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VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection 1. Meiotic Drive: -

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Presentation on theme: "VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection 1. Meiotic Drive: -"— Presentation transcript:

1 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection 1. Meiotic Drive: - Stalk-eyed flies, Cyrtodiopsis dalmanni and C. whitei (Presgraves, et al.1997). X(d) meiotic drive element on the X chromosome causes female-biased sex ratios spermatid degeneration of Y-bearing sperm in male carriers of X(d). balanced by Y-linked and autosomal factors that decrease the intensity of meiotic drive. Even a Y-linked polymorphism for resistance to drive which reduces the intensity and reverses the direction of meiotic drive. When paired with X(d), modifying Y chromosomes (Y(m)) cause the transmission of predominantly Y- bearing sperm, and on average, production of 63% male progeny.

2 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection 1. Meiotic Drive: 2. Transposable Elements

3 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection 1. Meiotic Drive: 2. Transposable Elements these genes replicate themselves independently of cell division... they are gene parasites that make nothing for the cell. yet they increase in frequency relative to other genes in the genome.

4 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection 1. Meiotic Drive: 2. Transposable Elements 3. 'Selfish' Genes (Richard Dawkins)

5 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection 1. Meiotic Drive: 2. Transposable Elements 3. 'Selfish' Genes (Richard Dawkins) - genes are the fundamental replicators

6 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection 1. Meiotic Drive: 2. Transposable Elements 3. 'Selfish' Genes (Richard Dawkins) - genes are the fundamental replicators - genes which confer an advantage, when averaged across other genetic backgrounds, will be selected for. (Analogy of 'crews')

7 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection 1. Meiotic Drive: 2. Transposable Elements 3. 'Selfish' Genes (Richard Dawkins) - genes are the fundamental replicators - genes which confer an advantage, when averaged across other genetic backgrounds, will be selected for. Analogy of 'crews') - co-adaptive assemblages and non-additive effects are not explained

8 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection B. Organelle Selection

9 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection B. Organelle Selection - some mitochondria in yeast are non-respiring parasites - they survive but don't produce much energy for the cell. They reproduce fast in a cell.

10 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection B. Organelle Selection - some mitochondria in yeast are non-respiring parasites - they survive but don't produce much energy for the cell. They reproduce fast in a cell. - In small populations of yeast, where selection at the organismal level is weak, there is no cost to the cell to reproducing slowly and the parasitic mitochondria dominate within cells.

11 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection B. Organelle Selection - some mitochondria in yeast are non-respiring parasites - they survive but don't produce much energy for the cell. They reproduce fast in a cell. - In small populations of yeast, where selection at the organismal level is weak, there is no cost to the cell to reproducing slowly and the parasitic mitochondria dominate within cells. - In large populations, where aerobic respiration is advantageous at a cellular level, cells with parasites are selected against and the frequency of parasitic mitochondria is reduced.

12 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection B. Organelle Selection - some mitochondria in yeast are non-respiring parasites - they survive but don't produce much energy for the cell. They reproduce fast in a cell. - In small populations of yeast, where selection at the organismal level is weak, there is no cost to the cell to reproducing slowly and the parasitic mitochondria dominate within cells. - In large populations, where aerobic respiration is advantageous at a cellular level, cells with parasites are selected against and the frequency of parasitic mitochondria is reduced. - There is a balance of selection at different levels that must be understood to explain the different frequency of parasitic mitochondria.

13 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection B. Organelle Selection C. Cell Selection

14 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection B. Organelle Selection C. Cell Selection - Cancerous Tumour - cell division increases, and the effects may be balanced at a higher level (organism).

15 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection B. Organelle Selection C. Cell Selection D. Organism Selection (Darwinian)

16 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection B. Organelle Selection C. Cell Selection D. Organism Selection (Darwinian) E. Kin Selection

17 …bees make me sad… 1. Darwin’s Dilemma

18 2. W. D. Hamilton related individuals that help one another increase their OWN fitness, because their alleles occur within THOSE relatives.

