Does learning vary with body temperature in a eurythermic lizard?

Researchers: R. Anderson, W. Boyle, R. Cockrel, O. Munzer, A. Segars

Western Washington University

Subject Species: Elgaria coerulea,

the northern alligator lizard

Effects of body temperature on learning in Elgaria coerulea: Habituation of OKR

• Learning is:– a durable, relatively permanent modification of behavior that occurs

through practice or experience, and is usually adaptive (presumably improves fitness).

• Habituation is: – perhaps the simplest form of learning. – the response decrement resulting from repeated stimulation– learning not to respond to a specific stimulus that has occurred

frequently without significant consequences (nonassociative learning)

• Habituation is useful because – the animal no longer wastes attention, time or energy responding to the

stimulus;– not responding also is less likely to draw the attention of the individual to

other animals (predators or prey).

• Habituation is not the same as a simple loss of responsiveness to a stimulus from sensory adaptation or fatigue.

Learning in Elgaria coerulea: Non-Associative Learning:

Habituation of OKR • One device used to study habituation is one that provides

optokinetic stimulation. It is a cylinder with a series of vertical black and white stripes along its inner surface.

• The cylinder is placed vertically with the stationary subject animal in the center-bottom, and the cylinder revolves so the vertical stripes move around the subject animal, horizontally, across its visual field.

• Response to this optokinetic stimulation, named the optokinetic response (OKR), may be universal in all vertebrates (DuLac et al. 1995) and has been examined in a diverse array of animals, including teleost fish, turtles, lizards and humans.

The device that stimulates or “releases” the Optokinetic Response (OKR)

OKRStimulator

Habituation of the OKR• The most commonly studied OKR is “head” OKR because the

behavior is readily evident.

• Head OKR occurs when the individual follows the stripes with oscillatory head movements; the head drifts laterally with the stripe movement, then quickly resets back to a central or forward position.

• The study of habituation of head OKR is a measure at the whole organism level.

• The whole organism level is more directly relevant to the ecology of learning than studying organ systems and/or cellular mechanisms (Bennett and Huey 1990).

• Studying head OKR should be an effective means of testing the relationship of learning to body (brain) temperature in lizards and other poikilotherms.

“Cooperative subject” in the OKRS

E. coerulea is eurythermic, cool-bodied; relatively slow moving.

Northern Alligator Lizard, Elgaria coerulea

Undergraduate co-researchers: Amanda Segars, Olivia Munzer, Robert Cockrel

The performance patterns for learning at ecologically relevant body temperatures in the lizard, Elgaria coerulea are not readily predictable.

Field Active Tb

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Body Temperature Scale 38oC18oC

29oC

Green = slow rise in performance ability with temperature to a broad peak (optimum) coinciding near the center of the behaviorally regulated temperature range, then a drop in performance as body temperature rises above the regulated range.

Blue = rise in performance ability through and above the preferred temperature range to about the upper limit of temperature observed for field-active animals, then a sharp drop in performance when temperatures cause severe dysfunction.

100%

50%

?

?

The effect of body temperature on optokinetic response: habituation of the alligator lizard, Elgaria

coerulea.• Two Experiments, both 6 revs per minute (3.7 stripes/ sec):

– Initial Experiment: • Body temperatures 22, 26, 30oC

10 consecutive minutes at each temperatureCCW cylinder rotation onlyanecdotal fatigue check

Follow-up: • Body temperatures 19, 24, 29oC

9 consecutive minutes at each temperature: 1st set: 4 min, CCW2nd set: 4 min, CW (and fatigue check)3rd set: 1 min, CCW (fatigue check)

Elapsed Time (sec)0 100 200 300 400 500 600

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22oC, habituating 22oC, habituated 26oC, habituating 26oC, habituated 30oC, habituating 30oC, habituated

The effect of body temperature on optokinetic response: habituation of the alligator lizard, Elgaria coerulea.

