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Antler development is usually on the 2 permanent pedicles which developed a few months after birth, but they also can develop at other locations. A paper published in 1894 reported a 9.8 cm antler grew at the location where a broken piece of glass had pierced the skin and periosteum (a tissue covering bones) of a roe deer’s face. Since then, a number of papers have described antlers growing on other facial bones. Pedicles then develop at these locations and antlers continue to be grown on them. Experiments found that pedicles and antlers can be removed and then grafted to other locations on the face. These findings suggest that sometimes the nervous system may be more important than the endocrine system in regulation of antlerogenesis.
The occurrence of more or fewer antler points on one antler than the other, difference in main beam or tine lengths, missing tines, and abnormal curvature of an antler, etc. are some examples of antler asymmetry. However, the term also applies to the effects which result when a growing antler is damaged or injured. In these situations, that antler grows to be much larger than the other antler and the effect is even greater if the injury occurs early in antler growth. That antler is even larger the next year. Then, the difference between the two antlers decreases over the following years. Damage to the beam of a growing antler results in an extra tine at that location and also persists for a number of years.
The term trophical memory has been applied to this year after year recurring effect caused by damage to growing antlers. It is speculated that a nervous connection of the growing antler and the central nervous system is required to store this memory.
Antler asymmetry can also result from injuries to the body. An accidental injury to the left hind leg of a sambar deer necessitated amputation through the metatarsal. In future years, the right antlers were always much smaller than the left antlers. Similarly, the amputation of a barking deer’s injured right hind leg at the tibia resulted in the left antlers of this deer being much smaller than those on the right side. The reduced antler weight on the opposite side from the amputation helps the animal compensate for the missing limb thereby improving the deer’s balance. This benefit is lost when the antlers are shed. It was noticed that these deer would tip their head to the side of the amputation to further aid their balance. In time, the pedicle on the side of the amputation grew larger and heavier and helped compensate for the shed larger antler.
Caribou and reindeer are the only cervids in which both sexes normally grow antlers. The brow tines of their antlers are of special interest. They grow from the base of the antler barely above the pedicle and are in front of the face. Usually, the distal end of the brow tine is enlarged somewhat and has a few points or may even be palmate. The brow tines are often called shovels as a common belief was that they were used to dig through snow to feed on lichens. However, the antlers of many are shed several (4 – 6) months before the snow melts. Also, the feet are usually used to dig through snow. Other, more likely thoughts are that they shield the face during fights or that they have social importance.
The size and shape of brow tines are extremely variable. They may be well developed on both antlers, one may be much larger than the other, both may be quite small, or there may be none. Additionally, the size, shape, presence, or absence of brow tines can change from year to year for any individual. Therefore, there is no genetic influence on an animal’s brow tines, or lack thereof. This, too, is an example of antler asymmetry.
Examination of 360 sets of caribou/reindeer antlers from the Northern Hemisphere found that brow tines on 52.6 percent were larger on the left side, 29.7 percent were larger on the right side, 15.0 percent had small brow times on both sides, and 2.6 percent had no brow tines. There are only two islands in the Southern Hemisphere that have introduced and increasing reindeer herds. Examination of 70 sets of these antlers found 27.1 percent had larger brow tines on the left side, 38.6 percent were larger on the right side, 8.6 percent had large brow tines on both sides, and 25.7percent had no brow tines. The largest percentage of animals with larger brow tines on the left side in the Northern Hemisphere is the opposite of that found in the Southern Hemisphere where the largest percentage of larger brow tines was on the right side. This mirror image result has yet to be explained. Some suggest that geo-physical forces may be involved.
I have not mentioned that antlered does are found occasionally. Sometimes there is an antler on only one side, sometimes on both sides. Often the velvet is never shed, other times it is shed. The only explanations offered for the cause of pedicle and antler growth in wild female deer were an increase in circulating hormones from the adrenal glands or the ovaries and by trauma to the periosteum of the frontal bones.
Next time: The purpose of antlers and their significance in social behavior.
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