Behavioral Ecology and Sociobiology

, Volume 65, Issue 6, pp 1229–1235 | Cite as

Body size and sexual selection in the koala

  • William A. H. Ellis
  • Fred B. Bercovitch
Original Paper


Sexual selection is often characterized by polygynous breeding systems, size dimorphism, and skewed operational sex ratios. Koalas are sexually dimorphic in multiple domains, yet are absent from the literature on sexual selection and the structure of their mating system is unclear. We provide the first documentation of the strength of sexual selection in koalas by using microsatellite markers to identify sires. We combine the genetic data with morphological data in order to assess the role of body size in regulating reproductive output. During our 4-year study, 37% of males were identified as possible sires. Males were significantly larger than females, with sires heavier than non-sires. Male body mass correlated with annual reproductive output, with Crow’s Index of Opportunity for Selection revealing that variation in male reproductive success was threefold higher than that of females. Since it appears that male koalas rarely engage in physical confrontations over access to females, size dimorphism could be based upon non-agonistic competition and/or female mate choice. We propose that size dimorphism in koalas evolved as a consequence of endurance rivalry promoting vocal sexual advertisements that attract females. We suggest that female choice is a key mediator of male reproductive output.


Koalas Sexual selection Size dimorphism Reproductive success Mate choice Microsatellite DNA 



This study could not have been completed without the valuable input of Sean FitzGibbon and Alistair Melzer, both of whom contributed data and ideas to this report. The project was funded by The Earthwatch Organization and The San Diego Zoo Institute for Conservation Research. Field work was supported by Queensland Marine Parks Mackay. Kristen Lee oversaw all genetic analyses. Delma Clifton, Gail Tucker, Steve Burke, and Steve Fisher assisted with fieldwork. Queensland Department of Environmental and Resource Management provided the permits to work with koalas (WISP00491302), and the project was carried out under The University of Queensland animal ethics permit (ZOO/ENT/115/04/RT) and approved by the Institutional Animal Care and Use Committee of the Zoological Society of San Diego.


