Stachowicz Lab University of California, Davis

Ecology and Evolution of Decorator Crabs

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ABC News segment on "Animals that Dress Up for Halloween", featuring decorator crabs and Jay Stachowicz. Aired 31 October 2006

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. 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".

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Click to see decoration in action on a Pugettia richii. Note the hooks used to secure the algae. You can see them in more detail in the picture below, this time from a Loxorhyncus crispatus

I became interested in decorator crabs when I ran across a crab that was highly specialized in its choice of decoration, deliberately choosing a specific chemically defended seaweed for decoration. Its choice of this seaweed was cued by the presence of chemicals that deterred fishes from consuming both the algae and the crab. Thus the crab behaviorally sequestered algal chemical defenses in the same way that some sea slugs physiologically sequester defenses from their prey.

Current work on decorator crabs in my lab focuses on studying the ecology and evolution of this group in a phylogenetic context. With Kristin Hultgren, I developed a molecular phylogeny of this group based on two mitochondrial and one nuclear loci. This tells us that decoration has clearly been lost many times within the majoid crabs.

The decorator crab Libinia dubia, decorated with the chemically noxious brown seaweed Dictyota menstrualis. See Stachowicz and Hay (1999) for details.

Within a particularly well resolved clade of these crabs, the epialtids that dwell in kelp forests of western North America, we are studying the forces responsible for driving the evolution of the loss of decoration and what alternative anti-predator strategies have evolved in their place. These studies have mostly focused on 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. We continue to use our decorator crab phylogeny to examine patterns of decorator crab community assembly and evolution.

Pugettia producta from California. Individuals 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 for more details).

Relevant Papers

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-]

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-]

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. In Press.