Seasonal Variation in Sex Ratios Provides Developmental Advantages in White-tailed Deer, Odocoileus virginianus

The potential for offspring sex ratios to differ from parity has been well documented in a number of mammalian species, including White-tailed Deer (Odo coileus virginianus) (Verme and Ozoga 1981; Kojola and Eloranta 1989; Kucera 1991; Landete-Castillejos et al. 2001; Landete-Cas tillejos et al. 2004; Sheldon and West 2004). This strategy could enhance the lifetime fitness of a female by producing the sex with the greatest potential reproductive value. Some factors shown to influence this variation include: maternal age, condition, social status, and habitat quality. Tri vers and Willard (1973) proposed that females of sexually dimorphic, polygynous species in good condition would benefit more from producing sons, because the mother’s condition would more strongly influence the future reproductive success of sons than daughters. Conversely, females in poor condition would benefit most by producing daughters, since female offspring require less maternal investment (i.e., milk production) and will likely reproduce regardless of maternal condition. Poor quality male offspring likely will not develop the physical characteristics necessary to compete successfully for females later in life. Assumptions for the Trivers and Willard hypothesis include: condition of offspring is correlated with condition of the mother after the parental investment period, condition of the young following the parental investment period will carry over to adulthood, and conditional advantages will differentially benefit male offspring in reproductive success (Trivers and Willard 1973). Since most ungulate species are polygynous, sexually dimorphic species which commonly exhibit these three assumptions (Hewison and Gaillard 1999), numerous studies have been conducted to test the Trivers-Willard hypothesis. In several of these studies, support for the Trivers-Willard hypothesis has been documented, where older or more dominant individuals gave birth to more males, and younger or subordinate females gave birth to more females (Landete-Castillejos et al. 2001; Landete-Castillejos et al. 2004; Sheldon and West 2004). Despite the many findings that support Trivers and Willard (Landete-Castillejos et al. 2001; LandeteCastillejos et al. 2004; Sheldon and West 2004), numerous studies have reported data that seem to contradict their hypothesis. In a review of published papers on Seasonal Variation in Sex Ratios Provides Developmental Advantages in White-tailed Deer, Odocoileus virginianus