  1. Andersson M (1994) Sexual selection. Princeton University Press, PrincetonGoogle Scholar
  2. Bercovitch FB (1997) Reproductive strategies of rhesus macaques. Primates 38:247–263CrossRefGoogle Scholar
  3. Bercovitch FB (2007) Connecting conservation biology with evolutionary ecology: the case of the koala. Biodiversity 8:33–37Google Scholar
  4. Bercovitch FB, Bashaw MJ, del Castillo SM (2006a) Sociosexual behavior, male mating tactics, and the reproductive cycle of giraffe, Giraffa camelopardalis. Horm Behav 50:314–321PubMedCrossRefGoogle Scholar
  5. Bercovitch FB, Tobey JR, Andrus CH, Doyle L (2006b) Mating patterns and reproductive success in captive koalas (Phascolarctos cinereus). J Zool 270:512–516CrossRefGoogle Scholar
  6. Breuer T, Robbins AM, Polejniczac C, Parnell RJ, Stokes EJ, Robbins MM (2010) Variance in the male reproductive success of western gorillas: acquiring females is just the beginning. Behav Ecol Sociobiol 64:515–528CrossRefGoogle Scholar
  7. Clutton-Brock TH (2004) What is sexual selection? In: Kappeler PM, van Schaik C (eds) Sexual selection in primates: new and comparative perspectives. Cambridge University Press, Cambridge, pp 24–36CrossRefGoogle Scholar
  8. Cornwallis CK, Uller T (2010) Towards and evolutionary ecology of sexual traits. TREE 25:145–152PubMedGoogle Scholar
  9. Crow JF (1962) Population genetics. Am J Hum Genet 13:137–150Google Scholar
  10. Darwin CR (1871) The descent of man and selection in relation to sex. John Murray, LondonCrossRefGoogle Scholar
  11. Derocher AE, Andersen M, Wiig O, Aars J (2010) Sexual dimorphism and the mating ecology of polar bears (Ursus maritimus) at Svalbard. Behav Ecol Sociobiol 64:939–946CrossRefGoogle Scholar
  12. Dique DS, Thompson J, Preece HJ, de Villiers DL, Carrick FN (2003) Dispersal patterns in a regional koala population in south-east Queensland. Wildl Res 30:281–290CrossRefGoogle Scholar
  13. Eberhard W (1996) Female control: sexual selection by cryptic female choice. Princeton University Press, PrincetonGoogle Scholar
  14. Ellefson JO (1968) Territorial behavior in the common white-handed gibbon, Hylobates lar Linn. In: Jay PC (ed) Primates: studies in adaptation and variability. Holt, Rinehart, & Winston, New York, pp 180–199Google Scholar
  15. Ellis W, Carrick FN (1992) Total-body water and the estimation of fat in the koala (Phascolarctos cinereus). Aust Vet J 69:229–231PubMedCrossRefGoogle Scholar
  16. Ellis WAH, Melzer A, Green B, Newgrain K, Hindell MA, Carrick FN (1995) Seasonal variation in water flux, field metabolic rate and food consumption of free-ranging koalas (Phascolarctos cinereus). Aust J Zool 43:59–68CrossRefGoogle Scholar
  17. Ellis WA, Hale PT, Carrick F (2002) Breeding dynamics of koalas in open woodlands. Wildl Res 29:19–25CrossRefGoogle Scholar
  18. Ellis WAH, Melzer A, Bercovitch FB (2009) Spatiotemporal dynamics of habitat use by koalas: the checkerboard model. Behav Ecol Sociobiol 63:1181–1188CrossRefGoogle Scholar
  19. Ellis W, Bercovitch FB, FitzGibbon S, Melzer A, de Villiers D, Dique D (2010) Koala birth seasonality and sex ratios across multiple sites in Queensland, Australia. J Mammal 90:177–182CrossRefGoogle Scholar
  20. Ellis W, Bercovitch F, FitzGibbon S, Roe P, Wimmer J, Melzer A, Wilson RJ (2011) Koala bellows and their impact on the spatial dynamics of free ranging koalas. Behav Ecol (in press)Google Scholar
  21. Gordon G, McGreevy DG, Lawrie BC (1990) Koala population turnover and male social organization. In: Lee AK, Handasyde KA, Sanson GD (eds) Biology of the koala. Surrey Beatty, Chipping Northon, pp 189–192Google Scholar
  22. Haldane JBS (1932) The causes of evolution. Longman, LondonGoogle Scholar
  23. Johnston SD, McGowan MR, Phillips NJ, O'Callaghan P (2000) Optimal physicochemical conditions for the manipulation and short-term preservation of koala (Phascolarctos cinereus) spermatozoa. J Reprod Fertil 118:273–281PubMedCrossRefGoogle Scholar
  24. Jones AG (2009) On the opportunity for sexual selection, the Bateman gradient and the maximum intensity of sexual selection. Evolution 63:1673–1684PubMedCrossRefGoogle Scholar
  25. Kamilar JM, Pokempner AA (2008) Does body mass dimorphism increase male–female dietary niche separation? A comparative study of primates. Behaviour 145:1211–1234CrossRefGoogle Scholar
  26. Krockenberger A (2003) Meeting the energy demands of reproduction in female koalas, Phascolarctos cinereus: evidence for energetic compensation. J Comp Physiol B Biochem Syst Environ Physiol 173:531–540CrossRefGoogle Scholar
  27. Le Boeuf BJ, Reiter J (1988) Lifetime reproductive success in northern elephant seals. In: Clutton-Brock TH (ed) Reproductive success. University of Chicago Press, Chicago, pp 344–362Google Scholar
