Quantitative genetics leftovers

1
Quantitative genetics leftovers

• Examples of heritabilities
• Humans h2
• height 0.65
• serum immunoglobin level 0.45
• Cows
• adult body weight 0.65
• butterfat 0.40
• milk yield 0.35
• Pigs
• weight gain per day 0.70
• litter size 0.05

2
Adaptation

• Key questions
• Are all traits adaptations? Other possible
  hypotheses to explain current traits?
• How can we test hypotheses about selection that
  might have taken place in the past?

3
Concealed estrous in humans. Adaptive?
Most primates advertise ovulation why dont
human females know? (Female pygmy chimp with
genital swelling)
4
Case study laryngeal nerve
Laryngeal nerve anatomy
1. down the neck
4. to larynx
2. behind the aorta
3. up neck
Is it adaptive? For giraffes?
5
Historical constraint the laryngeal nerve
For fish, no problem
But the basic anatomy has been modified since
then.
6
Case study sutures in the human skull

• Are they adaptive?
• If so, what is the selective force?
• Was this the historical cause?
• adaptation
• exaptation

7
A metaphor spandrels
The basilica of St. Marks was designed to have
many spandrels to decorate . . .
8
Case spotted hyenas
Male
9
Case the female hyena penis
Female
10
Case the female hyena penis

• High levels of fetal androgens
• Clitoris is enlarged
• Birth canal exits through clitoris
• First born often dies in birth (75)
• Mothers often die in birth (8)
• Clitoris rips, allowing passage of other cubs
• Adaptive? How and why?

11
Case Testes size in bats

• Testes size varies between species
• Does increased male-male competition lead to
  larger testes?
• Hypothesis larger groups, more mating, more
  sperm competition, so larger testes
• How to test?

12
First approach plot group size vs. testes mass
Is the regression significant?
Figure 10.12
13
Phylogenetic inertia
14
Phylogenetic non-independence
Group Testes Species Size Mass A 5
8 B 5 8 C 5 8 D
20 16 E 20 16 F 20 16
Figure 9.12
15
Phylogenetic non-independence
Figure 9.12
16
Strategy Independent contrasts
Figure 9.13
17
Strategy Independent contrasts
Figure 9.13
18
Bat testes independent contrasts
Figure 9.14
19
Bat testes the sequel (2005)

• Testes are expensive
• Brains are expensive
• Can bats afford both?
• Approach independent contrasts.
• Compare mating system, testes, brains.

20
Pitnick et al. 2005
21
Case Male sterility in flowers
Some flowers are female
Some flowers are hermaphrodites
Female flowers produce 1.5 x as many seeds as
hermaphrodites
Which would natural selection favour?
22
Mechanism of male sterility

• Known
• Mutation to mitochondrial gene (ATPase)
• Produces toxic compound
• Transgenic yeast, E. coli dead
• Unknown
• Why kill anthers and pollen, not ovules, not
  entire plant?

23
Selection?

• Pollen no mitochondria
• Ovules have mitochondria

24
Case Aperts syndrome

• Symptoms fused fingers, facial abnormalities,
  cranial sutures close early

Cause mutation to fibroblast growth factor
receptor 2 (FGFR2). Mutation in male germ line
increases with age
25
Aperts syndrome puzzle

• Cause mutation at one nucleotide TCG gt TGG.
  
• Puzzle This mutation is common other mutations
  are not (eg TCG gt TAG).
• Hypothesis TCG TGG is favoured by selection.

26
Case genome size in plants

• Two species of sunflowers in the southwest
• 17 pairs of chromosomes, but genome size 11 or
  7 pg

Helianthus anomalus (dunes) and H. annuus
(plains)
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Why the larger genome?

• Adapted to different habitat?

Baack et al 2005
28
Sources

• Baack et al 2005. Hybridization and genome size
  evolution timing and magnitude of nuclear DNA
  content increases in Helianthus homoploid hybrid
  species. New Phytologist 167623-630.
• Crow, J. 2006. Age and sex effects on human
  mutation rates an old problem with new
  complexities. J. Radiation Research 47B75-B82.
• Diamond, J. 1992, The third chimpanzee.
  Harper-Collins.
• Goriely, A et al. 2005. Gain-of-function amino
  acid substitutions drive positive selection of
  FGFR2 mutations in human spermatogonia. PNAS
  1026051-6056.
• Pitnick et al., 2006. Mating system and brain
  size in bats. Proceedings of the Royal Society
  Biology.

29
Questions

• 1. Imagine that you are examining shrubs that
  grow on two isolated islands, A and B. The
  shrubs appear to be very similar, and you perform
  test pollinations to confirm that they can mate
  with one another. DNA markers suggest that they
  are very closely related to each other. On
  island A, the shrub grows at higher elevations
  that are cooler and moister. On island B, the
  shrub grows at lower elevations which are hotter
  and dryer. Island B has lizards, while island A
  does not. You discover that the leaves of B
  shrubs contain many more toxic compounds than
  island A shrubs, and suspect that this is due to
  the herbivorous lizards. What alternate
  hypotheses should you consider, and what
  experiments could you perform to test your
  hypotheses?
• 2. Many plant species contain toxic compounds,
  and many of these compounds have been
  demonstrated to deter insect attacks or prevent
  attacking insects from growing. Why aren't
  plants more poisonous so that they are able to
  prevent all herbivory? Consider three
  hypotheses, and describe ways that you might put
  these to the test.
• 3. Like bats, primate species differ in the
  relative size of testes (compared to the total
  body mass). Describe how you would test an
  adaptive hypothesis. (Remember, not all tests
  are experimental!)

30
Questions

• 4. The persistence of female plants in Silene is
  puzzling, since they have 75 of the fitness of
  hermaphrodite plants. Although they produce 1.5x
  as many seeds, they do not pass their genes on
  via pollen, which should be half of the
  reproductive success of hermaphroditic plants.
  Explain why female plants would be favored from
  the point of view of mitochondria. What would
  happen to a mutation to a nuclear gene that
  counteracted the ability of mitochondria to
  eliminate pollen production?
• 5. On many Pacific islands, bird species are
  going extinct because human travel has introduced
  new predators to the islands. Brown tree snakes
  were introduced to Guam in 1952. Birds
  previously had no snake predators on the island
  a dozen species have gone extinct since the
  snake's introduction. Why didn't the birds
  evolve to defend themselves against the snake?
  Was there no heritable variation in response to
  snakes, or simply insufficient time for selection
  to act on this variation? Describe how you might
  study this question using bird species from
  Pacific islands where the brown tree snake has
  not yet eliminated the birds.