19 2. W. D. Hamilton related individuals that help one another increase their OWN fitness, because their alleles occur within THOSE relatives. a. Inclusive Fitness 1/2 1 several relatives have more of YOUR genes, cumulatively, than YOU do! ½ + ½ + ½ > 1

20 1/2 1 a. Inclusive Fitness

21 If I save myself… 1/2 1 I save one “set” of my genes… XX XX X X AAAAAAAAA !!!!! 1

22 If I save my relatives… I save 1.5 sets of my genes. If this has a genetic basis, selection will favor altruism among relatives. 1/2 1 …ow… 1/2 What a guy!

23 3. Examples 1. Helping among relatives – a function of kin selection

24 3. Examples 1. Helping among relatives – a function of kin selection

25 3. Examples 1. Helping among relatives – a function of kin selection

26 3. Examples 2. Haplodiploidy and Social Insects …bees make me sad… W. D. Hamilton – 1964 rb > c

27 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection B. Organelle Selection C. Cell Selection D. Organism Selection (Darwinian) E. Kin Selection F. Group Selection (Wynne-Edwards)

28 - Can groups replace one another simply by reproductive success??

29 F. Group Selection (Wynne-Edwards) - Can groups replace one another simply by reproductive success?? - First, it would have to be recognized by it's contradiction with organismal selection.

30 F. Group Selection (Wynne-Edwards) - Can groups replace one another simply by reproductive success?? - First, it would have to be recognized by it's contradiction with organismal selection. - (Sacrifice of fitness at the organismal level with increase at the level of the group).

31 F. Group Selection (Wynne-Edwards) - Can groups replace one another simply by reproductive success?? - First, it would have to be recognized by it's contradiction with organismal selection. - (Sacrifice of fitness at the organismal level with increase at the level of the group). - Altruism is a possible example - sacrifice reproduction for benefit of the group... but it usually doesn't work because f(altruism) declines within the pop if organisms are unrelated!

32 F. Group Selection (Wynne-Edwards) - But – there are caveats with kin selection, too Naked mole-ratsNaked mole-rats: Live for 31 years Don’t get cancer; division inhibited by cell- cell contact, and have an odd hyaluronan protein…5x larger than humans and cancer-prone species in which the normal form increases rate of metastasis. MUCH lower mutation rate Only mammals that are thermoconformers Eusocial: one ‘queen’, 2-3 males, the rest sterile workers in two size castes. “Vertebrate of the Year” in 2013

33 Problem: To show group selection, distinct from individual selection, it must be shown that a net ‘cost’ to the individual is outweighed by a net ‘benefit’ to the group, without invoking relatedness and kin selection. This is different than an individual benefiting MORE by helping the group than by acting selfishly. THIS is still maximizing individual fitness. PRO GROUP: WilsonANTI GROUP: PinkerWilsonPinker

34 VI. Levels of Selection Selection can occur wherever there is differential reproduction among variable entities. A. Gene Selection B. Organelle Selection C. Cell Selection D. Organism Selection (Darwinian) E. Kin Selection F. Group Selection (Wynne-Edwards) G. Species Selection

35

36 - Selection for sexually reproducing species: Parthenogenesis arises spontaneously, but extinctions are rapid due to lack of variation and Muller's rachet. Muller's ratchet is the continuous accumulation of mutations in a lineage. In sexual reproduction, since only 1/2 of the genes are passed from each parent, there is a 50% chance that a deleterious new mutation will be purged from the genome just by chance. And also, even if it is expressed, there will be other organisms in the pop that did NOT receive it and have higher fitness. So, selection can purify this sexual population of the deleterious alleles. But in an asexual lineage, all offspring get the whole genome - even a new deleterious allele. So, there is no way to purge it from the genome. In fact, in Daphnia pulex, asexual lineages accumulate deleterious amino acid substitutions at 4x the rate of sexual lineages (Paland and Lynch 2006, Science 311: ).

37 G. Species Selection - Selection for sexually reproducing species: - Parthenogenesis arises spontaneously, but extinctions are rapid due to lack of variation and Muller's rachet. So, extinction rates in parthenogenetic lineages are high... and so most lineages that radiate and produce lots of descendant species are sexual.

38 G. Species Selection - Selection for sexually reproducing species: - Certain lineage are more likely to speciate (beetles - small, tough, and easily isolated...)

39 G. Species Selection - Selection for sexually reproducing species: - Certain lineage are more likely to speciate (beetles - small, tough, and easily isolated...) SO, as a consequence of survival and speciation rate (reproduction), sexual lineages and also more rapidly speciating lineages will leave more species and replace other lineages that die out over time.


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