Homework 3. Due Wed Feb 6, by noon.
1. Go back to Kevin Padian's testimon regarding homology, tasmanian wolves, kangarroos, etc.
Based on the traits presented, draw a phylogeny that shows the relationship between N. American wolves, dogs, tasmanian wolves, kangaroos, and oppossums. On the phylogeny, mark and label the appropriate branches with synapomorphic characters that unite subgroups.
The following questions refer to the squirrel article by Mercer et al.
In class we'll cover: What data were used to estimate the squirrel phylogeny? ; In figure 1, which branch do we have the least confidence in? Which one(s) do we have the most confidence in?
- In
figure 2, how did the authors determine the timing (in years (Ma) before present) of branching events?
- Aplodontidae
(Mountain Beaver, found only on the PNW coast) is not a squirrel. Why is
it included in the phylogeny?
- Do the results suport the traditional
claim that flying squirrels form a group relatively distant from all other
squirrel lineages?
- Bishop
thinks that the congruence of major diversification events and major changes
in sea-level or formation of land bridges is remarkable. One reason is that
this congruence required agreement of several independent types of data:
1) Identifying the nature and timing of geological/sea-level changes based
on the geologic & biological (non-squirrel) record; 2) The branching
pattern of the phylogeny, based on three different genes; and 3) the calibration
of DNA substitution rates using fossil squirrel ancestors (note, this last
item really requires several independently collected types of data – fossil
position in geologic record, radiometric dating of fossil age, and DNA substitution
rates on each branch).
Questions : 4a) What do these congruences suggest about factors affecting squirrel diversification? Your answer
should refer to figure 3 as an example.
4b) What does this study suggest about scientist's ability to reconstruct pre-historical events? You may wish to reference the 7 criteria for supporting scientific theories or hypotheses.
In case you'd like to know what the heck Ratufa is, see the following
web sites.
http://www.scarysquirrel.org/special/enemy/ratufa/
http://www.scarysquirrel.org/ratufa/ratufa.html