Das Schwimmen der Talitridae (Crustacea, Amphipoda): Funktionsmorphologie, Phänomenologie und Energetik

Abstract

The Talitridae, well-known for their jumping behaviour, swim with help of the tail-flip. This movement of the abdomen is also known from other amphipods like the Gammaridae which are normally not able to move by jerks outside the water. The suspected homology between the tail-flip when swimming and the jerky movement of the abdomen when jumping gave rise to this investigation, mainly based on high frequency film recordings, on the swimming ofHyale nilssonii, Orchestia cavimana, andTalitrus saltator (family Talitridae) as well as three related species of the families Gammaridae and Corophiidae. Comparative morphometrical and SEM-studies on the habitus of the species and the build of the involved limbs reveal the rather uniform construction of the Gammaridea; functional adaptation to the environment and to the way of living become apparent in minor alterations. The joints of the pleopods and uropods show a clear structural adaptation to the mechanical strain during swimming. The pleopods are moved metachronally in all examined species; angular velocity and rate of beating indicate the efficiency of the swimming movement. In the Talitridae, the metachronal beat of the pleopods is nearly always coupled with the tail-flip while in the Gammaridae and Corophiidae the tail-flip, in addition to the beat of the pleopods, is mostly used for a start from the subsoil or for a change in swimming direction.H. nilssonii, Gammarus locusta, andCorophium volutator, all inhabitants of the tidal zone in the North Sea shallows, turned out to be the “best” swimmers while the (semi-) terrestrially living species,O. cavimana andT. saltator, proved to be rather “poor” swimmers. This clearly indicates the ecological significance of swimming for the different species. Furthermore, the tailflip is found to be of rather subordinate importance. It contributes to a higher velocity if used moderately but is rather obstructive if a large angle is covered while extending and flexing the abdomen. The efficiency of swimming is inversely proportional to the efficiency of jumping in the three talitridean species. Thus, better adaptation to terrestrial life is accompanied by loss of swimming efficiency. Examined under the aspect of locomotional homology, it is concluded that the tail-flip used while swimming is homologous to the jerky movement of the abdomen used for jumping. The comparison of the swimming performance of the examined species with other crustaceans and some fishes illustrates the over-all good results of the Gammaridea.