  28. Lee A, Martin R (1988) The koala, a natural history. University of New South Wales Press, SydneyGoogle Scholar
  29. Lee KE, Seddon JM, Ellis WAH, Johnston SD, de Villiers DL, Preece HJ, Carrick FN (2010) Genetic variation and structuring in the threatened koala populations of Southeast Queensland. Conservat Genet 11:2091–2103CrossRefGoogle Scholar
  30. Martin R, Handasyde KA (1999) The Koala: natural history, conservation and management. University of New South Wales Press, SydneyGoogle Scholar
  31. Mitchell P (1990a) The home ranges and social activity of koalas—a quantitative analysis. In: Lee AK, Handasyde KA, Sanson GD (eds) Biology of the Koala. Surrey Beatty and Sons, Sydney, pp 171–187Google Scholar
  32. Mitchell P (1990b) Social behaviour and communication of koalas. In: Lee AK, Handasyde KA, Sanson GD (eds) Biology of the koala. Surrey Beatty and Sons, Sydney, pp 151–170Google Scholar
  33. Mitchell P, Martin R (1990) The structure and dynamics of koala populations—French Island in perspective. In: Lee AK, Handasyde KA, Sanson GD (eds) Biology of the koala. Surrey Beatty, Chipping Norton, pp 97–108Google Scholar
  34. Moore BD, Foley WJ (2005) Tree use by koalas in a chemically complex landscape. Nature 435:488–490PubMedCrossRefGoogle Scholar
  35. Pontzer H, Raichlen DA, Shumaker RW, Ocobock C, Wich SA (2010) Metabolic adaptation for low energy throuhput in orangutans. PNAS. doi: 10.1073/pnas.1001031107 PubMedGoogle Scholar
  36. Ruckstuhl K, Neuhaus P (2006) Sexual segregation in vertebrates. Cambridge University Press, CambridgeCrossRefGoogle Scholar
  37. Schultz AH (1969) The life of primates. Weidenfeld and Nicolson, LondonGoogle Scholar
  38. Selander R (1972) Sexual selection and sexual dimorphism in birds. In: Campbell B (ed) Sexual selection and the descent of man, 1871–1971. Aldine, Chicago, pp 180–230Google Scholar
  39. Smith M (1980a) Behaviour of the koala, Phascolarctos cinereus (Goldfuss), in captivity. 3. Vocalizations. Wildl Res 7:13–24CrossRefGoogle Scholar
  40. Smith M (1980b) Behaviour of the koala, Phascolarctos cinereus (Goldfuss), in captivity. 5. Sexual behaviour. Wildl Res 7:41–51CrossRefGoogle Scholar
  41. Tobey JR, Andrus CH, Doyle L, Thompson VD, Bercovitch FB (2006) Maternal effort and joey growth in koalas (Phascolarctos cinereus). J Zool 268:423–431CrossRefGoogle Scholar
  42. Tobey JR, Nute TR, Bercovitch FB (2009) Age and seasonal changes in the semiochemicals of the sternal gland secretions of male koalas (Phascolarctos cinereus). Aust J Zool 57:111–118CrossRefGoogle Scholar
  43. Tucker GM (2009) Ecology, behaviour and growth of sub-adult koalas (Phascolarctos cinereus) on St Bees Island, Central Queensland. In: Centre for Environmental Management. Central Queensland University, Rockhampton, pp 285Google Scholar
  44. Tucker GM, Melzer A, Ellis W (2007) The development of habitat selection by subadult koalas. Aust J Zool 55:285–289CrossRefGoogle Scholar
  45. Utami SA, van Hooff JARAM (2004) Alternative male reproductive strategies: male bimaturism in orangutans. In: Kappeler P, van Schaik C (eds) Sexual selection in primates. Cambridge University Press, Cambridge, pp 196–207Google Scholar
  46. Vannoni E, McElligott AG (2009) Fallow bucks get hoarse: vocal fatigue as a possible signal to conspecifics. Anim Behav 78:3–10CrossRefGoogle Scholar
  47. Wade MJ, Arnold SJ (1980) The intensity of sexual selection in relation to male sexual behaviour, female choice, and sperm precedence. Anim Behav 28:446–461CrossRefGoogle Scholar
  48. Wade MJ (1987) Measuring sexual selection. In: Bradbury JW, Andersson MB (eds) Sexual selection: testing the alternatives. Chichester, New York, pp 197–207Google Scholar
  49. Wade MJ, Shuster SM (2004) Sexual selection: harem size and the variance in male reproductive success. Am Nat 164:E83–E89PubMedCrossRefGoogle Scholar
  50. Wells KD (2001) The energetic cost of calling in tree frogs. In: Ryan MJ (ed) Anuran communication. Smithsonian Institution Press, Washington, DC, pp 45–60Google Scholar
  51. Wells KD, Schwartz JJ (2006) The behavioural ecology of anuran communication. In: Narins PM, Feng AS, Fay RR, Popper AK (eds) Hearing and sound communication in amphibians. Springer, New York, pp 44–86CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  1. 1.San Diego Zoo Institute for Conservation ResearchZoological Society of San DiegoEscondidoUSA
  2. 2.Koala Ecology Group, School of Biological Sciences and Centre for Mined Land RehabilitationThe University of QueenslandBrisbaneAustralia
  3. 3.Primate Research InstituteKyoto UniversityInuyamaJapan
  4. 4.Wildlife Research CenterKyoto UniversityInuyamaJapan

Personalised recommendations