Klassifikation und phylogenetische Einordnung der Lautäußerungen von Ocypodiden und Grapsiden (Crustacea, Brachyura)1

Abstract

SUMMARY Classification and evolution of sound production in ocypodid and grapsid crabs (Crustacea, Brachyura) The sounds of semiterrestrial ocypodid and grapsid crabs - mostly epiphenomenal characters of vibrations signals - were studied outdoors as well as in a special indoor terrarium allowing observation of underground behaviour. Sounds are classified in four groups according to the method of sound production. They are produced by respiration, stridulation, percussion, and convulsion, respectively. “Convulsion” is a descriptive name of free vibrations (shivering or shaking movements) the amplitude of which is very small. In Uca they can be heard as humming or honking noises. Contrary to previous assumptions, they are strictly synchronous with movements of the cheli-peds. Being subdivided in syllables these sounds can be understood as derivatives from unaccented percussive sounds (“drum whirls”). An exaggerated form of percussion of these honking species of Uca probably became integrated into the waving display (in this group always known as “jerking wave”). The non-directional character of evolution as visible in the sound production of the Uca species mentioned above can also be read from the relations between percussion and stridu-lation in semiterrestrial crabs. Apparently, there was an evolution from stridulation to rapping movements within the grapsid genus Sesarma. In the ocypodids Ocypode and Uca, however, stridulation evolved from percussion.