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Escape Behavior of Flesh-Fly ( Sarcophagidae): Verifying the mechanism of escape initiation

Dae-eun Kim School of Biological Sciences. Escape Behavior of Flesh-Fly ( Sarcophagidae): Verifying the mechanism of escape initiation. Contents. Introduction Methods Results Discussion Future studies. I. Introduction. I-1. Escape Behavior

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Escape Behavior of Flesh-Fly ( Sarcophagidae): Verifying the mechanism of escape initiation

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  1. Dae-eun Kim School of Biological Sciences Escape Behavior of Flesh-Fly (Sarcophagidae):Verifying the mechanism of escape initiation

  2. Contents • Introduction • Methods • Results • Discussion • Future studies

  3. 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

  4. I-2. Previous Studies in Controversy • “Peak spiking/angular size threshold” hypothesis (Fig) • “Angular speed/spiking rate threshold” hypothesis (Fig) These two hypotheses originated from studies on locusts.

  5. H1: “Peak spiking/angular size threshold”

  6. H2: “Angular speed/spiking rate threshold”

  7. 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.

  8. 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 • Angular size is constant, or • Angular velocity is constant  Decide which hypothesis is better to explain escape behavior.

  9. 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

  10. 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.

  11. II. Methods: presenting visual stimuli • Date :05/12/08 ~05/30/08 • Time : 1000~1800 • Location : Jahayeon, Central Library, and Social Sciences Dept.

  12. II. Methods: presenting visual stimuli • Defining independent variables • Size (categorized by radius) : 4cm, 8cm, 15cm • Speed (categorized by linear approach speed) : Fast, Medium, Slow (moving the stick manually)

  13. 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

  14. II. Methods: Video analysis • Videotaping the whole experiments • Check flight initiation (FI) point • Measure the distance between fly and stimulus • One frame (33ms) before FI point  measure the distance • Two frame (66ms) before FI point  measure the distance

  15. II. Methods: Calculation • Calcualting angular properties - 2*Arctan(Radius/Distance) = Angle - (Angle1 – Angle2)/(33msec) = Angular Velocity

  16. II. Methods: Statistical analysis • 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)

  17. III. Results Distribution of the speed and the size of the stimuli (after the removal of outliers)

  18. 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)

  19. 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

  20. 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)

  21. III-3. Effects of model size on angular properties Angular size distribution Kruskal-Wallis test: H (2, N= 64)=10.40, p =.0055

  22. III-3. Effects of model size on angular properties Angular velocity (log transformed) distribution Kruskal-Wallis test: H ( 2, N= 64) = .37,p =.8312

  23. 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.

  24. 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

  25. 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

  26. 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)

  27. 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.

  28. Thank you

  29. 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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