W10L1 Sexual conflict Flashcards
Why is there sexual conflict
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
Background cause for sexual conflict
*Parents = two individuals with no genetic interest in each others future
*Their offspring = the joint genetic interest of the parents
Battle of the sexes
-Cost of reproduction itself
-each parent exploit resources invested in offspring from each other
- conflict of interest
Darwin-Bateman-Trivers paradigm replaced
- 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
Two type of sexual conflict
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
Autosomal antagonistic genes
- 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
issue of sex linked antagonistic alleles
*Unequally expressed in the two sexes
-place under selection more frequently
Property of X-linked recessive allele
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
X-linked dominant allele
Expressed more frequently in the homogametic sex
- 2/3 in XX
- 1/3 in XY
Y-linked alleles
- Transmitted only to the offspring of the same sex as the parent
- Only selected in one sex
Sex-linked antagonistic alleles summary
- 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
Accumulation of antagonistic alleles in D.
melanogaster
- 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
Result of the experiment in melanogaster
- As predicted males carrying genes confined to females only had reduced fitness
- increased mortality
- lower mating success
Core takes-away for Sexually antagonistic alleles
- Cause Feminizing/masculanizing selection
- Genomic-tug-of-war
- Each sex can hold back adaptation of the other (Rice 1984)
Sexually antagonistic in collared flycatcher
- Tarsus length correlated in males and females
- Selection acts in opposite direction
- Large female
- Small males
Sexually antagonistic in zebra finches
- 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
DDT-resistance alleles in flies
- 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?
What leads to Accumulation of SA alleles on sex chromosomes?
- 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
Saxi hyphothesis
- 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)
Selection for modifier genes
- Promote sex-limited expression of the allele
- At fixation, allele only expressed in one sex and transmitted silently in the other
Sex-limited gene expression
- Gene only expressed in one sex
- All Y- and W- linked genes
- Loci expressed in both sexes could be regulated by the sex chromosomes
Sex-biased gene expression
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
Unresolved in dimorphic beetles
- 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
Imprinting In gene
- Either maternal or paternal allele is expressed in offspring
- Sex determination in some insects
- Seems common in mammals
- Methylation and other unknown mechanisms?
Identifying Differential gene expression
- 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?
Gene duplication
- Origin of new genes and functions
- Generate sex-biased and sex specifically expressed genes –resolve conflict?
Example for gene dulication
- 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
Inter-locus: Co-evolution
- 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
Evidence for conflict over maiting in body structure
- Hypodermic insemination in bed bugs
- Abdominal spines in female water-striders
Conflict over sex in hermaphrodites
-due to female would have to invest more, the hermaphrodites would prefer to be the male
-hypodermic insemination and penis fencing
Genital sacrifice in spiders
- Males brake off the tip of their pedipalps, and use it as a maiting plug
- Males cannot mate again
- Enjoy increased paternity
Manipulation in Accessory Gland Proteins
(Acps) in D. melanogaster
- > 100 different Acps
- Manipulate female reproductive physiology
- Increase male fertilization success
- Costly to females
-the fastest evolving molecule
Sexual conflict lead to new conflict
- Sex peptides in D. melanogaster reduced female longevity
- Persistent guarding reduces female foraging
- Prolonged copulation increase predation risk
possible method of conflict resolution
- 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?
