Genomic conflict

Question 1

what is MSR? what is its strategy?

Answer 1

Maternal sex ratio
degenerate bacterium in cytoplasm of parasitoid Nasonia cells. Produces female biased sex ratios.
inherited from the mother,as cytoplasm is maternal.
to MSR, males are an irrelevant waste of resources as cytoplasm wont be passed on. MSR benefits from causing all femaleseggs to be female, by doubling chr numbers so egg is diploid without being fertilised.

Question 2

describe how antibiotic treatment has altered the sex ratio

Answer 2

Stouthamer et al, 1991
trichogramma - parasitoid wasp, gave female asexual sp antibiotics and suddenly 50% males produced. treatment over generations turned pop permanently sexual. the distorter was a bacterium similar to MSR.

Question 3

What is psr?

Answer 3

Paternal sex ratio.
also found in nasonia.
It is a selfish genetic element (parasite), chromosone which doesn’t encode useful proteins. when an egg is fertilised, it breaks down other paternal chr, turning the zygote haploid, so male, favouring its own spread. Only works in short term.

Question 4

how does meiotic drive distort Aedes sex ratio?

Answer 4

mosquito that spreads sleeping sickness.
some populations are male biased due to 2 tightly linked genes on Y chr which breaks down the X in meiosis. one gene encodes toxin which breaks down X at meiosis, and the other confers resistance to it on the Y.
Y genes only passed on in males, so meiotic drive has no interest in females. resistant X chr have evolved in pops where driver genes are common - antagonistic coevolution on a genetic level.

Question 5

how has intra and inter- locus conflict resulted in evolution of sex chromosomes?

Answer 5

sex chr dont cross over much.
Intra locus conflict arises when at one locus, one allele is beneficial when in females, and the other allele is beneficial in males. initially this limits the rate of adaptive evolution in each sex. if costs are high then sex limited expression evolves.
Inter-locus conflict: 2 diff loci, 1 has alleles that do better in males, other for females. if there was a gene near these loci which caused the org to be m or f, then it will be massively favoured and become linked - Genetic sex determination. other genes with sex limited advantages will be favoured if near the sex determining gene. favours evolution of reduced crossing over. forms specialised sex chr.

Question 6

why isnt meiotic drive more common? 3 points.

Answer 6

• it is found on other chr, not just sex chr but the effects are less seen.
• resistance evolved in other chr, as seen in aedes.
• successful drivers spread unopposed, either turn population extinct or, in haplodiploids like Trichogramma, turn the species asexual.
• Haig and Grafen 1991 - perhaps crossing over in meiosis evolved to stop the spread of selfish driver genes,

Question 7

how does crossing over prevent meiotic driver genes working?

Answer 7

by splitting up tightly linked genes encoding toxin and resistance so they dont spread.this is intruiging as it suggests that genomic conflict has a great influence on sexual rep and how chr structured.

Question 8

how was sexually antagonistic coevolution tested?

Answer 8

Holland and Rice 1999 -
2 lineages of drosophila. One high sexual conflict, females mate polyandrously (male interest in female is very short term)
one low conflict, monogamous (male and f interests are the same).
after 47 gen, monogamous lifespan longer.
Cost of sexual conflict is seen in the lower fitness of the polyandrous line, as males will harm the female for their own fitness.

Question 9

what demonstrated the phenomenon of genetic imprinting?

Answer 9

First attempts at cloning by using 2 nuclei from the same individual in one egg failed. If both nuclei maternal, no placenta. if both paternal, huge placenta, tiny head.
suggests genes are ‘imprinted’ as coming from mother or father.
Goes against mendelian genetics, and showed that for some genes it is always either the maternal or paternal homologue which is expressed. very strange.

Question 10

what has further study by Haig 1993 in genomic imprinting shown?

Answer 10

it is possible to ‘de-imprint’ genes, and the resulting foetus is fine.
It is the result of sexual conflict.
present in mammals because of high parental investment.

Question 11

What did Haig realise the functions of genomic imprinted genes were?

Answer 11

Male imprinted genes seem only to increase maternal investment (increased placenta growth, increase insulin production in the mother, so releasing energy for the embryo)
Female imprinted genes seem to reduce effects of male ones.

Question 12

example of genomic imprinting.

Answer 12

2 closely related species of deer mouse:
1. Peromyscus maniculatus: promiscuous, high conflict.
2. P. polionotus: monogamous, low conflict.
can hybridise.
Predict: maternally imprinted genes in monogamous females will be weak at resisting paternally imprinted genes in promiscuous males. this cross gave Giant babies.
Also, mat imprinted genes in promiscuous females will be strong at resisting pat imprinted genes in mon. males. this cross gave tiny babies.

