Lecture 13: Multilevel selection and conflict

Question 1

levels of selection:

Answer 1

selection can occur not only between individuals, but within individuals

Question 2

a ______ organism is a hierarchy of replicating units

Answer 2

multicellular

Question 3

cells and organelles show ___,___&___ so all subject to natural selection

Answer 3

heredity, variation & reproduction

Question 4

simple hypothetical example of 2-level selection with genomic conflict: newly formed cell with 2 types of mitochondrial A and a (3 scenarios, conflict?)

Answer 4

-mitochondrial replication occurs inside cell
-cell segregates into two daughter cells
(Cell is higher level, mitochondria is lower level)

• if both mitochondrial types (a&A) replicate at same time and fairly distributed–> there is no selection at lower level
• if mitochondria replicate at different rates (Say A faster than a) then segregation results in change in ratio of A:a & natural selection does work on mitochondria (LL)

A has a selection adv at lower levels

-if mitochondria replicate same, but distribute in segregation different. Biased segregation favours A at lower level

does conflict occur?

• if A benefits cell more than a then no conflict.
• if a benefits cell more than A then there is!

Question 5

2-level selection real life example:

Answer 5

Bakers Yeast

• small petite colonies often develop with defective mitochondria, severe metabolic problems, poor growth
• Petite mutations are often large deletions, they allow faster replication of their mt genome, outcompetes other mt in cell
• -> mutation is favours at mitochondrial level
• but against at cell level (as impairs cellular growth) === genomic conflict!

Question 6

Genomic conflict and sex: Genomic conflict arises less easily in __ systems

Answer 6

asexual

• -> lower levels of selection (e.g.mitochondria) share the same fate as higher levels of selection (e.g. cell or clonal individual)
• sex combines genomes from different lineages through RECOMBINATION
• -sex allows greater scope for genomic conflict

Question 7

Selfish genes:

Answer 7

• selfish genetic elements are transmitted at a higher rate than the rest of the genome
• detrimental (not adv) to the organism

Question 8

segregation distortion:

Answer 8

genes which break the rules of Mendelian inheritance and are consistent overrepresented in offspring
-they bias segregation & drive meiosis away from equality, producing >50% gametes with a particular allele (meiotic drive)

Question 9

Sex ratio meiotic drive in Drosophila

Answer 9

• Sex ratio males only produce x-bearing sperm
• female biased broods (SR will be passed onto all subsequent offspring resulting from matings with carriers)
• should result in heavily female-biased pop
• BUT SR males only produce 1/2 number of sperm, so poor competitors

Question 10

Sex-ratio meiotic drive in drosophila: DR

Answer 10

PRICE ET AL 2010

• polyandry females may protect from SR by increasing sperm competition intensity & therefore undermining the transmission freq of the driving chromosomes
• -polyandrous populations had higher proportion of males
• 5/12 monogamous lines went extinct
• lower SR freq in polyandrous

Question 11

higher levels? WHERE DOES SELECTION REALLY ACT?

Answer 11

• selection can theoretically act at levels higher than the individual organism (population, species)
• ALL U NEED IT HEREDITY, VARIANCE and REPRODUCTION

Question 12

genetic conflicts occur when

Answer 12

a trait is selected for at one level but against at another

Question 13

___ increases the scope for genetic conflict to occur

Answer 13

SEX

Question 14

____ may reduce populations under sex-linked meiotic drive from extinction

Answer 14

polyandry

Question 15

selfish genetic elements (segregation disorders) can drive ___ away from equality by …

Answer 15

meiosis

-by disrupting segregation to favour certain alleles (e.g. SEX ration in drosophila)