Lecture 11: Evolutionary Complexity

Question 1

What is Lamarck’s view of evolution

Answer 1

That organisms have an inherent tendency to become more complex over time WRONG some organisms are just more complex than others

Question 2

Which lineages have more complexity?

Answer 2

Bacteria and eukaryotes (archea are less diverse)

Question 3

greater complexity in an organism comes from…

Answer 3

Co operation between previously independent organisms

Question 4

What are endosymbiotic events and how did they allow for complexity to develop

Answer 4

Endosymbiotic theory attempts to explain how prokaryotes evolved into eukaryotes. Theory states that mitochondria and plastids were likely individual prokaryotic cells that were engulfed. Three cells, one kind of useless (host cells), one that was capable of aerobic respiration and converting energy and the other that capable of photosynthesis (last two are endosymbionts).

Question 5

prokaryote

Answer 5

single celled organism with no membrane bound organelles. Oldest form of life on earth

Question 6

eukaryote

Answer 6

complex cells with membrane bound organelles and a nucleus

Question 7

unit of selection for evolution

Answer 7

GENES (argued by Richard Dawkins). Traits that increase the fitness of individual. Traits that are good for the species but reduce fitness cannot be favoured by individual selection.

Question 8

Individual selection

Answer 8

favours traits that increase survival or fitness of individual NOT of species

Question 9

Cooperation Adaptive

Answer 9

cooperation of individuals between species. High relatedness genes that lead to helping relatives can spread via natural selection (if you help your relative and die in the process, your genes might still be passed on through the relative)

Question 10

Reciprocal Altruism

Answer 10

Part of cooperation adaptive; favours cooperation. Cooperation of individuals between species leads to higher fitness. When species interact a lot they co-develop behaviours. Ex. Predator warning behaviour, if one individual risks harm to warn group of predator they help group members survive even if they die in the process. An organism will act in a way that will temporarily reduce their own fitness to benefit another organism with the idea that they will do the same later.

Question 11

What does reciprocal altruism necessitate

Answer 11

1. the behaviour must reduce the organism’s fitness relative to a selfish alternative
2. the fitness of the recipient must have elevated fitness relative to a non-recipient
3. The performance of the behaviour must not rely on an immediate reward/benefit
4. all above stipulations must apply to both organisms in the relationship

Question 12

What aspect of cooperation is like a cycle?

Answer 12

Conditions for cooperation lead to selection to cheat. Subsequent breakdown leads to selection for cooperation again. Selection favours cheaters and selfish behaviours but then eventually selection will favour cooperation again via restorer genes

Question 13

Is selection on individual organisms co operation?

Answer 13

Yes. Genes are being passed on from generation to generation, and they were independently inherited (long long ago). There must be some synchronicity (cooperation) to allow for genes to be passed on.

Question 14

How do individual genomes stay cooperative?

Answer 14

1. Mitosis and meiosis
   - ensures that alleles don’t compete within an individual. Alleles from both parents are in every body cell which means that interests are aligned. There aren’t some body parts with maternal alleles and some with paternal alleles
   which would result in competition for resources. (also segregation, recombination, and random mating ensure genes are passed on independently)
2. Development and multicellularity
   - development from a single cell means there is not competition between lineages because all cells originate from one single cell (one set of DNA)
3. Uniparental inheritance of organelles (chloroplast and mitochondria)
   - prevents competition within cells of different organelle genomes. Mitochondria and cytoplasm inherited from mother only thing from sperm are paternally inherited chromosomes.

Question 15

How does cooperation break down?

Answer 15

1. Meiotic drive
   - biased meiosis, alleles are distributed unevenly. If an allele can enhance it’s own transmission, it can spread even while reducing fitness. Cheats mendel’s laws of segregation and is over represented. This can RAPIDLY eliminate alleles that have higher individual fitness.
2. Over replication
   - self replicating segments of DNA. The segment doesn’t spread because it’s beneficial rather it copies and inserts itself into the genome. Large fractions of genomes are composed of transposable elements. However, this leads to silencing mechanisms.

Question 16

DNA methylation and RNA interference

Answer 16

Host silencing mechanisms. DNA methylation is when methyl groups are added to the DNA molecule. Changes the activity of the DNA sequence without actually changing the sequence. Works as a gene repressor. RNA interference is when mRNA inhibits gene expression by neutralizing targeted mRNA molecules.

Question 17

Transposition-selection balance

Answer 17

Abundance is increased by over replication, but also reduced by natural selection against harmful effects on organism. Final abundance = the result of the balance between over replication and selection against.

Question 18

How is mitochondria inherited?

Answer 18

Maternally. There is no mitosis or meiosis involved in organelles. This creates conflict in that mitochondrial mutations that enhance maternal fitness can spread even if it is detrimental to male fitness (ex. mutations in hermaphroditic plants can make sterile males if the same genes correspond to higher fitness of females).

Question 19

How do collections of cells stay co operative?

Answer 19

1. Starting from a single cell
2. Separation of germ-line (differentiated series of cells each developed or descended from earlier cells in the series that will pass on genes to
   progeny) with limited number of cell divisions
3. tumour suppressors: other features inhibit unregulated cell division
   - however somatic mutation is inevitable in long-lived multicellular organisms.

Question 20

example of faulty meiotic drive

Answer 20

Drosophila Segregation distorter locus, SD

• Large S allele is bad because it prevents proper sperm formation
• mating of ss female x Ss male would predict half Ss and half ss progeny, but in reality its 95%-99% Ss
• indicates S is able to bias the process
• silencer genes are present elsewhere in genome

Question 21

How is cancer related to the concept of cooperation or the lack thereof in an organism?

Answer 21

cancer is the evolution of selfish cell lineages within an individual. Spreads commonly in tissue that is relatively undifferentiated. It also evolves resistance to treatment/immune system.

Question 22

How do individual genomes stay so cooperative?

Answer 22

• many features of individual organisms limit the variance of fitness WITHIN an individual
• genes succeed by enhancing the fitness of the group (the organism)
• presence of policing necessary to maintain higher-level cohesion (silencing/ suppressing mechanisms)