Natural history miscellany: the adaptive significance of sexually dimorphic scale rugosity in sea snakes

Carla Avolio*, Richard Shine, Adele J. Pile

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

23 Citations (Scopus)
56 Downloads (Pure)


In terrestrial snakes, rugose scales are uncommon and (if they occur) generally are found on both sexes. In contrast, rugose scales are seen in most sea snakes, especially in males. Why has marine life favored this sex-specific elaboration of scale rugosity? We pose and test alternative hypotheses about the function of rugose scales in males of the turtle-headed sea snake (Emydocephalus annulatus) and conclude that multiple selective forces have been involved. First, rugosities may aid male positioning during courtship, because histology shows that tubercles are more highly innervated than adjacent flat areas of each scale and hence are presumably more sensitive to tactile cues, and because biomechanical tests show that rugosities enhance friction between the bodies of males and females. Second, the occurrence of rugosities over the entire body of males and (albeit less well developed) in females as well suggests that rugosities also play a hydrodynamic role by modifying water flow across the snake's surface. Flow tank tests show that rugosities reduce the thickness of the boundary layer by almost 50% and create turbulent flow that should massively enhance rates of cutaneous oxygen uptake and hence prolong maximal courtship duration by males.

Original languageEnglish
Pages (from-to)728-738
Number of pages11
JournalAmerican Naturalist
Issue number5
Publication statusPublished - May 2006
Externally publishedYes

Bibliographical note

Copyright 2006 by University of Chicago Press. Originally published in The American Naturalist, American Naturalist 167, no. 5 (May 2006): 728-738. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


  • biomechanics
  • courtship
  • marine
  • mate recognition
  • sexual selection


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