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An Analysis of Behaviour Sequences in Automeris Aurantiaca Weym (Lepidoptera)

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[I. The normal ethogram for certain non-sexual activities of adult Automeris aurantiaca is described. The events following emergence from the pupa are treated quantitatively, and an account is given of the behaviour of resting adult moths when disturbed. 2. On hatching, the moths climb upwards, settle, and commence to expand the small pupal wings. After expansion the wings are dried and then folded into the adult resting position in two stages (called spreading and tenting) The interval between the beginning of expansion and spreading is at 22° C relatively constant (mean for males: 70,5; females: 67,1 mins), and does not vary significantly between sexes, despite a gross sexual size-dimorphism involving the wings; evidence is presented to suggest that it is controlled by a short-term internal clock. 3. During the first phase of expansion bursts of an activity termed 'rocking' are performed. This is a fast, rhythmic movement in which all the legs of each opposing side alternately go into flexion and extension. The head, antennae and abdomen also perform complex movements in phase. Later in life rocking is exclusively associated with the movement of settling into the rest position. Its function is not known. Two single bursts of rocking are performed at spreading and tenting 4. The development of flight behaviour in the life-histories of the individuals is traced. While flight movements may often be elicited from moths dissected from the pupal case some twenty-four hours before emergence is due, after that time until some one or more hours after tenting the threshold for the release of flight is high, and overt flight is never normally shown. 5. The events which may follow the disturbance of a resting moth are (I) a Sustained Static Display; (2) Flight and its preparatory movements; (3) Neutral Posture, in which there is a sustained loss of muscular tone lasting from five minutes to more than one hour; (4) Walking; (5) Settling, accompanied by Rocking. Any of these activities may occur in the same sequence, but the order in which they may occur is limited to ten alternatives. All begin with (I) and end with (5), and neutral posture, if it occurs, always immediately follows display. 6. These activities were examined in experiments in which, two hours after tenting, individual moths were stimulated by a series of strong tactile disturbances, each stimulus after the first being given five minutes after the end of the sequence elicited by its predecessor. Flight and neutral posture were scored as the number of trials out of ten in which they occurred. Display was scored as a duration. 7. It was found that the flight and neutral posture frequencies were inversely correlated, and so were the flight frequency and the total duration of display summed for the ten trials. Further, the sum of the number of rocks delivered at spreading and tenting (= rocking score) showed relationships with certain other items, of which the most important were an inverse correlation with the flight frequency, and a direct correlation with the neutral posture frequency. 8. An analysis was made to determine the influence of the components of the ten types of sequence (DNS, DFS, DWFS, DNFS, DNWFS, DFWS, DNFWS, DS, DNWS, DWS) on the number of terminal settling rocks. The number of rocks is reduced when flight is present in the sequence, is least when flight is the penultimate component, and with one exception, the sequence DNS (for which rocking is minimal), is greatest when flight is absent altogether. 9. The results are discussed and a model proposed. It is postulated that rocking is linked with the causal system controlling settling and the maintenance of the rest position, and relates quantitatively to the motivation of that system. It is argued that at spreading and tenting the settling system is uninhibited by the competing flight system, so that the number of rocks given at these points is an absolute measure of the activity of the system which they represent. The correlations between this measure and Behaviour XII 20 the later measures of flight and neutral posture imply that the excitability of this system is held constant during the first few hours of adult life. Neutral posture is considered to be a sustained conflict state between the simultaneously excited causal systems of flight and settling. Evidence for this and a possible alternative view is discussed. A distinction is made between three lower level systems (Display, Flight, and Settling) responsible for the reflex co-ordination and reciprocal exclusion of corresponding overt acts; and two higher level systems (Flight, Settling) responsible for the facilitation of the lower mechanism and hence the differential selection of particular acts. The minimal number of interactions between these hypothetical systems which need be postulated to explain the results is listed in the form of a model. 