Unit 13 Behavioral Patterns

UNIT 13 BEHAVIORAL PATTERNS Structure 15.1 Introduction Objectives ' 15.2 Taxis and Kinesis Taxis Kinesis 15.3 Biological Rhythms Control of Biorhythms Biological Clock 15.4 Communication Behaviour Visual Signals Mechanical Signals Chemical Signals Communication among Honeybees, the Dance Language 15.5 Courtship Behaviour Need for ~ourtshipBehaviour Sex rlifferences in Courtship Behaviour V:sual, Mechanical and Chemical Displays Nuptial Gilts Sperm Competition and Mate Guarding Alternative Tactics of Mate Competition Rejection and Deceit in Courtship 15.6 Social Organisation in Insects Advantages and Disadvantages of Social Behaviour Social Wasps Ants Honey Bees Termites 15.7 Parasitism Types of Parasites Effects of Parasitism on Parasites 15.8 Summary 15.9 Terminal Questions 15.10 Answers INTRODUCTION Behavioural patterns of animals are the patterns of their gestures and movements in response to stimuli in their environment. Behaviour patterns are purposeful and may be for procurement of food, finding mate, for locating convenient and sheltered site, or 1 communication with animals belonging to the same species or to different species. When an animal moves its body in response to a stimulus, the movements are termed taxes and kineses. Behavioural activities occurring with clock work precision at regular intervals are called biorhythms. Elaborate ritualistic behaviour patterns are associated with courtship and mating, communication with members of one's own species as well with other species. Certain groups of animals live in groups to form societies and exhibit social behaviour. They also possess special means of communication with members of their own species. Some communication signals are for self defence. In this Unit you I shall learn about the various taxes and kineses, rhythms, social organisations, courtship I and communication behaviour and the behaviour of parasites, with reference to non ) chordates. I Objectives After studying this Unit you shall be able to: distinguish between taxis, kinesis, explain endogenous and exogenous biological rhythms, describe different types of communication methods in non-chordates, I illustrate how non-chordates attract their partners and mates, I describe the caste system, division of labour and advantages of living in social groups, o distinguish between different types of parasites, and discuss parasitic adaptations. Adaptation and Rchavia~~ral Pattern 15.2 TAXIS AND KINESIS Atiitnals are characterised by great mobility. Stimuli from the environment direct these movements. These movements may be either taxis or kinesis. 15.2.1 Taxis Taxis (plu Taxes) is a directional movement, either toward or away from a source of stimulation. The animal is oriented along a line that runs through the source of stimulation and the long axis of the animal's body. Taxis is termed positive if the movement of the animal is towards the stimulus and negative, if away from it. Taxis is a behavioural response that cannot be modified by learning. A moth flying towards light (Fig. 15.1) is a classicql example of taxis. So is the migration of an earthworm to the surface of soil after a heavy rain. [Taxes are easily demonstrable in animal - like protists such as Amoeba and Paramecium (Fig. 15.2).] Taxes are classified according to the nature of stimulus. Table 15.1 shows the various types of taxes - thermotaxis, phototaxis, thigmotaxis, rheotaxis, galvanotaxis and geotaxis. Table 15.1: Different kinds of Taxes. Fig. 15.1: A moth flying towards a Nature of Name of Type of taxis. ' Examples source of light is an Stimulus Taxis (positive +or negative -) example of taxis. Teniperilture Thermotaxis +or - Animals thrive in different ranges of temperature. Optimum range 20-2S°C, cold blooded animals avoid temperatures above and below the range of temperature that,they can tolerate. Light Phototaxis Hydra, Musea (housefly), Ranaha (an aquatic insect) move towards light. Earthworms, mosquitoes, cockroaches, woodlice move away from light. Mechanical Thigmotaxis Contact with food causes positive taxis in most animals. Contact with barriers brings about avoidance reaction. Chemicals Chemotaxis Odour from chemical ingredients of food orient house flies towards it, also Hydra; Mosquitoes avoid mosquito repellents Animals show negative response to injurious chemicals. Water and Rheotaxis Moths and buttedies fly wind currents into wind current. Planaria, the free living flatworm moves against water current. Electric Galvanotaxis Hydro reacts to weak currents current of electricity, it bends toward: the anode. Gravity Geotaxis + Cnidarian larva planula swims towards sea bed. Ephyra larvae ofjelly fish swim away from sea bed. Drosophilids (hit fly) fly up against gravity to dry parts of a iar. -. Bchavioural Patterns THIGMOTAXIS THERMOTAXIS PHOTOTAMS I Fig. 15.2: Reaction to various stimuli in Amoeba, arrows indicate the direction of movement. 