Thigmotaxic Variation Between Cephalic and Caudal Regions in Planaria
Evrhett Davis, Andrew Staub
Saint Joseph’s University
Organismal Lab Tuesday
Dr. Jonathon Fingerut
December 1, 2013
Thigmotaxic Variation Between Cephalic and Caudal Regions in Planaria The development of a centralized nervous system in primitive animals provided a significant advantage resulting in the continuance of many species. Nervous tissue allowed organisms to expand into new methods of predation, protection and reproduction; encouraging specialization and eventually increased speciation. However, there may exist other factors which could have also contributed to the perseverance of nervous tissue. Does the presence of primitive nervous tissue affect an organism's response to localized mechanical stimulation? To understand this question better, a primitive organism is best suited. Planaria were chosen as the most appropriate model organism for their easy maintenance, attainability and their existence of a light sensing organ, or primitive cephalization. "Planarians are the first example of organisms displaying cephalization, including a primitive brain, with many features common to a vertebrate nervous system"1. This relationship provides a strong relevance to vertebrate animals. Twenty Planaria specimen were studied. Each were isolated and then mechanically stimulated in a 'poking' manner via a blunt dissecting probe. To study the difference in thigmotaxis between areas of abundant cephalization, hereby referred to as the organism's 'head', and the rest of the organism's body, stimulation was localized to three regions: the head, the tail and the body (the body consisting of the estimated intermediate area between the head and the tail). The resulting reactions were then recorded and categorized by the subjective intensity of the response on a scale of 1 to 5, with 1 being an agreed neutral response and 5 being an uncharacteristically extreme response. Furthermore, reactions were also recorded qualitatively in an attempt to find a
Saint Joseph’s University
Organismal Lab Tuesday
Dr. Jonathon Fingerut
December 1, 2013
Thigmotaxic Variation Between Cephalic and Caudal Regions in Planaria The development of a centralized nervous system in primitive animals provided a significant advantage resulting in the continuance of many species. Nervous tissue allowed organisms to expand into new methods of predation, protection and reproduction; encouraging specialization and eventually increased speciation. However, there may exist other factors which could have also contributed to the perseverance of nervous tissue. Does the presence of primitive nervous tissue affect an organism's response to localized mechanical stimulation? To understand this question better, a primitive organism is best suited. Planaria were chosen as the most appropriate model organism for their easy maintenance, attainability and their existence of a light sensing organ, or primitive cephalization. "Planarians are the first example of organisms displaying cephalization, including a primitive brain, with many features common to a vertebrate nervous system"1. This relationship provides a strong relevance to vertebrate animals. Twenty Planaria specimen were studied. Each were isolated and then mechanically stimulated in a 'poking' manner via a blunt dissecting probe. To study the difference in thigmotaxis between areas of abundant cephalization, hereby referred to as the organism's 'head', and the rest of the organism's body, stimulation was localized to three regions: the head, the tail and the body (the body consisting of the estimated intermediate area between the head and the tail). The resulting reactions were then recorded and categorized by the subjective intensity of the response on a scale of 1 to 5, with 1 being an agreed neutral response and 5 being an uncharacteristically extreme response. Furthermore, reactions were also recorded qualitatively in an attempt to find a