LAUSR

Marine driftwood, both when floating at the sea surface and after stranding in the supralittoral of a beach, has been inadequately sampled for talitrids throughout the world. It is probable that many more talitrids than the seven currently recognized as driftwood species are extant. Because they are obligate xylophages all seven species are considered to be specialized driftwood talitrids. They contrast with talitrids able to feed on either wrack or driftwood, as has been established experimentally in Platorchestia platensis (Krøyer, 1845). For the best known genus of specialized driftwood talitrids, Macarorchestia, there are two zoogeographic series: Northeast Atlantic: M. microphtalma – M. roffensis –M. martini and Mediterranean: M. remyi – M. pavesiae. Both geographic series are characterized by increasing dwarfism. Experimental studies suggest that dwarfism evolved to allow talitrids to occupy the small burrows made by gribbles (Isopoda, Limnoridae) in driftwood, and/or because driftwood was a poor quality food by comparison with wrack. The phylogenetic advantages of talitrids living in driftwood are that: they are protected from shorebird predation, they are provided with a long distance dispersal mechanism, and they have a relatively long term, albeit poorer quality, food source. Molecular genetic studies confirm that both Macarorchestia and Neotenorchestia have evolved by dwarfism from larger Orchestia ancestors.