New Zealand Journal of Marine and Freshwater Research abstracts

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First encounter with a live male blanket octopus: the world’s most sexually size-dimorphic large animal

M. D. Norman^1,2
D. Paul²
J. Finn³
T. Tregenza⁴

¹Sciences, Museum Victoria
GPO Box 666E, Melbourne
Vic 3001, Australia
email: mnorman@unimelb.edu.au
²Department of Zoology
University of Melbourne
Vic 3010, Australia
³Institute of Antarctic and Southern Ocean Studies
University of Tasmania, Hobart
Tas 7000, Australia
⁴Ecology and Evolution Group
School of Biology, University of Leeds
Leeds, LS2 9JT, United Kingdom
email: T.Tregenza@leeds.ac.uk

Abstract   The first encounter with a live male blanket octopus, Tremoctopus violaceus Chiaie, 1830, illustrates the most extreme example of sexual size-dimorphism in a non-microscopic animal. Females attain sizes of up to 2 m long-almost 2 orders of magnitude larger than the 2.4-cm-long male. Weight ratios between the sexes are at least 10 000:1 and are likely to reach 40 000:1. Sexual selection and the unique defensive strategy of carrying cnidarian stinging tentacles may both have contributed to the evolution of this extreme size-dimorphism. Such dimorphism is not seen in any other animal remotely as large.

Keywords   blanket octopus; Tremoctopus; sexual dimorphism; evolution; defences; Physalia

M02017 Received 8 March 2002; accepted 24 June 2002; published 14 November
New Zealand Journal of Marine and Freshwater Research, 2002, Vol. 36: 733-736
0028-8330/02/3604-0733 $7.00 © The Royal Society of New Zealand 2002

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