise brain development causing the song nuclei to shrink or become dysfunctional in some way
Due to this when those birds with the poorly developed song nuclei become adults they won’t be able to sing properly and so can’t attract a mate
Sex differences in the males ability to sing are caused by sex differences in the forebrain's song nuclei The sex differences become established at the time of hatching Due to this early experiences effect adult sexual behaviour in birds Good early nutrition and low stress are important for male birds to develop good singing abilities Poor songs are typically unattractive to female birds
Explain what sexual imprinting is and it’s adaptive value
Sexual imprinting is the rapid learning of cues associated with adults of the opposite sex of your own species
Sexual imprinting has the adaptive functions of:
- training species recognition into animals
- avoiding inbreeding
What are the 2 types of functional explanations and explain what they mean?
Proximate functions
Proximate functions are functions that benefit/increase successful sexual behaviour and copulation
Ultimate functions
Ultimate functions are functions that benefit/increase adaptive fitness
In some species the act of copulation acts as a positive reinforcer for both species, explain how this happens?
In some species the act of copulation acts as a positive reinforcer for both sexes
This is because the act of sex feels good for both the individuals which means that they’re both likely to try again
Copulation is a powerful reinforcer for both sexes
This means that both sexes show very high motivation when causal factors are optimal
What does some evidence show about neurological pathways during and after sex?
Some evidence shows that all neurological pathways are stimulated during and after copulation are also stimulated:
- in humans during drug recreation
- associated with positive affective states
What is seen in a few rare species with non-oestruos females and explain why this is seen?
In a few rare species even non-oestruos females remain sexually motivated
This suggests that copulation must be pleasurable for those animals since there is no other biological reason to do so if the act has no chance to lead to pregnancy
Give some examples of animal species that engage in sexual behaviour even when the female is not in oestrus
Humans
Bonobos
Chimpanzees
Dolphins
Bottle-nosed dolphins are also known to do male-male copulationGive 2 examples that suggest that animals perform sexual behaviour to meet a need
In ferrets being in persistent estrous in the absence of mating is very dangerous for female ferrets
This is because the developed ovarian follicles will secrete a lot of oestrogen which will become toxic if oestrogen is at high concentrations for a long period of time
The excess oestrogen will cause the female ferrets fur to thin and bone marrow suppression
This means that the bone marrow will stop producing blood cells which can lead to anemia and infection
This means if female ferrets can’t mate during oestrus they can die from lack of copulation
In male rats it’s know that if they’re allowed to mate and then forced into a 4 week sexual abstinence they’ll:
- show signs of depression
- be more motivated to take recreational drugs offered to them
In sex-naïve virgin male rats of the same age they do not show the above signs
This shows that male rats need to have the experience first or they won’t suffer in a period of abstinence
What do the 2 examples of how animals perform sexual behaviour to meet a need tell us?
They show that copulation provides pleasure but is also done to satisfy internal built-in needs of the individual
Why might copulation be painful?
Copulation may also be necessary to induce ovulation in some species
In some species copulation is painful but necessary to induce ovulation
Copulation is necessary to induce ovulation in most carnivore species
Give an example of an animal where copulation is painful for the female but necessary for them to undergo ovulation
Cats
What is the Bruce effect?
The Bruce effect is where the mere presence of a male can induce termination of a pregnancy
True or false
Copulation in some species can also be used to induce termination of pregnancy
True
How might copulation also be done as a way of preventing other males from mating with the female?
This is because in some species the male will also ejaculate a substance to plug the females vagina to prevent other males fertilising the females ovum
This can be seen with ‘plugs’ in rodents
In other species the males penis has a feature that basically traps the penis inside the female for a set period of time
This is seen in candids with their copulatory ‘tie’
What is the ultimate function of sexual behaviour in terms of adaptive value?
The ultimate function of sexual behaviour in terms of adaptive value are not just to produce offspring but also to produce successful offspring who themselves produce lots of offspring
Why is the adaptive value of sexual behaviour especially important to females?
1) Females produce fewer gametes
For a female any conception represents a large percentage of their total maximum lifetime reproductive output
For a male any conception represents just a small percentage of their maximum total lifetime reproductive output
2) Females invest more in rearing offspring usually
The ratio of reproductively available males to reproductively available females is very male-biased
Due to this males are in competition with other males while females can be choosy
What is the ratio of reproductively available males to reproductively available females known as?
Operational sex ratio
The ratio of reproductively available males to reproductively available females is known as the operational sex ratio
True or false
The operational sex ratio is always female biased
False
The operational sex ratio is always male biased
How does a male skewed operational sex ratio alter male sexual behaviours?
For males their Proceptive behaviours has to be very persuasive since the female won’t just mate with anyone
Due to this, sexual behaviour should maximise a males chances of producing successful offspring, while minimising the chances that other males will be successful
Give some examples of adaptions to increase a males own reproductive success
Blocking the females vagina to prevent other males from copulating
Being able to unblock the females vagina to be able to copulate successfully
Produce larger ejaculate
Outcompete other males
How does a male-biased operational sex ratio affect female behaviour?
