Concepts:

1. Evolution of Sexual Reproduction in Lineages
2. Benefits and Limitations of Sexual and Asexual Reproduction
3. Environmental Conditions Favoring Each of These Mechanisms

Skills:

1. Information gathering via WWW or library resources
2. Concept building - Comparison of Asexual / Sexual Systems
3. Construction of Hypotheses

Information:

1. Ecological Conditions Correlated to Sexual / Asexual Reproduction
2. Major Lineages and Their Reproductive Strategies
3. Ecological Characteristics of a Wide Range of Lineages
4. Evolution of Sexual Reproduction

1. Students will successfully collect information on asexual vs. sexual reproduction.
2. Students will complete a handout table in order to make comparisons.
3. Students will construct a hypothesis concerning the evolution of asexual and sexual reproduction.
4. Students will understand the relationship between an organism's environment, evolutionary history, and current condition and relate that to evolutionary-stable reproductive strategies.

1. Computer with access to the WWW, otherwise, library resources
2. Handout
3. 1 Instructor per 5-6 students

Procedure

Opener

Prior to starting the lab, students should have an introduction to the basic mechanisms behind asexual and sexual reproduction. For instance, students should understand that sexual reproduction involves the sharing of genetic material, and a heterogametic offspring is the result. Offspring carry new combinations of genes, and are therefore unique individuals genetically. In contrast, asexual reproduction results in an identical copy of the parent organsisms, and therefore does not lead to new combinations of genetic material via recombination. For our class, students had previous labs on human reproduction and Nematostella, an asexually-reproducing cnidaria which can be found in the local area. Students had experience with each of these labs in-depth, and each lab was reviewed before the handout was given to them.

Procedure:

Students should be given the handout provided HERE: once students have read through the instructions, begin a conversation about some of the lineages listed on the page. For instance, students should have a good idea of whether or not mammals have evolved sexual reproduction. However, some of the more obscure lineages (protists, monera, fungi), may be a bit harder to figure out. Encourage students to explore the answer to these questions online or at the library. Students should spend a class perios filling out the supplied table, and a second period may be used to discuss this table and formulation of a hypothesis on the second page of the handout.

Closure

Students should, by the end of the laboratory, clearly understand the role that evironment, evolutionary history, and current condition plays in what reproductive strategy is used by a variety of lineages. Organisms that are in constant environements or are limited by time or space often fair better by reproducing asexually, as this is a fast reproductive strategy which can increase a population exponentially (think bacteria). On the other hand, sexually-reproducing organisms have the advatage of creating new mutations and traits in their offspring, which may be helpful in a constantly changing environment, where rapid reproduction may not be an adavantage. Lineages that are capable of both asexual and sexual reproduction (invertebrates, plants, fungi, etc.) get the best of both world in a sense, and can adjust their reproductive behaviors based on current environmental conditions. Students should think about other factors, such as size (large, complex multicellular organisms would have a hard time reproducing asexually) when formulating their hypotheses.

Students should be evaulated on based on the completion of their table on the handout and the quality/thoroughness of their hypothesis development.

Students may choose a lineage to further explore in depth. Presentations can be made so that the class as a whole may be able to see a variety of information on a wide range of organisms without spending the time to explore them individually. Included in the prensentations may be the role that sexual / asexual reproduction plays in a variety of organisms within the chosen lineage.

http://www.tol.org