Quantitative genetics leftovers Examples of heritabilities Humans h 2 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
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serum immunoglobin level 0.45
adult body weight 0.65
milk yield 0.35
weight gain per day 0.70
litter size 0.05
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?
Most primates advertise ovulation: why don’t human females know? (Female pygmy chimp with genital swelling)
Laryngeal nerve anatomy
1. down the neck
4. to larynx
2. behind the aorta
3. up neck
Is it adaptive?
For fish, no problem
But the basic anatomy has been modified since then.
The basilica of St. Mark’s was designed to have many spandrel’s to decorate . . .
Adaptive? How and why?
Is the regression significant?
Species Size Mass
A 5 8
B 5 8
C 5 8
D 20 16
E 20 16
F 20 16
Some flowers are female
Some flowers are hermaphrodites
Female flowers produce 1.5 x as many seeds as hermaphrodites
Which would natural selection favour?
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
Cause: mutation at one nucleotide: TCG –> TGG.
Puzzle: This mutation is common; other mutations are not (eg TCG –> TAG).
Hypothesis: TCG – TGG is favoured by selection.
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)
Baack et al 2005
Baack et al 2005. Hybridization and genome size evolution: timing and magnitude of nuclear DNA content increases in Helianthus homoploid hybrid species. New Phytologist 167:623-630.
Crow, J. 2006. Age and sex effects on human mutation rates: an old problem with new complexities. J. Radiation Research 47:B75-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 102:6051-6056.
Pitnick et al., 2006. Mating system and brain size in bats. Proceedings of the Royal Society: Biology.
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!)
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.