GENOME SIZE VARIATION IN TARDIGRADA

The genome size of tardigrades has been documented to date in seven sp ecies of eutardigrades, and it is among the lowest in invertebrates. I n this paper the evaluation of genome size is extended to eight other species of eutardigrades and to one species of heterotardigrades, in o rder to obtain a more comprehensive picture of minimum DNA content evo lution in this phylum. The genome size of the heterotardigrade Pseudec hiniscus juanitae (0.6 pg), measured using 1c cells, is found to resem ble that of some eutardigrades. Thus, it is not possible to discrimina te between the two classes of tardigrades on this basis. Literature an d new data on eutardigrades also suggest that families or subfamilies cannot be discriminated on the basis of genome size. Nevertheless, gen ome size and sperm cell shape are correlated. A lower DNA content alwa ys corresponds to a more specialized male gamete. In general, in tardi grades, the low genome size and its low variation could be related to the high specialization of the phylum. Preliminary data on nuclear AT contents suggest that the variations in those values are correlated wi th genome size variations. (C) 1996 The Linnean Society of London