Island dwarfism in a tropical Australian python (Simalia amethistina)

Alastair Freeman; Ian Bell; Daniel J. D. Natusch

doi:10.1071/ZO25030

RESEARCH ARTICLE (Open Access)

Contents Vol 73(5)

Island dwarfism in a tropical Australian python (Simalia amethistina)

Alastair Freeman

^A ^C , Ian Bell ^B ^D and Daniel J. D. Natusch

^E ^*

+ Author Affiliations

- Author Affiliations

^A Aquatic Species Program, Wildlife and Threatened Species Operations, Department of Environment, Science and Innovation, Atherton, Qld 4883, Australia.

^B Aquatic Species Program, Wildlife and Threatened Species Operations, Department of Environment and Science, Townsville, Qld 4810, Australia.

^C Present address: Nature North, P.O. Box 1536, Atherton, Qld 4883, Australia. Email: alastairfreeman@naturenorth.com.au

^D Present address: P.O. Box 6163, Yatala Gold Coast, Qld 4207, Australia. Email: ian.bell@my.jcu.edu.au

^E School of Natural Sciences, Macquarie University, Sydney, NSW 2105, Australia.

^* Correspondence to: d.natusch@epicbiodiversity.com

Handling Editor: Alexis Levengood

Australian Journal of Zoology 73, ZO25030 https://doi.org/10.1071/ZO25030

Submitted: 24 June 2025 Accepted: 3 August 2025 Published: 22 August 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Dwarfism in insular populations of snakes has been documented at several localities around the world and it has been largely attributed to a phenotypic response of these isolated populations to food availability and composition. The incidental collection of size data for the Milman Island population of Simalia amethistina in north Queensland has brought to light a previously unknown example of island dwarfism in a tropical python species in Australia. Simalia amethistina on Milman Island are significantly smaller than conspecifics from the nearby mainland, with the maximum recorded size being only as large as the smallest 50% of mainland specimens. We attribute this dwarfism to the lack of large-bodied prey species available on Milman Island.

Keywords: Cape York, food availability, insular, Lockerbie Scrub, Milman Island, prey composition, Simalia kinghorni, snake.

References

Aubret F, Shine R (2009) Genetic assimilation and the postcolonization erosion of phenotypic plasticity in island tiger snakes. Current Biology 19(22), 1932-1936.
| Crossref | Google Scholar | PubMed |

Boback SM (2003) Body size evolution in snakes: evidence from Island populations. Copeia 2003(1), 81-94.
| Crossref | Google Scholar |

Boback SM (2006) A morphometric comparison of Island and mainland boas (Boa constricta) in Belize. Copeia 2006, 261-267.
| Crossref | Google Scholar |

Cogger H (2014) ‘Reptiles and amphibians of Australia.’ 7th edn. (CSIRO Publishing: Melbourne)

Dobbs KAL, Miller JD, Card MA, Mather M, Haselmeyer J (1997) Birds of Milman Island. Corella 21(2), 37-43.
| Google Scholar |

Fearn S, Sambono J (2000) A reliable size record for the scrub python Morelia amethistina (Serpentes: Pythonidae) in north east Queensland. Herpetofauna 30(1), 2-6.
| Google Scholar |

Fill JM, McBride P, Powell AJ, Shanahan LK, Stark JR, Freeman AB, Curran TJ (2012) Diet of amethystine (Morelia kinghorni) and carpet pythons (Morelia spilota) in north Queensland, Australia. Herpetological Review 43(1), 30-34.
| Google Scholar |

Greer AE (1997) ‘The biology and evolution of Australian snakes.’ (Surrey Beatty and Sons: Chipping Norton)

Jessop TS, Madsen T, Sumner J, Rudiharto H, Phillips JA, Ciofi C (2006) Maximum body size among insular Komodo dragon populations covaries with large prey density. Oikos 112(2), 422-429.
| Crossref | Google Scholar |

Luiselli L, Petrozzi F, Mebert K, Zuffi MA, Amori G (2015) Resource partitioning and dwarfism patterns between sympatric snakes in a micro-insular Mediterranean environment. Ecological Research 30(3), 527-535.
| Crossref | Google Scholar |

Natusch DJD, Lyons JA, Shine R (2021) Rainforest pythons flexibly adjust foraging ecology to exploit seasonal concentrations of prey. Journal of Zoology 313(2), 114-123.
| Crossref | Google Scholar |

Natusch D, Lyons JA, Shine R (2022) Spatial ecology, activity patterns, and habitat use by giant pythons (Simalia amethistina) in tropical Australia. Scientific Reports 12, 5274.
| Crossref | Google Scholar | PubMed |

Shine R (1987) Ecological comparisons of island and mainland populations of Australian tigersnakes (Notechis: Elapidae). Herpetologica 43(2), 233-240.
| Google Scholar |

Shine R, Slip DJ (1990) Biological aspects of the adaptive radiation of Australasian pythons (Serpentes: Boidae). Herpetologica 46, 283-290.
| Google Scholar |

Tanaka K (2011) Phenotypic plasticity of body size in an insular population of a snake. Herpetologica 67(1), 46-57.
| Crossref | Google Scholar |