For females male skewed operational sex ratios mean that each copulation could lead to a big investment
Due to each copulation potentially leading to a big investment for the female it makes functional sense to be picky about who to mate with
Females can be picky because there’s a surplus of males ready and willing to mate with
What 4 things do females take into consideration when choosing a mate?
1) Inbreeding avoidance
2) Signs of a good ability to protect the female and provide resources
3) Signs of good genes to pass to their offspring
4) Female choice makes functional sense
How do some species females avoid inbreeding?
The smell of sweat can let you know how closely related you are to each other
The females will smell the sweat and choose the males with the histocompatibility complex that are most different from their own
In choosing males with different histocompatibility complexes to them the females increase genetic heterogeneity in their offsprings histocompatibility complexes
In doing so choosing a male with with different histocompatibility complexes will increase their offsprings immune protection from disease
Give examples of animals that can detect histocompatibility complex type via smell
Humans
In tests with humans if the female was on the pill then their ability to discriminate between histocompatibility complexes was lost
Mice
Give examples of sings of a good ability to protect the female and provide resources
Fighting ability
Good territories
Good ability to provide food
Dominance
Which mating system uses signs of a good ability to protect the female and provide resources?
Polygyny
Which mating system used signs of good genes to pass to their offspring as a female choice criteria?
Promiscuity
It is also used by females of polygynous and monogamous species as well in varying degrees
Give some examples of signs of good genes to pass to their offspring
Signs of good health and low parasite levels
Symmetry
Good songs in birds
Low anxiety
If a male with better signs of good genes is seen what do some species females do?
Some species females can do things to prevent pregnancy if a better male is seen
Examples of this are:
- Bruce effect
- Expelling sperm and/or plugs
In some species of animal females may copulate with many males to induce paternity uncertainty, why is that?
Paternity uncertainty is done so that the offspring have more males to protect them
In some species males will help the offspring if it’s there’s or kill it if it’s not their own infant to induce the female to go back into estrous
So female promiscuity is hypothesised to confuse males into being nice and not killing the females offspring
This is more common in social species
What do I mean by phylogenetic explanations of sexual behaviour?
A phylogenetic explanation will be about traits that confer success being more likely to be passed on leading to gradual changes along the branches of a family tree
The changes will be in terms of which specific behaviour and traits develop in that particular species
What was Darwin’s opinion on sexual characteristics?
Darwin actually did not like sexual behaviours and in particular Darwin did not like sexual characteristics that are used in courtship
This is because at the time Darwin saw the evolution of sexual characteristics as going against natural selection
Darwin actually wrote in his field journal that the sight of a peacock’s feathers made him feel sick
This is because some sexual characteristics like the peacock’s tail seem to increase the individuals risk of predation in Darwin’s view
Darwin was wrong about sexual behaviour due to the adaptive value of the sexual behaviour
What 2 things prove Darwin was wrong?
1) For a female any conception represents a large percentage of their total maximum lifetime reproductive output
Vice versa for males
Thus picky females will be fitter
2) The operational sex ratio is very male-biased
Thus attractive males and competitive males will be fitter
Sexual behaviour is a special form of natural selection known as what?
Sexual selection
Sexual behaviour is a special form of natural selection now referred to as sexual selection
What does sexual selection show?
Sexual selection shows us that there’s a differential fitness based on an individual’s ability to mate
Basically the fitness of an individual varies based on its ability to mate
What are the 2 different types of selective pressures on an individual in terms of sexual selection?
1) Intrasexual selection
Direct competition between members of 1 sex for mates
This is usually between competitions between males to gain access to females
2) Intersexual selection
Intersexual selection is driven by mate choice
This mainly focuses on differential attraction to particular characteristics in the opposite sex
Intersexual selection is usually driven by the females choosing
What is intrasexual selection about?
Intrasexual sexual selection is about the direct competition between members of 1 sex for mates
Intrasexual selection is where individuals directly compete with other members of their own sex to gain access to a mating opportunity
Intrasexual sexual selection pressures on males has led to what in males?
Males being larger than females
Males being better armed than females
Males being more aggressive than females
Males are especially more aggressive in breeding seasons
True or false
Intrasexual sexual selection also happens in females but is little understood
True
Which mating system is male-male aggression especially seen in?
Polygyny
What does harm-holding species mean?
Harm-holding = they’ve developed traits/characteristics to injure their opponent
What can non-harm-holding species males compete with?
Body size
Large testis
Faster swimming sperm
What 2 things can comparing the relative weight of an average male testes compared to the average male body weight give us an idea of?
1) The type of mating system used by that species
2) The intensity of male-male competition in that species
What is Intersexual selection driven by?
Intersexual selection is driven by mate choice
It’s usually the females picking which male they want
It’s usually the females driving Intersexual selection
What does intersexual selection focus on and how does it link to evolution?
Intersexual selection focuses on differential attraction to particular characteristics in the opposite sex
This means it’s the study of what in the opposite sex attracts an individual to them, and what about that trait/characteristic attracts the individual to it the most
This selection of 1 sex choosing the most desirable trait, and versions of that trait, in the opposite sex drives the evolution and development of that trait, and makes it spread throughout the species population
Give some examples of intersexual selection
Birds prefer elaborate ornaments and songs
In some species females pick a male based on their resources
Some females prefer males with age and status
