Chapter 11: Electroreception 3/31/11 Lecture # 15 Chapter 11: Electroreception 3/31/11

Class survey on midterm Developing individual questions Helpful 1.8±1 Interesting 2 ±1 Developing group questions Helpful 2.8±2 Interesting 2.9 ±2 Using questions to study Helpful 1.7±1 Interesting 2.2 ±1.3 Questions on midterm Good coverage 1.8 ±1.3 Time to study 3.2 ±2 My grade 2.4 ±1.1 Final study questions 28 Y Class designed questions 24 Y

My suggestions Final - only do individual questions and skip the group questions Will be fewer questions on final and more time to prepare Do chapter assignments now so you can think about these as you go through the chapters

Chapters 10 Chemical signals (2) 20 Signal honesty (1) 11 Electroreception (2) 21 Conflict resolution (2) 12 Optimizing comm (1) 22 Territorial signaling (2) 13 Amount of info (1) 23 Mating games (2) 14 Value of info (1) 24 Social integration (2) 15 Coding (1) 25 Environmental signal (2) 16 Signal evolution (1) 26 Autocommunication (2) 17 Costs and constraints (1) 18 Signal design rules (1) 19 Evolutionary game theory (1)

Final project Assignment is on class web page For next time, give one sentence each: What is your topic? Why is it important? Why is it interesting to you? Based on this, I will try to find each of you a few references

Chemoreception - Ways of sampling Taxis - orientation with respect to chemical gradient Sampling Simultaneous - uses two nostrils or receptors which are compared Sequential - samples two nearby locations Usually move head Not as sensitive as simultaneous sampling so requires steeper gradient

Dog tracking scent Wander back and forth across scent trail to find its edges Then can figure out which way scent is increasing - getting closer to source

Snake tracking Female leaves a trail Male samples trail with forked tongue Touches vomeronasal organ on room of mouth Follow females pheromones

Sampling in a current Concentration may be discontinuous Use current flow to also guide upstream If lose scent, fly across current till find plume Gypsy moth Star marks pheromone release site. Arrows show wind direction. Thick line show when in plume. Light line shows when out of plume - at that point flies perpendicular to current till finds plume again

Electroreception Sense which humans do not have Only found in aquatic organisms Fish Amphibians Mammals? Book calls platypus a mammal. I think it is a monotreme

Forces Coulomb’s law gives force between two charged particles Same form as gravitational force  Is the permittivity constant

Fields Field is force felt by a unit charge Tells you what a single charge would feel (and so would do) as it moves around in a space containing other charges Measure in newtons / couloumb

Electrical potential Work you would have to do to move a point charge from infinity to a particular location Field is slope of potential Measure potential in volts (Joules / coulomb)

Electric field around single charge - monopole Symmetric Force is stronger as move closer to charge Charges would move along dashed lines If charge same sign they repel and if opposite sign then attract Solid lines like a contour map. Connect points of constant potential or constant field Force increases with distance squared

Electric field around single charge - monopole Symmetric Force is stronger as move closer to charge Charges would move along dashed lines If charge same sign as center, repelled and if opposite sign then attracts + Solid lines like a contour map. Connect points of constant potential or constant field Force increases with distance squared

Electric field around dipole Two charges, one + and the other - Dashed lines show directions particle moves along + -

Physics simulations

Electric hockey

Generation of bioelectric fields How can animals generate electric field? Use electric potential across cell membrane

Ion pump creates a concentration gradient across cell membrane Cl- K+ Na+ K+ Cl- Na+ Na+ K+ Cl- Na+ K+ Na+ Cl- K+ Na+ Cl- 3 Na/K ATPase Cl- Na+ K+ K+ 2 Na+ K+ Get concentration gradients Also get charge gradient since 3 Na+ go out and 2 K+ go in. Net neg charge inside cell. Cl- Na+ K+ Cl- Na+ K+ Na+ Cl- K+ Cl- K+ K+ K+ Cl- Cl- K+ Outside cell Inside cell