15.2.2 hinesis Cinesis is a non-directional movement. Here the animal's body is not oriented with espect to the source of stimulation, but the rate 03 speed of movement changes with the ntensity of the stimulus. Hydra moves its .tentacles at random in search of food but if ood is kept close to tentacles, they are moved faster. Fig. 15.3: Kinesis in Woodlice. r Adaptation and Behavioural Pattern If the woodlice Porcellio scaber are given a choice between humid and dry areas, they tend to collect in humid areas gradually. hisis due to their non-directional movement. In other words, they do not seek out humid areas, but movement is random. What happens here, is that their movement increases on dry areas but their movement decreases when they occupy humid areas. The random movement with speed is an attempt to fmd out optimal conditions. Once they reach humid areas, their speed slows down and they settle there (Fig. 15.3). SAQ 1 1. What is taxis? ....................................................................................................... 2. What is kinesis? ...................................................................................................... ....................................................................................................... 3. What are flte terms used for the following taxes (i) movement towards light. ................................................................................................ (ii) movement away fiom electric current. ................................................................................................ (iii) movement in response to gravity. ................................................................................................. 15.3 BIOLOGICAL RHYTHMS Many behavioral.activities are carried out by animals at regular intervals of time. Most animals are active during the day and rest at night (diurnal animals), while some animals such as cockroaches are active during the dark hours of the night and rest during the day (nocturnal animals). Similar behavioral activities occurring with cyclical regularity constitute biorhythms. Some biological activities .which showf rhythmic oscillations are feeding, mating, egg laying, emergence from pupa (in case of insects) and migratory.behaviour. The rhythmic activities are co-ordinated with the cycles of nature such as day and night cycles, annual seasons, lunar cycle of one moon-rise to the next. This kind of rhythmi5 activity is to avoid adverse environmental factors and to hlly make use of favourable factors. Fot example, it will be beneficial for bees and other diurnal insects like butterflies, to be active during the day when the flowers they visit open so that they can collect nectar and 1 pollen. Thus organisms have evolved their own rhythms which co-ordinate their activities with environmental rhythms. Daily rhythms such as feeding, drinking and sleep follow a cycle of approximately twenty four hours and are termed circadian rhythms (Latin circa: approximately; diem, day). Many littoral shore animals become active when the tide - leaves them exposed. This is tidal rhythm eg. fiddler crab emerges fiom its burrow to feed at low tide. Certain intertidal snails release eggs at very high tides which occur once in two months. The palolo worm and some other polychaete annelids show lunar rhythm. They rise to the surface of the sea t'o spawn (lay eggs) during certain phases of the moon. Certain animals show courtship behaviour, mate and reproduce once a year ' (circa annual rhythm). Many animals migrate to and from breeding grounds twice a year. Many insects or their stages go illto a state of dormancy or diapause during winter when the climate is not congenial. For example, eggs of the mosquito Aedes, larvae of flesh fly (Sacrophaga) and-certain dragonfly nymphs show diapause in winter. Thus biorhythms are behavioural activities performed at regular intervals. 153.6 Controll of Biorhythms Certain activities require an external stimulus to maintain them at regular intervals. These rhythmic activities are termed exogenous rhythms. A major external factor regulating rhythmic activities is photoperiod or relative length of day (or light hours) and night (or dark hours). Temperature and humidity are other such factors which may control rhythms Behavioural Patterns ' in animals. The palolo worm swarms and mates once a year, on the first day of the lasr lunar quarter of the year. Lunar cycle is the exogenous factor triggering this activity. However an internal biological clock exists in almost all eukaryotes which can detect the passage of time even if the environmental

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