Food availability and secondary sex ratio variation in wild and laboratory house mice (Mus musculus) D. B. Meikle and L. C. Drickamer Department of Biology, Williams College, Williamstown, MA 01267, U.S.A. Summary. Female house mice deprived of food intermittently for 1 week before mating gave birth to fewer male young, but litters of females deprived of food for 2 weeks did not differ from control litters. Since mean weights of females did not differ between the two treatments, our results suggest that females were initially stressed by food deprivation, but recovered in the second week. Introduction Recent data and theory suggest that secondary sex ratios (sex ratio at birth) of mammals can vary in relation to maternal nutritional status (Trivers & Willard, 1973; Rivers & Crawford, 1974; Clutton-Brock, Albon & Guinness, 1981; Verme, 1983; Labov, Huck, Vaswani & Lisk, 1986). Trivers & Willard (1973) proposed that, since the reproduction of males varies more than that of females in polygynous and promiscuous species, the development and subsequent reproduction of sons is probably more closely associated with maternal 'condition' (e.g. size, dominance rank, nutritional state) than is the reproduction of daughters. The model therefore predicts that, all else equal, females in poor condition give birth to more daughters than sons, while females in good condition gave birth to more sons than daughters. There have been a few reports of offspring sex ratio variation in rodents in relation to maternal nutritional status. Female albino house mice (Mus musculus) fed a low-fat diet ( < 1 % lipid) gave birth to fewer male than female young (Rivers & Crawford, 1974). Labov et al. (1986) also reported that females of the LVG/LAK strain of golden hamster (Mesocricetus auratus) gave birth to fewer male offspring and that males grew more slowly than females when their mothers were consistently underfed (kept at about 75% of full body weight). In addition, when female wood rats (Neotoma floridanus) were underfed during lactation (about 70-90% of maintenance requirement for non- reproductive females) their sons did not gain weight as rapidly as and had higher mortality than did their daughters, apparently due, in part, to maternal rejection of male offspring (McClure, 1981). In the above studies females were fed an inadequate diet on a daily basis. However, large fluc¬ tuations in food availability and dominance rank-related access to food may occur daily for species like mice (Jakobson, 1981; Ward, 1981; Bronson, 1985). We therefore tested the Trivers-Willard model by alternately depriving female house mice of food and feeding them ad libitum every other day just before mating. In addition, we compared the responses of wild and albino laboratory mice to this treatment, since the latter are not subject to natural selection by food scarcity and resource competition as are their wild conspecifics. Materials and Methods We used nulliparous females from a random-bred ICR/Alb-derived strain (N = 97) and F1 progeny of wild mice (M. musculus) trapped at a poultry farm in West Simsbury, Connecticut * Present address: Department of Biology, Indiana University, Bloomington, IN 47405, U.S.A. Downloaded from Bioscientifica.com at 02/10/2023 03:12:34PM via free access