(Values are means of head resets for each 15-second interval )

Data for intervals of 105-120 and 120-135 seconds are excluded to enable visual separation of habituating and habituated phases.

(N= 18, 11, 13 at 22, 26, 30oC).

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22oC 26oC 30oC

Habituation rates for Elgaria coerulea in Optokinetic Response, OKR at 3 temperatures.

The more negative the slope, the faster the habituation of head re-sets.

Symbols are means of slopes, bars are SD, Ns are 18, 11, and 13, in order of ascending temperature* indicates significantly difference for time to habituation

ANOVA for slopes: F2,42 = 8.7, P = 0.002

148min*

124min

114min*

Rate of OKR habituation is greater and time to reach habituation is shorter at the higher body temperature in Elgaria coerulea

Time elapsed since onset of OKR response

0 20 40 60 80 100 120 140 160 180

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Time to habituation: 22oC = 148 + 11 sec 26oC = 124 + 9 sec 30oC = 114 + 4 sec

Learning at 30oC is 30% faster than learning at 22oC

2nd Experiment: No fatigue! means for all 3 temperatures: End ccw = 4, begin cw = 13 End cw = 4, begin ccw = 14

The performance patterns for learning at ecologically relevant body temperatures in the lizard, Elgaria coerulea are not readily predictable.

Field Active Tb

Rel

ativ

e pe

rform

ance

val

ues

Body Temperature Scale 38oC18oC

29oC

Green = slow rise in performance ability with temperature to a broad peak (optimum) coinciding near the center of the behaviorally regulated temperature range, then a drop in performance as body temperature rises above the regulated range.

Blue = rise in performance ability through and above the preferred temperature range to about the upper limit of temperature observed for field-active animals, then a sharp drop in performance when temperatures cause severe dysfunction.

100%

50%

?

?OKR

Effects of body temperature on learning in Elgaria coerulea: Associative Learning in a Y- Maze

Associative Learning* also known as “trial-error-and-trial-success learning,” and is:learning to associate a behavior with the consequences of that behavior

(e.g., associating pouncing on a prey item or dipping snout in water, or using a particular refuge with ingesting prey and allaying hunger or drinking water and allaying thirst, or resting and recovering from exercise)

Associative learning usually requires several to many episodes or trials, in which the animal eventually cognitively associates (learns) success with one behavior versus failure with another behavior in the same situation.

There will be a greater frequency of successes as the animal experiences more trials, because the beneficial behavior is performed more often than the unsuccessful behavior. (success is reinforcement of benefit, whereas failure is no reward)

Avoidance Learning is a form of associative learning, wherein the animal learns to not perform a behavior

that has a detrimental consequence or “punishment” in a particular context

(e.g., a chase by a predator or damage from a predator, conspecific, or prey item).

Avoidance learning usually requires only one, two, or a few episodes to acquire the learned response of reducing or not performing the behavior that leads to the “punishment.”

Avoidance learning can be “active” (avoiding & evading the predator) or passive (aversion to food).

(*in psychology parlance, is similar to “appetitive conditioning,” a variant of “operative conditioning”)

Y-Maze methods challenges• Five separate attempts by both grad students

and undergrad students over a 10 year period to study maze learning in lizards in our lab failed to discern clear patterns in the data.

• There were weak hints of trends related to body temperature along with overwhelmingly strong variation in behavior among individual lizards.

• Finally in 2009, R. Anderson & W. Boyle tried a simplified experiment….

Effects of body temperature on learning in Elgaria coerulea:

Associative Learning in a Y- Maze William Boyle, co-researcher

Refugium

open blocked

Y-maze Methods, 2009Two widely separated body temperatures:

21oC v. 29oC

One trial per lizard at each body temperatureThe first trial for half of the lizards was at 21oC The first trial for half of the lizards was at 29oC

Sample size was 24 individuals:12 lizards studied in late spring quarter12 lizards studied in early fall quarter

Y- maze Methods

We varied color of end wall between sides

Half of all lizards were presented with green on right.Half of all lizards were presented with brown on right.

