|Guidelines for Take Home Exam 1
There are 8 questions for consideration in this exam. Undergraduate students must answer three questions. Graduate students must answer four questions. You will notice that some questions are more detailed than others, but that does not mean they are any easier to answer. Your answers to these questions should reflect the knowledge you gained in class and knowledge you can gain from reading various publications. Since this is an “open book” exam, I expect you to cite at least 2 sources per answer from the primary literature (journal publications, not textbooks, not my lectures). There is no word limit or page limit to answering any question, but please make your answers as succint as possible. As always, grammar is important. Each answer is worth 100 points maximum. Your answers must be turned in on Turnitin.com. The Class ID is 7695268. The password is ‘spider’. Late exams (up to 24 hrs) will receive a 25% deduction in the grade. Exams more than 24hrs late will receive a zero.
Grading Rubric for Individual Questions
Scientifically sound – Do you present a good argument? Do you use available evidence? Are there misterpretations? Total Available Points: 50.
Grammar – Are there consistent misspellings, poor word choice or misuse of punctuation? Total Availabe Points: 20
Clarity: Regardless of scientific valdity, are your points cogent? Can the logic be followed? Total Available Points:20
References: Are at least two references used to answer each question, and are these references valid and properly formatted? Total Available Points: 10.
** Please copy the questions you will be answering into a separate file prior to answering them. If you intend to answer Question 7 and illustrate your specimen, be sure to scan the image and place it in the file prior to upload.
1. Some researchers think lobopods represent a grade of organization while other researchers think lobopods might represent a monophyletic clade, i.e., Lobopodia. Provide an argument to support one or the other case using available data from your notes and the literature.
2. The terminology we use to describe arthropods and their body plans can be overwhelming and potentially misleading. We all know that words carry meaning, both overt and implied. Consider the case of the researchers who study chelicerates. They often use the words like ‘cephalothorax’ and ‘prosoma’ interchangeably, as they often do with ‘opisthosoma’ and ‘abdomen.’ Is this a good idea based on what you have learned about arthropod body segmentation and tagmata? Should they be interchangeable? Why or why not? Choose members of select chelicerate taxa (any 3 groups at the level of your interest) to support or argue against the use of the terms cephalothorax and prosoma when speaking of chelicerate body plans.
3. Arthropods evolved in the early marine seas. However, much of the diversity in the crown lineage is known from terrestrial species. Prevailing hypotheses suggest that “terrestrialization” occurred several times independently within the Arthropoda. Explain the major challenges faced by chelicerates as they adapted to the terrestrial environment. Consider specific taxa when making your argument. And remember, all animals are products of their past, so be sure to use available evidence from phylogenetic studies to follow the course of evolution from the marine environment to a terrestrial one.
4. This question may sound similar to question 3, but they are not identical. Arachnids are proposed to have evolved from a terrestrial ancestor, and their book lungs are therefore homologous (serial homologous) to the book gills of Xiphosura and potentially Eurypterida. Provide an argument using available evidence to show that these structures are indeed homologues despite their anatomical differences. Utilize different lines of evidence to support your argument including genetics, embryology, adult anatomy and fossil specimens.
5. Pycnogonids are highly unusual arthropods. Some people consider them chelicerates, while others consider them either a sister group to the chelicerates (sharing a common ancestor) or the most ‘primitive’ taxon of the crown Arthropoda. Provide an argument for either including the Pycnogonida within the Chelicerata or as a taxon separate from the Chelicerata (but perhaps sharing some affinities). Use all available evidence to support your argument and remember that a single study (or even a single species) may not have sufficient evidence for upholding your view, so consider more than one of each, including any potential fossil taxa.
6. The Arthropoda contains an enormous collection of animals, many of which are still around today, some of which are extinct and have left a good fossil record, and some that are extinct and left poor fossil traces. While defining what an arthropod is might seem like a straightforward task when dealing with the crown lineage, things get a bit more ambiguous when we begin to incorporate the stem groups into our understanding of the arthropod definition. Make a case for defining each of the two clades below (Clade 1, Clade 2) as part of the Phylum Arthropoda. Assume the topology of the cladogram is accurate based on our current knowledge, i.e., don’t add additional taxa to the tree.
7. Arthropods show unique forms of development relative to other animals. Still, an understanding of arthropod development has provided important insights in their evolutionary history and has allowed us to homologize developmental patterns and adult body plans. Using any specific taxon of chelicerates (Pycnogonida, Xiphosura, specific Arachnida taxa), describe how developmental patterns (segmentation, appendage development, gene expression data) have provided insight into chelicerate evolutionary history.
8. The following photograph shows a fossil animal. But is it a member of the crown arthropods, stem arthropods, or perhaps something else? With your newly acquired expertise in all things arthropodan, make an interpretation of the fossil specimen. Does it conform to your impression of a member of the Arthropoda? What features does it have that suggest an affinity with arthropods, or alternatively, what features does it lack that suggest to you this animal was not an arthropod. You may choose to draw the specimen and use that drawing to guide your interpretation. Caveat: If you do think this animal fits into your definition of a member of the Arthropoda, then be sure to point out the potentially homologous features. If this animal does not fit your definition of an arthropod, then be sure describe how it deviates from your definition of what an arthropod is. Be sure you understand the differences between a crown and stem arthropod if you choose to answer this question.