Ontogenesis Flashcards
What does precocial mean?
Precocial = young are independent and well-developed at birth
PREcocial = PRE-developed in de womb
What does altricial mean?
Altricial = young are helpless at birth and need more maternal care
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Do all species with altricial young carry them constantly?
No, some park their babies in a tree hole e.g. tarsier
What are the 2 nursing styles observed in primates?
- Nursing on demand
2. Nursing on schedule
When do young nurse on schedule?
If they have limited access to their mother, i.e. parked babies
What 3 nutrients are in mother’s milk and what are they for?
- Fat to burn for thermoregulation
- Protein for growth
- Sugar to meet energy demands
Which babies require more fat?
Altricial parked babies; they are not being carried and must await mother’s return for long periods, need to keep warm
Which babies need more protein?
Altricial non-parked babies: do not need as much fat or sugar as are carried by mother, focus on growth
Which babies need more sugar?
Precocial babies as they are running around after their mothers
Non-human ape babies nurse on demand. Do human babies?
No: social convention dictates they sleep separately from the mother and are fed on schedule
Why is it theorised that human babies cry?
Because they are supposed to be on-demand feeders and they are deprived of this due to social convention. This is described as a ‘forced shift in ontogeny’. Humans can adapt although there is a trade-off.
Why is it thought that SID happens?
Because human babies are left alone at night, potential trade-off for ontogeny shift.
Some female monkeys/apes have one nipple longer than the other. True or false?
True, theorised that this may correlate to infant feeding preference.
What is weaning conflict?
When the mother wishes to stop nursing an offspring and the offspring wishes to continue.
When does weaning conflict occur?
When the mother has a new infant that she needs to wean instead. This is a trade-off; a reduction of investment into the first infant in order to invest in the second
What happens to the older infant in weaning conflict?
It regresses to a more helpless state in an effort to gain attention from the mother
There are 2 reproductive strategies, r and K. What are they?
r = fast-breeding K = slow-breeding
Describe r strategy.
List 3 examples of r.
In an unpredictable environment there are seasonal fluctuations of population growth and breakdown correlating to resource availability. Organisms therefore must breed quickly when resources are abundant. As there are fewer organisms surviving, population growth is determined by intrinsic factors (r).
r = age of first repro, litter size, birth intervals
Describe K strategy.
In a predictable environment non-seasonality promotes stable populations and efficient resource use. Therefore population growth is determined by extrinsic factors like K, environmental carrying capacity.
Number of offspring is relative to reproductive strategy. True or false?
True.
If young are altricial, do parents have more or less?
Less because they each require more investment
If young are precocial, do parents have more or less?
More because they require less investment
r and K selection strategies cannot be changed. True or false?
False: humans have adapted around them
If you are r selected, what kind of offspring do you have?
Altricial
If you are K selected, what kind of offspring do you have?
Precocial
Why are humans strange?
Our young are altricial despite us being K selected
Why are human young altricial?
The evolution of bipedalism: in order to stand upright, the pelvic girdle/birth canal of females became narrower. Human babies have large heads so they had to be born earlier so they would fit through the birth canal. This means there is ‘extra-uterine growth of the brain’. Also explains why human infant skulls are malleable.
What can be said about the altriciality of human babies?
It is a secondarily acquired characteristic.
Which sex is more fragile to environmental conditions?
Males.
Can females manipulate the sex of their offspring?
Yes.
If females want to have offspring there must be group cooperation. True or false?
True.
There is disparity in sex of offspring between high and low ranking females. What is the Trivers-Willard hypothesis?
High ranking females control resources
Able to channel these into environmentally-sensitive males
High ranking females therefore have sons
Sons will produce more grandchildren than a daughter can
Bigger spread of genes
What is the local resource competition (LRC) hypothesis?
Many groups female philopatric
Females benefit from having daughters that act as allies in resource competition (nepotism)
High ranking females have daughters
Low ranking females have sons as they will disperse
What is the LRC intensity hypothesis?
High ranking females produce sons in times of population growth when resources are abundant as can channel into sons
High ranking females produce daughters in times of scarcity to aid in resource acquisition and defence
Low ranking females do the opposite
What is a proximate mechanism?
HOW you achieve something
What is an ultimate function?
WHY you are doing something
For example what are the a) proximate and b) ultimate mechanisms for having sex?
a) it’s fun, arousal due to hormones
b) for reproduction
What is the ultimate function of females manipulating the sex ratio of their offspring?
To better spread their genes.
How are females able to manipulate the sex ratio?
Due to the differential fertilisation abilities of the X and Y sperms.
Which type of sperm is heavier, X or Y?
X
Thus which type of sperm is slower at swimming?
X
Thus if copulation occurs around the time of ovulation, when an egg is readily available, which sperm usually succeed in fertilisation?
Ys as they are faster than Xs.
Thus if copulation occurs around the time of ovulation females are more likely to have which sex offspring?
Male.
Which sperm survives longer, X or Y? Why?
Xs as they contain more nutritive material.
Thus if copulation occurs before ovulation, which sperm type succeeds in fertilisation?
Xs, because they can hang around longer and survive until the egg drops.
Thus if copulation occurs before ovulation females are more likely to have which sex offspring?
Female.
What are the two forms of ovulation?
- Spontaneous, the eggs drop as and when
2. Induced, eggs are induced to drop by copulation
What has been speculated about humans?
We are spontaneous ovulators however it is speculated that extreme sexual excitation can cause induced ovulation. Thus this would skew the sex ratio of offspring e.g. data from just after WWII showed lots of boys produced.
Which primates park their babies?
Strepsirhines and tarsiers
Give 3 characteristics of an r-strategist.
Short gestation
Faster growth
Small-bodied
Give 3 characteristics of a K-strategist.
Long gestation
Slower growth
Large-bodied
What are the 3 hypotheses for manipulating offspring sex ratio?
- Trivers-Willard
- Local Resource Competition
- Local Resource Competition Intensity
