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2013 WINTER BIO A02.tif LAB 5 Behavioural Responses in Terrestrial Isopods1 Overview In this lab, you will consider an example of Behavioural Ecology, specifically, the behavior of terrestrial isopods in response to environmental stimuli. To analyze the results of this experiment, you will be using a statistical test known as the Chi-Square Test. Objectives: 1. Be familiar with all bolded terms in introductory information. 2. Conduct an experiment using proper experimental design to determine the effects of environmental stimuli on the behavior of a group of terrestrial invertebrates known as isopods. 3. Collect and analyze a categorical data set using the Chi-Square test. Required Preparations 1. Read Lab 5 carefully and review relevant lecture material. 2. Bring your laboratory coat, safety goggles, print out of Lab 5, as well as a pencil and eraser Lab 5 Exercises: 1. Collect Data on Behavioural Responses of Terrestrial Isopods (done in the lab) 2. Analyze Data on Behavioural Responses of Terrestrial Isopods (done at home before you complete Lab #5 Assignment on Quercus) 3. Complete Labster Simulation - Behavioural Thermoregulation: Help keep a gecksi alive! in either the 24 hours before your scheduled lab or 24 hours afterwards 4. Submit Lab #5 Assignment to Quercus 24 hours following completion of Lab #5 Background Information Ethology is the study of animal behavior. This involves observing an animal’s behaviors and interpreting its reactions to the surrounding environment. Many factors in the animal’s environment can affect its ability to survive and reproduce. These factors can be divided into two categories: (1) abiotic and (2) biotic. Abiotic factors are physical and chemical characteristics in the environment. Examples of abiotic factors include climate, light, pH, nutrient availability, etc. Biotic factors are interactions among organisms whether from the same species (intraspecific) or different species (interspecific). Competition, predation, parasitism, symbiosis are examples of biotic factors. Any of these factors can be limiting factors that control the maximum size of a given population of organisms. Favourable conditions are desired by all animals to maximize survival and reproduction. Because of this, animals must search for the environment that best suits its structure and lifestyle. This is called habitat selection. The consequences of habitat choice are obvious: individuals settling in areas near their tolerance limits (marginal habitat) often experience decreased growth and reproductive success, while those settling in optimal habitat enjoy a competitive advantage over their conspecifics, or other members of their species. An animal can display many different types of behaviours in its search for an optimal habitat. Orientation behaviours (eg. migration and navigation) are well studied and refer to the spatial organization of movements of an animal. Two common orientation behaviours are (1) taxis and (2) kinesis. Taxes (plural form of taxis) refers to behaviours that are deliberate movements toward or away from a stimulus. During taxis, the animal’s body is oriented in some linear manner relative to a stimulus; either directly toward it, directly away from it, or at a fixed angle to it. Locomotion may or may not be involved. These behaviours often indicate the physiological needs of the animal (eg. requirement for particular light, chemical, moisture, or pH level). For example, the response would be termed phototaxis if the stimulus were lights, geotaxis, if the stimulus were gravity, and chemotaxis if the response involved a chemical stimulus. To be more even more precise, if an organism was oriented towards light, its response may be described as positive phototaxis. Taxis can be dependent on bilaterally symmetrical receptor organs. The animals orients either directly toward or directly away from the stimulus source by positioning itself with reference to the stimulus such that both organs are receiving equal stimulation (think about your behavioural response to loud noise). This type of orientation can be recognized in the terrestrial isopods in the genus Armadillidium (pillbugs). Under certain conditions, this animal is photopositive and will move toward a light source by orienting so that its bilateral photoreceptors are equally stimulated. If blinded in one eye and then exposed to diffuse light, it will continuously attempt to equalize stimulation through circling movements. It should be noted that pillbugs are not always positively phototactic but show this behaviour after a sudden rise in temperature or a period of starvation or desiccation. Kinesis involves random movements that are not oriented toward or away from a stimulus but that reflect a preference or avoidance of certain environmental conditions. In a kinetic response, the stimulus produces either a change in the speed of the animal’s movement (orthokinesis) or in the animal’s turning rate (klinokinesis). These two responses effectively change the position of the animal with respect to the stimulus source. As an example, isopods (terrestrial crustaceans) prefer moist habitats. In some species, as the relative humidity of the environment increases, the amount of time the animal is stationary also increases. This kinetic response tends to keep the isopod in damper areas, a key habitat preference. Remember, these orientation behaviours are not as rigid as is sometimes assumed. For example, the response of an animal to light may be changed or strengthened according to whether it is hungry or satiated, desiccated or has access to water, or whether it has most recently been in the dark or not. It is biologically important for animals to be able to change their behavioral responses in order to survive. For instance, the terrestrial isopod, Porcellio spp. (sowbugs or woodlice) prefer to be clustered under bark in darkness and relatively high humidity but they must emerge at some time to feed, which may mean moving from these desired conditions. It is not surprising, therefore, that as the temperature drops in the evening their positive-humidity response weakens, and they emerge to run about and feed. Most animals possess several different orientation responses, even those involving the sensory receptors and compromised responses may be observed. Terrestrial Isopods Terrestrial isopods (‘woodlice’ or ‘pillbugs’) are frequently used in animal behaviour experiments, especially those involving orientation behaviours. These animals are not insects but actually arthropods (Phylum Arthropoda, Sub-phylum Crustacea, Order Isopoda) that are closely related to shrimps, crabs, lobsters, and crayfish. These isopods are the only members of the order Isopoda that are terrestrial and do not live in water. Despite their terrestrial existence, these isopods have retained external gills as respiratory organs. Because of this morphological characteristic, they are restricted to moist habitats. Description The sowbug (Porcellio spp.) are oval or slightly elongate with a flattened body and measures about 13mm (1/2 inch) in length. They are wingless and the body is grayish or brownish and composed of segmented, overlapping plates. There are two pairs of antennae (only one pair readily visible), well-developed eyes, and a group of short appendages at the tip of the abdomen near the uropods and telson (see Figure 6.1). They have seven pairs of legs with one pair of legs per thoracic segment. Sowbugs generally prefer to scurry away (at most they can curl into a C- shaped posture). Pillbugs (Armadillidium spp.) are similar to the sowbug but is generally larger (15mm – 2/3 inch), darker (dark slate grey) and have no appendages at the tip of the abdomen (see Figure 5.1). The overlapping “armoured” plates of the thorax make them look like “little armadillos”, hence the genus name. Each of the thoracic segments has a pair of legs. Pillbugs are capable of rolling themselves into a neat, circular ball (“pill”) for protection or when disturbed. This behavior has led to the reference to “roly-polies”. Figure 5.1. External anatomy of several species of terrestrial isopods. Life Cycle Sowbugs and pillbugs overwinter as adults. Both mate throughout the year, with most activity in the spring (April to June). The female carries the eggs (7 to 200) in a special brood "pouch" located on the underside of the body. The eggs mature over a period of 50 to 90 days and then hatch. The immatures are similar to the adults, except that they are smaller in size, lighter in color and sometimes have fewer legs. They remain in the brood pouch for six to eight weeks until they are able to take care of themselves. Generally speaking, it takes a full year for the immatures to reach adulthood. There may be one to two generations per year. The adults may live for 2 or 3 years if the environment is favorable. Ecology Habitat Preferences The biology of sowbugs and pillbugs is very similar. Sowbugs and pillbugs are scavengers and feed mainly on decaying organic matter (e.g. leaf litter, mulches, grass clippings, garbage, animal material (manure and carrion), as well as organic soils). They occasionally feed on plants (garden crops, flowers, and fallen fruit), but the damage inflicted is seldom significant. These creatures can be a nuisance by their presence in homes and buildings but they are harmless. They do not bite humans, nor damage structures or household possessions. Terrestrial isopods are often found during the day in groups beneath stones, woody debris and in leaf mold in gardens, forests, and around the foundations of buildings. But what environmental features of such places draw them to congregate there? Sowbugs and pillbugs prefer dark (or low light), moist, and warm conditions. They thrive only in areas of high moisture, and tend to remain hidden in damp and dark areas. Since most isopods are marine, differences in humidity, or moisture content of the air, are thought to be important cues for habitat selection in terrestrial isopods. Furthermore, terrestrial isopods exchange gases with their environment through external gills and will die if the humidity (or moisture levels) are too low. This need for humid conditions is the reason these