Circannual Rhythms, Seasonal Change, Climate and Stress

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Circannual Rhythms, Seasonal Change, Climate and Stress - Darrell Senneke

Current Global Weather Conditions - Darrell Senneke

In December an experienced tortoise keeper in Argentina purchases a Russian tortoise (Testudo horsfieldii) and places it in a habitat that should be perfect for it. The temperature is correct, the light quality and duration are both correct, proper food is provided. A week goes by, then a second week, then the keeper starts sending emails trying to determine what is wrong with this animal that refuses to eat and sits in the corner of its habitat, obviously declining.

In November a keeper in Amsterdam purchases a Speke’s hingeback tortoise (Kinixys spekii). Again the animal is placed in a habitat perfect for it in every way. The keeper studies the care sheets, provides everything that can be done to insure that this animal is properly cared for and will fulfill its role in the keeper’s breeding group. Again in this situation the animal does not eat, but it is active, too active. Long after sunset it can be heard pacing the pen, finally after a week or so of this it no longer paces, becomes immobile and declines.

In October a child in Kansas captures a Three-toed box turtle, (Terrepane carolina triunguis) ,sets it up in a carefully prepared indoor environment only to have it refuse to eat, develop puffy eyes and slowly decline despite everything the keeper does to care for it.

These situations are repeated hundreds and thousands of times a year. If the keeper is lucky the animal perks back up after a month or so and regains it vitality. If he or she is unlucky the animal eventually dies, despite the fact that the keeper did everything in his or her power to provide a perfect habitat.

In the first case above the key to the problem is the time of the year. This is a wild caught animal, perhaps 30 years old. For every one of its 30 years this Russian tortoise has been hibernating at this time. By moving it across the equator it suddenly finds itself thrust into early summer just when its physiology is telling it that it should hibernate. It cannot hibernate though because the temperature is too high, the light intensity is too high and the light duration is too long. The result is extreme stress.

In the second example again we have a seasonal reversal. In this case the animal is thrust into late fall North of the equator after being captured and sold into the trade in “its” late spring South of the equator. The Speke’s hingeback , in this case a female, is gravid and in need of a nesting location, but in addition to that the tortoise needs the clues telling it to nest and exactly where. The light is of low intensity and duration, the temperature is different from what is expected and once again the result is extreme stress, complicated in this case by possible egg binding if the eggs are retained.

In the third example the Box turtle is not being moved half way across the planet, it is merely being moved indoors, effectively changing its seasonal stimulus even though it could have lived quite comfortably in the person’s own garden. A turtle or tortoise does not have to be moved from a continent away for captive care to upset its internal clock. As the box turtle is a recent captive the commonly accepted practice is to over-winter (keep it awake) it to avoid the stress of hibernation on an animal of unknown health. In this situation the desire to reduce the dangers of hibernation actually create the stress of seasonal reversal in the animal.

Behavioral cycles or rhythms that repeat at regular intervals are driven by biological clocks.

A 24-hour cycle is called a circadian rhythm, which comes from the Latin meaning "about a day." The best example of this is the sleep-wake cycle, In the sleep-wake cycle an animal will settle into a 24-hour cycle of activity and sleep even if deprived of light. Cycles longer than 24 hours are called "infradian," and if they last a year, such as migration and hibernation, they are called "circannual" rhythms. In the cases cited above the circannual rhythms are confused.

Research has shown that generating these biological rhythms internally, rather than depending completely on environmental cues, helps organisms anticipate important changes in the environment before they occur, thus providing the organisms with sufficient time to prepare. An example of this was an experiment observing the occurrence of summer molt and winter molt in two species of birds. The birds were born into a fixed photoperiod of 10 hours of light and 14 hours of dark each day. They lived under these conditions for 8 years. Yet even under fixed conditions they still molted at the same time as they would have in the wild. Their physiology is literally “hard wired” to go through these changes regardless of external stimuli.

