Colour polymorphism in the coconut crab (Birgus latro)

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 e...

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Bibliographic Details
Published in:Evolutionary ecology 2018-02, Vol.32 (1), p.75-88
Main Authors: Nokelainen, Ossi, Stevens, Martin, Caro, Tim
Format: Article
Language:English
Subjects:
Adults
Analysis
Animal Ecology
Biomedical and Life Sciences
Birgus latro
Color
Coloration
Crabs
Crustaceans
Ecology
Evolutionary Biology
Function analysis
Gene polymorphism
Genetic aspects
Genetic polymorphisms
Integument
Life Sciences
Original Paper
Pigmentation
Plant Sciences
Polymorphism
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Summary: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.
ISSN:0269-7653
1573-8477
DOI:10.1007/s10682-017-9924-1