Flashcards in Reproduction Deck (119):
What are the 2 types of selection?
1. Natural selection
2. Sexual selection
What are the 2 categoriess of sexual selection?
1. Inter-sexual selection
2. Intra-sexual selection
What is inter-sexual selection?
Female choice, selection of fitness-dependent traits in males
What is intra-sexual selection?
What are the 3 dimensions of social structure?
1. Grouping system, who lives with who
2. Mating system, who mates with who
3. Breeding system, who has babies with who
Are the grouping, mating and breeding systems always the same?
No, e.g. not all copulation leads to offspring
Which dimension of the social system is the most important?
The breeding system (in evolutionary terms)
There are 4 main mating systems. What is monogamy?
There are 4 main mating systems. What is polygyny?
One male mates with multiple females, controls a harem.
There are 4 main mating systems. What is polygynandry?
When multiple males mate with multiple females and vice versa (err'body doin it wit err'body else)
There are 4 main mating systems. What is polyandry?
When one female mates with multiple males.
In monogamous systems, there is drastic sexual dimorphism. True or false? Why, why not?
False: there is very little sexual dimorphism. For example both animals would be of similar size.
This is because the male and female do not need to compete with others for access to their mate.
In monogamous systems, males exhibit more paternal care. True or false?
In polygynous systems, males are much larger than females. Why?
They face somatic competition with each other for access to females.
What is somatic competition?
Competition based on physical attributes like body or teeth size. Usually males must enter physical combat for access to females and thus bigger is better.
In polygynandrous systems, males are slightly larger than females. Why?
Because every one gets to mate with multiple partners (instead of one male monopolising all the females as in a polygynous system) there is less competition, however it is likely that bigger males will get to mate with MORE partners. So there is still a slight advantage of being a bigger male.
In polyandrous systems, males are bigger than females. True or false?
False: females are bigger than males. This is because there is competition between females for access to males (reverse of polygyny)
In polyandrous systems there are multiple males. Who sires the offspring?
Males take turns fathering 'batches' or sometimes there are mixed paternity batches of offspring.
How do mixed paternity batches of offspring arise?
From mating with multiple partners in quick succession, ejaculate can be stored, form of cryptic female choice
Females display ano-genital swellings around their ovulatory periods. There are multiple theories for this, the most common being?...
That it incites intra-sexual selection, i.e. competition between males. The males fight and the female will mate with whichever one prevails.
Thus female ano-genital swellings are generally only observed in which mating system?
Why don't female ano-genital swellings appear in monogamous/polygynous systems?
In monogamous systems there is no competition between males.
In polygynous systems competition between males is determined by male somatic competition.
Female ano-genital swellings are sometimes observed in polyandrous systems. Why might this be?
Females compete for access to males, ano-genital swellings could be a fitness-dependent trait indicating quality.
Non-human primates tend to prefer older females. Why?
There is increased likelihood that a baby will survive with a multiparous female (one that has had multiple babies) than with a primiparous/nulliparous one (one baby or no babies).
In monogamous primates, the testes are considered 'medium' relative to body size. Why?
Because there is some competition: although animals are in male-female pairs, the small group size means there is increased proximity of mating pairs as they require less space. Thus there is some likelihood of extra-pair copulation across the shared territory.
The testes of polgynous primates are very small. Why? Give 2 reasons.
1. Males face somatic not genital competition: the male gains his females due to size/power and does not need large genitals as after he has secured females there is no competition to mate with them.
2. Polygynous systems are organised into harems. This larger group size means that a larger territory is needed, thus harems are spatially segregated across a landscape, reducing the likelihood of extra-group copulation.
Why are the testes of polygynandrous and polyandrous animals large?
Males within these two mating systems face sperm competition as many males are mating with the same female.
What is the advantage of having bigger testes?
The larger the testes the more sperm produced, thus the chance of your sperm achieving conception is increased.
What is the term for this kind of selection that affects the size of the testes?
What is cryptic female choice?
Sexual selection within the genital tract of the female, whereby the sperm of particular males is chosen over others' e.g. store of ejaculate etc.
What are the 4 dimensions of sexual selection?
1. Somatic selection, e.g. male-male competition
2. Genital competition
3. Sperm competition
4. Cryptic female choice
The coitus of both monogamous and polygynous primates is long in duration. Why?
Because there is no competition, the male can take his time.
The coitus of both polygynandrous and polyandrous primates is short in duration. Why?
Because there is lots of competition for mates, males need to be quick.
Where are gibbons from?
How do gibbons move?
They are the only true brachiators and are fully arboreal.
What is the basic mating system of gibbons according to textbooks? What evidence is there for this?
Monogamous: there is no sexual dimorphism, for example the skulls of both species are exactly the same.