10. The results are briefly compared with those of other descriptive and neurophysiological studies. A note on the nature of ethological models and their suitability for handling results obtained from arthropod material is included in the final section., I. The normal ethogram for certain non-sexual activities of adult Automeris aurantiaca is described. The events following emergence from the pupa are treated quantitatively, and an account is given of the behaviour of resting adult moths when disturbed. 2. On hatching, the moths climb upwards, settle, and commence to expand the small pupal wings. After expansion the wings are dried and then folded into the adult resting position in two stages (called spreading and tenting) The interval between the beginning of expansion and spreading is at 22° C relatively constant (mean for males: 70,5; females: 67,1 mins), and does not vary significantly between sexes, despite a gross sexual size-dimorphism involving the wings; evidence is presented to suggest that it is controlled by a short-term internal clock. 3. During the first phase of expansion bursts of an activity termed 'rocking' are performed. This is a fast, rhythmic movement in which all the legs of each opposing side alternately go into flexion and extension. The head, antennae and abdomen also perform complex movements in phase. Later in life rocking is exclusively associated with the movement of settling into the rest position. Its function is not known. Two single bursts of rocking are performed at spreading and tenting 4. The development of flight behaviour in the life-histories of the individuals is traced. While flight movements may often be elicited from moths dissected from the pupal case some twenty-four hours before emergence is due, after that time until some one or more hours after tenting the threshold for the release of flight is high, and overt flight is never normally shown. 5. The events which may follow the disturbance of a resting moth are (I) a Sustained Static Display; (2) Flight and its preparatory movements; (3) Neutral Posture, in which there is a sustained loss of muscular tone lasting from five minutes to more than one hour; (4) Walking; (5) Settling, accompanied by Rocking. Any of these activities may occur in the same sequence, but the order in which they may occur is limited to ten alternatives. All begin with (I) and end with (5), and neutral posture, if it occurs, always immediately follows display. 6. These activities were examined in experiments in which, two hours after tenting, individual moths were stimulated by a series of strong tactile disturbances, each stimulus after the first being given five minutes after the end of the sequence elicited by its predecessor. Flight and neutral posture were scored as the number of trials out of ten in which they occurred. Display was scored as a duration. 7. It was found that the flight and neutral posture frequencies were inversely correlated, and so were the flight frequency and the total duration of display summed for the ten trials. Further, the sum of the number of rocks delivered at spreading and tenting (= rocking score) showed relationships with certain other items, of which the most important were an inverse correlation with the flight frequency, and a direct correlation with the neutral posture frequency. 8. An analysis was made to determine the influence of the components of the ten types of sequence (DNS, DFS, DWFS, DNFS, DNWFS, DFWS, DNFWS, DS, DNWS, DWS) on the number of terminal settling rocks. The number of rocks is reduced when flight is present in the sequence, is least when flight is the penultimate component, and with one exception, the sequence DNS (for which rocking is minimal), is greatest when flight is absent altogether. 9. The results are discussed and a model proposed. It is postulated that rocking is linked with the causal system controlling settling and the maintenance of the rest position, and relates quantitatively to the motivation of that system. It is argued that at spreading and tenting the settling system is uninhibited by the competing flight system, so that the number of rocks given at these points is an absolute measure of the activity of the system which they represent. The correlations between this measure and Behaviour XII 20 the later measures of flight and neutral posture imply that the excitability of this system is held constant during the first few hours of adult life. Neutral posture is considered to be a sustained conflict state between the simultaneously excited causal systems of flight and settling. Evidence for this and a possible alternative view is discussed. A distinction is made between three lower level systems (Display, Flight, and Settling) responsible for the reflex co-ordination and reciprocal exclusion of corresponding overt acts; and two higher level systems (Flight, Settling) responsible for the facilitation of the lower mechanism and hence the differential selection of particular acts. The minimal number of interactions between these hypothetical systems which need be postulated to explain the results is listed in the form of a model. 10. The results are briefly compared with those of other descriptive and neurophysiological studies. A note on the nature of ethological models and their suitability for handling results obtained from arthropod material is included in the final section.]

Affiliations: 1: Department of Zoology and Comparative Anatomy, University Museum, Oxford

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