180: Biology Week 5 study questions
Autumn 2007
1. Squid are molluscs. Humans are vertebrates. a. Both have image-forming, camera eyes. Is this type of eye homologous in these species, or is it an example of homoplasy? Explain your answer. Because squid and humans are not closely related, and because other mollusks and vertebrates do not image-forming, camera eyes, the similarity is due to homoplasy. They result from convergent evolution, based on natural selection favoring the ability to see focused images. b. Both have a muscular heart that is involved in circulating body fluids. Is the presence of a heart homologous in these species, or is it an example of homoplasy? Explain your answer. Other mollusks and vertebrates have hearts, as do most species of animals that are closely related to mollusks and vertebrates. Thus, the traits are homologous. The trait is shared because it existed in a common ancestor.
2. Consider the following phylogeny of the mammal group called artiodactyls. |-------------------------artiodactyls--------------------------------| Carnivores
(dogs/cats/seals/bears)
Camel
Pig
Peccary
Whale
Hippo
Cow
Deer
Common ancestor of whales & hippos Outgroup
Common ancestor of all artiodactyls Root a) Identify and label: the root of the tree 3 monophyletic groups (many are possible) the outgroup the common ancestor of whales and hippos the common ancestor of all artiodactyls b) Name a shared, derived trait that helps identify the whales, dolphins, and porpoises as a monophyletic group. What logic did you use to support the hypothesis that this character is derived from a common ancestor? Many traits possible: aquatic habitat, streamlined bodies, lack of hind limbs, paddle-like forelimbs, etc.
Other close relatives (e.g. other artiodactyls) lack these features and all are shared by whales, dolphins, and porpoises. c) Are the limbless, streamlined bodies of whales and dolphins homologous or due to homoplasy? Explain your reasoning. Homologous--they are similar because they were present in the common ancestor of these two groups. 3. Consider the phenomenon known as adaptive radiation. a) Give an example of an adaptive radiation. many possible answers b) How does your example fulfill the criteria given in the definition of an adaptive radiation? Needs to represent relatively rapid generation of many species from a single common ancestor, with descendants occupying many different habitats and using many different food sources. c) Suggest a hypothesis for why this adaptive radiation occurred. Why is this hypothesis plausible? Need to relate the radiation to an ecological opportunity, morphological innovation, or both.
4. Two populations of apple maggot fly have been identified. One lays eggs in hawthorn fruit; the other lays eggs in apple fruit. Fly larvae eat the fruit. Hawthorn and apple trees often grow side by side. Individuals from the two populations look identical but have distinctive genetic characteristics. Only about 5% of all matings occur between members of the two populations. 95% of matings occur within each population because most matings take place on fruit. a) How would you test whether these two populations should be considered separate species under the following species concepts? * Biological: Need to determine if 5% hybrid matings are enough to homogenize gene frequencies in the two populations. Apparently not, if the two populations are genetically distinct. * Phylogenetic: Need to estimate the phylogeny of these populations to determine if they each have enough unique, shared, derived characters to make them come out as independent tips. * Morphospecies: Need to study morphological traits to see if there are any distinguishing features--need to include traits like chemical attractants, courtship displays, etc. b) If speciation is occurring, what is causing the two populations to become genetically isolated? Lack of gene flow, because individuals select different fruits and mate there. c) If speciation is occurring, generate a hypothesis for which evolutionary force or forces is causing the populations to diverge genetically. Natural selection might favor alleles that allow offspring to thrive on apple fruit better than hawthorn fruit, and vice versa.
5. In many areas of the world, habitats are being fragmented into tiny patches as cities and agricultural areas expand. Does this process qualify as a vicariance event? If so, what affect might it have on the populations that occupy the isolated patches? Fragmentation of habitats is called vicariance. If populations inside patches are isolated in terms of gene flow, they should begin to diverge due to genetic drift and natural selection.
6. Consider the small group of iguanas that rafted onto an island in the Caribbean, where no iguanas existed previously. Suppose that the new population remained genetically isolated from other iguana populations in the Caribbean. Would you expect that the new population will eventually form a new species? Why or why not? Yes--genetic drift will cause them to be genetically distinct from the source population, and if the habitat on the new island is unlike that on the source island, then natural selection should cause further divergence.
7. The phylogenetic tree below shows the evolutionary relationships among eight species. Three of these are nocturnal (they are active at night) and five are diurnal (active during the day.)
a) Species A and F are both nocturnal. Is nocturnal activity in these two species homologous or due to homoplasy? Explain. It is due to homoplasy. The common ancestor of species A, B, and C was probably diurnal. The common ancestor of species D,E,F,G, and H was also probably diurnal. Thus, nocturnal behavior evolved independently in the lineages leading to species A and F. b) Species F and G are also both nocturnal. Is nocturnal activity in these two species homologous or due to homoplasy? Explain. It is homologous. The common ancestor of F and G was probably nocturnal, so the two species share the derived trait.
8. Why do phylogenies have to be estimated via an analysis of homologous traits? Otherwise, species might be grouped on the basis of traits that appear similar but are not derived from a common ancestor. might Why DNA sequences qualify as a homologous traits? Because genes are transmitted from parents to offspring, DNA sequences from related individuals and populations are derived from a common ancestor. How can a researcher determine if a morphological trait is homologous? Homology has to be inferred on the basis of its presence in closely related species.