Is it always true that gibbons are monogamous?
Gibbons of the same species can be different colours. This is based on their biological sex. True or false?
False: Lar gibbons can be either black or white and this has no correlation to sex.
Gibbons have a throat sac. What is this for?
Amplification of their voices as they sing to each other.
What are 2 contrasting theories as to why gibbons sing?
1. Textbook monogamy hypothesis: they are singing for pair-bonding
2. Research suggests: the female is advertising her own quality or the lack of quality in her mate
Is there a difference in body size between male and female gibbons?
No, indicating monogamy
Do female gibbons display ano-genital swellings?
Sometimes, indicating monogamy is not always true as swelling incite intra-sexual selection
What is the testes size of male gibbons and what does this show?
Medium, indicating that monogamy is not always true in which case they would be small. There must be mate competition.
Is coitus duration long or short in gibbons?
Long, indicating monogamy
What is a typical orangutan 'unit', i.e. the group you would find in the wild?
A lone mother and baby, or a lone male.
Why is it hypothesised that orangutans are solitary? Refer to their diet.
Orangutans rely on ripe fruit for high energy. Ripe fruit is fairly rare so it is better if they travel alone as this reduces resource competition.
Some male orangutans have throat sacs and cheek flanges whilst others do not. Why is this?
They are fitness-dependent traits. That means only the best males can produce them and they are an 'honest indicator' of quality.
Are male cheek flanges in orangutans equivalent to female ano-genital swellings of other primates? Why, why not?
Yes, they are both fitness-dependent traits
What are arrested male orangutans?
Males that have not developed cheek flanges.
Can arrested males ever develop cheek flanges?
Yes: generally they do not develop when a bigger, more dominant male is in the vicinity. If he disappears, cheek flanges can develop in arrested males.
Why is it advantageous for arrested males not to have cheek flanges?
They look much like females and the dominant male will not try and fight them.
Mating between females and arrested males is often termed rape, as females protest. Give 3 theories as to why they might protest.
1. They do not want to mate with arrested males because they are not of the highest genetic quality
2. In theory they may actually protest to mating with the dominant male but they know they cannot overpower him
3. They are trying to test the arrested male's dominance
In which position do orangutans usually mate?
What is placentophagia?
When the mother eats the placenta, this is very common in orangutans.
Give 3 theories for why placentophagia happens.
2. Can stimulate maternal behaviours
3. Removes traces of the baby, method of predator evasion
Is there a difference in body size between male and female orangutans?
Yes: the female is roughly 1/2 the size of the male.
Do female orangutans display ano-genital swellings?
What is the size of the testes in male orangutans?
What does the dimorphism in body size, lack of female ano-genital swelling and small testes of male orang-utans indicate about their breeding system?
It is polygynous: males face somatic competition but not genital/sperm competition.
If orangutans are polygynous, what can be said about the duration of coitus?
It is long, up to 10mins
Orangutans are polygynous but do not live in close-proximity harems. What is their breeding system called?
Dispersed polygyny, males will move between females across the whole territory as they are all ovulating at different times.
Do gibbons have overlapping home-ranges?
Yes, which is why extra-pair copulations are common.
Male orangutans call to each other. Why?
To warn off other males and communicate with females.
Is there sexual dimorphism in gorillas?
Yes, drastic sexual dimorphism.
How much smaller is the female gorilla than the male.
She is usually 1/2 his size. Males are very large and face somatic competition.
Generally, according to textbooks, what is the grouping system of gorillas?
A single dominant male with a harem of females.
What kind of diet do gorillas have?
They are folivorous.
What is the fitness-dependent trait in gorillas that indicates male quality?
Chest-drumming: males bang their chests as an indictaor of physical size. Larger males sound different to smaller males and thus are preferred.
Do female gorillas display ano-genital swelling?
Are male gorillas' testes large or small?
Is coitus duration long or short in gorillas?
Gorillas are polgynous. What 5 features of gorillas indicate this?
1. Huge sexual dimorphism
2. Males display fitness-dependent traits
3. Female gorillas do not show ano-genital swelling
4. Male gorillas have small testes
5. Coitus is long
In gorilla harems the males control the females and they cannot leave. True or false?
False: female gorillas can change harem if they wish. The male simply monopolises the females but doesn't control them, which is fairly unique.
The gorilla is the largest living primate. What can be said of its penis?
It is 2cm long when erect (so tiny). This is because males face somatic not genital competition.
In what two positions do gorillas have sex?
Sibling jealousy in gorillas in manifest in weaning conflict. What does this mean?
The older sibling, perfectly independent, regresses to a state of helplessness for attention seeking. It may then attempt to wean when it no longer needs to, purely because the newer infant is doing it and thus monopolises the mother.
