Sensory processing and the evolution of female preference in Neoconocephalus

1. Sensory processing andthe evolution of female preference in Neoconocephalus Rhett Hartman Thesis presentation, Spring 2013 Committee: Johannes Schul (Chair), Robert Sites, David Schulz

2. OUTLINE • Study background • Female preference • Behavior, evolution, and Neoconocephaluskatydids • Auditory neurophysiology • Neoconocephalus: From neurons to the preference for leading signals • Experiments & Results • Katydids, the female leader preference, and everything

3. Background • Female preference behavior (proximate explanation): • Mate advertisement signal produced • Receiver sensory system encodes signal characteristics • Information sent to call recognition network • Decision produces a preference behavior (acoustic call) (high frequency sounds) (neural response) Receiver (female) (chirp duration) (silent duration) Sender (male) (neural network) (decision) watchingtheseasons.blogspot.com To move to the signal or not to move, that is the decision To phonotaxis or not to phonotaxis, that is the decision

4. Background • Evolution of female preference • Why exaggerated male traits? Direct benefits (male trait correlates with non-genetic benefits) Indirect benefits (male trait correlates with better genes) Fisherian runaway selection (self-reinforcing female preference for a male trait) Pre-existing sensory bias (ancestral sensory bias for a signal characteristic) “female preference” “male trait”

5. Background • Evolution of female preference by a pre-existing sensory bias • Increased relative sensory neural response to signal characteristic • i.e., neural activity increases as signal intensity increases. • Increased relative behavioral response • i.e., movement towards recognized signals with higher intensity • Sensory bias: 40 dB 80 dB • Female preference:

6. Background • Evolution of female preference by a pre-existing sensory bias • Ancestral lineage acquires a biased response (b+)to certain signal traits • Bias (b+) is integrated into call recognition network (new d+) • Male traits (t+) evolve to match preference behavior F b+ d+ Fb+ d+ F b+ d+ Fb+ d+ d+ d+ M t+ M t+ M t+ Mt+z t+ • Ryan & Rand, 1993

7. Background • Evolution of female preference by a pre-existing sensory bias • The bias appears before the evolution of the male trait • Biased neural responses may not be incorporated into call recognition networks F b+ d+ M t+

8. Background • Evolution of female preference by a pre-existing sensory bias • Biases can evolve in a context other than mating: • changes in body size • detecting predator signals • genetic drift (wild boar)

9. Background • Female preferences in Neoconocephalus • Females move toward “attractive” acoustic signals (N. triops) N. exiliscanorus

10. Background • Temporal pattern • One characteristic used for call recognition • Continuous: • Discontinuous: minutes… (most synchronize with neighboring males) 1000 ms

11. Background • Relative timing L L F F Delay of follower Imperfect synchrony gives rise to leading and following positions Synchrony because of the female preference • Cooperative calling (preference for temporal pattern) • Competitive calling (preference for leading caller) = Leader preference (LP)

12. Background • Relative timing L L F F Delay of follower Delay of follower Synchrony because of the female preference • Cooperative calling (preference for temporal pattern) • Competitive calling (preference for leading caller) = Leader preference (LP) • Female preference can act on call timing • Preference for leading call (LP) is found in many insect and anuran species

13. Background • A pre-existing bias for LP would exist in the ancestral lineage • Phylogenetic context for LP in Neoconocephalus

14. Background • Call evolution • Ancestral state is continuous calling • Discontinuous calling evolved twice, independently • Preference evolution • LP evolved twice • Independent evolution Phylogeny (Synder et al. 2009)

15. Background • No behavioral bias in ancestral lineage • No pre-existing sensory bias for leading calls in Neoconocephalus • Is there a neural bias for leading calls? • If so, it would not be important for mating behavior in ancestral species Comparative approach: • 4 species without LP • 1 species with LP Phylogeny (Synder et al. 2009)

