Sexual dimorphism in a marsupial: seasonal and lifetime differences in sex-specific mass
J. L. IsaacDepartment of Tropical Biology, James Cook University, Townsville, Qld 4811, Australia. Email: joanne.isaac@graduates.jcu.edu.au
Australian Journal of Zoology 54(1) 45-50 https://doi.org/10.1071/ZO05060
Submitted: 22 September 2005 Accepted: 13 February 2006 Published: 23 March 2006
Abstract
Whereas sexual dimorphism in body mass is common in many vertebrates, the developmental mechanisms leading to diverging growth patterns between the sexes are poorly understood in mammals. In the present study, I investigate seasonal and lifetime differences in sex-specific mass in a marsupial, the common brushtail possum (Trichosurus vulpecula). From the age of 2 years, males were heavier than females, but significant dimorphism was evident only at the age of 4 years. Annual mass gain was greater in males than in females from 2 to 4 years of age. The body mass of both sexes fluctuated throughout the year, although patterns differed: females lost mass during lactation in winter, whereas males lost mass during the breeding season in later summer and autumn. The mass of a juvenile predicted its mass as an adult for males, but not females. Male-biased sexual dimorphism in mass of possums appears to arise through a combination of a greater rate and duration of mass gain in young males, and the diversion of somatic reserves away from growth and into reproduction in females.
Acknowledgments
I thank Jane Degabriel, Marco Festa-Bianchet, Brett Goodman and an anonymous reviewer for improving previous versions of the manuscript. Chris Johnson and Andrew Krockenberger provided support during all aspects of this research. Euan Ritchie, Tanya Cornish, Bryan Leighton and Nick Mann helped in the field. Queensland Parks & Wildlife Service provided possum-trapping permits and the Australian Research Council, James Cook University, Joyce W. Vickery Fund (Linnaean Society of New South Wales) and the Ecological Society of Australia provided financial support.
Badyaev, A. V. (2002). Growing apart: an ontogenetic perspective on the evolution of sexual size dimorphism. Trends in Ecology & Evolution 17, 369–378.
| Crossref | GoogleScholarGoogle Scholar |
Festa-Bianchet, M. , Jorgenson, J. T. , King, W. J. , Smith, K. G. , and Wishart, W. D. (1996). The development of sexual dimorphism: seasonal and lifetime mass changes in bighorn sheep. Canadian Journal of Zoology 74, 330–342.
Ganzhorn, J. U. (2002). Distribution of a folivorous lemur in relation to seasonally varying food resources: integrating quantitative and qualitative aspects of food characteristics. Oecologia 131, 427–435.
| Crossref | GoogleScholarGoogle Scholar |
Johnson, C. N. , and Ritchie, E. G. (2002). Adaptive biases in offspring sex ratios established before birth in a marsupial, the common brushtail possum Trichosurus vulpecula. Behavioral Ecology 13, 653–656.
| Crossref | GoogleScholarGoogle Scholar |
Schulte-Hostedde, A. E. , Millar, J. S. , and Hickling, G. J. (2001). Sexual dimorphism in body composition of small mammals. Canadian Journal of Zoology 79, 1016–1020.
| Crossref | GoogleScholarGoogle Scholar |
Weckerly, F. W. (1998). Sexual-size dimorphism: influence of mass and mating systems in the most dimorphic mammals. Journal of Mammalogy 77, 33–42.
Winter, J. W. (1980). Tooth wear as an age index in a population of the brush-tail possum, Trichosurus vulpecula (Kerr). Australian Wildlife Research 7, 359–363.
| Crossref | GoogleScholarGoogle Scholar |
