project INDEPENDENTPROJECTI:DESIGN&IMPLEMENTATION
This will involve your exploration of some anatomical feature of vertebrates and a poster presentation that reports your results. This project is not a literature review and will require both examination of anatomical descriptions in morphological literature and anatomical investigation of vertebrate specimens available to you in the laboratory. SelectingaProject To begin you should select an anatomical structure(s) in which you have some interest. You may choose any structure that is feasible to study within the limits of the facilities available and which is not explored in significant detail in lecture or laboratory. Paying some attention to function (or at least function as inferred from anatomical structure) will likely be important. The functional connection would be especially important for structures such as muscles for which function can be clearly inferred from structure. You MUST clear your choice of structure with your instructor. No two groups of students may study the same structure. Once you have selected your structure, you must propose an evolutionary hypothesis that you will test. Your hypothesis or question should be based on your knowledge of vertebrate relationships and anatomy. Keep in mind that your hypothesis can suggest that a structure will vary based solely upon function, based solely upon ancestry, or (preferably) based upon some combination of the two. Your hypothesis can be very general to start. However, it is expected that after some examination of specimens you will be able to propose a more refined hypothesis (Table 1). ResearchingBackground With any scientific study you must begin by looking into what already exists in the published literature. The best place for you to start will be your texts. If your structure is not mentioned, then read about any associated structures (e.g., if you are exploring the vasculature of the pancreas, then you should read about the pancreas AND the visceral vasculature in your lecture text and review the sections on the visceral vasculature of Squalus acanthias, Necturus maculosus, Oryctolagus cuniculus, and Felis cattus in your lab manual). It is assumed that you have read and fully understand the pertinent sections of the textbook. After reading what is available in the texts, you should proceed to the library. Do not let the age of some of the anatomical sources dissuade you. Unlike in molecular biology where resources more than a couple of years old are considered out of date, anatomical resources over a hundred years old are often better than some recent works as sources of information. WARNING: In some older sources, different names are given to structures based on past naming conventions or older hypotheses of homology (if you are confused about a term used in one of these works ask your instructor). For some organisms you should be able to get detailed anatomical information from the literature. I expect that you will get your data concerning human, Homo sapiens, anatomy from outside sources since we will not have access to a cadaver lab. The sources available on human anatomy should be sufficient for your purposes. The sources must be of sufficient detail to be considered academic (meaning greater detail than is presented in an undergraduate human anatomy textbook). Simply examining the human anatomy models available in the biology department will NOT be sufficient. A type-written complete draft of your Introduction and Materials and Methods (with at least 5 academic sources cited in text and the full citations of these sources) will be due earlier in the semester to ensure that you have completed your background research early in the project and have examined enough specimens to refine your hypothesis. Table1.Exampleinitialandrefinedhypothesesdevelopedafter examinationofspecimensandtheprimaryliterature. InitialHypothesis RefinedHypothesis More active vertebrates will Endothermicvertebrates,which have more extensive typically have more active coronarybloodvessels lifestyles, will have more extensive coronary vasculature and thus rely less upon oxygen from blood in the heart lumen thanectothermicvertebrates. Tetrapodvertebratesthatuse Tetrapod vertebrates that their forelimbs for typicallymovetheirmanuswith manipulation of objects will greater precision will have a have more complex muscles more complexly divided intheforelimb. forelimbmusculatureandthese muscles will have longer tendonsconnectingtoinsertion pointsonthemanus. The ligaments supporting the Similarity in the position, liver in vertebrates will be number, and extent of hepatic mostsimilarincloselyrelated ligamentsinvertebrateswill be vertebratesregardlessofhow similar among more closely thevertebratesmove. relatedvertebratesandwillnot correlate with the type of locomotion utilized by the animal. GettingStarted For these projects you will likely need to examine as many species and individuals as possible (Table 2). Any hypothesis about anatomical evolution requires the examination of a lot of animals to be reasonably supported (or rejected). Keep in mind that some species may be more readily available than others. The variety of whole preserved specimens will be greater than that of prepared skeletal material. Some material that Regis owns may not be available for dissection. If you are ever in doubt about whether or not you are allowed to dissect a specimen, WAIT AND ASK YOUR INSTRUCTOR. Additionally, do not expect to be able to convert whole preserved material into skeletal material. This process can take months depending on the size of the specimen being prepared. You must use your lab notebook for gathering data. There are no specific requirements for the structure of this notebook (e.g., spiral bound, sewn binding, loose sheets in a binder). Your data should be gathered as sketches and descriptions. For each specimen examined you should:
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Write the scientific species name of the specimen being examined. Indicate any individual peculiarities of each specimen. Is its coloration distinctive? Has it been damaged in some distinctive way (e.g., missing left hindlimb)? Is it labeled in some way? Describe the features of your structure. It is not uncommon to have to re-examine specimens after you have looked at other species. Your perspective may change after observing how something varies in another species. Be certain that you gather and record as much general information as possible about each individual before you record your anatomical information. Measure each specimen's size. For lampreys use total length to measure size (length from tip of nose to tip of tail). For sharks use fork length to measure size (length from tip of rostrum to fork of caudal fin). For actinopterygiians use standard length to measure size (length from tip of nose to distal edge of hypural plate). For non-mammalian tetrapods use snout-vent length to measure size (length from tip of nose to center of cloaca). For mammals use snout-anus length to measure size (length from tip of nose to anus).
