Dr. Paul Tabor
1. We are most familiar with the human heart and circulatory system but circulatory systems have evolved quite differently (click on Evolution of the circulatory system in the headings list) in other animals to meet the needs of oxygenation and waste removal from tissues. For each group of animals below can you suggest why the circulatory system is appropriate to meet their metabolic needs? Although there is little in the way of a developed heart, the annelid worms (click on Annelids in the headings list) have a closed circulation system. Why don't they need a strong heart? Crabs and lobsters certainly have higher metabolic activities than annelids but they have an open circulatory system but a strong central heart (click on Crustacea in the headings list). The hemolymph of lobsters is sucked through the gills and reoxygenated before going to the heart. It then heads out the arteries to the open body cavity. Why would this be beneficial for lobsters? Within the Molluscs, (click Molluscs in the headings list) there is a wide diversity in amount of metabolic activity and a wide range of circulatory system development. The fast-swimming squids have two hearts that act as inline pumps. What is the role of each heart? Insects have a tracheae system to provide oxygen to the tissues. This modification along with others makes it possible for flying insects to achieve higher metabolic rates than any other animals. The open circulatory system with a heart that has muscles that cause it to expand (click Insects in the headings list) and act like a sump pump to collect returning blood. Although the insect heart is not needed to supply oxygen to the tissues, it has two important roles. One role is to efficiently supply nutrients to tissues. For an animal that has a very high sustained metabolic rate, what do you think the circulatory system might be removing? Ray fish (click Fish circulatory system in the headings list) have closed circulatory systems and the blood flows to the gills for oxygenation after leaving the heart. Lung fish have both lungs and gills and the circulatory system can determine if blood should flow into the lungs or through the gills only. What conditions in the lung would determine if blood should flow there? Frogs are amphibians (click on Amphibians in the headings list) and have hearts that still allow oxygenated blood to mix with non-oxygenated blood before being pumped to the tissues. What is the construction of the heart that allows this to happen? What is the first animal that evolved a heart that entirely separates pulmonary and systemic blood flow?
2. We classify animals for many purposes. One of the most important reasons is to group animals that are similar into the same groups. The major tool that biologists use for classifying organisms is cladistics. The importance and usefulness of cladistics to biologists is that this method is based on evolution of organisms. A cladogram can be useful, for example, to explain the split of two major groups of dinosaurs. Another way to present information is to construct a phylogenetic tree. Let us suppose you have been thinking about having a pet dog, a cat and a skunk and you want to know which two are more closely related. Fortunately, there are sources on the Internet that allow you to discover the answer. You want a customized phylogenetic tree. You already know that your pets are vertebrates so you can choose vertebrates to find more information. Since you want to discover more about interrelationships between animals, you need to choose the systematics button on the Introduction to Vertebrates page. The cladogram on the Vertebrate Systematics page has the group that you are interested in -the Tetrapoda. On the Introduction to the Tetrapoda page you can discover an important common characeristic of all of these vertebrates. Your pets are all mammals and on the Phylogeny of Mammals page you want to discover more about the placental mammals, of which your three pets are included. To continue to specify how you pets are related, you need to look at the systematics of the Eutheria (placental mammals). The cladogram on the Eutheria systematics page contains Carnivora, the group that includes all of your pets. The discussion on the Carnivora page metions the numerous human (primate) - Carnivora interactions, including having carnivores as pets. Finally, you can find the interrelationships of your pets by learning more about Carnivora systematics. On the Carnivora systematics page you find a phylogenetic tree classifying animals down to the family level. Are you surprised about the interrelationships of your pets?
3. Throughout the history of the Earth animals have become extinct. For example, most of the animals of the midwestern US 40,000 years ago are extinct today. In fact, all species will eventually become extinct through the process of evolution. Extinction decreases the biological diversity. Some forces that lead to extinctions are natural and some are the results of man's activitie (even man's activities 40,000 years ago). There have been mass extinctions in the past. Does that mean that mass extinctions can be expected again? There is concern about man's activities causing mass extinctions and endangering many species. These activities are decreasng the biodiversity on Earth. It is easy to understand that decreasing biodiversity will remove some benefits to man such as ecosystem services (natural recycling for example), biological resources and social benefits. But the greatest value of biodiversity is in respect to the process of evolution. What is the greatest value of biodiversity? There is a tremendous reference on the www for information on endangered species.