Skip to main content
Log in

Male-biased reproduction and sex-ratio adjustment in muskrats

  • Original Papers
  • Published:
Oecologia Aims and scope Submit manuscript

Summary

Sex ratios of a population and of litters were sampled in muskrats in Ontario, Canada. Sex ratios of litters sampled from nests were male biased (54% male). Until weaning, no differential costs of producing and rearing male and female young were identified that could account for this greater production of males. Following weaning, however, male-biased dispersal of juveniles from their natal site and more frequent acquisition by females of these sites as breeding sites the following year suggested a greater investment by adult females in female young. Therefore, competition between female siblings for the acquisition of their natal site may be sufficient to result in the greater production of males. In addition, the simultaneous occupation of, and competition between, siblings and parents for the resources of the natal home range may not be necessary for local resource competition to result in a greater production of the dispersing sex. Greater-than-expected binomial variance in sex ratios of litters suggested that adjustment of sex-ratios occurred. However, we were unable to associate the adjustment of litter sex ratios with changes in maternal condition. The greater production of males and the predominance of monogamous associations between adults in this population may have lead to slightly greater variation in male fitness than female fitness. Therefore, a female in better-than-average condition may have benefited by producing more males. Similarly, a lower cost of producing dispersing males may allow nutritionally-stressed females to reduce their total expenditure on offspring by producing more males. Because these experiments were non-manipulative, maternal condition may not have varied sufficiently during this study to detect adjustments of litter sex ratios resulting from either of the above mechanisms acting separately, but the combined effects of small differences in matermal condition and selective pressures operating in the same direction may have resulted in the observed deviation from the binomial.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Similar content being viewed by others

References

  • Altmann J (1980) Baboon mothers and infants. Harvard University Press, Cambridge

    Google Scholar 

  • Baumgartner LL, Belrose FC (1943) Determination of sex and age in muskrats. J Wildl Man 7:77–81

    Google Scholar 

  • Beer JR, Truax W (1950) Sex and age ratios in Wisconsin muskrats. J Wildl Man 14:323–331

    Google Scholar 

  • Bodmer FW, Edwards AWF (1960) Natural selection and the sex ratio. Ann Hum Genet (Lond) 24:239–244

    Google Scholar 

  • Bulmer MG, Taylor PD (1980) Dispersal and the sex ratio. Nature (Lond) 284:448–449

    Google Scholar 

  • Burley N (1982) Facultative sex-ratio manipulation. Am Nat 120:81–107

    Google Scholar 

  • Caley MJ (1987) Dispersal and inbreeding avoidance in muskrats. Anim Behav 35:1225–1233

    Google Scholar 

  • Caley MJ, Boutin S (1987) Sibling and neighbour recognition in wild juvenile muskrats. Anim Behav 36:60–66

    Google Scholar 

  • Caley MJ, Nudds TD (1987) Sex-ratio adjustment in Odocoileus: does local resource competition play a role? Am Nat 129:452–457

    Google Scholar 

  • Clark AB (1978) Sex ratio and local resource competition in a prosimian primate. Science 201:163–165

    Google Scholar 

  • Clutton-Brock TH, Iason GR (1986) Sex ratio variation in mammals. Q Rev Biol 61:339–374

    Google Scholar 

  • Clutton-Brock TH, Albon SD, Guinness FE (1982) Competition between female relatives in a matrilocal mammal. Nature (Lond) 308:178–180

    Google Scholar 

  • Clutton-Brock TH, Albon SD, Guinness FE (1984) Maternal dominance, breeding success and birth sex ratios in red deer. Nature (Lond) 308:358–360

    Google Scholar 

  • Cockburn A, Scott MP, Dickman CR (1985) Sex ratio and intrasexual kin competition in mammals. Oecologia (Berlin) 66:427–429

    Google Scholar 

  • Errington PL (1963) Muskrat populations. Iowa State University Press, Ames

    Google Scholar 

  • Fisher RA (1930) The genetical theory of natural selection. Oxford University Press, Oxford

