Dominance
Terry Spivey, USDA Forest Service, www.forestryimages.com
Terry Spivey, USDA Forest Service, www.forestryimages.org
Relatedness in females plays a larger role in social behavior. Females are in fact less aggressive toward relatives than toward strangers (Clutton-Brock et al. 1982). Because females tend to remain around the natal area, they are though to be more knowledgeable of their relatives’ identities than are males (Bartos, 1986). This familiarity between relatives is responsible for providing strong, matrilineal relationships among females.
There exists a correlation between a cow’s dominance and the sex of her offspring. Dominant animals were found to give birth to more males than females at a ratio of 65 males to 35 females (Clutton-Brock, Albon, and Guinness, 1984, 1986). Subordinate females were found to give birth to more female young than male. Why dominant animals would give birth to more males is unknown, but there are several possibilities that are being considered. Milk and care resources of a mother may be better invested in male young if in the next generation males have greater reproductive success as a result of mating with multiple females. After birth, males are more apt to move away while females tend to remain in the natal area (Lowe, 1966). Another possibility argues that this variation in secondary sex ratio is adaptive. The variation could be explained if there were proof that a young male’s reproductive success is more dependent upon the quality of parental investment than is the young female’s (Trivers and Willard, 1973; Maynard Smith, 1980). If this were true, the mother would achieve higher fitness down the line if she committed her resources the more demanding growth requirements of the maturing male young. Another possibility that has been considered for Red Deer involves a status-dependent maternal endocrine environment that may induce selective blastocyst mortality soon after fertilization (Flint, Albon, Loudon, and Jabbour, 1997).
Dominance Status among females correlates with the rate that the progesterone concentration rises after ovulation (1997). This rate also indirectly affects dominance status because the increase in animal weight allows it to be more successful when competing for food (Thouless and Guinness, 1986). It is also thought that the relationship between social status and progesterone concentration is an indicator of endocrine control of ovarian function. Both stress and an inferior diet are associated with decreased LH levels in subordinate female elk (Flint, Albon, Loudon, and Jabbour, 1997). Such patterns of stress may be evidence of a female enforced dominance hierarchy wherein the dominant females are able to suppress others through aggression. There is no research indicating a pattern of stress-related aborted pregnancies or aborted male pregnancies among subordinate females.
