• To explore the general anatomy of representative vertebrates.

• To locate and identify major vertebrate organs and structures in the digestive and cardiovascular systems in species from three vertebrate classes.

• To understand major evolutionary trends and specializations among three vertebrate classes.

• To learn dissection techniques.

• To recognize the relationship between structure and function in vertebrate organs and systems.

• To construct hypotheses and interpret quantitative data.

Your preserved specimens have been fixed in mild formalin (liquid formaldehyde), thoroughly washed and then preserved in Carosafe. Carosafe is an odorless preservative primarily made up of propylene glycol. Propylene glycol is considered safe by the Food and Drug Administration and is used in numerous foods. Although concentrations of formaldehyde are extremely low please discuss this lab with your instructor if you are, or think you are pregnant.

• Write the Lab Title on a new page on the right-hand side of your notebook. *Remember to include the Lab Date!*

• Write the Background, Aim and your Hypotheses for the lab

• Copy the Data Collection Template (see Part I. Procedures) into your lab notebook.

• Add an entry for this lab in your Table of Contents.

• Model Organisms: yellow perch, leopard frog, mudpuppy, American mink and domestic pig

• Experimental Question: Does relative heart size differ among vertebrates? If so, why?

• Independent Variable: Type of vertebrate

• Dependent Variable: Relative Heart Mass (RHM): the ratio of heart mass to body mass

• The Endothermy Hypothesis:

  • I hypothesize that thermoregulation strategy (choose) will / will not have a significant influence on Relative Heart Mass (RHM). I predict that the Relative Heart Mass (RHM) of ectotherms (fish and amphibians) will be (choose) higher / lower / not significantly different from the Relative Heart Mass (RHM) of mammals (mink, pig)

• The Terrestrial Hypothesis:

  • I hypothesize that habitat type (choose) will / will not have a significant influence on Relative Heart Mass (RHM). When comparing fully aquatic organisms (fish) to amphibians (frogs and mudpuppies) to mammals (mink, pig) I predict the following differences: [List which groups you think will be higher / lower / not significantly different from others]

• The Tetrapod Hypothesis:

  • I hypothesize that locomotion strategy (choose) will / will not have a significant influence on Relative Heart Mass (RHM). I predict that the Relative Heart Mass (RHM) of finned animals (fish) will be (choose) higher / lower / not significantly different from the Relative Heart Mass (RHM) of 4-limbed walking animals (frogs, amphibians, mudpuppy, mink, pig)

The Vertebrates

Phylum Chordata

As primate representatives in the Subphylum Vertebrata, we are one of just under 50,000 species. The Chordates contain both invertebrate and vertebrate groups.

The defining characteristics of the Phylum Chordata are:

• hollow, dorsal nerve cord

• notochord

• pharyngeal gill slits

• post anal tail

Subphylum Vertebrata

The vertebrates have a backbone composed of vertebrae and include the fishes, amphibians, reptiles, birds and mammals. Vertebrates include the following classes: Chondrichthyes (rays, sharks, and relatives), Actinopterygii (ray-finned fishes), Amphibia (frogs, salamanders, and caecilians), Reptilia (turtles, snakes, lizards, crocodiles and their relatives), Aves (Birds) and Mammalia (Mammals).

In this lab, we will explore model organisms from these three vetebrate classes:

Class Actinopterygii (Ray-finned fishes)

Actinopterygians, or ‘ray-finned fishes,’ are the largest and most successful group of fishes and make up half of all living vertebrates.

This group will dissect a yellow perch as an example of a ray-finned fish.

Class Amphibia (frogs, salamanders, and caecilians)

The Amphibians are the first terrestrial vertebrates and include three Orders:

• Anura (frogs and toads) with about 5,800 species

• Caudata or Urodela (newts and salamanders) with about 580 species

• Gymnophiona or Apoda (caecilians) with about 170 species

All amphibians are cold-blooded animals and most metamorphose from a juvenile to an adult form.

This group will dissect a leopard frog or a mudpuppy (necturus) as an example of an amphibian.

Class Mammalia (Mammals)

All mammals share at least three characteristics not found in other animals: 3 middle ear bones, hair, and the production of milk by modified sweat glands called mammary glands. The three middle ear bones, the malleus, incus, and stapes (more commonly referred to as the hammer, anvil, and stirrup) function in the transmission of vibrations from the tympanic membrane (eardrum) to the inner ear. The malleus and incus are derived from bones present in the lower jaw of mammalian ancestors. Mammalian hair is present in all mammals at some point in their development. Hair has several functions, including insulation, color patterning, and aiding in the sense of touch. All female mammals produce milk from their mammary glands in order to nourish newborn offspring. Thus, female mammals invest a great deal of energy caring for each of their offspring, a situation which has important ramifications in many aspects of mammalian evolution, ecology, and behavior (Klima and Maier, 1990; Vaughan, et al., 2000).

This group will dissect either an American mink or a domestic pig as an example of a mammal.

Dissection is a tool to examine organismal form and function

This week, you will be working in groups to explore one of the classes of the subphylum Vertebrata. You will present your findings to the class at the beginning of next week's lab. Each student or pair of students will have a representative animal to examine external and internal anatomy.

