Today – 2/20Today – 2/20

• Test results

• Critter in the News – Spanish flu

• Evolution

Administration

3-pt XC opportunity, 7 pm, Steward Observatory N210, Andrea Ghez on the supermassive black hole at the center of our galaxy

Read The Beak of the Finch

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Spanish flu of 1918

Killed .6% of all Americans, reduced average lifespan by 10 years!

1998 exhumed Native American female 1918 flu victim from the Alaska permafrost

Sequenced DNA, reconstructed virus, studying how it kills – attacks the lungs, gets the body to attack itself

The evolution happened entirely within birds

Clades: know it, love it, live itA clade is a clade because the critters in that clade share a set of derived characters that are unique to themTherefore, dinosaurs are not defined by their eggs or the holes in their skulls because other reptiles (crocs, lizards, turtles, etc.) lay the same kinds of eggs and/or have the same number of skull holes. The number of holes in the dinosaur skull makes the clade Dinosauria part of the larger clade Diapsida, while the kind of eggs dinosaurs laid makes them part of the much bigger clade Amniota

Clades: know it, love it, live it

A clade says there is something different about these animals from any other creatures that makes them unique and groups them together

For dinosaurs, the hips and ankles and some other things are distinctive. These changes gave them upright posture

Evolutionary relationships between HIV and SIV

Evolution in action: drug resistance

AZT, azidothymidine replaces the T (normal thymidine) in the HIV DNA during replication, ruining the DNA strandA tiny percentage of HIV particles in any generation have a mutation that make them better at screening out AZT, survive and pass the mutation to the next generationThese are less vigorous than normal HIV, but eventually thrive enough to cause AIDSIf AZT goes away, HIV reverts to normal

Evolution key point I

Evolution is not pursuing an ideal goal - it is adapting to current conditions. It is not trying to create a “perfect” organism, it is trying get organisms as perfectly adapted to their current environment as possible. When conditions change, so does the evolutionary pathway

Evolution key point II

Trade-offs: a given trait may have both costs and benefits, so that a change in environment radically changes the competitive edge of the individual that has it. The scientific term for this competitive edge is fitness - the ability of an individual to survive and reproduce in its environment

Evolutionary relationships between HIV and SIV

Trade-off example #2

Virulence kills host faster (less time for transmission to new hosts), but increases ability to transmit easily (so less time may be needed)

Therefore, in populations where the norm is unprotected sex with many partners, virulence is favored. In monogamous populations, more benign strains are favored

Evolution key point III

Parsimony – we assume that the evolutionary pathway that requires the least number of changes is the right one, the Occam’s Razor of evolutionary biology. The simplest explanation is usually the right one

In our example, this means that swim bladders evolved from lungs, not the other way around

Spread of marsupial mammals

Evolution key point IV

Physical processes on and in the Earth drive evolution (in addition to biological interactions). Energy for both physical and biological processes on Earth comes from two sources – the Sun and the interior of the Earth. Energy from the interior drives plate tectonics, energy from the sun drives weather. The two combine to determine the physical environment of Earth’s surface – continental and oceanic positions and climate. This is evolution’s canvass

http://helios.bto.ed.ac.uk/

www.clark-shawnee.k12.oh.us

Yucca and yucca moth

Darwin’s four postulates

1. Individuals within species are variable2. Some of these variations are passed on to

offspring3. In every generation, more offspring are

produced than can survive4. The survival and reproduction of

individuals are not random: the individuals who survive and reproduce the most are those with the most favorable variations. They are naturally selected

Natural selection

Usually associated with “survival of the fittest”. General usage refers to ability to deal with the physical and ecological environment – obtain food, avoid predators, survive winter (summer, around here), etc.

Selective agent is the environment

The Problem of the Peacock

Sexual selectionGuys showing-off to get mates, or battling each other for mates. Trade-off: often leads to traits that are disadvantageous in other ways – makes them more visible and/or vulnerable to predators, less effective hunters, etc.Often leads to two types of guys – very sexy versus very sneakySelective agent is the potential mate or the rivalNatural selection and sexual selection are often at odds

Group work

How does sexual selection work in field crickets?

Is sexual selection happening in European praying mantises?

Work in pairs, read one of the two short chapters, explain it to your partner

2-point quiz