VARIATION IN THE SEX-RATIO OF A LOW DIMORPHIC POLYGYNOUS SPECIES WITH HIGH-LEVELS OF MATERNAL REPRODUCTIVE EFFORT - CUVIERS GAZELLE

A population of 266 Cuvier's gazelles, descendants of two males and two females from the Western Sahara and living in the Estacion Experimental de Zonas Aridas, was analyzed. Results show that the energy cost of producing and rearing offspring, measured as offspring body weight, does not vary between males and females. But more males than females die during the Ist month of life. The advantages of producing one or the other sex are discussed. The cost of the parents' future reproductive success of producing male or female offspring was also investigated. Interbirth intervals following a twin male-female birth are longer than the other possibilities. However, no effects were observed of sex and litter size of the previous birth on sex and litter size of next birth nor on survival to 1 month of the next birth. Also no relationships were observed when we compared the components of the lifetime reproductive success of mothers (mother's longevity, fecundity, 1 month survival rate, abortion rate and age at first birth) and the sex ratio of their progeny, except that primiparous females that delay breeding produce more males than females during their lifespan. Physical attributes of the mother, such as birth weight, adult weight, and body size, as much as social rank were not related with her offspring sex ratio. But the mother's age influences the sex ratio. Older mothers produce more males than females. The bitch period does not influence the sex ratio, although it has a great effect on litter size via higher proportion of twins at the beginning of the birth period.