Question 13

why is there parental conflict?

Answer 13

costs of parental care depend on what both parents do.

game theory involved.

Question 14

what are benefits of parental care?

Answer 14

• offspring do better, but diminishing returns as offspring grow
• mate has reduced costs, good if breeding again with the same mate as mate is in better condition.

Question 15

costs of parental care

Answer 15

• reduced locomotor performance in pregnant snakes, lizards, bats, birds with eggs.
• increased predation risk
• time and energy costs - lost opportunitie.

Question 16

when may it be better to desert?

Answer 16

if food is scarce
long lived animals shouldn’t risk own life for young.
if food is plentiful, partner could rear young alone.

Question 17

which parent is more likely to desert?

Answer 17

male - mammals, birds like ducks, grouse, hummingbirds.

females - fish, some birds eg jacana and shorebirds.

Question 18

who was the first to model parental care?

Answer 18

Maynard smith 1977
classic game theory of care vs desertion.
ESS concept

Question 19

what is an ESS?

Answer 19

EvolutionARILY stable outcome

cannot be invaded and no other strategy can spread by NS.

Question 20

describe maynard smiths analysis

Answer 20

1977
1. establish pay offs: each parent has 2 options, care/desert. these affect no. eggs laid, egg survival, chance of male future mating.
4 patterns: both care, both desert, male deserts, female deserts.
2. find stable outcome given the payoffs.
All 4 possibilities could be ESS.

Question 21

when is caring by both an ESS

Answer 21

if cares, male does better by caring than deserting, and vice versa.
Neither can do better by changing beh.

Question 22

why is Maynard smith’s model internally inconsistent?

Answer 22

• males have chance of breeding again but females dont.
• probability the male remates is a fixed parameter, which surely should depend on beh.
• if all females care, who will be the second mate?
• the rest of the pop is not involved. there are actually 2 levels of interaction, with partner and with pop, as beh of other m and f determines probability of remating.

Question 23

define: 
monogamy	
polygyny	
polyandry	
polygynandry

Answer 23

monogamy ♂ ♀
polygyny ♂ ♀ ♀
polyandry ♂ ♂ ♀
polygynandry ♂ ♂ ♀ ♀

Question 24

how is dunnock parental care modelled.

Answer 24

• in a population, can have many diff mating systems
• each group member prefers others to do the work.
• individual effort gives a shared benefit but personal cost, creates tension in groups.
• parental care is optimised by finding outcome which neither male nor female can gain from changing effort
• so each’s effort is best response to partners effort.
• Male’s best effort maximises his lifetime rep success
• to find a stable level of care for each partner, draw graphs for each, with level of care given partners care, and overlay. where crossed = stable.

Question 25

whats the best male effort for a given female effort? -

Answer 25

• stable if make undercompensates : increase is less than partners decrease.
• if compensate fully, not stable, as then partner can desert without any reduction in youngs survival.

Question 26

in a trio of dunnocks, how is stability of parental care found?

What conflicts are there?

Answer 26

Female, a male, b male
undercompensation is vital.
males share paternity, a gets 60%. if b’s paternity below critical level, wont help rear brood, if above, then all 3 parents help.
Conflicts: a and b both want paternity
f vs aM, f wants to give enough paternity to b but a doesn’t want. a guards f, f tries to sneak away to mate w b.

Question 27

what was found from a negotiation model?

Answer 27

Houston, Davies and McNamara- modelled the situation where each partner could adjust their effort in response to the partner.
found an ES negotiation rule, instead of ES action. negotiation predicts less care, so has a different outcome to the standard model.

Question 28

how is negotiation different

Answer 28

it is not the best response to partners effort. it is the best way of responding to the partners way of responding. undercompenstion still occurs.

Question 29

how can parental care be experimentally manipulated

Answer 29

1. wright and cuthill 1989
   added weights to starlings and feeding rate dropped. partner compensates but not fully.
2. artificially elevate testosterone, which is naturally high in monogamous birds in territory and mate aquisition. level drops after. when manipulater, instead of care, increased song and aggression.

Question 30

example of sex differences in care roles

Answer 30

sandgrouse - female’s expenditure greatest during laying and incubation. less time for foraging and loses condition.
male’s expenditure greatest during chick rearing - brings water with specially modified belly feathers