Both sides had the same dark refugium entrance.

The lizard had to try to enter and begin walking up a ramp in the box to know whether the entrance was open or blocked.

More Y-maze methodsOn the 1st trial of 5 or 6 trials for that day, the lizard was

permitted a free choice to enter the refugium on either side.

Once a lizard entered a refugium, it was given about 10 minutes to rest-and-hide before the next trial began.

On the 2nd and later trials the lizard could only enter the side it chose on the first trial.

The lizard was gently harassed by tapping it at the base of the tail when it attempted cryptic behavior or if it began moving away from the Y-end; occasionally taps on the head were required because it was attempting to climb (always unsuccessfully, given the smooth walls).

Hence, its reward was resting-and-hiding in the refugium

Y-maze results:• Strong effects of temperature, trial, and individual lizard on

time taken to enter the refugium (ANOVA). Lizards at 29oC learned faster than when at 21oC

• At both body temperatures, lizards appeared to realize the refugium was a “faux refugium” by the 2nd trial (1-trial learning?!):– They spent significantly longer in the maze before entering the refugium during

the second trial than during the first trial. – They appeared to be pursuing alternative means of escape, rather than entering

the refugium immediately as they had done in the 1st trial.

– Individuals at putative optimal body temperature, 29oC tried alternative means of escape more in the 2nd & 3rd trials.

– Individuals at 21oC did not reach peak levels of alternative means of escape until the 5th & 6th trials.

• For trials 5 and 6, individuals at 29oC entered the refugium significantly earlier than they did at 21oC. They learned faster.

Y-Maze Statistics• Body Temperature: F = 8.5, P = 0.004• Lizard ID: F = 3.6, P = 0.0001• Trial: F = 2.4, P = 0.036• Day order F = 0.5, P = 0.5• Post hoc test of temperature dependent time difference

= 2.18 , p= 0.004Mean times to enter refugia (not including long climb episodes):

Trial 21C 29C 1 4.8 3.9

2 9.0 6.33 8.3 7.44 7.8 6.35* 9.0 5.66* 8.2 4.2

• At 29oC there were more investigative episodes than at 21oC at trials 2-3: chi-square = 4.91, P = 0.028

Comparisons? Perspective?

• How do the temperature-related patterns of learning by Elgaria coerulea compare with similar temperature-and-performance patterns of learning in other lizards?

• Answer: – We do not know, because other careful

studies yet must be performed.…

On-going lab and field studies comparing among lizards that vary in FAM and

temperature-dependence• Ongoing:

– Antipredation risk v. vulnerability

– Sprinting Speed

– Bite force & Bite Speed

– Endurance and recovery times

– Agility & Acceleration

– Behavioral responses and learning in a Y-maze

– Rates of habituation via OKR (simple form of learning)

Planned lab and field studies comparing among lizards that vary in FAM and temperature-dependence

• Planned:

– Reaction Time

– Stalking Behavior, Lunge Distance & Lunging Speed

– T-maze learning (associative learning)

– Exploratory behavior (i.e. curiosity)

– Field study of the microevolutionary consequences of variation in antipredation risk & vulnerability among Aspidoscelis tigris.

Lives in desert scrub Is a wide, intensive forager Almost always on the move Crosses open ground often Seeks hidden prey under shrubs

Lives in desert scrub Is an ambush predator Remains still as it visually seeks prey, Often stations itself near a shrub Captures mobile prey as they approach

Gambelia, wislizenii, the Leopard LizardAspidoscelis tigris, the Whiptail Lizard Summer

field courses!

Lizards as model systems Lizards that vary in modes of food acquisition (e.g., ambusher,

wide forager) and habitat types should have different sets of challenges among their four basic tasks.

Identifying and sorting out these phenomena may help us understand variation among lizards in their capacities for

cognition,exercise capacity (speed & recovery), body temperature, and metabolism,

that is, in the salient features that distinguish birds and mammals from other vertebrates.