We have all noticed how photographs and diagrams look quite different to the real thing— hence the need to experience animal dissections. This teaching tool should allow you to relate more closely to the structure and function of the various organs and organ systems found in vertebrate animals.

Dissection Procedures

You have been assigned one of a variety of vertebrate species to dissect (larger specimens will be dissected by two students). As a whole, the class will examine digestive, cardiovascular and reproductive systems in three vertebrate classes:

• Class Osteichthyes, the ray-finned fishes represented by the perch, a geologically young species

• Class Amphibia, the amphibians, represented by an ancient species, the mudpuppy, and the more recently evolved leopard frog

• Class Mammalia, the mammals, represented by a carnivore, the mink, and the fetus of an omnivore, the pig.

Printed copies of dissection guides and procedures for each organism will be provided during the lab.

Data Collection Template

PreLab Prep! Copy the following table into your lab notebook as part of your pre-lab assignment. You will record these observations and measurements during the dissection.

The science of comparative anatomy is the study of structure and function and how that varies across evolutionary history. More than just naming veins or bones, comparative anatomy tries to make sense of morphology (anatomical shape) by comparing closely related organisms with one another. Alternately, if an organism’s identity is unknown (as it is in many fossils), we can compare the morphology to other species with known diet, habitat and evolutionary history. Comparative anatomy bridges the disciplines of physiology and evolution.

The anatomy and physiology of animals is shaped by their environment through natural selection. Cardiovascular systems have evolved in a variety of different ways in both invertebrates and vertebrates. Some animals, like sharks, are poikilothermic or "cold-blooded." This means they rely on external heat sources to supplement the body’s metabolic heat. Others, like birds and mammals, are endothermic or "warm-blooded." Their metabolism is raised so high that the body maintains a constant internal temperature, regardless of the environmental temperature. Even within these categories, animal lifestyles differ greatly, as does their cardiovascular function. Desert-dwelling mammals (which are endothermic) may have extremely vascularized ears of very large size, allowing excess body heat to escape. In contrast, whales have an arrangement of blood vessels that help trap heat as blood flows through their flukes-- a great adaptation in the icy arctic waters these mammals call home. The science of comparative anatomy allows us to explore what differences or similarities there might be and how they may have arisen.

The vertebrate heart has evolved in how it allows oxygenated and deoxygenated blood to mix, resulting in hearts evolving from a 2 to 3 to 4 chambered organ. Yet in each case the heart must use tremendous power to move even a small volume of blood through enormous numbers of tiny capillaries. Elephants use gigantic hearts that pump enormous volumes relatively slowly (~30 beats per minute), whereas mice have tiny hearts but extremely rapid (600 beats per minute) heartbeats. There are far greater differences between the different vertebrate classes.

There are many reasons why heart size might differ among vertebrate classes. Obviously heart size could be large in large animals, so instead we compare the relative heart mass (RHM). The RHM is calculated by dividing the mass of the heart by the body mass (before dissecting).

1. Discuss Hypotheses

There are many reasons why heart size might differ among vertebrate classes. Obviously heart size could be large in large animals, so we can compare the relative heart mass (RHM). The RHM is calculated by dividing the mass of the heart by the pre-dissection body mass.

With your lab group, discuss and formulate three alternative hypotheses regarding why relative heart size differs among the organisms dissected the lab.

Think about how the heart may have evolved for each of the specimens. For each of the hypotheses below (except the null), think of a biological reason why heart size would need to change, and complete the statement. Hint: Would RHM respond to changes in blood volume? Flow rate? A change in resistance to blood flow? How are these variables related to body form?

2. Examine the data

We know that experiments are improved by having many people help generate data. This is why we pool data on heart mass/body mass from other lab sections and past semesters, and make it available to all BIO 131 students for the comparative analysis portion of the lab.

Your instructor will provide you with a link to the dissection data sheet for these pooled data. You will add your own data to this spreadsheet.

3. Manipulate your data to create a testable variable

Often scientists collect data that cannot be analyzed directly, due to confounding variables. For instance, heart size may (or may not be) impacted by evolutionary history, but it IS impacted by the age and size of the species. Rather than work with heart mass, you will take into account the size of the organism by creating a ratio of heart mass to specimen mass. This is the relative heart mass (RHM).

Relative Heart Mass = (Mass of heart in grams) / (Mass of whole specimen in g)

First, download the Google spreadsheet to Excel. Then, calculate the relative heart mass for each specimen and enter these values into your downloaded Excel spreadsheet.

4. Summarize your data with descriptive statistics

• Decide what organismal groups (independent variable) to include in your analysis. These can include each of the five vertebrates included in the data set, but also may include additional groups relevant to your hypothesis. Hint: Think about the animals' morphology, thermoregulatory strategy, lifestyle, etc. Can any of the organisms be grouped together?

• Calculate mean and standard deviation for RHM for each of your organismal groups.

• Generate a figure that illustrates a relationship of RHM to another variable. Be sure to include a figure caption!

• Decide whether you should use a t-test or an ANOVA to determine whether differences between your groups are statistically significant. Perform the appropriate statistical test.

• Write a description of your results with a brief conclusion. Do your data strongly support the alternate hypotheses?