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Primate Study (Actual) > Sex Ratios and Evolution > Flashcards

Sex Ratios and Evolution Flashcards

1
Q

Fishers principle

A

an evolutionary model that explains why the sex ratio of most species that produce offspring through sexual reproduction is approximately 1:1 between males and female

‘more females should be produced as one male can foster multiple offspring’ BUT:

a. if male birhts < female births then a new born male has better mating prospects and produces more ofspring
b. so mothers produce more males as ‘male producing gene’ increases
c. thus more males than females exist= need for females to meet demand
= results in an equillibrium (and challenges group selection! as individual selection)

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2
Q

“Selfish” gene theory:

A

A model of evolution, a gene’s eye view of natural selection.

Genes are replicators, individuals are their vehicles.

Replicators make copies of themselves. Successful replicators make more copies than unsuccessful replicators. Improved vehicles (bodies) promote their success.

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3
Q

Group selection:

A

(Wyrne-Edwards 1960s) A model of evolution. Some researchers believe that natural selection can favor traits benefiting groups to the disadvantage of individuals.

Selection at the group level is expected to be weaker than selection at the individual level because groups do not reproduce as quickly as individuals and because group altruism can not resist the introduction of “selfish individuals.”

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4
Q

trivers willards 1973 hypothesies

A

Female mammals are able to adjust offspring sex ratio in response to their maternal condition
–> sex is favoured that advantages females more

i.e. if youre powerful= you should give more birth to sons (So high ranking females produce more sons; low ranking females produce more daughters)

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5
Q

local resource competition (silk 1981) hypothesis

A

ffemales benefit from having a adaughter if rank is inhiereted in philopatric matrillines

so HRF= more daughters

LR= more sons

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6
Q

Local Resource Competition Intensity (Vanshai and Hrdy 1991)

A

dynamics between maternal rank and secondary sexy ratio vary in local conditions:

  1. HRF overproduce sons when populations grow and Local resource competition is relaxed
  2. HRF overproduce DAUGHTERS when population shrinks and local resource competition is intense (due to threat of sons)
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7
Q

violations of fishers 1:1 SSR principle (in humans)

A

us african americans produce more girls than boys

but on average; its 100 girls to 105 boys in human population

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8
Q

why are more boys born than girls

A
  1. boys more fragile and exposed to trauma/ilness/fightinng = more liklely to die
  2. repaire mechanisms cant be selected for as this would mean low reproductive success
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9
Q

sex ratios

A 
primary= at conception
secondary= at birth (SSR)
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10
Q

hypergyny

A

to marry ‘up

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11
Q

Trivers-Willards Hypothesis Evidence: Rajasthan

A

high social status= prefer sons
low status= prefer daughters

girls experience infanticide in HR

girl sin LR experience hypergyny (marry up)

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12
Q

Trivers-Willards Hypothesis Evidence: Germany

A

high status= prefer sons
low rank= prefer daughters

due to hypergyny

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13
Q

example of Silks LRC theory in primates

A

in macaques: mothers + grandmothers stick together when males leave (female philopatry and male dispersal): daughter stays to help mom= hence daughters help mothers if sons leave

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14
Q

facultative sex ratio adjustment: why is conception the best time to manipulate sex ratios?

A

post natallay- infanticide and differential investment
pre-natally= abortion
at conception= manipulation of sex ratio of fertilized ovum (more economical than other two)

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15
Q

“X vs Y Sperm” hypothesis

A

x sperm= slower but long life
y sperm= faster but short lie

hence females mate during ovulation if they want a son, and before ovulation if they want a daughter

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16
Q

SSR: mechanism

A

timing ofovulation

differential sperm speed

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17
Q

SSR function

A

a particular sex has better fitness returns

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18
Q

why are there more boys at the end of a war?

A

–> selection acts on INDIVIDUALS
sex= post war triggers sex at ovulation as more males have been lost (supports fishers principle)

Females= shoratege of men= advatnages to produce boys!

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19
Q

issues with group selection

A

‘free-rider problem’: genes that produce selfishness would outcompoete altruists

so ‘girl producing moms’ would be selected against

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20
Q

paradigm of group selection; alternative?

A

selection acts on INDIVIDUALS not groups

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21
Q

example of SSR + maternal rank…

A

cercopithecine monkeys; support trivers willard

i.e. barbaracy macaques:
if high female rank= 58% of ifnants are male
if low female rank= 43% of species are male

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22
Q

intersexual mate choice: which certain traits selected?

