Sex Ratios and Evolution

Question 1

Fishers principle

Answer 1

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)

Question 2

“Selfish” gene theory:

Answer 2

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.

Question 3

Group selection:

Answer 3

(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.”

Question 4

trivers willards 1973 hypothesies

Answer 4

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)

Question 5

local resource competition (silk 1981) hypothesis

Answer 5

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

so HRF= more daughters

LR= more sons

Question 6

Local Resource Competition Intensity (Vanshai and Hrdy 1991)

Answer 6

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)

Question 7

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

Answer 7

us african americans produce more girls than boys

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

Question 8

why are more boys born than girls

Answer 8

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

Question 9

sex ratios

Answer 9

primary= at conception
secondary= at birth (SSR)

Question 10

hypergyny

Answer 10

to marry ‘up

Question 11

Trivers-Willards Hypothesis Evidence: Rajasthan

Answer 11

high social status= prefer sons
low status= prefer daughters

girls experience infanticide in HR

girl sin LR experience hypergyny (marry up)

Question 12

Trivers-Willards Hypothesis Evidence: Germany

Answer 12

high status= prefer sons
low rank= prefer daughters

due to hypergyny

Question 13

example of Silks LRC theory in primates

Answer 13

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

Question 14

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

Answer 14

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

Question 15

“X vs Y Sperm” hypothesis

Answer 15

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

Question 16

SSR: mechanism

Answer 16

timing ofovulation

differential sperm speed

Question 17

SSR function

Answer 17

a particular sex has better fitness returns

Question 18

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

Answer 18

–> 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!

Question 19

issues with group selection

Answer 19

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

so ‘girl producing moms’ would be selected against

Question 20

paradigm of group selection; alternative?

Answer 20

selection acts on INDIVIDUALS not groups

Question 21

example of SSR + maternal rank…

Answer 21

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

Question 22

intersexual mate choice: which certain traits selected?

Answer 22

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

Question 23

advantages of big body size

Answer 23

• male to male compeittion

- dominance over females

Question 24

examples of sexually monomoprhic species

Answer 24

prosimians
new world monkeys
gibbons
old world monkeys

Question 25

examples of sexually dimorphic polandrous species

Answer 25

lemurs (females bigger!) sifakas callitrichids

Question 26

moutain gorillas vs olive baboons and sex ratio

Answer 26

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

Question 27

operational sex ratio

Answer 27

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

Question 28

advantages of operational sex ratio

Answer 28

takes into account: - birth itnerveals - duration of estrous cycles - number of cycles - number of days when female are ovulating

Question 29

how do phylogentic constraints affect sexual selection in primates

Answer 29

- population variation= hence second vharacteristics must be variable and inheritable

Question 30

how do ecological contraints affect sexual selection

Answer 30

- diet and locomotion energetics= affects body size | i. e. distance travelled per day and energetic costs of parenting/reproduction

Question 31

examples of large primate

Answer 31

gorillas | cheek-pouched orangutatns

Question 32

why did knuckle walking evolve

Answer 32

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

Question 33

what is more common in terrestial primates (traits)

Answer 33

sexual dimorphic body size larger canine size colours striking gentitatlia due to visilibtiy of respective terrains?

Question 34

who studied the seasonality thermostat and when

Answer 34

power, sommer and watts 2015

Question 35

why do hanuman grey longers desynchronise

Answer 35

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

Question 36

why do langurs synchronize

Answer 36

confuse parternity and reduce infanticide= creates a polygyandry

Question 37

why do primates hide their fertility

Answer 37

confuse paternity to avoid infatnaicde | can more easily manipulate by NOT showing sexual swellings

Question 38

operational sex ratio

Answer 38

ratio of fertilizable females to sexually active males

Question 39

cattartine primates vs hominin ancestors

Answer 39

males compete for food vs males are net producers

Question 40

pros of having more males in a group

Answer 40

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

Question 41

cons of more males in group

Answer 41

food competition | higher patertnity certainity

Question 42

encephalization

Answer 42

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

Question 43

what is the female seasonality thermostat model

Answer 43

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

Question 44

Bateman's principle

Answer 44

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)

Question 45

the higher the reproductive variance...

Answer 45

the stronger the effects of sexual selection

Question 46

whyare sexually monomorphic species monoprhic

Answer 46

- 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)

Question 47

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

Answer 47

as a result of intersexual selection

Question 48

Fishers Arbritary Principle

Answer 48

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

Question 49

when does sexual selection act

Answer 49

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)

Question 50

what is sexual conflict

Answer 50

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

Question 51

examples of sexual conflict

Answer 51

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

Question 52

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

Answer 52

COMPETITION; 1. precopulatory: i. e. monopolize a harem; elephant seal i.e. monopolize a female; i.e. rhinoiceros beetle 2. postcouplatory i. e.having greater relative testicle size

Question 53

intersexual competition: Pre + Post Copulatoryexamples in non primates)

Answer 53

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)

Question 54

sexual conflict examples in pre and post copulatory competition

Answer 54

precopulatory; - sexual harrasment post copulatory: traumatic inseemination in bed bugs