Decorator crabs are a diverse group of brachyuran crabs within the superfamily Majoidea that have the unusual habit of “decorating” their carapace with bits of algae and invertebrates. They accomplish this by attaching these materials to specialized hooked setae on their carapace that hold decorations in place much in the same way that Velcro latches onto fabric (see video, below). One example is shown at left where the decorator crab Libinia dubia has decorated itself with the chemically noxious brown seaweed Dictyota menstrualis. See Stachowicz and Hay (1999) for details. We study the fascinating natural history of these crabs and use phylogenetic methods to examine what these crabs can tell us about the ecology and evolution of antipredator behaviors in general. These crabs and our work on them was featured on the ABC evening news on Halloween 2006 in a piece on animals that “dress up for Halloween“. A more recent video that I helped the folks at KQED’s Deep Look put together does a really nice job of showing the decoration process up close.
We have assembled a molecular phylogeny of the superfamily that includes the decorator crabs to examine the evolution of this behavior (see Hultgren and Stachowicz 2009, below). Although it likely arose only once, the morphology (hooked setae) and behavior associated with decoration has subsequently been lost many times within the majoid crabs, where it is often replaced with other camouflage strategies including cryptic coloration, the ability to sequester pigments into the carapace or mimicry of specific plants or plant parts. Within a particularly well resolved clade of these crabs, the epialtids that dwell in kelp forests of western North America, we have described tradeoffs between decoration and carapace color change in crabs in the genus Pugettia. At least two independent times, decoration has been lost or reduced in crabs that have become intimately associated with kelps during some portion of their life cycle. In the figure at right, Pugettia producta from California match the color of the seaweed on which the live by incorporating pigments from their diet into their shell. These crabs only change color when they molt (See Hultgren and Stachowicz 2008, Oecologia for more details).
Hultgren, K. and J.J. Stachowicz. 2011. Camouflage in decorator crabs: Integrating ecological, behavioural and evolutionary approaches. Pages 214-229 in M. Stevens and S. Merlaita (eds). Animal Camouflage. Cambridge University Press. [-pdf-]
Hultgren, K.M. and J.J. Stachowicz. 2010. Size related habitat shifts facilitated by positive preference induction in a marine kelp crab. Behavioral Ecology 21: 329-336.[-pdf-]
Hultgren, K. and J.J. Stachowicz. 2009. Evolution of decoration in majoid crabs: a comparative phylogenetic analysis of the role of body size and alternative defensive strategies. American Naturalist 173:566-578.[-pdf-]
Hultgren, K. and J.J. Stachowicz. 2008. Molecular phylogeny of the brachyuran crab superfamily Majoidea indicates close congruence with larval morphology-based trees. Molecular Phylogenetics and Evolution 48:986-996. [-pdf-]
Hultgren, K. and J.J. Stachowicz. 2008. Alternative camouflage strategies mediate predation risk among closely related co-occurring kelp crabs. Oecologia. 155:519-528.[-pdf-]
Stachowicz, J. J., and M. E. Hay. 1999. Reducing predation through chemically mediated camouflage: Indirect effects of plant defenses on herbivores. Ecology 80:495-509. [-pdf-]
Stachowicz, J. J., and M. E. Hay. 2000. Geographic variation in camouflage specialization by a decorator crab. American Naturalist 156:59-71. [-pdf-]
Wicksten, M. and J.J. Stachowicz. 2013. Mimulus Stimpson, 1860, a junior synonym ofPugettia Dana, 1851 (Decapoda: Brachyura: Majoidea: Epialtidae). Zootaxa 3693:358-364 [-pdf-]