9. The evolution of the limb in the lineage that became known as tetrapods was one of the great events in the history of life. Why? Describe the fossil evidence that limbs evolved from the fins of lobe-finned fish. It is considered a "great event" because the limb allowed tetrapods to move about efficiently on land. Fossil evidence: phylogenies estimated on the basis of morphological traits observed in fossils other than the limb show that lobe-finned fish and tetrapods are closely related (they are sister groups that are next to each other on the phylogeny). The dates of early lobe-finned fish and early tetrapods and sequence of branches in the phylogeny of these groups describe a sequence of changes that elongated homologous bones into a functioning limb in terrestrial groups.
10. Several lines of evidence suggest that a 10-km wide asteroid hit the Earth about 65 million years ago. Which piece of evidence do you find most convincing, and why? Several answers are possible. Why would the impact event have resulted in the extinction of large numbers of species? Evidence in the fossil record indicates that a huge tsunami occurred, along with widespread forest fires and possibly extensive volcanism. In addition, a huge quantity of sulfur-laden particles would have been released to the atmosphere at the impact site. Dramatic global cooling would have resulted. Which region of the world should have experienced the highest extinction rates, and why? North America, because it was in the "splash zone" near the impact site.
11. Label the tree that correctly depicts the relationships among Bacteria, Archaea, and Eukarya according to morphology. Label the tree that correctly depicts the relationships among the three groups according to molecular data.
Bacteria Archaea Eukarya Bacteria Archaea Eukarya
_____Molecular data
____Morphology__
12. Give one example of how bacteria and archaea differ in terms of morphology. Cell wall is made of different molecules. Cell membrane is made of different molecules. Many enzymes and molecular components inside the cell are very different. 13. Consider the metabolic diversity observed in bacteria and archaea. a) Name an electron donor other than a reduced carbon-containing compound used by these cells. Many possible answers--H2, CH4, S, H2S, NH3, NO2b) Name an electron acceptor other than molecular oxygen (O2) used by these cells. Many possible answers--SO4-, CO2, Fe3+, NO3c) Denitrifiers use NO3- as an electron acceptor and excrete N2. Nitrosifiers use NO2- as an electron donor and excrete NO3-. Nitrogen fixers use N2 to synthesize compounds containing NH3 groups. Nitrifiers use NH3 as an electron donor and excrete NO2-. Describe the nitrogen cycle by putting the appropriate italicized name in each blank and the appropriate nitrogen-containing molecule in each box. N2 ___Denitrifiers___ __Nitrogen fixers_
___Nitrosifiers____
__Nitrifiers__
14. SINES are genes that can be inserted into chromosomes. SINEs numbered 1-18 have been analyzed in
the group called artiodactyls. At each point indicated on the tree, list the number (e.g. 1, 17) of two SINEs that were inserted at that point. Then explain why they act as synapomorphies.
SINE # Cow Deer Whale Hippo Pig Peccary Camel 1 0 0 1 0 0 ? 0 2 0 0 1 1 ? ? 0 3 0 0 1 1 0 ? 0 4 0 0 1 1 0 ? 0 5 0 0 1 1 0 ? 0 6 1 1 0 0 0 ? 0 7 1 ? ? 1 ? ? 0 8 1 1 1 1 0 ? 0 9 1 1 0 0 0 ? 0 10 1 1 1 1 0 ? 0 11 1 1 1 1 1 1 0 12 1 1 0 0 ? ? 0 13 1 1 0 0 0 ? 0 14 1 ? 0 0 0 ? 0 15 1 1 ? ? 0 ? 0 16 1 1 1 1 1 1 0 17 0 0 0 1 1 ? 0 18 0 0 0 1 1 ? 0
Camel
Peccary Pig
Hippo
Whale
Deer
Cow
Why are these traits considered synapomorphies? They are homologous traits that appear in some species but not others, so they identify those species as members of a monophyletic group.
6 9 12 13 15
11
16
15. Mimulus cardinalis has red flowers with a long nectar-containing spur and is pollinated by hummingbirds.
Mimulus lewisii has broad purple flowers and is pollinated by bumblebees. The two species are each others' closest relative and live side by side. Using data from Go Dawgs! experiments in Toby Bradshaw's lab, explain how they became different species.
Cause of genetic isolation: A change in pollinators that reduced or eliminated gene flow.
Cause of genetic divergence: Natural selection for traits that attract hummingbirds (in M. cardinalis) versus traits that attract bumblebees (in M. lewisii).
16. Biologists claim that the tetrapod limb evolved from the fins of lobe-finned fish. Describe evidence that
backs this claim. Evidence from phylogenetic trees and the fossil record: The phylogeny and fossil record of fossil lobe-finned fish and early tetrapods shows that limbs evolved in a step-wise, simple-to-complex manner. This supports the hypothesis that the bones that support lobe-finned fins and the bones that support the tetrapod limb are homologous. (an example of structural homology) Evidence from molecular genetic studies: Homologous genes are involved in the formation of the fish fin and the tetrapod limb. This is additional evidence that the structures are homologous.
17. The diagram on the right shows the relative potential energy of some molecules or ions. Species X uses H2 as an e donor, O2 as an e acceptor, and releases H2O Species Y uses NH3 as an e donor, O2 as an e acceptor, and releases NO2 Species Z uses NO2 as an e donor, O2 as an e acceptor, and releases NO3 Which species grows the fastest? Explain your reasoning. Species X, because more potential energy is released during its redox reactions, and thus it can manufacture more ATP and grow faster. Two of these species are almost always found growing next to each other. Which are they? Explain your reasoning. Species Y and Species Z, because Species Z uses a waste product from Species Y as an electron donor.
-
High glucose H2 NH3 H2S SO4
2-
NO2 NO3 O2 Low