Teacher and Student Guides

The cannibalism and interspecific predation lab uses both T. thermophila and T. vorax. Morphogenetic change is addressed by observing the T. vorax shift from microstome to macrostome form. As part of the lab, stomatin, the transformation inducing substance produced by T. thermophila is isolated using simple techniques that can easily be carried out in high school classrooms. The change in morphology is obvious even under relatively low magnification. The lab can be used to address chemical induction of morphological changes, evolutionary differences among different species within the same genus, and, since the macrostome forms consume their own species as well as other Tetrahymena species, inter- and intra-specific predation. The use of inexpensive digital cameras to record morphological changes and predation events adds enormously to student interest and enthusiasm for this exercise.

Module Kit Request Form
Relevant Concepts

Organisms; Relationship of Structure to Function; Mechanisms of Evolution; Population dynamics; Diversity of Organisms; Growth and Survival of Organisms; Diversity and Adaptation of Organisms; Interorganismal Relationships; Species Variation

Next Generation Science Standards Relationships

High School

HS-LS2-6 Evaluate the claims, evidence, and reasoning that the complex interactions in ecosystems maintain relatively consistent numbers and types of organisms in stable conditions, but changing conditions may result in a new ecosystem. 

HS-LS2-8 Evaluate the evidence for the role of group behavior on individual and species’ chances to survive and reproduce. 

HS-LS3-2 Make and defend a claim on evidence that inheritable genetic variations may result from: (1) new genetic combinations through meiosis, (2) viable errors occurring during replication, and/or (3) mutations caused by environmental factors.

HS-LS3-3 Apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population.

HS-LS4-2 Construct an explanation based on evidence that the process of evolution primarily results from four factors: (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition from limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment. 

HS-LS4-3 Apply concepts of statistics and probability to support explanations that organisms with an advantageous heritable trait tend to increase in proportion to organisms lacking this trait.

HS-LS4-5 Evaluate the evidence supporting claims that changes in environmental conditions may result in: (1) increases in the number of individuals of some species, (2) the emergence of new species over time, and (3) the extinction of other species.


●Gronlien HK, Berg T, Lovlie AM. 2002. In the polymorphic ciliate Tetrahymena vorax, the non-selective phagocytosis seen in microstomes changes to a highly selective process in macrostomes. J.Exp.Biol. 205 (Pt 14):2089-2097.

●Ryals PE, Bae S, Patterson CE. 1999. Evidence for early signaling events in stomatin-induced differentiation of Tetrahymena vorax. J.Eukaryot.Microbiol. 46 (1):77-83.

●Ryals PE, Buhse HE Jr, Modzejewski J. 1989. Lipid modification during cytodifferentiation of Tetrahymena vorax. Whole cell phospholipids and triacylglycerols of microstomal and macrostomal phenotypes. Biochim.Biophys.Acta 991 (3):438-444.

●Smith-Somerville HE, Hardman JK, Timkovich R, Ray WJ, Rose KE, Ryals PE, Gibbons SH, Buhse HE Jr. 2000. A complex of iron and nucleic acid catabolites is a signal that triggers differentiation in a freshwater protozoan. Proc.Natl.Acad.Sci.U.S.A. 97 (13):7325-7330.

●Yang X and Ryals PE. 1994. Cytodifferentiation in Tetrahymena vorax is linked to glycosyl-phosphatidylinositol-anchored protein assembly. Biochem.J. 298 Pt 3:697-703.

See our glossary for the terms used in the modules.