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Joan Sharp
Teaching Professor
Department of Biological Sciences
Simon Fraser University
A Deadly Passion: Sexual Cannibalism in the Australian Redback Spider

This "clicker case" teaches students about the distinction between proximate and ultimate causes of behavior using the fascinating courtship and mating rituals of the Australian redback spider. The case is presented in class via a PowerPoint presentation (~3MB) punctuated by multiple-choice questions that the students answer using personal response systems, or "clickers." It could be adapted for use without these technologies. Although developed for a general biology class, the case would also be suitable for use in non-majors introductory biology or behavioral ecology courses.

A Tale of Three Lice: A Case Study on Phylogeny, Speciation, and Hominin Evolution

This “clicker case” explores the questions of when hominins lost their body hair and began wearing clothing by examining the surprising phylogeny of human head, body, and pubic lice. Students are led through the scientific process as they are asked to think about hypotheses, predictions, results, and conclusions, and learn about phylogeny, speciation, and hominin evolution. The case is presented class using a set of PowerPoint slides (~1.5MB) that includes multiple-choice questions students answer using personal response systems (“clickers”). It could be adapted for use without these technologies.  Developed for a general biology class focusing on evolution and ecology, the case is also suitable for use in a non-majors introductory biology course.

Animals Can Run Away, but Plants Must Stay: Responses to Herbivory

In this PowerPoint-driven case study, students consider the many challenges faced by plants and discuss which of these might induce a morphological response. Examples of phenotypic variation within a plant species are presented and students discuss in small groups how to determine whether the observed variations have a genetic basis. The concept of a "common garden" experiment, in which plants are grown in a common environment and variation is measured, is elucidated and discussed. A specific example of phenotypic variation is introduced: Plectritis congesta from islands without herbivores (deer) are taller than the same species from islands with deer. An experiment with simulated herbivory is described and students are asked to predict results, assessing whether modification of pattern of growth is an induced response or a constitutive defense. A field experiment involving deer predation is introduced. The morphological response of Plectritis to predation is presented as an evolutionary tradeoff. The case is appropriate for introductory general biology (majors and non-majors), ecology, and plant biology courses and, with some modification, introductory evolution courses.

Cross-Dressing or Crossing-Over?: Sex Testing of Women Athletes

In this “clicker case,” students learn about sex determination, meiosis, and chromosomal “crossing over” through the story of Santhi Soundararajan, an athlete from Kathakkurichi, India, who was stripped of a medal at the 2006 Asian Games after failing to pass a sex test. The case is called a clicker case because it combines the use of student personal response systems (clickers) with case teaching methods and formats. The case itself is a PowerPoint presentation (~2 MB) shown in class that is punctuated by questions students respond to using their clickers. It can be adapted for use without these technologies. Developed for an introductory biology class for both majors and non-majors, the case could also be used in an anatomy and physiology course or an endocrinology course.

Selection and the Blond Beach Mouse 

This "clicker" case study explores ultimate and proximate explanations for cryptic coloration in animals through the work of Dr. Hopi Hoekstra of Harvard University, who studies Gulf and Atlantic Coast beach populations of oldfield deer mice that have evolved blond fur coloration. An ultimate question addresses the adaptive value of blond coloration, exploring how cryptic coloration increases the evolutionary fitness of a beach mouse. Proximate questions address the mechanisms that produce blond coloration, such as the genetic and developmental mechanisms that alter mouse coat color. Students work in small groups to plan an experiment to assess the design of a published experiment and analyze the results. They learn about roles of mutant alleles of two pigment genes (Mc1r and Agouti) in producing blond coloration in several subspecies of beach mice, as well as woolly mammoths. Finally, students weigh evidence from genomic analysis to select between two contrasting hypotheses about the origin of the blond Mc1r allele. The case is presented in PowerPoint format and includes both a detailed and simplified slide set, allowing instructors to select the most appropriate version for their class. Several recommended videos make it possible to teach the case in a "flipped classroom" setting.

Sex and the Komodo Dragon 

In this clicker case study for a flipped classroom, students familiar with the stages of meiosis work in small groups to determine the predicted genetic makeup of the parthenogenetic offspring of a Komodo dragon, based on four different types of parthenogenesis. Students then learn about the actual genetic makeup of the offspring and determine how meiosis was modified to allow parthenogenesis in this fascinating lizard. The sex of the offspring is explained, based on ZW/ZZ sex determination. A video specifically made for this case prepares students for the in-class activities, which are guided by a PowerPoint presentation. The case also examines how facultative parthogenesis may be adaptive in Komodo dragons and the implications of facultative parthogenesis to conservation of these vulnerable lizards. The case was developed for a general biology class, but could also be used in an introductory course on conservation or cell biology.

Something’s Fishy in Paxton Lake: Speciation in Sticklebacks

In this interrupted case study, students explore the mechanisms of speciation while working in groups to design a series of experiments to determine whether two populations of sticklebacks in Paxton Lake in British Columbia represent separate species or not. As the case progresses, the instructor and teaching assistants move from group to group, prompting students to consider the biological species concept in designing these experiments and encouraging them to think carefully about what data they need. As students design their lab experiments and plan their field data collection, they are supplied with appropriate data (a set of 11 data sheets for this purpose is included in the teaching notes). Due to the open-ended nature of the activity, there is no separate answer key for this case.  This 60–90 minute activity was designed for use in the final week of a general biology course organized around the general theme of evolutionary mechanisms and the history of life on earth. [For an updated, flipped version of this case study, see “Speciation and the Threespine Stickleback,” also in this case collection.]

Speciation and the Threespine Stickleback 

This case study teaches students about allopatric speciation through an investigation of the benthic and limnetic sticklebacks of Paxton Lake, which are among the youngest species on Earth, diverging from each other after the Pleistocene glaciers melted and the Gulf Islands formed. Researchers at the University of British Columbia have carried out a variety of fascinating studies on these hardy little fish. Results from this research (formatted as data sheets included in the teaching notes) are provided to students who design experiments and then compare actual data to investigate why benthic and limnetic sticklebacks seldom interbreed in Paxton Lake. Developed for a first-year biology course for majors organized around the general theme of evolution and the history of life on Earth, this case study is an updated version of another case in the collection, “Something’s Fishy in Paxton Lake” (Sharp, 2001). The current version is especially suited for a flipped classroom in which students prepare for class ahead of time with a reading assignment that also involves the viewing of a video by the case authors that introduces the mechanisms of allopatric speciation.

What is a Species?: Speciation and the Maggot Fly

This "clicker case" is modified from Martin Kelly's case study "As the Worm Turns: Speciation and the Apple Maggot Fly," also in our collection. Classic cases of incipient speciation such as the apple maggot fly and the hawthorn maggot fly are an excellent way to teach students about the mechanisms of speciation. In this case, students learn about the natural history of apple and hawthorn maggot flies, then apply various species concepts to decide if they should be considered separate species and decide what evidence is relevant to each species concept. The case is designed for use in a general biology course for majors. It consists of a PowerPoint presentation (~8MB) punctuated by questions that students respond to using their clickers before moving on to the next slide. It could be adapted for use without these technologies.