W10 L3 evolutionary conflict Flashcards
What does evolutionary conflict mean
-Conflict occur when gene have different patterns of transmission but interact directly or indirectly in the organism
-obvious example is gens of pathogen and gene of host
-endless cycle of damage and damage control lead to evolution arm race
consequence of evolutionary conflict
-affect evolution of gene , genome, cell and gene regulation
-constrain evolution
-sex determination
-population density
-direct impact on biodiversity
- influence behavior
the consequence of arm race
-lead to lots of adaptation
-can also lead to serious constraint on adaptation and the “red queen”
Evolutionary conflict type
-interspecific: host/ parasite, predator and pre
-intraspecific:
Intragenomic: cytoplasmic vs nuclear gene
-inter genomic: sexual antagonistic alleles, male female behavior
What are selfish genes
Gene that subvert Mendelian pattern of inheritance to increase in frequency in the next generation
-hence the name
-selfish genetic element are present in all living organism
Example of selfish genetic element
-transposable element (autonomous replicator)
-segregation disorder (driving chromosome)
-post-segregation disorder (maternal effect lethal, endosymbiont)
-persist due to their selfish nature
SGE and Intra genomic conflict
-genomic tension
-counter selection: silencing and inactivation
-adaptation and coutner adaptation
-genomic tug of war
-unresovalble
When does genetic conflict occur and effect of SGE on host
- When different components of the genetic system are selected in the opposite direction
- SGEs are elements that enhance their own transmission relative to their host genome
- Can be detrimental to their host
Segregation distorted: meiosis drive
- Segregation distorter genes cheats during meiosis or gametogenesis and are present in more than a half of the functional gametes
- Often found in inverted regions of chromosomes, and hence protected from recombination
-exp: t haplotype in mouse, S.D in melanogaster
meiosis drive
-segregation distorted that are present in sexual chromosome (as the Y chromosome in human s) are called sex ratio distorter
-most well studied are sex ration in D.simulan and pseudoobscura
Sex linked meiotic drive are
-common
-associated with sex ratio distortion
- strong selection for suppression of drive to restore sex ratio
- drive only detected in population crosses
- risk of population extinction due to lack of one sex
inherited endosymbionts
-asymmetric (uni parental ) inheritance
-commonly in cytoplasm of eggs
-male evolutionary dead end (no cytoplasm)
Wolbachia diversity and abundance
-infect 20% of insects, possible 75%
20-30% of terrestrial isopods are infected
-wide spread in mite and spider
cause of sex ratio skewing in wolbachia
- Because the bacteria have zero fitness in males, there is strong selection pressure to bias the sex ratio towards females
= males represent an evolutionary dead end
Way wolbachia cause genetic conflict
-parthenogenesis induction
-feminization
-Cytoplamic incompatibility
-male killing
-different strain of wolbachia can cause speciation
Does only wolbachia lead to speciation?
- gut bacteria in an organism can also lead to incompatibility and speciation
Genetic conflict and sex determination
- Sex determination systems are very diverse and rapidly evolve
- When components of the sex determination system are selected in opposite directions
*lead to Genes have different inheritance patterns (e.g. cytoplasmic, autosomal, and sex chromosomal) - Genes have different sites of expression (maternal, paternal, and zygotic)
Type of genetic conflict in sex determination
- Intra-genomic conflict (e.g. meiotic drive sex chromosome and autosomes)
- Conflicts between parents and offspring over offspring sex
- Conflict between masculanizing and feminizing genes
Cyto-Nuclear Conflict
- Conflict between cytoplasmic and nuclear genes over sex determination
- Nuclear genes r F=0.5 , r M=0.5
- Cytoplasmic genes (mitochondria, some bacterial endosymbionts) r F=1, r M=0
- Enhance their own transmission if they manipulate their host to produce a more female biased sex ratio.
Males are a dead end. Can result in extinction - Promote suppression to restore sex ratio - new sex determination system
SGEs and sex chromosomes
- Sex chromosomes are magnets for SGEs
- Reduced recombination between X and Y favour accumulation (Hurst & Pomiankowski 1991)
- Suppressors favoured on different genomic regions = conflict over sex chromosome transmission
SGEs promote sex determination turnover
- Birth of a W sex chromosome by horizontal transfer of Wolbachia genome
-ZZ male, ZW female after infection become ZZ and ZZ+wo
-wolbachia nucler intergration lead to creation of new sex chromosome W for female
Conflict result in unusual sex determination
- Conflict between SGEs and their suppressors leads Multiple sex chromosomes in rodents
Sex-ratio conflicts in social insects
- Mother queen: equally related to sons and daughters (rF =0.5, rM =0.5) > Wants to invest equally in both sexes
- Workers: 3 x more related to sisters than to brothers (rF =0.75, rM =0.25) > Prefer 3:1 F:M sex-ratio
- Parent-offspring conflict !
Fratricide in ants
Wood ant Formica exsecta: facultative sex-ratio biasing. Some colonies with single mated queen, others with double mated queen. Workers only eat their brothers in colonies headed by a single mated queen
Parent-Offspring Conflict cause
- Parents and offspring are not genetically identical
- You are always more related to yourself than to your siblings
- Parents are equally related to all their children
- So, there is conflict due to differences in resource allocation desire and actually receive
Pre-Natal Conflict (Haig 1993)
- Investment during pregnancy reduced ability to invest in current/future children
- Fetus ʻdesiresʼ more investment than motherʼs optimum
- Fetal genes try to increase nutrient transfer, maternal genes try and resists, leads to arms race
conflicts of interest in mating system
-In monogamous species mother and father interests coincides
* If polyandrous, there is conflict over mother and father allocation
* Mother wants even allocation to this and future offspring
* Father wants relatively more allocation to this offspring at the expense of other due to paternity uncertainty
Genomic Imprinting
- Gene effect are absent/present depending which parent it is inherited from
- Maternally inherited copy of genes has different effect than paternally inherited copy
- Gene is turned on or turned off during spermatogenesis
- Likely caused by methylation
Genomic Imprinting example
- Paternally imprinted genes code for nutrient extraction
- Placenta appears to be coded for by paternal genome
Genomic Imprinting, which animal have this
- In mice, there is a paternally imprinted gene
- When this gene is removed from mice, this slows growth in offspring
- Possible human analog: syndrome of missing chromosome 7, causes abnormal fetal growth
- Effects of arms race may include gestational diabetes and hypertension (include. pre-eclampsia)
The ultimate parent-offspring conflict consequences
- Potential killing or abandoning offspring
- Only favoured when there are better future opportunities
- More likely when young as reproductive opportunities declines with age
- Predict abandonment and infanticide should decline with mother’s age
What does parental investment depend on
- Relatedness between parent and offspring
- Ability of offspring to translate investment into reproduction
- Alternatives: other possible uses of resources allocated to a given offspring
