Download HOMEWORK 05: ANSWER KEY

BIO 295
Islands & Evolution
- from the Galapagos to New York City
HOMEWORK 05: ANSWER KEY
The Beak of the Finch: Chapters 14-16
Answer each question in at least one paragraph (ca. 150-200 words). Refer to the syllabus (section “Written
assignments”) for formatting instructions.
1. Why are there so many kinds of animals? Explain the concept and list some examples mentioned in
the book (historic and current).
adaptive radiations, lineage of one species radiated into many, Darwin’s finches in Galapagos, fruit flies in
Hawaii, cichlids in African lakes, Cambrian explosion, jawless vertebrates in Ordovician, fish in Devonian,
amphibians & insects in Carboniferous, dinosaurs & mammals in Triassic, angiosperms and insects in
Cretaceous, etc.
p. 207-208
2. Historians learn from spelling errors in a similar way as evolutionists learn from DNA. Explain how
Darwin’s spelling errors are relevant to understanding how different finch species are related to each
other. When Darwin talked about invisible characters, what was he referring to?
Darwin’s spelling errors “evolved” during the course of his voyage, allowed historians to zero in on date when
he wrote famous phrase “undermined the stability of species”, mutation in gene (cytochrome b) only present
in certain group of finch species, likely to have arisen after they diverged from rest  more closely related;
genes
p. 218-221
p. 214 (bottom)
3. What is the so-called “SOS response” and what is its purpose? Use E. coli as an example. What role
does hybridization in Darwin’s finches play in the light of this process?
high number of mutations when under stress, increases chance that a few cells survive new conditions; when
E. coli cells are under stress (e.g. chemicals, UV radiation), open pores in membranes and take in DNA that is
floating around outside their cell walls to patch up their own genes; Darwin’s finches respond to stress (e.g.
flood, young volcanoes settling) by increasing variability, mixing gene pools through hybridization
p. 221-223
4. Revisiting: In what situation could the tameness of island-inhabitants become a problem? Give an
example from the book (Lyell and Darwin each provided one in their writings).
adding/subtracting species to/from an ecosystem causes disruption, introduction of new species might be
evolutionary event, invader evolves rapidly to adapt to new home, everything else adapts to invader; e.g.
when polar bears landed in Iceland might have resulted in fewer deer and foxes, fewer deer  more plants 
more insects, fewer foxes  more ducks  fewer fish
p. 224-226
5. Hermon Carey Bumpus published a famous story of evolution in action. Explain the study. (Are the
birds he was studying native to the New World? How did they arrive in New England? What did
Bumpus find? Which modes of selection did he encounter? What did Peter Grant find when he
reanalyzed the data?)
English sparrows introduced to New England in 1851 (birds from Shakespeare’s play); survivors were mostly
males, shorter & lighter than average, birds that died were the ones that diverged most from original type;
stabilizing selection; Peter Grant reanalyzed Bumpus’ data and concluded that for female sparrows selection
was stabilizing (killed smallest and largest, preserved mean) but for males it was directional (towards smaller
size)
p. 226-228
6. The book gives a great example of rapid evolution when a new “beast” is introduced. Explain the
soapberry bug story.
soapberry bug uses long needle-shaped proboscis (beak) to pierce walls of seeds inside fruit, native hosts are
soapberry tree, serjania vine and balloon vine; bugs also feed on introduced species like golden rain trees and
heartseed vine; fruit of introduced flat-podded golden rain tree has smaller radius than native hosts,
consequently beaks of soapberry bugs that feed on it have evolved to be shorter, golden rain trees introduced
in 1950s; fruit of introduced heartseed vine has larger radius than native hosts and beaks have evolved to be
longer, heartseed vine introduced in ca. 1970; both cases of rapid evolution in action
p. 228-230
7. Haw flies lay their eggs in hawthorn but some flies have switched to apples. Why do most
evolutionists regard the possibility of speciation in haw flies as unorthodox? What are the two forms
of sexual selection described in apple flies? Hypothesize into which categories of sexual selection
they fall. (not mentioned in book, extra points for this) Does molecular evidence support the
hypothesis of apple flies as a distinct species? What did Jeffrey Feder find?
standard model of speciation requires geographic isolation, considered universal pattern; earlier in season
male and female flies inspect each other at close range (female or male choice (unclear from information
given)), later in season male flies battle each other for territory (apple) and then wait for females (male-male
competition and female choice); genetic differences are only slight, flies differ in proportions of variant forms
of DNA; may be early stage of divergence
p. 231-235