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Escape Behavior of Flesh-Fly (Sarcophagidae): Verifying the mechanism of escape initiation Dae-eun Kim School of Biological Sciences
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Contents Introduction Methods Results Discussion Future studies
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I. Introduction I-1. Escape Behavior -Escape behavior is important in predator-prey relationship -For the prey, escape behavior determines one’s chance of survival -Each species have evolved according to changes in the environment -Important to decide when to escape
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I-2. Previous Studies in Controversy “Peak spiking/angular size threshold” hypothesis (Fig)(Fig) “Angular speed/spiking rate threshold” hypothesis (Fig)(Fig) These two hypotheses originated from studies on locusts.
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H1: “Peak spiking/angular size threshold”
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H2: “Angular speed/spiking rate threshold”
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I-4. Hypotheses and Objectives Hypotheses If the escape response follows one of the angular properties of the model, this will support one of the previously suggested theory on escape of locust. If escape response in fly is similar to that in locust, it may suggest an evolutionary link between two species on the development of visual system in terms of predator-prey relationship.
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I-4. Hypotheses and Objectives Objectives Predator-like object approaches the subject and measure the behavioral properties of the escape of fly. Using video-recording of escape initiation, calculate angular properties (i.e., angular size and angular velocity) See if 1)Angular size is constant, or 2)Angular velocity is constant Decide which hypothesis is better to explain escape behavior.
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I-5. Study subject : Flesh-fly (Sarcophagidae) “flesh-fly” (sarco- = corpse, phage = eating, in Korean: “ 쉬파리 ”) Body length :6~19mm Three lines on the dorsal area Easily seen in decaying food or animal’s excrement “Jahayeon”: natural habitat in SNU
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Visual System of Fly Compound Eye : poor image resolution a very large view angle the ability to detect fast movement In some cases, detection of the polarization of light Optical axes of the fly developed to see front and dorsal side well.
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II. Methods: presenting visual stimuli Date :05/12/08 ~05/30/08 Time : 1000~1800 Location : Jahayeon, Central Library, and Social Sciences Dept.
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II. Methods: presenting visual stimuli Defining independent variables 1.Size (categorized by radius) : 4cm, 8cm, 15cm 2.Speed (categorized by linear approach speed) : Fast, Medium, Slow (moving the stick manually)
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II. Methods: Controls 1. Avoiding replication - Time interval - Kill or catch after trial 2. Applying random order of stimuli 3. Reducing the effects of time of the day on behavior - 1000-1400
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II. Methods: Video analysis 1)Videotaping the whole experiments 2)Check flight initiation (FI) point 3)Measure the distance between fly and stimulus 4)One frame (33ms) before FI point measure the distance 5)Two frame (66ms) before FI point measure the distance
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Calcualting angular properties - 2*Arctan(Radius/Distance) = Angle - (Angle1 – Angle2)/(33msec) = Angular Velocity II. Methods: Calculation
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Coefficient of variation (CV) - To compare the degree of distribution of two data set; angular size and angular velocity - CV = 100 X (average/standard deviation) II. Methods: Statistical analysis
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III. Results Distribution of the speed and the size of the stimuli (after the removal of outliers)
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III-1. Signal conduction time Signal delay time -Considering the time that takes to transmit signals from nervous system to muscles (ca. 1-3 ms; Wyman 1980) -Re-calculating distance -= Original distance + (Linear Speed X delay time)
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III-2. Comparison of CVs CV from angular size: 45.66 CV from angular velocity (after logarithmic transformation): 24.91 Data set of angular velocity are less distributed Angular velocity data are more converged
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III-3. Effects of model size on angular properties Assumption: If certain angular properties are irrelevant to the size of models, it may suggest the existence of the threshold (either this is angular size or angular velocity). Statistical analysis: using analysis of variance (ANOVA) Results from normality tests non-normal distribution of data sets Using non-parametric tests (Kruskal-Wallis ANOVA)
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III-3. Effects of model size on angular properties Angular size distribution Kruskal-Wallis test: H (2, N= 64)=10.40, p =.0055
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Angular velocity (log transformed) distribution Kruskal-Wallis test: H ( 2, N= 64) =.37, p =.8312 III-3. Effects of model size on angular properties
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III-4. Summary Comparison of CVs Angular velocity is more constant than angular size Effects of model size on angular properties Effect of model size on angular velocity is few Conclusion : Angular velocity could be the constant threshold : The “Angular speed/spiking rate threshold” hypothesis give better explanation of escape initiation.
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IV. Discussion Significance of the study Application of previously suggested hypotheses to new species; fly (Sarcophagidae). Able to finding evolutionary links between insecta species Conducting field experiments in natural habitats (not in unrealistic lab conditions) Giving background of electrophysiological experiment
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IV. Discussion Angular size or angular velocity? Flesh-fly is more sensitive to velocity than to size In evolutionary perspective, flesh-fly has evolved to be sensitive to the motion of predator
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IV. Discussion Existence of similar evolutionary mechanism in two species with high visual acuity - Case of locust, there is still disagreement which hypothesis is right - If similar result will be gained in locust, they might have similar evolutionary pathway - If they are simialr, it may be because they had similar predator or similar habitat - If they are different, it may be because they have different visual system (difference in distribution of ommatidia in their compound eyes)
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V. Future studies Conducting electrophysiology experiments -I may conclude that angular velocity threshold hypothesis is better to explain the behavior properties of escape initiation. -To prove the hypothesis, research on nervous system level should be carried out.
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Thank you
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I-3. Related Studies Model Species : Orthoptera (locust) Electrophysiology experiments Identifying escape neural mechanisms Comparison of neurophysiological and behavioral properties Measuring other behavioral properties in escape behavior (Cooper 2006) Distance the prey fled Flight initiation distance (FID) Flight direction
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