structure varies within a species. This is not an uncommon occurrence. Be certain that you have some means of telling individuals apart. If the information on size, sex, and individual characteristics are not sufficient to tell individuals apart, label them. You will likely want to examine all of the species available. However, your hypothesis or question may make that unnecessary (e.g., a study of knee joint anatomy would be useless on nontetrapods and snakes). If you do not examine one of the available species be certain that you clearly understand why you did not examine those species in light of your hypothesis/question. If you are only examining a few species (5 or fewer), then your hypothesis is evolutionarily too narrow for this project and you should expand it or devise another Dissection one. When dissecting specimens you must try to do as little damage as possible. If the structure you need to dissect is bilateral, then dissect only the right side leaving the left side intact. The specimens you examine will likely be examined by the rest of the class. Treat them gently and try not to destroy something that someone else may need to examine. Use the dissection microscopes whenever appropriate. These microscopes do not bite and are designed to facilitate dissection of small specimens. Dissecting microscopes are simple to use and they will make structures more visible.
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Identify each specimen's If you need to remove something gender and its from a specimen to observe it, (1) reproductive condition, YOU CANNOT BEGIN EXAMINING SPECIMENS make all of the observations you sexual maturity or what TOO EARLY! can with the organ or structure in stage of sexual activity it place, (2) discuss with your START LOOKING AT SPECIMENS AS SOON AS is at (e.g., pre-spawning instructor which specimens would POSSIBLE EVEN IF YOUR HYPOTHESIS HAS female with ovary full of be appropriate for destructive NOT BEEN COMPLETELY FLESHED OUT ova, pregnant female with dissection, (3) discuss with your embryos of about 2 cm COMPARATIVE ANATOMICAL STUDY instructor when you should fork length) Determining REQUIRES A LOT OF SIMPLY LOOKING AT perform these dissections, and (4) gender will be easy for SPECIMENS AND NOTING SIMILARITIES AND replace the removed organs if specimens with clearly DIFFERENCES possible, otherwise place them in identifiable external labeled jars in preservative as genitalia. However, for directed by your instructor. Some some species you may have to examine their internal specimens will not be available for this kind of dissection. reproductive anatomy to determine sex. Reproductive condition will have to be determined internally. BeginningToConsiderYourData Determination of reproductive condition is most important An interpretation of your data may be obvious. However, for non-amniotes since these species usually have very rearranging your data can often make interpretation easier or allow pronounced seasonality and high fecundity. Remember that you to see patterns that were not obvious otherwise. Some ways to anatomy can vary based upon sex (sexual dimorphism) and look at your data are: can vary with season, especially reproductive season, as 1. Arrange rough drawings, descriptions, or summaries of the well. structures in various organisms in a table with organisms 6. Indicate the anatomical preparation and preservation of each grouped taxonomically. specimen (e.g., Is it preserved in ethanol, Carosafe, 2. Arrange rough drawings or very short descriptions of what Wardsafe, or some other substance? Has its vascular system varies along the top of the phylogenetic tree provided in the been injected with colored latex? Is it single injected, double manual. injected or triple injected?) Don't go crazy with this. A simple indication of kind of preservative is sufficient. Don't 3. Arrange rough drawings, descriptions, or summaries of the list all the ingredients in Carosafe or Wardsafe. structures in various organisms in a table with organisms grouped based on pertinent qualities mentioned in your 7. Examine your structure and associated structures in the hypothesis. (Physiology, Diet, Function, etc.) specimen. Sketch the structure and/or write a prose description of the structure. How is it shaped? How is it 4. Consider what anatomy would be intermediate between the colored? To what is it attached and how? anatomical forms you saw in the species you examined. Would these intermediates be functional? For each species examined you will want to examine as many individuals as possible. Do not be surprised if your anatomical 5. Consider how each type of structure would develop.
