1. In 2009 it was discovered by marine biologist Gary Dickinson and colleagues that some amino
acid sequences in a species of barnacle (a marine invertebrate) exactly matched sequences in a
human blood clotting protein.
Read the following description of their experiment and then
discuss the question that follows.
Although they have hard shells like mussels and snails,
barnacles are actually crustaceans—related to crabs and
lobsters. A barnacle is “basically a shrimp that is glued
down to the ground with its head, and kicks food into its
mouth with its feet,” says marine biologist Gary Dickinson.
Prior to his co-authored study, published in 2009 in the
Journal of Experimental Biology, Dr. Dan Rittschof had
been studying marine invertebrates for 30 years. He already knew that when you took certain
chemical factors derived from human blood they sometimes triggered specific reactions in their
ancient evolutionary cousins. For example, when he took factors C5A and C3A—blood clotting
chemicals that attract white blood cells in the human body—and gave them to blue crabs that had
eggs attached to their bodies, it caused the eggs to be released.
So Rittschof proposed the seemingly far-fetched idea that perhaps barnacle glue was related to
blood clotting and scab formation in humans, and his graduate student, Dickinson, set out to try
to prove his professor wrong. Funny thing was, he couldn’t. It turned out that despite a number
of independent analyses using atomic force microscopy, gel electrophoresis, and mass
spectrophotometry, all of Dickinson’s experiments indicated that in fact barnacle glue was very
similar, and in some respects identical, to the chemical components of human blood clotting.
Dickinson started by figuring out how to use the barnacles as living glue sticks, prodding and
gently squeezing them to release the glue. Using techniques called gel electrophoresis and mass
spectrometry, Dickinson separated out the glue’s components.
His first breakthrough was identifying a protease—an enzyme that cuts human blood proteins
apart in preparation for scab formation. Next he found that the barnacle cement’s proteins had
amino acid sequences that, despite a billion years of evolution, exactly matched factor XIII, a
human blood clotting factor that cross-links scab fibers.
Dickinson’s team suggests that barnacle cement is an evolutionary modification of wound
healing, and suspects that this ancient chemical pathway is used by many other marine
invertebrates that need to “get a grip.”
Based on the description of this study provided on the previous slides, what do the researchers
appear to be interpreting from their study about evolutionary history of barnacles and humans?
a.
It’s just a coincidence, since barnacles and humans are not evolutionarily related.
b.
Humans and barnacles share a common ancestor.
c.
The presence of this protein is likely an ancestral, homologous trait.
d.
Both b and c
e.
None of the above
2. Many very distantly related species of birds (e.g., penguins, ostriches, flightless ducks, and rails)
share the trait of flightlessness even though their ancient common ancestors were able to fly.
This independent evolution of flightlessness in many distantly related taxa exemplifies what
type(s) of evolutionary/phylogenetic patterns?
a.
Convergent evolution
b.
Evolutionary reversal
c.
A homoplastic trait
d.
A synapomorphic trait
e.
a, b, and c
3. In a hypothetical study, physical fitness was measured in humans from seven European
countries. Physical fitness levels were classified according to a scale from 1 (lowest) to 10
(highest).
Do you think it would be problematic to infer phylogenetic relationships (i.e., create a
phylogeny) from such data?
Why or why not?
4. Using this hypothetical table of traits (left column) for these imaginary taxa (top row), construct
a phylogeny, assuming that the Priltezon is the outgroup:
5. In the following figure, which of the following groups are correctly described?
a. Chimpanzees, humans, and gorillas are polyphyletic.
b. Orangutans, gorillas, and humans are monophyletic.
c. Humans and gorillas are paraphyletic.
d. Chimpanzees, humans, and gorillas are paraphyletic.
e. None of the above
6. In which of the following scenarios are allele frequencies are likely to change, leading to
evolution, according to Hardy–Weinberg assumptions:
a. An isolated and highly endangered population of 50 woodland caribou
b. A large population of lizards whose males have red, blue, or green tails; females
preferentially mate with red-tailed males
c. A large population of fish in an isolated lake; every 5 years a flood results in some fish
from a population in an adjacent lake mixing with this population
d. All of the above
e. None of the above
7. A flock of 150 tiny orange and brown sparrows is blown off course and ends up on a huge island
where there is a lot of open shrubby land adjacent to low hills with trees. There are mammals,
many plants, some insects, lizards, and a few hawks, but there are no other small birds. There are
two types of plants with seeds edible for the sparrows: a small-seeded tree and a large-seeded
bush.
Discuss what you think might happen to this population of birds over many generations with
respect to the three different types of selection discussed in the text:
•
Stabilizing
•
Directional
•
Disruptive
8. Discuss the validity of following statements given what you have learned about evolution:
•
Pesticide resistance exhibited by insects in agricultural settings provides direct evidence
that evolution is occurring.
•
Antibiotic resistance is an example of evolution that helps to keep pharmaceutical
companies in business.
•
In vitro evolution at the molecular level, as described in Figure 15.23 of the textbook, is
analogous to the artificial selection of pigeons and dogs that Darwin was interested in
more than two centuries ago.
9. Examine the following animal phylogeny and focus on the major patterns in animal evolution in
terms of body plan.
Discuss in particular the evolution of different types of body symmetry. As organisms diverge at
the point shown by the arrow on this phylogenetic tree, does symmetry remain fixed as evolution
proceeds?
10. Insects were the first animals to evolve flight. Flight allowed insects to disperse widely into
many different habitats. However, some insects that exploited specialized habitats, such as the
inside of caves, subsequently evolved a lack of flight.
Other insect species have evolved a polymorphism such that some individuals are able to fly,
while others have wings too small to permit flight.
These polymorphic species are ideal organisms for examining the evolutionary advantages of
flight since the question can be turned around to ask, “What are the evolutionary benefits of
being wingless?”
The following graph examines fecundity (number of eggs laid by a female) in a cricket that is
polymorphic for short-winged and long-winged individuals
Consider the data shown below comparing fecundity of flighted (long-winged) versus flightless
(short-winged) insects.
Discuss the advantages versus disadvantages of being able to fly. [Hint: Energy is a limited
resource.]