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ANT211H5 Study Guide - Final Guide: Spotted Sandpiper, Paramesonephric Duct, Pseudohermaphroditism

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Sherry Fukuzawa
Study Guide

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Written by: D. V. D.
Sex, Evolution and Behaviour
All Readings
The Animal with the Weirdest Sex Life
Diamond (Ch.1)
oVery few animals are paired off in single male-female partnerships
oOf the over 4,000 mammals, humans are one very weird species in terms of sexuality
oFor one, people have sex in private, unlike the vast majority of mammals that do not
care where or in front of who they have coitus
oIn the human species, females do not advertise when they are ovulating like those in the
majority of animal species
Though there are some primates that do not advertise themselves as sexually
available only when in estrus
oIn humans, sex does not have to be for reproductive reasons (as proven by the
emergence of contraceptives)
Sex for fun
oAnimals do not have the concept of marriage
Most do not have sexually exclusive rights to only one partner either
oHuman males and females take part in the rearing of babies
oHumans do not defend a territory – instead they share it with other couples and solitary
dwellers in large communities
oWomen who live past 50 undergo menopause and can not longer reproduce
oMultiple wives, one husband
oMultiple husbands, one wife
oIn most human societies, men engage in long term pair bonding with a single woman
oSexual cannibalism
oThe male mates with a female and allows her to consume him
Occurs in praying mantises
This happens because the meeting of a male and female is very rare – the chances
of the male finding another female is unlikely, so while mating, he allows her to
consume him for nutritional purposes – the more energy she has, the more eggs
she can produce
oHe continues to fertilize her while she consumes him – though he dies, he has
successfully reproduced – if the young survive to the point where they too
reproduce, he will have succeeded in passing down his genetics
oOrangutans are very solitary and only mate once every few years – until the female has
reared her offspring and is ready to have another baby – hence, they meet rarely
oBonobos have recreational homosexual and heterosexual sex to bond
oChimpanzee females mate with many males to confuse paternity and prevent infanticide
o“Sexual evolution is […] constrained by inherited commitments and prior evolutionary
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Written by: D. V. D.
The Battle of the Sexes
Diamond (Ch.2)
oMale animals in general do not provide as much care for offspring as do females
oIn some bird species, however, it is the male that incubates and raises the chicks while the
female looks for another male to inseminate her
oSpotted Sandpiper
oSome amphibian males take care of the eggs until they hatch and through to the tadpole
oTaking care of the offspring is a choice that both parents have to make – these choices are
programmed into the animal via natural selection
oBoth mother and father can care for the offspring
If both parents are feeding a helpless baby, then the chances of its survival are very
oOnly the mother could take care of the offspring
In this case, the father leaves to go off and copulate with another female
Females often invest more in the offspring, hence they stay to protect, feed and tech
the offspring until it is capable of surviving on its own
oOnly the father could take care of the offspring
This is a rare situation, but if the father is the one that invests more in the offspring –
like with the Spotted Sandpiper – it makes sense that he would see the offspring
through until they can take care of themselves
oBoth parents could abandon the offspring, leaving it to fend for itself, while they find
new partners to have more offspring with
If the offspring is capable of taking care of itself from birth (like snakes), then there
is no need for the parents to stick around – they can leave and copulate more,
spreading their genes further
oNatural selection does not occur for the good of the species – it is all on an individual level
oChildrearing is like a race for parents – who will leave before the other, forcing the
other to take care of the offspring
If both parents leave (they do not out-bluff each other), then the offspring could die
and both parent fail in passing on their genetics
oLive birth as a result of internal fertilization
oThis requires more investment from the mother – a larger obligation
Nutritional requirement
Time requirement for pregnancy
Due to the heavy investment even before the baby is born, it becomes much
harder for the female to bluff her way out of taking care of it after it is born
oIn external fertilization, neither mother nor father is automatically obligated to take care of
the offspring
oWith internal fertilization, the female is immediately committed to the embryo until she
lays it as an egg, or gives birth to it
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Written by: D. V. D.
oIt does her no genetic good to go off an copulate with another male as she cannot get
pregnant while already pregnant
oThe male on the other hand, is more than capable of getting another female pregnant
and further diversifying his genes
This is why in the majority of animal species, the male does not help in the raising of
oIf the male decides to stick around, he needs to be certain in his paternity
He does not want to be cuckolded (raise someone else’s offspring)
The female will always pass her genes on – whether the male does depends on
whether he was the only one to have had coitus with the female (sperm competition)
This is another reason males are likely to leave the childrearing to the mother – if
he leaves to have coitus with other females, he might father offspring – where if
he stays, he may be cuckolded
oExternal Fertilization
oOnce a female lays eggs, males will fight to see who will fertilize what
In some species, males scoop up as many eggs as possible, fertilize them, and raise
oSex-role-reversal polyandry
oBig females compete for males
Once they mate, they lay eggs and let the male take care of them; afterwards, the
female leaves to find new males
In Sandpipers, every clutch the female lays are about 80% of her body weight
The chicks hatch capable of walking and eating – all they require is protection
from the father
oOffspring helplessness
oIn some cases, the offspring is born so helpless, that the father has to stay for it to
In these cases, the father often tries to get away with doing as little as possible
oPied Flycatchers, though normally monogamous, are sometimes polygynous
The males will have one primary female, and then a side chick (mind the pun)
He will distance both females away from each other so they do not know about
each other, and he will inseminate both – helping raise both chicks
oThe secondary female, however, gets significantly less help from the male than
the primary female does
oHe must keep both females satisfied though, or they will leave in search of
another male
In the long run, the polygynous males sire more chicks than the monogamous ones
oEvery time the male leaves his mate, he risks another male coming in and copulating
with his female (extra-pair copulation)
A study found that 24% of chicks belonged to another male
For this reason, the male will stick around until the female has laid her eggs
before going off to see if he can score with another female
oRecord number of children for a single woman: 69
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