A
  1. traits which increase the fitness of females
  2. traits which are indicators of good genes, which would thereby improve the fitness of offspring
  3. traits which have little adaptive significance, but were preferentially selected by females over many generations
23
Q

advantages of big body size

A
  • male to male compeittion

- dominance over females

24
Q

examples of sexually monomoprhic species

A

prosimians
new world monkeys
gibbons
old world monkeys

25
Q

examples of sexually dimorphic polandrous species

A

lemurs (females bigger!)
sifakas
callitrichids

26
Q

moutain gorillas vs olive baboons and sex ratio

A

both ahve same sex ratio but because olive baboons have shorter birth intrevals (2 yrs), as opposed to gorillas (3-6 years) more male baboons are liklely to encounter an estrous female

27
Q

operational sex ratio

A

availabilit of ovulating males and the number of breeding females/males in a group

28
Q

advantages of operational sex ratio

A

takes into account:

  • birth itnerveals
  • duration of estrous cycles
  • number of cycles
  • number of days when female are ovulating
29
Q

how do phylogentic constraints affect sexual selection in primates

A
  • population variation= hence second vharacteristics must be variable and inheritable
30
Q

how do ecological contraints affect sexual selection

A
  • diet and locomotion energetics= affects body size

i. e. distance travelled per day and energetic costs of parenting/reproduction

31
Q

examples of large primate

A

gorillas

cheek-pouched orangutatns

32
Q

why did knuckle walking evolve

A

to let large mammals (chimps and gorillas) walk on group easierly despite big bogy size

33
Q

what is more common in terrestial primates (traits)

A

sexual dimorphic body size
larger canine size
colours
striking gentitatlia

due to visilibtiy of respective terrains?

34
Q

who studied the seasonality thermostat and when

A

power, sommer and watts 2015

35
Q

why do hanuman grey longers desynchronise

A

freedom of ecological contraints= results in polygynous system (as less resource competitino that way) to conceal fertility

36
Q

why do langurs synchronize

A

confuse parternity and reduce infanticide= creates a polygyandry

37
Q

why do primates hide their fertility

A

confuse paternity to avoid infatnaicde

can more easily manipulate by NOT showing sexual swellings

38
Q

operational sex ratio

A

ratio of fertilizable females to sexually active males

39
Q

cattartine primates vs hominin ancestors

A

males compete for food vs males are net producers

40
Q

pros of having more males in a group

A

more protection
less infanticide
undermine male monopoloy
increase levels of male care (LR males want friendship)

41
Q

cons of more males in group

A

food competition

higher patertnity certainity

42
Q

encephalization

A

evolutionary increase in brain size and complexity by shift of functions to neocortex ratio

43
Q

what is the female seasonality thermostat model

A

females hide their fertility/menstruation/ovulation in times of seasonalitt to induce pair bonds/confuse parternity/create monogamy

44
Q

Bateman’s principle

A

female reproduction is primarily limited by their access to resources to nourish and produce these large gametes, whereas male reproduction is mainly limited by access to females (Bateman 1948)

45
Q

the higher the reproductive variance…

A

the stronger the effects of sexual selection

46
Q

whyare sexually monomorphic species monoprhic

A
  • usualyl when egaliatrian and high parental care= males can invest less time to competition/look for other mates as mor econtigentn on female choice/cooperation (eqaligatrian)
47
Q

The evolution of elaborate behavioral displays and morphological traits can often be explained by…

A

as a result of intersexual selection

48
Q

Fishers Arbritary Principle

A

this model suggests that female preference can evolve for arbitrary traits that do not provide information about the male’s quality, and that therefore do no reinforce the effects of natural selection.

The fitness advantage of the arbitrary trait exists only as a result of its covariance with the preference.

By choosing a male with a particular trait value, the females gain the indirect benefit of producing offspring that will be more sexually attractive to females that carry the preference

can result in a runaway positive feedback loop, whereby the trait becomes more exaggerated as selection on the preference increase

49
Q

when does sexual selection act

A
  1. processes that lead to acquiring mating opportunities (pre-copulatory)
  2. Post-copulatory selection refers to the events that occur during and after mating. Post-copulatory male-male competition is known as sperm competition
  3. female cryptic choice(occurs inside the female reproductive tract and cannot be detected from behavioral studies alone; eberhard)
50
Q

what is sexual conflict

A

Although both sexes are seeking to optimize their reproductive success, their genetic interests are not aligned, resulting in sexual conflict

can often result in an evolutionary arms race, whereby the evolution of a trait that imposes harm on one sex will result in evolution of a counter-trait to mitigate the harm on the affected sex, with subsequent escalation in both

51
Q

examples of sexual conflict

A

Examples of sexual conflict include traumatic insemination in bed bugs, copulatory grasping and anti-grasping structures in water striders, and genital coevolution in waterfowl.

52
Q

intrasexual competition: Pre + Post Copulatory (examples in non primates)

A

COMPETITION;

  1. precopulatory:
    i. e. monopolize a harem; elephant seal

i.e. monopolize a female; i.e. rhinoiceros beetle

  1. postcouplatory
    i. e.having greater relative testicle size
53
Q

intersexual competition: Pre + Post Copulatoryexamples in non primates)

A

FEMALE CHOICE
precopulatory:
i.e. male displaying in manakins

postcouplatory
i.e. female morphology preventing sperm from entering (i.e. HYENES ‘pee out’ sperm and have weird vaginas)

54
Q

sexual conflict examples in pre and post copulatory competition

A

precopulatory;
- sexual harrasment

post copulatory:
traumatic inseemination in bed bugs

Primate Study (Actual) (32 decks)

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