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Consider the natural history/ecology of the organisms examined and how that natural history would affect the functioning of your organ.
Table2.Thespeciesofspecimensthatwillbemadeavailabletoyou.
ClassPetromyzontida OrderPetromyzontiformes Petromyzonmarinus,sealamprey ClassChondrichthys OrderSqualiformes Squalusacanthias,spinydogfishshark ClassActinopterygii SubclassAmiiformes OrderAmiiformes Amiacalva,bowfm SubclassTeleostei OrderPerciformes Moronsamericana,whiteperch Percaflavescens,yellowperch Pomadasysmagranthus,Mexicangrunt ClassLissamphibia OrderUrodela Necturusmaculosus,mudpuppy OrderAnura Ranacatesbeiana,bullfrog ClassReptilia SubclassTestudinea OrderCryptodira Chrysemyssp.,paintedturtle SubclassLepidosauria OrderIguania Anoliscarolinemis,Americanchameleon OrderSerpentes Nerodiasp.,watersnake SubclassArchosauria InfraclassCrocodylia OrderAlligatoroidea Alligatormississippiensis,alligator* InfraclassAves OrderColumbiformes Columbalivia,rockdove(pigeon) OrderGalliformes Gallusgallus,domesticchicken** ClassMammalia SubclassEutheria OrderCarnivora Feliscatus,domesticcat Mustelavison,mink OrderLagomorpha Oryctolaguscuniculus,domesticrabbit OrderRodentia Rattusnorvegicus,Norwayrat
* Thealligatorspecimenmustberequestedfromtheinstructorandisnotavailablefordestructiveexamination. ** Additionalspecimensshowingthemusculoskeletalsystemandcertainorgansareavailablefromgrocerystores. Wemaynotbeabletomakealloftheseavailableifnot,thelistwillbemodified.
AddressingYourHypothesis Remember that a single conflicting datum is enough to reject a hypothesis. If your hypothesis is that endothermic organisms will have only one of some kind of duct and ectothermic organisms will have two or more of some duct and your data agree except that the frog (an ectotherm) has only one duct, then you MUST say that your hypothesis is rejected. If you have some idea why the exception was an exception, you can then suggest a revised hypothesis that could be tested in the future. If your hypothesis concerns the correlation of a type of structure with a specific function, then the implication is that the similarity is due to function NOT due to ancestry. Therefore, finding two or more members of a closely related group that have differing function will be the best data to use for supporting or rejecting your hypothesis, (e.g., If all the mammals in your study exhibit a specific structure the simplest explanation is that they share it simply because they are mammals and not because they are functionally similar since many of the mammals examined may use the structure very differently.) Whatever your hypothesis is based upon be certain that you understand very well what characteristics each organism examined exhibits. For example, a study exploring the hypothesis that the liver will have a specific structure in endothermic organisms requires that you know about and can categorize the thermal physiology of all the specimens examined. This means that for this hypothesis you need to know, not only that birds and mammals are endothermic, but also more detailed facts about comparative vertebrate physiology. For this hypothesis this would mean that you would need to know that birds usually have higher metabolic rates and body temperatures than mammals and also that testudineans, lepidosaurs, and crocodylians (ectotherms) typically have a higher metabolic rate and usually regulate their body temperature to be higher than the lissamphibians (ectotherms) etc. You will likely have to do literature research to learn these things. Remember that the flexibility, texture, and especially the color of structures can be altered by the method of preservation and injection used. A red, blue, or yellow color could be the result of latex injection. Additionally, certain colors fade more rapidly in certain preservatives.
Modified from M. J. Ghedotti, Regis University