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

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)(Fig)  “Angular speed/spiking rate threshold” hypothesis (Fig)(Fig) These two hypotheses originated from studies on locusts.

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

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

9. 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.

10. 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.

11. 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

12. 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.

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

14. 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)

15. 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

16. 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

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

18. 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

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

20. 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)

21. 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

22. 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)

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

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

25. 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.

26. 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

27. 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

28. 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)

29. 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.

30. Thank you

31. 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