16. Background • Following signals can be suppressed in the sensory system • Precedence effect (echo suppression), via forward masking • Directional processing in sensory system • Lateral inhibition may suppress following signals • This would results in a neural bias for leading signals • Wallach 1949, Greenfield 1994, Wyttenback & Hoy 1993 • Römer et. al 2002 Follower Leader

17. Background • Following signals can be suppressed in the sensory system • Is LP the result of a neural bias in the sensory system? • Can directional processing explain the evolution of LP in Neoconocephalus? • Wallach 1949, Greenfield 1994, Wyttenback & Hoy 1993 • Römer et. al 2002

18. Background • Auditory sensory system of Neoconocephalus

19. Location of hearing organ (N. triops) Peripherial sensory neurons connect to ipsilateral interneurons in the CNS BACKGROUND N. exiliscanorus N. triops

20. Auditory interneurons Ventral side, prothoracic ganglion • From N. triops (Triblehorn and Schul 2009) (to brain) TN-1 (ear) (ear) 150 μm

21. Ascending auditory interneurons (to brain) TN-1 (ear) (ear) 150 μm 150 μm 150 μm N. triops Three ascending auditory neurons (bilaterally paired) • TN1 – Responds only to stimulus onset (predator detector) • AN2 – Most sensitive to frequencies higher than male calls • AN1 – Reliably encodes temporal call pattern • (Triblehorn and Schul 2009)

22. Local auditory interneuron (to brain) AN1c AN1c AN1i ON1c

23. Local auditory interneuron (to brain) Omega neuron (ON1) • Inhibits contralateral auditory neurons AN1c AN1i • Enhances contrast of responses between left and right sides • Movement to side of most active “attractive” call ON1i ON1c • Pollack 1998, Stumpner & Helversen2001

24. Local auditory interneuron (to brain) AN1c AN1i ON1c ON1i

25. Local auditory interneuron (to brain) TN1c AN1c AN1i ON1i ON1c

26. Local auditory interneuron (to brain) Weak inhibition by contralateral ON1 TN1c AN1c AN1i ON1i ON1c Ipsilateral activity would increase

27. Background • Katydid with LP:Mecapodaelongata • ON1 and TN1 on the side of the leader responded stronger • Neural correlate to LP behavior • Behavior and neural activity respond in the same manner • Contralateral inhibition was important for leader bias • Leader bias disappeared after removing contralateral inhibition • Possible sensory bias for leading calls in M. elongata Römeret. al 2002, Siegertet. al 2011

28. Background • Big-picture questions: • Is there a neural bias for leading calls in Neoconocephalus? • Auditory neural responses • Contralateral inhibition • Compare species with and without LP

29. Background • Questions: • Does TN1 or AN1 respond stronger to leading calls? • If there is a leader bias in AN1 or TN1, how important is contralateral inhibition to this process? • How does the response of AN1 and TN1 differ among species with and without LP?

30. Experimental Methods • Present directional and leader-follower stimulus • Record extracellularly • Measure neural activity (AN1, TN1)

31. Experimental Methods • Stimuli based on male calls • 1000 ms • 150 ms chirp interval • 76 ms • 324 ms chirp interval (longest chirp interval) • Similar to N. exiliscanorus(no LP) and N. spiza(LP) • 36 ms • 44 ms chirp interval • Simiar to N. ensiger(LP) • Call types • Without LP: • 1000 ms verse length, 150 ms gap length (N. retusus, N. bivocatus) • 76/324 (N. exiliscanorus) • 1000/800 (N. nebrascensis) • With LP: • 36/44 (N. ensiger) • 76/324 (N. spiza) • 250/200 (Mecapoda elongata)

32. Experimental Methods • Present directional and leader-follower stimulus • Record extracellularly • Measure neural activity (AN1, TN1)

