W10L1 Sexual conflict

Question 1

Why is there sexual conflict

Answer 1

Bateman 1948
* Females invest more into (eggs) than males (sperm)
* Generate conflict of interest
-male fitness increase linearly with the number of mating while female eventually plateau

Question 2

Background cause for sexual conflict

Answer 2

*Parents = two individuals with no genetic interest in each others future
*Their offspring = the joint genetic interest of the parents

Question 3

Battle of the sexes

Answer 3

-Cost of reproduction itself
-each parent exploit resources invested in offspring from each other
- conflict of interest

Question 4

Darwin-Bateman-Trivers paradigm replaced

Answer 4

• Sexual competition a ʻconstructiveʼ process (weed out poor-quality males)
  *ʻTypical sex rolesʼ
• Female choice of ʻgood genesʼ
• 1970ies: mating males and resisting females = sexual conflict (Parker 1979)
• sexual competition Can be ʻdestructiveʼ
• Mate choice = resistance in female
• Male courtship = sensory exploitation

Question 5

Two type of sexual conflict

Answer 5

Inter-locus conflict
* Different traits in males and females involved in reproduction
* Can result in co-evolutionary sexual arms-race and population divergence (forcing the other sex to mate in their optimum)
Intra-locus conflict
* Sexes share a genome but have different phenotypic optima
generating a genomic tug-of-war
* Can constrain evolution

Question 6

Autosomal antagonistic genes

Answer 6

• Equal probability of being expressed in males and females
• Invade only when the advantage to one sex is larger than the disadvantage to the other

Question 7

issue of sex linked antagonistic alleles

Answer 7

*Unequally expressed in the two sexes
-place under selection more frequently

Question 8

Property of X-linked recessive allele

Answer 8

Expressed more frequently in the heterogametic sex (e.g. XY)
- always expressed in in the hemizygous (XY) sex
- rarely expressed in the homozygous XX sex

Question 9

X-linked dominant allele

Answer 9

Expressed more frequently in the homogametic sex
- 2/3 in XX
- 1/3 in XY

Question 10

Y-linked alleles

Answer 10

• Transmitted only to the offspring of the same sex as the parent
• Only selected in one sex

Question 11

Sex-linked antagonistic alleles summary

Answer 11

• Recessive X-linked alleles favoured in XY sex
• Dominant X-linked alleles favoured in XX sex
• Y-linked only selected in one sex (XY)
  Even when their advantage to one sex is smaller
  than the disadvantage to the other

Question 12

Accumulation of antagonistic alleles in D.
melanogaster

Answer 12

• Genetic marker transmitted with the X
• Selected line: X-linked markers pass from mother to daughter
• Should favour accumulation of female-benefit-male-detriment genes
• Control line: genetic marker found in both males and females = no accumulation

Question 13

Result of the experiment in melanogaster

Answer 13

• As predicted males carrying genes confined to females only had reduced fitness
• increased mortality
• lower mating success

Question 14

Core takes-away for Sexually antagonistic alleles

Answer 14

• Cause Feminizing/masculanizing selection
• Genomic-tug-of-war
• Each sex can hold back adaptation of the other (Rice 1984)

Question 15

Sexually antagonistic in collared flycatcher

Answer 15

• Tarsus length correlated in males and females
• Selection acts in opposite direction
• Large female
• Small males

Question 16

Sexually antagonistic in zebra finches

Answer 16

• Beak colour genetically correlated in males and females
• Sexual antagonism in the lab
• Red beaked males higher reproductive rate
• Least red beaked females higher reproductive rate and survival

Question 17

DDT-resistance alleles in flies

Answer 17

• TE insertion in cytochrome P450 gene
  (Cyp6g1) = upregulated
• DDT-R females more fecund (McCart et al 2005)
• But did not spread until DDT
• Suggest cost in males which does happen
• DDT-R sexually antagonistic allele?

