By Bill Gray, Wildlife Biologist
The major histocompatability complex (MHC) is a grouping of genes closely related to the immune system in all vertebrate animals. Its relationship to the immune system is rooted in its important role in recognizing and responding to pathogens that enter the body. Consequently, the MHC is considered an indicator of genetic quality because of the severe threat posed by parasites and diseases. Researchers have long considered the possibility that secondary sexual characteristics such as antler development and body size may be an outward expression of genetic fitness. The relationship between certain physical characteristics and the MHC was the focus of a study completed with deer from the McAlester Army Ammunition Plant (McAAP) in southeastern, Oklahoma.
The “good-genes” theory predicts that highly ornamented (i.e. large antlers) males should have lower internal parasite loads because they possess a superior immune system (MHC) better suited to cope with parasites. This may be further supported by the McAAP study in that the total number of stomach parasites present was found to be negatively associated with average antler score (more internal parasites/lower antler score). Additionally, Type 12 deer tended to have lower levels of both internal and external parasites than Type 11 or Type 22 deer. Conversely, the average number of external parasites showed a positive association with both antler size and body mass (more external parasites/higher average body mass and antler score). The latter finding may be supported by other studies indicating increased density of external parasites as host body size increases. Increased antler size relative to external parasite density is thought to be coincidental to a positive relationship between increased body size and increased antler development.
Antler quality in male deer has long been an area of fascination and prolific research. Most of the focus concerning antlers has been directed at the “how” of antler development in terms of techniques that may be used to enhance or otherwise produce large antlers. In this rush to produce a bottom line that can be measured in inches – deer managers have often overlooked equally important aspects that are only beginning to be addressed as we begin to consider the “why” of antler development.
Ditchkoff, S.S., Robert L. Lochmiller, Ronald E. Masters, Steven R. Hooper, and Ronald A. Van Den Bussche. 2001. Major-Histocompatibility-Complex Associated Variation in Secondary Sexual Traits of White-tailed Deer (Odocoileus Virginianus): Evidence for Good Gene Advertisement. Evolution 55 (3): 616-625