    Google Scholar 

  • Gashwiler JS (1950) Sex ratios and age classes of Maine muskrats. J Wildl Man 14:384–389

    Google Scholar 

  • Hamilton WD (1967) Extraordinary sex ratios. Science 156:477–488

    Google Scholar 

  • Harmsen RH, Cooke F (1983) Binomial sex ratio distribution in the lesser snow goose: a theoretical enigma. Am Nat 121:1–8

    Google Scholar 

  • Kleiman DG (1977) Monogamy in mammals Q Rev Biol 52:39–69

    Google Scholar 

  • Kolman WA (1960) The mechanism of natural selection for the sex ratio. Am Nat 94:373–377

    Google Scholar 

  • Le Boulenge E, Le Boulenge-Nguyen PY (1981) Ecological study of a muskrat population. Acta Theriol 26:47–82

    Google Scholar 

  • Leigh EG (1970) Sex ratio and differential mortality between the sexes. Am Nat 104:205–210

    Google Scholar 

  • Meikle DB, Tilford BL, Vessey SH (1984) Dominance rank, secondary sex ratio, and reproduction of offspring in polygynous primates. Am Nat 124:173–188

    Google Scholar 

  • Myers JH (1978) Sex ratio adjustment under food stress: maximization of quality or numbers of offspring. Am Nat 112:381–388

    Google Scholar 

  • Neal TJ (1968) A comparison of two muskrat populations. Iowa State J Sci 43:193–210

    Google Scholar 

  • Olsen PF (1959) Muskrat breeding biology at Delta, Manitoba. J Wildl Man 23:40–53

    Google Scholar 

  • Proulx G, Gilbert FF (1983) The ecology of the muskrat, Ondatra zibethicus, at Luther Marsh, Ontario. Can Field-Nat 97:377–390

    Google Scholar 

  • Shaw RF, Mohler JD (1953) The selective significance of sex ratio. Am Nat 89:337–342

    Google Scholar 

  • Silk JB (1983) Local resource competition and facultative adjustment of sex ratios in relation to competitive abilities. Am Nat 121:56–66

    Google Scholar 

  • Silk JB (1984) Local resource competition and the evolution of male-biased sex ratios. J theor Biol 108:203–213

    Google Scholar 

  • Speith PT (1974) Theoretical considerations of unequal sex ratios. Am Nat 108:837–849

    Google Scholar 

  • Taylor PD (1981) Intra-sex and inter-sex sibling interactions as sex ratio determinants. Nature (Lond) 291:64–66

    Google Scholar 

  • Taylor PD, Sauer A (1980) The selective advantage of sex-ratio homeostasis. Am Nat 116:305–310

    Google Scholar 

  • Trivers RL, Willard DE (1973) Natural selection of parental ability to vary the sex ratio of offspring. Science 179:90–92

    Google Scholar 

  • Verner J (1965) Selection for sex ratio. Am Nat 99:419–421

    Google Scholar 

  • Werren JH, Charnov EL (1978) Facultative sex ratios and population dynamics. Nature (Lond) 272:349–350

    Google Scholar 

  • Williams GC (1979) The question of adaptive sex ratio in outcrossed vertebrates. Proc R Soc Lond B 205:567–580

    Google Scholar 

  • Wilson DS, Coldwell RK (1981) Evolution of sex ratio in structured demes. Evolution 35:882–897

    Google Scholar 

Download references

Author information

Authors and Affiliations

Authors

Rights and permissions

Reprints and permissions

About this article

Cite this article

Caley, M.J., Boutin, S. & Moses, R.A. Male-biased reproduction and sex-ratio adjustment in muskrats. Oecologia 74, 501–506 (1988). https://doi.org/10.1007/BF00380046

Download citation

  • Received:

  • Issue Date:

  • DOI: https://doi.org/10.1007/BF00380046

Key words

Navigation