This is a great thing if you are a tortoise coping with an early Spring or a late Fall and your internal clock is keeping you from being fooled into thinking that it is summer merely because of an unusually warm period but a very bad thing if your seasons are suddenly reversed.

Unfortunately in the experiment with the birds they did not try to change the stimuli to reflect different seasons to see if the birds would adapt. In keeping chelonia we inadvertently do this with nearly every acquisition and must be aware of it.

When obtaining a recently wild caught animal the keeper should endeavor to determine what the climate is like at the present moment in its native range. There are a number of web sites that can provide this information; if web access is not available a trip to the library may be in order.

In the case of the Testudo horsfieldii cited above, it is obviously not a long-term option to encourage it to hibernate at an inappropriate time in its new location. It is important though to realize that the animal instinctively is predisposed at this time to hibernate. Knowing this, the keeper can determine how best he or she can deal with the situation. People who attempt to over-winter animals that would naturally hibernate, even if being kept in their natural range, also face this problem.

The key understanding is that the animal is under extreme stress. There may be no external symptoms of disease, though with stress comes susceptibility and lowered resistance to various pathogens, which may manifest as various ailments. Rather than just treating the symptoms as they appear, the underlying stress must be addressed as well for the animal to make a successful transition. The keeper must reduce the stress on recent imports in every way in his power to do so while transitioning it to its new habitat. If after checking you find that the animal in its native range at this time would be experiencing 8 hours of light a day, cool temperatures and lowered food availability and this is vastly different from what you are providing, realizing that this is a major problem will help you address it.

If the animal wants to hibernate, providing at least 14 hours of light a day and warmth will in time break the hibernation urge. If possible, natural daylight should be provided, if not high intensity lighting such as Mercury vapor lights may be used. During this time the stress will be at its height and the animal must be kept hydrated as it may not eat be eating. Daily soaks in tepid water combined to maintain hydration along with a habitat or enclosure in a very low traffic area will help to allow the animal security while it acclimates. Record keeping is very important; a sustained weight loss is indicative of problems and should be taken as a warning by the keeper. Handling should be kept to a minimum during this time. Food should be provided daily, even if it is not eating presently. In time as the animal begins to eat and put on weight it can be moved into a more public area and, after quarantine, incorporated into the population.

In the case of the Kinixys spekii cited above forcing the animal to adapt immediately to its new seasonal situation is not an option. If it is gravid a provision must be made for it to naturally lay the eggs it is carrying. If the keeper is in doubt as to the presence of eggs, a veterinarian can confirm the situation with a radiograph. In this situation the keeper must attempt to duplicate the climate that the animal came from, again a trip to the library or web search will be useful in determining this. If it is the monsoon season with high temperatures and extended daylight an attempt should be made to provide this. In addition if the animal is indoors a nesting box should be provided by sinking it into the surface of the habitat or an area conducive to laying provided if outdoors. Hydrotherapy to reduce dehydration should again be a daily practice in this situation as is the lowered stress environment. If the animal will not deposit the eggs naturally, upon the advice of your veterinarian, egg laying may be induced. After the eggs are deposited, the transition to the new seasonal conditions may be proceeded with as in the above situation.

The procedure to follow with the Terrapene is the same as you would take with the Testudo horsfieldii , again providing at least 14 hours of light a day and warmth will in time break the hibernation urge. With the box turtle the hydration aspect cited above is very critical as they come from a naturally high humidity environment and our dwellings tend to be arid in the winter. Box turtles maintained indoors MUST have a damp substrate and free access to water.

It is the author’s experience that it typically takes at least two years for an animal to fully adapt to a seasonal reversal. Prior to that time close observation will help you determine if it is once again succumbing to seasonal stress.

References:

Howard Hughes Medical Institute, http://www.hhmi.org , “Seasonal Rhythms / Biological Clocks”

University of Michigan Medical School, Physiology 510, Integrative Physiology, Handouts, Biological Rhythms, Course Director: Fred Karsch, Ph.D.

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