Neuroethology: Sound in insects

1. Neuroethology:Sound in insects http://biolpc22.york.ac.uk/404/

2. References • Young, D (1989) Nerve cells and animal behaviour CUP [1st edition, chapter 7] • Also, chapters in: • Carew Behavioral neurobiology • Zupanc Behavioral neurobiology • papers are on the web http://biolpc22.york.ac.uk/404/cjhe/cricket_singing/insect.htm

3. What is neuroethology? • approach to analyse neural function in terms of evolutionary advantage

4. Main points of lecture • Sound transmission is inefficient • Insects use sound in a major way • Overcoming physical obstacles • Modifying • wings for sound production • the environment for sound production • cuticle to hear • Private communication

5. About sound • sound is a wave of particle compression and rarefaction    • energy (or power) is transferred from sender to hearer • sound gets quieter further away • sound has to be discriminated according to species, context and from random noise

6. Sound properties • speed c (330 m s-1) • wavelength l (m) • frequency f (Hz, cycles/s) • for 330Hz, wavelength 1m • for 3.3kHz, wavelength 0.1m • for 33kHz, wavelength 0.01m = 10mm

7. Power transfer - i • First problem for an insect - • for air/water interface about 0.02%

8. Power transfer - ii • Usually other insect far away - • With distance, power decreases • more bad news for insects!

9. Power transfer - iii • Usually insects small - • sound emitted is dependent on ratio of insect size / wavelength of sound

10. Power transfer - iv • if you are smaller than 0.2 * l more bad news!

11. Insects use sound in a major way • Mantids* • Grasshoppers/crickets* • bugs* • beetles* • diptera (true flies)* • lacewings • moths How do they manage this if physics is so unfavourable?

12. Overcoming physical obstacles • Resonance • Baffle • Horn • Sound production • Sound reception

13. Resonance • Mass and a spring; resonant frequency • s is stiffness, m mass • below fo in phase; at fo 90o; above fo out of phase

14. Gryllus • Field cricket • nice loud song, carries a long way • attracts females & males • territorial

15. oscillogram Gryllus EMGs sound sonogram

16. Females…

17. … walk to the loudest sound

18. Sound made by wing plectrum

19. add wax to harp • frequency reduced • resonator affected

20. remove teeth

21. Gryllus campestris • sound output 60 mW • muscle work 2 mW • efficiency 3% Can they do any better?

22. Bush crickets • Higher frequency • damped oscillation

23. Baffle • Bush cricket • Oecanthus • power * 12

24. Gryllotalpa • mole cricket

25. Horn shaped burrow

26. Gryllotalpa • sound output 1 mW • muscle work 5 mW • efficiency 20%

27. Summary so far • Modified wings for sound production • Modifying the environment for sound production Well done the male crickets! Now onto: what about hearing?

28. Hearing • locust = grasshopper ears

29. Tympanum structure

30. Tympanum structure side view • Muller’s organ has sensory endings in it • Tympanum (ear drum) taut membrane top view

31. Movement it’s the relative movement which will stretch the axons

32. Movement • peaks at 3 & 6kHz indicate resonance • resonance also shown by phase plot • folded body not in phase with membrane • even when at 4kHz amplitude is same • relative movement needed to stretch axons of Muller’s organ

33. Cricket hearing • acoustic trachea • acts like horn for 5kHz sound

34. Summary so far: Resonance!! • Modified wings for sound production • Modifying the environment for sound production • Modified cuticle to hear Now onto: shh, let’ keep this to ourselves?

35. Male has black tip Olfaction Singing Drosophila courtship

36. Detecting vibration • near field sound • movement detector • aristae - bristles on antennae

37. Private communication • Sound movement in dB • since sound is measured on a log scale, 80 << 95

38. Summary • The neuroethological approach relates the function of the nervous system to its evolutionary advantage • Many insects use sound • produce it quite efficiently • hear it effectively