Question 18

What leads to Accumulation of SA alleles on sex chromosomes?

Answer 18

• Dominant female-benefit alleles are under positive selection in females (2/3)
• Rare recessive male-benefit alleles are masked in females
• Drosophila and worms: male-biased genes strongly deficient; female-biased ~ overabundant
• Level of gene expression overlooked

Question 19

Saxi hyphothesis

Answer 19

• Sexual Antagonism and X Inactivation
• Importance of timing of gene expression
• X-chromosome inactivation during male meiosis (MSCI)
• Lead to Strong selection replace function onto autosomal genes or escape inactivation
• Example: Overabundance of X-linked active genes expressing sperm function (e.g. mouse)

Question 20

Selection for modifier genes

Answer 20

• Promote sex-limited expression of the allele
• At fixation, allele only expressed in one sex and transmitted silently in the other

Question 21

Sex-limited gene expression

Answer 21

• Gene only expressed in one sex
• All Y- and W- linked genes
• Loci expressed in both sexes could be regulated by the sex chromosomes

Question 22

Sex-biased gene expression

Answer 22

Genes expressed in both sexes, but at different levels
* Very common >50% genes
* Regulated by sex determination pathway or sex-hormone receptors
* Achieve optimal expression levels

Question 23

Unresolved in dimorphic beetles

Answer 23

• Broad-horn flower beetles sexually dimorphic
• Big mandible males = good fighters
• Big mandibles females = low fecundity
• Trade-off: big thorax needed for big mandibles
• Big thorax = small abdomen = low fecundity
• Importance of genetic correlations

Question 24

Imprinting In gene

Answer 24

• Either maternal or paternal allele is expressed in offspring
• Sex determination in some insects
• Seems common in mammals
• Methylation and other unknown mechanisms?

Question 25

Identifying Differential gene expression

Answer 25

• Sexes share a genome
• Identify the loci under sexual conflict
• Important WHEN genes are expressed
• Inform us about mechanisms of gene regulation
• Promote sexual dimorphism
• Does it resolve sexual conflict?

Question 26

Gene duplication

Answer 26

• Origin of new genes and functions
• Generate sex-biased and sex specifically expressed genes –resolve conflict?

Question 27

Example for gene dulication

Answer 27

• Example: pair of duplicate genes Apollo & Artemis in D. melanogaster
• Apl is needed for spermatogenesis but reduce female fertility
• Arts is required for oogenesis but reduce male fertility
• Apl strong testis-biased expression, Arts strong ovary-biased expression

Question 28

Inter-locus: Co-evolution

Answer 28

• Sexual conflict implies an evolutionary step forward for one sex is a slide backwards for the other
• May lead to a never-ending co-volutionary arms-race between the sexes

Question 29

Evidence for conflict over maiting in body structure

Answer 29

• Hypodermic insemination in bed bugs
• Abdominal spines in female water-striders

Question 30

Conflict over sex in hermaphrodites

Answer 30

-due to female would have to invest more, the hermaphrodites would prefer to be the male
-hypodermic insemination and penis fencing

Question 31

Genital sacrifice in spiders

Answer 31

• Males brake off the tip of their pedipalps, and use it as a maiting plug
• Males cannot mate again
• Enjoy increased paternity

Question 32

Manipulation in Accessory Gland Proteins
(Acps) in D. melanogaster

Answer 32

• > 100 different Acps
• Manipulate female reproductive physiology
• Increase male fertilization success
• Costly to females
  -the fastest evolving molecule

Question 33

Sexual conflict lead to new conflict

Answer 33

• Sex peptides in D. melanogaster reduced female longevity
• Persistent guarding reduces female foraging
• Prolonged copulation increase predation risk

Question 34

possible method of conflict resolution

Answer 34

• Sex-linkage and sex-limited expression (dimorphism)
• Sex-specific gene expression
• Genomic imprinting
• Gene duplication (free to take on new role)
• Does this result in new conflicts?