Experiment: taxic behavior in isopods
Different animal species have specific habitat requirements. Sensory receptors allow them to detect and
show behavioral responses to environmental variables such as humidity, light, mates, predators, and food
availability. Directional movement in response to a stimulus is known as
In contrast, an undirected
movement in response to a stimulus is called a kinesis.
An animal that moves toward
light exhibits positive
phototaxis, while an animal that moves away
from light is said to exhibit negative
Many types of taxes have been identified and named using prefixes to specify the stimulus that elicits
the response. These include anemotaxis (stimulation by wind), barotaxis (pressure), chemotaxis (chemicals),
galvanotaxis (electrical current), geotaxis (gravity), hydrotaxis (moisture), rheotaxis (fluid flow), thermotaxis
(temperature changes) and thigmotaxis (physical contact). These taxes help organisms locate favorable
environments and an understanding of these behaviors can help us manage organisms. For example, pests can be
controlled without dangerous chemicals or habitats can be preserved for endangered species.
Isopods are a group of crustaceans (not insects!) that occupy most major environments - terrestrial,
aquatic and marine. It is estimated that there are more than 10,000 species of isopods distributed over the planet.
Isopod means "the legs are alike". The species you will be studying is common throughout Texas, resembles in
name and morphology another unique Texas animal and has the scientific name
isopod, like most of the terrestrial species, lives in cool, damp areas, usually in association with rotting
In this exercise you will be testing the effects of two major environmental variables, humidity and light,
on the behavior of
Your two hypotheses need to be logical predictions of how
when exposed to two extreme conditions of moisture and light.
You need to take into account their choice of
natural habitat and previous research studies to predict positive or negative phototaxic and hydrotaxic behavior.