AUTHORS: Masahiro Ohnishi, Caesar Kleberg Wildlife Research Institute, Texas A&M University-Kingsville; Randy W. DeYoung, Caesar Kleberg Wildlife Research Institute, Texas A&M University-Kingsville; Charles A. DeYoung, Caesar Kleberg Wildlife Research Institute, Texas A&M University-Kingsville; Bronson K. Strickland, Department of Wildlife, Fisheries & Aquaculture, Mississippi State University; Don A. Draeger, Comanche Ranch; David G. Hewitt, Caesar Kleberg Wildlife Research Institute, Texas A&M University-Kingsville
ABSTRACT: Culling, or selective harvest, is a widely practiced strategy aimed at increasing antler size in managed populations of cervids. Recognizable microevolution of phenotypic traits through selection has long been practiced in laboratory or domestic populations, but the effect of culling on wild populations is poorly documented because of the difficulty in the field experimental settings [1]. Ideally, antler sizes of selected individuals between intergeneration at each age class are consistent or larger, and antler traits generationally improve via culling [2]. However, selective-harvesting young males can be genetically random due to unclear expression of their phenotypic potential in variable environments [3], and the environmental variations may also baffle the genetic potential for the mature antler growth [4]. We evaluated the effects of culling on demographic, genotypic, and phenotypic traits as part of a long-term experimental study of male white-tailed deer in southern Texas, USA. We established 3 treatments including, males at all age classes subjected to the intensive culling criteria (14.2 km2), males at the middle and mature age classes subjected to the moderate culling criteria (72.8 km2), and males without culling applications as control (20.2 km2). Each autumn during 2006–2016, we captured male deer, estimated age, and measured antler characteristics. Deer that did not meet culling criteria for their age class were sacrificed during 2006–2012. We recorded 5,447 captures of 2,937 individual bucks, and culled 1,333 of them. Most bucks were sired by males that exceeded the culling criteria. Nonetheless, the annual culling intensity for 1.5-year-old males at the intensive treatment ranged from 85 to 100% of bucks captured. Sixty-seven percent of 1.5-year-old males classified as culls would transition from cull to acceptable at 2.5 years old, while 56% would transition from acceptable to culls. The proportion of males changing, originally from acceptable to keep next year ranged 30 to 33% across all age classes. Heritability of antler points at 1.5year-old males is only 24% (Table 1). In other words, contributions of environmental effects to young antler growth are large. In the south Texas environment, phenotypes of physically immature males may not correlate to their genetic potential. Even though heritabilities of antler traits increased as deer aged, the empirical response for the genetic component of antler traits to culling were not recognizable due to the long interval between generations (Mean = 5-6 years), small numbers of male-offspring per sire (Mean = 1.0-1.3 male offspring), and the presence of phenotypically superior males with relatively lower breeding values. The results of this study will have important management implications for harvest management in male white-tailed deer.
