Week 6
How did the authors measure the effect of evolution?
Comparing hindlimb divergence from source population
What are examples of evolutionary innovations we've read about? What is the primary genetic driver of these innovations?
antifreeze protein in fish
hemoglobin in geese
trichromatic vision in primates
regulatory changes or gene duplication
Describe the newt/garter snake coevolutionary arms race
Newts produce toxin TXX to deter predators, garter snakes evolve resistance to toxin that allows them to predate on newts, newts increase toxin production, snakes increase resistance, will eventually stop bc there is a cost to resistance and toxin production.
Why does a crop monoculture promote the evolution of insecticide resistance?
Big population —> Many new mutations
Little genetic drift —> efficient selection
Simple adaptive landscape
How can we test whether trait differences between populations are due to heritable (genetic) differences?
1) Common garden experiment: individuals from both populations growing up in similar environment. --Adoption studies
2) Does the trait difference between populations stay the same across several generations? If not: the difference is environmental, not genetic. --Irish IQ gap has disappeared --Flynn effect
3) Is the heritability of the trait the same in both populations? Hardship can limit the development of a trait (e.g., height, IQ).
What are the two evolutionary predictions made by the authors of Adaptive differentiation following experimental island colonization in Anolis lizards (Losos et al. 1997)
Vegetation difference between Staniel Cay and islands should be associated with lizard shape difference between S.C. and islands and lizards on narrow vegetation will have shorter legs than lizards on wide vegetation
What is the function of Pax6, what role does it play in the evolution of camera eyes?
Pax6, regulating gene that helps to direct the development of eyes.
The original Pax gene and the eye-building genes of all the different animal lineages probably evolved more than 500 million years ago. As these descendent lineages further evolved, the basic eye-building gene was modified in different ways in the different lineages, giving rise to the diversity of Pax6-like genes seen in modern animals.
Is lactase persistence (adult tolerance of lactose) the result of a regulatory mutation or a protein-coding mutation?
Regulatory, the change is at the enhancer controlling the expression of lactase.
Why isn’t every bacterial infection resistant to all antibiotics by now?
Often, there’s a cost to resistance. This tradeoff can result in fluctuating selection.
Why race is not a biological category
Racial categories do not imply genetic similarity, race is real, it just isn’t genetic. It’s a culturally created phenomenon, we "categorized" people.
Did the authors consider explanations for the morphological differences other than adaptation via natural selection?
Yes, phenotypic plasticity which they eventually tested in a future experiment.
How did the authors test whether prothoracic horns are partially serially homologous to wings?
1. Genes that we know are important for normal wing development are also important for normal horn development (fig 1). Except nubbin.
2. vestigial is expressed in the developing wings (not shown) and also in developing prothoracic horns and carinated margin (fig 1).
3. Both wings and prothoracic horns are regulated by Scr.
4. There is a size tradeoff between ectopic T1 wings and prothoracic horns, suggesting that both structures are built out of the same source tissue
What are examples of alleles that have probably undergone selective sweeps?
• In humans: The DNA deletion that broke the function of the enzyme that adds the negative charge to sialic acid (Wills reading).
• In humans: The mutation that eliminates Duffy protein expression in red blood cells.
• In P. falciparum: the mutation that confers chloroquine resistance (and other drug-resistance mutations).
• In mosquitoes: alleles that confer DDT resistance.
If purifying selection on a trait is relaxed (weakened), what happens over time?
New alleles (mutations) that affect the trait don’t affect fitness much, so they are neither selected for nor against. Additional new mutations occur each generation and the new mutant alleles are not weeded out, so they accumulate in the population over time. As a result, the trait eventually deteriorates.
Describe positive and negative eugenics
“positive” eugenics: Improve the species through sexual selection: Emancipate women, so that women are free to choose men with good traits, so that more children will have good traits. Improve the species through better education and living conditions for the poor: The poor would develop better traits during their lifetime, and acquired characteristics were thought to be inherited (Lamarck!), so children would inherit the improved traits of their parents.
“negative” eugenics: preventing “inferior” people from having as many children. Social Darwinism: don’t help poor/insane/disabled people because that would interfere with natural selection. Forcible sterization or segregation of the "unfit". Genocide of “unfit” groups, often along racial lines.
What are Carroll's 4 secrets of evolutionary innovation?
1) Tinkering: modification of existing traits. New structures are modified versions of older structures.
2) Multifunctionality: One structure doing multiple jobs.
3) Redundancy: Multiple structures all doing one job.
4) Modularity: One element of a repeated structure becomes modified or specialized to do a new job while the rest of the structures keep doing the old job. Genes can be modular too: entire developmental pathways can be switched on or off. Modules can be added or removed.
How did insect wings evolve?
Multifunctionality, ancestral aquatic arthropods had branched appendages, the top lobe was gills and bottom functioned as legs. The gills were used for respiration but also served for gliding as arthropods transitioned to land. The gills overtime were modified into wings through selective pressures towards better gliding and then flying.
Describe the mother/grandmother hypothesis
A hypothesis to explain menopause as an adaptation. The idea is that women may leave more total descendant if they stop having children at a certain age, and thereby have more resources to give to their existing [grand]children.
How can organisms respond to climate change?
Evolve, plastic response, behavioral change, range shift, combination of the previous, they don’t…
Why does scientific racism persist?
Lack of understanding of genetics, political motivations
What evidence is given in the Losos 1997 paper of repeatability? predictability?
Evidence of repeatability: replicates (multiple experimental islands) show similar results
Evidence of predictability: followed previous observations, repeated results
How did beetle horns evolve?
Multifunctionality, wing tissue began to form a horn and wings became reduced, eventually the wings were lost and the horn was large.
What was Belyaev's research on?
Domestication of foxes, dumpster-diver hypothesis driven, selected for tameness, eventually were able to confirm with genetics it was heritable.
The Roy et al. paper gave evidence that human effects have reduced the size of these gastropods over time. Did the paper provide evidence that this change in size was an evolutionary change?
Not really, would need to compare more similar habitats, account for environmental variables, common garden experiment, look at genetics
How did biological determinism give rise to eugenics?
The idea that our genes (not our choices, culture, education, ideas, passions, etc.) make us who we are and that some groups of people have “natural genetic propensities” for certain traits.
The theory of evolution made pre-existing anxieties about differential birthrates more pressing because it felt like humans were evolving backward.
Wanted to find a way to "fix" this.