Evolutionary Ecology

, Volume 32, Issue 1, pp 75–88 | Cite as

Colour polymorphism in the coconut crab (Birgus latro)

  • Ossi NokelainenEmail author
  • Martin Stevens
  • Tim Caro
Original Paper


Coconut crabs (Birgus latro) are strikingly variable in coloration, but the significance of this colour diversity has never been investigated. We studied coloration, morphology, behaviour and background matching of adult coconut crabs, the world’s largest terrestrial invertebrate, at the western edge of its distribution on Pemba Island, Tanzania. Adults are evidently polymorphic; they come in red and blue types (3:1 ratio on Pemba). The best predictor of colour morph was ventral hue, which, using a discriminant function analysis, correctly classified 96% of the crabs assigned into a predefined colour group. In contrast, principal component analyses suggested a degree of overlapping colour variation. We found no evidence that coloration was sex or size-linked. Males were larger than females and the Pemba adult population appeared male-biased (3:1). We also report that red adults may match the background better than do blue adults on land, whereas blue match better near shore than do red. We postulate that although colour diversity in coconut crabs may be genetically determined, potentially through a crustacyanin gene polymorphism influencing the stability of integument pigmentation, its maintenance may involve several ecological drivers.


Background matching Colour variation Crustaceans Developmental plasticity Pemba Island Trade-off 



We thank the Revolutionary Government of Zanzibar for permission; the University of California, Davis for funding fieldwork; and two anonymous reviewers for comments.

Compliance with ethical statement

Conflict of interest

The authors declare that they have no conflict of interest.

Supplementary material

10682_2017_9924_MOESM1_ESM.docx (14 kb)
Supplementary material 1 (DOCX 13 kb)


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Copyright information

© Springer International Publishing AG, part of Springer Nature 2017

Authors and Affiliations

  1. 1.Centre for Ecology and Conservation, College of Life and Environmental ScienceUniversity of ExeterPenrynUK
  2. 2.Department of Biological and Environmental ScienceUniversity of JyväskyläJyväskyläFinland
  3. 3.Department of Wildlife, Fish and Conservation Biology and Center for Population BiologyUniversity of CaliforniaDavisUSA

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