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Bacterial Induction of Settlement and Metamorphosis in the Planula Larvae of Cassiopea andromeda (Cnidaria: Scyphozoa, Rhizostomeae)

1979; Inter-Research; Volume: 1; Linguagem: Inglês

10.3354/meps001021

1616-1599

Rainer Neumann,

Coastal wetland ecosystem dynamics

Planula larvae were collected from mature Cassiopea andromeda medusae at Key Largo (Florida, USA).Their development was analysed and compared with the development of vegetative buds from laboratory-cultured polyps of this species.In the presence of substrate, settlement of the larvae, i.e. attachment and pedal disc formation, occurred within 24 h; metamorphosis, i.e. elongation, segregation of stalk and calyx, and development of hypostome and tentacle anlagen, required another 2-3 days.Pedal-disc formation and metamorphosisinhibited in sea water containing antibioticswas shown to be initiated by substance(s) from manne bacteria of a standardized Vibrio sp.The inducing factor(s) is (are) released into the culture medium by bacteria growing in suspension cultures; centrifuged, non-growing bacteria cells, however, proved to b e ineffective.Inductive capacity was detected in ultrafiltrates of suspension cultures, which included substances of low molecular weights of between 1,000 and 10,000 daltons.Following transverse bisection of the planula larvae, most of the apical fragments developed in sea water containing antibiotics -in the absence of metamorphosis-inducing factorsinto polyp heads exhibiting neither stalk nor foot.Only a few fragments regenerated larvae of reduced size.In contrast, basal fragments quantitatively regenerated dwarf planulae capable of developing into complete polyps in the presence of substrate.These findings suggest that the basal pole of the larva directs both regeneration and head and stalk formation, the latter being under inhibitory control.When comparing the present results with those from observations of vegetative buds, striking similarities become apparent of developmental patterns and control mechanisms in scyphistoma morphogenesis, both in the generative and vegetative cycle.