Assignment Paper

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Populations of at least 20 asteroid species on the Northeast Pacific Coast have recently experienced an
extensive outbreak of sea-star wasting disease (SSWD). The disease leads to behavioral changes, lesions,
loss of turgor, limb autotomy, and death characterized by rapid degradation (“melting”). Viral metagenomic
investigations revealed the sea star-associated densovirus (SSaDV) as the most likely candidate virus
associated with tissues from symptomatic asteroids.
1. List the animal phyla you see in this photo. (You are not required to identify organisms to species, but you
can if you like!) Using Porifera as an outgroup, make a phylogeny for these animal phyla and you should label
the phylogenetic tree with the synapomorphies (“changed character states”) for each branch. (5 pts)
2. Should SSaDV mutate and become capable of spreading beyond asteroids, what animal phyla do you
consider to be at the highest risk of contracting this virus? Justify your reasoning using the phylogeny you
drew. (5 pts)
3. Calculate the species richness (S) and species diversity (Shannon diversity index – H), and species
evenness (Evenness – E) of this area. Explain your calculations. If the situation described in #2 were to occur,
explain how and why this would affect the values for species richness (S) and species diversity (Shannon
diversity index – H), and species evenness (Evenness – E) of the area? (Would each of these numbers
increase or decrease? Why?) (7 pts)
4. How would this disease affect species interactions? Identify a pair of species in the rocky intertidal
community that would be affected, explain what kind of interaction they normally have, and explain how it
would be affected by this disease. What are the potential ecological consequences for this community if this
species interaction is disrupted? Cite at least one source to support your answer. (8 pts)