Traditionally gorillas are polgynous, however polygynandry has been observed. How does this happen?
The sons of the dominant male may stay in the group and begin to take over breeding as he ages.
Homosexual sex has been observed in gorillas. True or false?
True, in bachelor groups.
Female chimps and bonobos are the same size as males. True or false?
False: they are approximately 3/4 of the size.
What is a primate culture?
Different customs that stem from living in different locations.
Is there dimorphism between the sexes in chimp skulls?
Yes, slight dimorphism
Do female chimps/bonobos develop ano-genital swellings?
Yes, large ones
When do female chimps/bonobos develop ano-genital swellings?
When they are ovulating
What do a) tumescent and b) detumescent mean?
The ano-genital swellings of female chimps/bonobos are very slight and barely noticeable, similar to those of gorillas and humans. True or false?
False: they are fucking huge.
Why do chimps mate out of sight of other chimps?
Due to mate competition.
Are the testes of chimps large or small in comparison to body size?
V. large, almost as big as their brains.
What can be said of the chimp's penis?
It is v. long in relation to body size and pointed, this facilitates sperm deposition as there is much competition
List 2 adaptations of a chimp's penis for sperm competition.
1. Long so can deposit sperm further inside the female
2. Penile spines: upon withdrawal of the penis it rakes out the ejaculate of other males.
Female chimps mate in quick succession with multiple males. Give 2 features of the males' sexual anatomy that are equipped for sperm competition.
1. Large testes: produces more sperm, increasing likelihood of fertilisation
2. Specialised penis: deposits sperm further inside the female and scrapes out that of competitors
Copulation is tiring for male chimps and they must rest after. Why?
Because their large testes become depleted.
Is coitus duration long or short in chimps?
Short, approx. 7 seconds, as there is much competition
Chimps live in polygynandrous societies. Give 4 indicators of this.
1. Slight sexual dimorphism
2. Ano-genital swelling of females
3. Large testes
4. Short coitus
All these indicate competition.
What do you call the groups that chimps live in?
How many individuals in a chimp community?
Chimp communities are always fixed. True or false?
False: they are dispersed and do not form a cohesive group at any given time.
What is a party?
A group of 4-5 individuals from the community that go around together.
Parties undergo regular fission-fusion. What does this mean?
Groups regularly split and reform into new groups.
In a chimp community females tend to stay apart. True or false?
Male chimps patrol the edges of the community and defend them, often leading to 'chimp wars'. Has this been observed in bonobos?
In all primate societies there are assortative (preferred) relationships, either affiliative or aggressive, due to differing personalities. True or false?
What is the ancestral mating system of humans? Why?
Females display slight ano-genital swellings
The testes of males are small
Coitus duration is long
These all indicate a lack of competition for males.
There is evidence of all 4 mating systems in human cultures. True or false?
Mating systems vary based on environmental conditions. True or false?
Among humans, we should always respect a behaviour that is 'natural'. True or false?
False, for example infanticide is natural but we should not support that in our own kind. Ethics must be considered.
Mating systems have 'environmental plasticity' which gives them flexibility. This is advantageous as we can adapt. The environment is full of phylogenetic inertia and constraints. What does this mean?
Inertia = conditions with no phylogenetic effects
Constraints = limiting conditions which may induce change
Basically our environments are full of stuff that make a difference or don't.
If the ancestral breeding system of humans was polygyny, why is sexual dimorphism so slight?
It is thought to be derived due to the Napoleon Effect. Humans are incredibly intelligent and face intellectual competition. Often the smarter male will gain access to females regardless of body size. For example he can produce tools to secure food.
What 4 factors can indicate the breeding system of primates?
1. Sexual dimorphism of body size
2. Ano-genital swellings in females
3. Testes size of males
4. Coitus duration
Gorillas are a textbook example of polygyny, but this is often not the case. What percentage of wild groups have been found to be polygynandrous?
Gibbons are a textbook example of monogamy, but this is often not the case. What percentage of wild groups have been found to be polygynandrous and where are they found?
2-3% in Khao Yai, Thailand
Gibbons are a textbook example of monogamy, but this is often not the case. What percentage of wild groups have been found to be polyandrous groups?
Gibbons are a textbook example of monogamy, but this is often not the case. What percentage of wild groups have been found to be polygynous?
Gibbons are a textbook example of monogamy.. What percentage of wild groups have been found to be monogamous?
In gibbons the two most common breeding systems are...?
Monogamy and polyandry
It is common for chimps to produce twins. True or false?
False; it is extremely rare
In egalitarian human society which breeding system is the common?
Monogamy, no monopoly of mates, everyone gets a chance
Where is it common to observe polygyny in humans?
Mormons in Utah, the U.S.
Where is it common to observe polygynandry in humans
In Southern India, the Nair people