Also creates charge difference: Pumps 3 Na+ out and 2 K+ in - 141 mM 124 mM 3.3 mM Na+ 10-20 mM 5-10 mM 120-140 mM Cl- Cl- Na/K ATPase K+ Fain Fig 3.6 K+ Outside cell Inside cell

Membrane potential When channels are open, there will be a balance of diffusion and electrostatics Concentration K+ K+ Charge - Concentration gradient will make K+ diffuse out. But charge distribution (neg charge inside) will attract K+ to diffuse in. This will happen until the two forces are balanced. This assumes K+ is only ion that can move through these channels Mass and charge make K+ move in opposite directions

Walther Nernst Won Nobel prize in chemistry in 1920 Original “Nernst equation” was written for electrochemistry

Personification of Nernst equation - students in a classroom Student metaphor - If there are 100 students inside a room and none outside, there would tend to be students going out the door. However if there were hot fudge sundaes inside the room, the students might tend to stay in or diffuse in rather than go out. The number of hot fudge sundaes necessary to keep the students in the room would depend on ratio of students in vs out. If only 10 hot fudge sundaes, then most of the students would go out. If 100 sundaes then more students would come in.

Students will move out until same density in and out

If there are a few hot fudge sundaes… Might get few students coming back in

If there are lots of sundaes… Hot fudge sundaes = membrane potential Students = K+ ions Everyone who wants one will come back in

Nernst equation At equilibrium, can determine membrane potential which offsets concentration gradient across membrane K+ K+ + - If the concentration outside is 1/10 that inside, it will take -59 mV inside the cell to compensate to reach equilibrium with this gradient If concentration outside is 1/100 that inside, it will take -118 mV inside the cell Nernst equation comes from Gibbs free energy and work dG = w = qE = nFE but this is all at standard conditions Need to correct for actual concentration quotients Ko - outside Ki - inside Vm

Membrane potential increases till there is equilibrium Na/K ATPase K+ - + 3.3 mM 141 mM 120 mM 15 mM Na+ Na+ At equilibrium, K+ diffusing out is same as K+ diffusing in. At this point the inside of the cell is negative -60 to -80 mV Outside cell Inside cell

Excite neuron and channels open Na/K ATPase K+ + Na+ Na+ At equilibrium, K+ diffusing out is same as K+ diffusing in. At this point the inside of the cell is negative +50 mV Outside cell Inside cell

Electrocyte discharge Electrocyte is innervated by neuron When receives signal, cell depolarizes = change in voltage K+ Na+ -80 mV Na+ K+ +50 mV

Excitable cells Discharge of single cell contributes -80mV to +50 mV 130mV change in potential 130 mV

Cell potentials add just like batteries Two electrocytes in series will produce twice the potential if they are both stimulated at same time + 130 + 130 mV = 260 mV 3.0 V 1.5 V

What voltage does this give? Why wire it this way? You get 1.5 V same as for a single battery. However, you get 2x as much current and so 2x operating life of whatever electronic device you are using.

Stacks of electrocytes add in series to increase total voltage in discharge 130 mV Up to 700 V 520 mV …

Electric eel Can have up to 6000 electrocytes 6000 * 130 mV = 720 V Can have more columns of electrocytes to deliver more current http://animals.nationalgeographic.com/animals/fish/electric-eel/

Why would an animal use two columns? Up to 700 V … … Can supply more current - better for stunning or killing

Electric organs Evolved multiple times in fishes Longer organs can generate larger potentials

Ohm’s law V = I R In freshwater, fewer salts in water Water resistance, R is higher Need higher voltage to get same current I = V / R

Electric organ discharge, EOD Temporal pattern varies between species Here electrocytes are shown oriented relative to fish picture. Black dots are points of innervation by stimulating nerve cells. Waveform goes up when anterior of fish is positive relative to tail. If innervated from back, go positive first. If innervated from front, go negative first

