STUDY QUESTIONS (Lectures 23-25) 1) Biologists have claimed that the jaws and limbs of terrestrial vertebrates evolved from structures that had a different function in their aquatic ancestors. What structures do biologists believe the jaw and limb evolved from, what is the evidence, and what was the significance of these events for vertebrate evolution? Biologists think the jaw evolved from gill arches and the support for this idea is morphological (both are hinged bony bars moved by muscle cells coming from the same embryonic cell population) and developmental (both are derived from neural crest cells). The jaw plays a huge role in animal feeding (in the capture and processing of food items). Biologists think the limb originated as a fish fin and the support for this idea is morphological (number and arrangement of bones is similar in both), developmental (Hox gene protein products are found at the same time and places in mouse limbs and zebrafish fins) and paleontological (a transitional &quot;fishapod&quot; has been unearthed in Canada). The limb plays an important role in tetrapod movement (e.g., on land). 2) You discover an organism you believe to be some sort of land snail laying eggs. You bring these eggs back to the lab with you and carefully observe the cellular development of the zygote and embryo under a powerful microscope. You observe radial cleavage at the 4-cell stage and that the pore formed by gastrulation in the developing embryo eventually ends up being the anus of the embryo. Why is this unexpected and what do you now know? Radial cleavage at the 4-cell stage of development and anus formation through gastrulation are diagnostic features of the deuterostomes (the &quot;second mouths&quot;). Because snails are gastropod mollusks, which are protostomes, these developmental features are unexpected (protostomes possess spiral cleavage at the 4-cell stage and mouth formation through gastrulation). Thus, you are most likely dealing with a deuterostome (or an amazing case of convergent evolution in a snail). 3) You discover another organism that again you suspect is a little slug (like snails, slugs are gastropods, a type of mollusk). Upon close inspection, you observe that this organism grows by molting and has a pseudocoelom. After noting this information, to what group might your organism belong? Molting is a defining feature of the Ecdysozoa and the nematodes are ecdysozoans that possess a pseudocoelom. Your little &quot;slug&quot; might be a roundworm (nematode). 4) Name a model organism in each of the following groups: GROUP Prokaryotes Fungi Plants Protostomes Deuterostomes MODEL ORGANISM Escherichia coli <a href="/keyword/saccharomyces-cerevisiae/" >saccharomyces cerevisiae</a> (yeast) Arabidopsis thaliana (thale cress) Drosophila melanogaster (fruit fly) &amp; <a href="/keyword/caenorhabditis-elegans/" >caenorhabditis elegans</a> (roundworm) Danio rerio (zebrafish) &amp; Mus musculus (mouse) 5) Using the tetrapod phylogeny to the right, a. Place a labeled notch on one branch where an increased investment in offspring evolved and explain. 1) The amniotic egg is packed with nutrients and fluids for a developing embryo. 2) Lactation occurs in mammals, where mothers provide their offspring with nutrientrich milk. lactation amniotic egg limbs b. Place a labeled notch on one branch where an innovation important for the transition from water to land occurred and explain. 1) The amniotic egg is encased in a watertight shell that prevents desiccation. 2) Limbs are important to tetrapod movement on land. c. If you point at a robin, starling or crow on campus and ask someone &quot;What's that?&quot;, they probably will not answer &quot;A reptile&quot;. Explain why the birds might be placed in the reptile group above. In the colloquial sense, &quot;reptiles&quot; generally refer to turtles, lizards, snakes, alligators, pterosaurs and dinosaurs (but not birds). However, according to current phylogenetic understanding, such a reptilian group would be paraphyletic (how do you know this?) For some systematists, terms to label groups must be monophyletic. If one wants to retain the term &quot;reptiles&quot; and wants this term to refer to a monophyletic group, then birds must be considered reptiles. 6) You go to a fancy fusion restaurant and are served a plate of salad with arugula (a dicot), shredded swiss cheese, grilled mushrooms, and roasted pi on pine seeds. The main course is lobster in clam sauce. For dessert you have kelp marinated in jalape o peppers (the fruit from a dicot). Explain which of the following groups made your meal possible: Group Prokaryotes Protists Mosses Gymnosperms Angiosperms Fungi Lophotrochozoa Ecdysozoa Chordata Part played (if any) in your meal Bacteria ferment lactose in the production of Swiss cheese The kelp in your dessert is brown algae No mosses were harmed in the preparation of your meal The roasted pi on seeds come from an gymnosperm (a pine) The arugula and jalape o are dicots The grilled mushrooms are basidiomycetes The clam sauce came from a mollusk (bivalve) Lobsters are arthropods (crustaceans) The milk for the cheese comes from a mammal 7) Name a few features in mollusks or arthropods that allowed a transition from water to land. Terrestrial arthropods have a watertight exoskeleton that minimizes water loss and insect eggs have thick membranes to prevent desiccation. Many land snails have a shell on their body and a thin calcium carbonate shell on their eggs to prevent water loss. 8) Using the phylogeny below, a. Place labeled notches representing the gain of the following: i. Hollow nerve cord ii. Radial symmetry iii. Triploblasty iv. Cephalization v. The coelom vi. Bilateral symmetry vii. Diploblasty viii. Protostome development ix. Deuterostome development x. Multicellularity xi. Growth by molting b. List two traits that are thought to be analogous among different organisms on the tree. Place notches on the appropriate branches where independent gain occurs. The following traits are thought to be analogous: 1) 2) 3) 4) Pseudocoeloms in rotifers and nematodes (labeled &quot;p&quot; notches) Segmentation in annelids and arthropods (labeled &quot;s&quot; notches) Radial symmetry in ecinoderms (compared to, say, cnidarians) (labeled &quot;r&quot; notch) Acoelomate condition in flatworms (compared to acoels) (labeled &quot;a&quot; notch) choanoflagellates ctenophores nematodes arthropods ecinoderms cnidarians flatworms annelids rotifers mollusks p a s p molting s r hollow nerve cord, notochord and muscular tail es tom tos pro deuterostomes coelom bilateral symmetry, triploblasty, cephalization radial symmetry, diploblasty multicellularity chordates sponges acoels c. Suppose that the most recent common ancestor to rotifers and chordates had no coelom. Also suppose that the most recent common ancestor of nematodes and arthropods lacked a coelom. It is possible to account for the coelom and pseudocoelom lineages solely through several independent gains of either the coelom or pseudocoelom. Using a fresh copy of the phylogeny below, place a small triangle over each branch where a gain of the coelom occurs and a small square over each branch where a gain of the pseudocoelom occurs. Use the minimum number of gains. choanoflagellates ctenophores nematodes arthropods ecinoderms cnidarians annelids rotifers no coelom gain of pseudocoelom gain of coelom chordates flatworms mollusks sponges acoels