Neuroethology: Understanding the Physical Basis of Behavior

1. Neuroethology • Study physical and chemical basis of behavior • 3 roles of nervous system in behavior • Relay information about environment • Processes information (brain and ganglion) • Relay instructions to muscles

2. Sign stimulus, releaser • Fix action pattern • Inner releasing mechanism – hypothetical neural system responsible for triggering an FAP in response to the appropriate sensory input • Super-normal stimuli • Illegitimate signalers

3. Praying mantis • Protocerebral gangalia (PC) inhibits subesophageal ganglion, and suppresses abdominal muscle activity

4. Bat and moth • Properties of bat sounds – ultrasound and pulsed • Bat navigation system has exerted strong selection on nocturnal moth • Biaural hearing in moth • A1 cell response to low to moderate intensity sound, fires much more frequently to pulses of sound than to steady, uninterrupted sound

5. Auditory capability of A1 cell • A1 begin firing when bats about 100’ away • Location of bats at 3-dimensional space • Antipredator response • Fly directly away from bats • Only effective when bats are 8’ away

6. Noctuid moths respond to sounds of bat-marking rings (Anim. Beh. 57: 829-835, 1999) • Playback of bat calls and ring sound, check neural & behavioral responses of moth • Peak energy of ring sounds occur closer in frequency to the moth’s best auditory frequency than calls

7. Ring sounds were detected at a threshold 5~6 dB, lower than calls • Moths performed evasive responses to playback of ring sound more frequently than to control -- 14/33 no response, 1 to both, 14 respond to rings, 4 to control

9. Retina  3 types of ganglia cell  optic nerve  optic chiasm  optic tectum (orienting) and thalamus (avoidance) • Type II tectal cells sum the excitory signal from type I tectal cells and inhibitory signal from thalamus

10. Circadian rhythm • Intrinsic or environmental-dependent? • w/o environmental cue – free-running cycle • Entrains w/ environmental cue • Environmental – independent biological clock • Environmental dependent entrainment

11. Neural mechanism • Disconnecting parts of brain and sensory organs • In cricket, cut nerve from eyes to optic lobes  free-running cycle begins • Severe optic lobes from rest of brain  free-running cycle breaks down • In mammal, destroying SCN cells of hypothalamus leads to arrhythmic cycle

12. Transplant SCN tissue from fetal hamster, normal rhythm restored ~ 40% • Transplant of other brain tissues remain arrhythmic

13. Environmental cues • Photoperiod • Moonlight – kangaroo rat • Temperature – green anoles • Food availability – breeding • Social interaction – regulating reprodution

14. Neural basis of behavior • Lesion and split-brain technique • Functional neuroanatomy • Cannulation • Transplantation • Transection-cut • Neural stimulation • Psychopharmacology & neurotransmitter

15. Effects of hormone on behavior • Organizational - influence development of structure • Metamorphosis • Brains - hormones regulate song nuclei sizes • Gonads - sexual differentiation

16. Activational - coordinate responses to environmental stimuli • influence sensation and perception • Courtship response - male mounts, female lordosis

17. Reproductive behavior of Anolis lizard • Females receptive in spring, affected by the degree of courtship by dewlap-displaying males • Courted females secret more gonadotropic hormones, speed ovarian development, and produce estrogen by the mature ovaries

18. Estrogen affects endocrine and neural targets  neck-arching behavior • Remove ovaries  abolish sexual receptivity • Implantation of estrogen pellet  restore sexual receptivity • Mated females cease receptivity in 5-7 min., attack males in next 10-14 days

19. Associated reproductive pattern – gamete production and sexual activity are linked by or associated w/ increases in particular hormones • Disassociated reproductive pattern • Diverse effects of testosterone – promote sperm production, activate sexual behavior, stimulates aggressive behavior, suppress immune system

20. Red-winged blackbird • Highest level of testosterone level in male during nesting season, territory defense, mate guarding • Higher level at high density areas • T level ~ # of females in territory ~ # of offspring fledge

21. Testosterone and mating

22. Testosterone and territory

24. Dispersal of male ground squirrel • Am. Sci. 77:232-239, 1989 • Background information of Belding's ground squirrel. • Physiological mechanism: activational vs. organizational?

25. Activational: lab (androgen level prior to dispersal), field (castrated male/control) • Organizational: female + androgen induce natal dispersal • External factor: aggression or avoiding conspecific • Internal factors: min. age, min wt. + behavioral changes: low level of fearfulness during 4-10 wks, high levels of locomotion & exploration=>shift of home range=>dispersal

26. Body fat and time of the year mediate dispersal in ground squirrel (Anim. Behav. 55: 606-614, 1998) • Early emergence: body mass as a good indicator of dispersal • Late emergence: time, body mass are not good indicator of dispersal

27. Methods in studying the hormone basis of behavior • Extirpation (removal) • Hormone replacement therapy • Blood transfusion • Bioassey • Radioimmunoassey • Autoradiography