EOD waveform control Skate Eel Knifefish Elephant fish Depends on how electrocyte is innervated - determines polarity of EOD pulse. Skate and eel only have one side excitable so only get one polarity. Gymnotiforms are excitable on both sides so go both positive and negative

Species specific discharges Gymnotiforms are wave fish: emit high pulse rates of 300-1700 Hz Mormyrids are pulse fish: emit variable rate pulses at 50-100 Hz Species live in murky water and are often nocturnal. Mormyrids using electrocommunication and sound while others just use electrocomm

Sodium channel activation shapes discharge

Electric discharge for different species A knifefish B brown ghost C electric eel D pintailed knifefish E Mormyrid

Voltage gated sodium channel

Sites undergoing rapid change

Electro-communication Some species can generate electrical signals Probe environment Communication Stun prey More species can detect electrical signals Navigation Prey detection

Coupling electrical signals to medium Use EOD to communicate with nearby fish or to sample environment Electric potential falls off as 1/distance2 But electric field is So signals fall of as 1/ distance3 so only short range

Electric field around fish Fish is a dipole - Head is positive, tail is negative Can sense nearby objects as perturbation in their dipolar field

Perturbations to idealized monopole electric field Distortion of electric field due to object with lower or higher resistance than surrounding medium

Reception of electric signals More common to detect electric signals than to generate them Fish: lamprey, rays, sharks, skates sturgeon, paddlefish, coelocanths catfish, gymnotiforms, mormyrids Amphibians: salamanders, frogs, toads Platypus

Electroreceptive monotreme Platypus bill can detect electric fields

Electroreceptors Similar to hair cells of lateral line and ear Stimulated by large voltage difference To maximize sensitivity to electric field, want to sample it at two locations as far apart as possible

Further apart measure Measured voltage Proportional to resistance V = IR Voltage Resistor

Further apart measure Bigger voltage if More resistance V = IR If R is 2x bigger V is 2x bigger Voltage Resistor

Electroreception Imagine fish is resistor that is part of larger circuit To maximize voltage sensed by fish, want its resistance to be larger than all other resistances

Salt water skates - ampullary receptors Skates detect electric field gradient from ampullary organ -canal with openings Use hair cells modified from lateral line Good for low frequency signals Hunting prey Longer canals will have larger potential drop across them and so can detect smaller changes in potential. Canals pointing in different directions will sense field oriented in different directions Cluster will average out internal field from skate itself so differences seen only from outside skate

Cartilagenous fishes Marine fish can detect fields as low as 5 x 10-9V/cm Freshwater sensitivities are less 5 x 10-5 V/cm This is like 9V battery over 2000 m or 1.2 miles Longer canals will have larger potential drop across them and so can detect smaller changes in potential. Canals pointing in different directions will sense field oriented in different directions Cluster will average out internal field from skate itself so differences seen only from outside skate

Noise Freshwater teleosts less sensitive 0.005 V / cm Freshwater noise is due to lightning Even far away burst causes noise Typically around 2 kHz

Swimming in magnetic field Ocean currents moving through earth’s magnetic field generate electric field 10-9 to 10-7 V/cm Rays may be able to navigate using these fields

Detecting prey Bodies of fish at different potentials If move generate potentials (breathing) Sharks and rays can detect these potentials, especially if they vary as breathing would

Gymnotiforms and mormyrids use tuberous receptors Designed to detect high frequency voltage changes Canal with high resistance plug Can tune to respond to species specific frequency

Frequency of electroreception is tuned to species signal frequency Receptive organ sensitivity Highest sensitivity is point where threshold is lowest. This matches quite nicely the peak of signaling frequency. Can also use receptors on each side of body to look at time delays, just as in hearing with two ears. This can help localize Divide response of receptors to those cells that detect pulse rates - species specific communication and those cells that detect amplitude for electrolocation

Mormyrid electrocommunication