33. recording wire electrode Extracellular recording setup

34. Measuring TN1 activity • Data analysis • Extracellular recordings are analyzed to extract AN1 activity • We end up with a number representing the neural response from the side of the leader, or the side of the follower • Stimuli presentation • Directionality presentation measures the effect of call angle on neural activity, cut leg tests for the effect of contralateral inhibition • LF presentation changes the timing between two separate calls. This allows us to measure any sensory bias for leading calls. In addition, different verse lengths are used. Original recording • TN1 spikes TN1 spike average (Brain) • Recordextracellularly • TN1 activity: • Count TN1 spikes during stimulus voltage time After spike removal 25 ms

35. Measuring AN1 activity • Data analysis • Extracellular recordings are analyzed to extract AN1 activity • We end up with a number representing the neural response from the side of the leader, or the side of the follower • Stimuli presentation • Directionality presentation measures the effect of call angle on neural activity, cut leg tests for the effect of contralateral inhibition • LF presentation changes the timing between two separate calls. This allows us to measure any sensory bias for leading calls. In addition, different verse lengths are used. Original recording TN1 spike average (Brain) voltage time • Subtract avg. TN1 spike After spike removal 25 ms

36. Measuring AN1 activity • Rectify recording • Average 25 recordings Rectified response Summed response to call • Summation of response represents AN1 activity • Summation window • Includes response during leading and following chirps 25 ms

37. Experimental results • Directional experiment • AN1 • TN1 • Leader-follower experiment • AN1 • TN1

38. AN1 Directionality Directional experiments • Present stimulus from separate speakers • Measure the how response • strength changes with • Direction of single stimulus • 2. After removing contralateral inhibition (cutting contralateral leg) Side of stimulus

39. AN1 Directionality Directional experiments • AN1 • Extracellular response • Relative responses • Contralateral cut-leg responses

40. AN1 Directionality 36 ms chirps 100 ms Tonic response to chirp duration Relative contralateral response = Activity during contralateral Activity during ipsilateral Response relative to ipsilateral only Directional response contra only ipsi + contra

41. AN1 Directionality 76 ms chirps 100 ms 100 ms 36 ms 76 ms 1000 ms Response relative to ipsilateral only 100 ms contra only ipsi + contra contra only ipsi + contra

42. AN1 Directionality 1000 ms chirps 100 ms 100 ms 36 ms 76 ms 1000 ms Response relative to ipsilateral only contra only ipsi + contra contra only ipsi + contra contra only ipsi + contra

43. chirp pattern: 36 ms 76 ms 1000 ms AN1 Directionality Species: N. ensiger (LP) N. exiliscanorus (no LP) • Takeaway: • All species and • all chirp types show directionality N. retusus (no LP) N. Bivocatus (no LP) N. Nebrascensis (no LP)

44. AN1 Directionality N. ensiger, 36 ms chirp Cut-leg response Contra only stimulation Response relative to ipsilateral only n=5 intact cut-leg

45. chirp pattern: 36 ms 76 ms 1000 ms AN1 Directionality Species: N. ensiger (LP) N. exiliscanorus (no LP) • Cut-leg: • Increased response when directionality was strong N. retusus (no LP) N. bivocatus (no LP) N. nebrascensis (no LP)

46. AN1 Directionality Conclusion • Directionality is present in all species • Contralateral inhibition is present • Varying degrees of strength of inhibition among species • How does TN1 respond to directional stimuli?

47. TN1 Directionality TN1 • Directional call response in TN1 • Histogram of TN1 responses • Directionality of TN1 response • Cut-leg

48. TN1 Directionality = (TN1 spike) • TN1 responses during ipsilateral only stimulus • Variation in TN1 responses in N. ensiger 25 repetitions

49. Variation in TN1 responses • Females were collected in the field as adults • Mated females may have weaker responses to male call stimuli

50. TN1 Directionality Ipsilateral only Contralateral only Ipsi + Contra Ipsi Contra • TN1 responds to beginning of chirps • Fewer TN1 spikes during contralateral only stimulus