Consequences of maternal effects on body and antler size of white-tailed deer
By Kevin L. Monteith (B&C Official Measurer), Jonathan A. Jenks (Distinguished Professor, South Dakota State University), R. Terry Bowyer (B&C Professional Member)
Although only one subspecies of white-tailed deer (O. v. dacotensis) inhabits South Dakota, deer occupying the Black Hills of southwestern South Dakota are smaller than those in the eastern portion of the state. Average body weight of adult females from eastern South Dakota is 25% heavier than females from the Black Hills. The Black Hills region is characterized by coniferous forests with little understory forage, whereas eastern South Dakota is dominated by high-quality agricultural crops. Disparity in size of deer between these two areas is probably related to differences in forage quality. What would be the effect of improving nutrition of deer from the Black Hills? Would they increase in size and how long would it take for a change in nutrition to have a positive effect on growth?
|Average 1st-generation males from the Black Hills (top-left) and eastern South Dakota (top-right), and 2nd-generation males of Black Hills (bottom-left) and eastern South Dakota origin (bottom-right) at 6 years-of-age.|
To answer these questions, we captured newborn fawns from both regions and hand raised the animals using comparable husbandry practices. This approach ensured there were no environmental differences influencing diet, growth, and variability in investment by nursing mothers. Animals were bred in captivity to obtain offspring from 1st-generation Black Hills and eastern South Dakota deer. We raised 2nd-generation animals under conditions identical to those for 1st-generation animals. Males were weighed frequently throughout the study and annual growth of antlers was measured with the Boone and Crockett scoring system for ages up to 7 years.
Despite being in good nutritional condition, adult males that originated from the Black Hills ceased rapid body growth 41 days earlier, were 29% smaller in body weight (170 lbs), and grew smaller antlers (104 inches) than bucks from eastern South Dakota. Male offspring of 1st-generation deer from the Black Hills attained a 30% larger body weight at maturity and grew larger antlers than their fathers. Body weight (222 lbs) and antler size (136 inches) of those 2nd-generation males of Black Hills origin approached that of 1st-generation males (240 lbs; 152 inches) from eastern South Dakota at maturity. In contrast, 1st and 2nd-generation males of eastern South Dakota origin differed little in body or antler size.
Identifying maternal effects on offspring is critical to interpreting population dynamics of ungulates, but the duration and influence of maternal effects on offspring are not well understood. Poor forage can negatively affect growth of male ungulates, and providing a high-quality diet is expected to improve growth. Contrary to that prediction, male white-tailed deer fawns from the Black Hills raised in a controlled environment on a high nutritional plane, remained smaller in both body weight and antler size compared with males acquired from eastern South Dakota. Nevertheless, offspring of those Black Hills males attained a markedly larger body and antler size than their fathers, which supported an influence of maternal and grandmaternal condition during gestation on subsequent growth of offspring. That pattern of growth is known as a negative maternal effect, which was likely caused by poor forage conditions in the Black Hills. Moreover, these outcomes do not support a strong genetic component because deer of Black Hills origin recovered in body and antler size in the 2nd generation.
Implications for research and management of ungulates:
• Increases in forage quality, whether brought about by a reduction in the deer population or improvement of habitat, may not immediately result in increased body and antler size of males—management agencies and hunters need to be patient.
• Maternal effects may be more pronounced than previously recognized and can complicate interpretation of population dynamics, especially about predictions of body and antler size with improved nutrition.
• Fawns born small to mothers in poor physical condition will likely never recover and remain smaller in both body and antler size to those fawns born under improved conditions.
• Maternal effects also may be confused with individual quality of deer. Individual quality requires a strong genetic component that we did not identify. Our results indicate that nutrition rather than genetics has a stronger influence on growth of antlers.
Funding for this research (Monteith, K. L., L. E. Schmitz, J. A. Jenks, J. A. Delger, and R. T. Bowyer. 2009. Growth of male white-tailed deer: consequences of maternal effects. Journal of Mammalogy 90:651-660) was provided by Federal Aid in Wildlife Restoration administered through the South Dakota Department of Game, Fish and Parks, South Dakota Agricultural Experiment Station, National Science Foundation/EPSCoR Grant, and a Griffith Faculty Research Award presented to J. A. Jenks. Readers can request a copy of the original paper from Kevin Monteith.
Trophy Points: Big Game Research On Line is complied and edited by David G. Hewitt, a Professional Member of the Boone and Crockett Club and the Stuart W. Stedman Chair for White-tailed Deer Research at the Caesar Kleberg Wildlife Research Institute.