TISSUE AND DEVELOPMENTAL SPECIFICITY OF A POLYSIALO-GANGLIOSIDE SPECIES IN THE AMPHIBIAN XENOPUS

Xenopus embryos contain a considerable amount of a polysialo-ganglioside not yet fully characterized; in this paper, we will refer to it as ganglioside X1. Preliminary experiments indicate asialo-GM1 as the core structure of the ganglioside X1 and palmitic and oleic acid as the fatty acids of the ceramide moiety. Further analyses by comparative 2D-TLC with adult fish and chick embryo brains indicate the pentasialilated ganglioside GP1c as the possible structure of X1. In the adult Xenopus, X1 characterizes the ganglioside pattern of the central nervous system while is absent in all the other tested tissues. At least two other more polar (presumably richer in sialic acid) bands are often visible under X1, both in embryos and in brain and spinal cord tissues of adult Xenopus. The persistence of polysialo-gangliosides in the brain and spinal cord of adult amphibians could serve to guarantee a proper functioning of the central nervous system at low body temperature.     

Rheotaxis In Uronychia Setigera (Ciliata, Hypotrichida)

ABSTRACT. The behavior of populations of Uronychia setigera (Ciliata, Hypotrichida) exposed to water currents flowing at increasing velocities (300, 400, 500, 900, 1,700 μm/s) was analyzed using two techniques: 1) the ethogram and 2) the numerical indices recently proposed to measure the development in space and time of tracks of ciliates. Beyond a certain threshold value of the water velocity (˜ 300 μm/s), this species shows a definite positive rheotaxis, only if it moves in a more or less direct contact with the substrate. No rheotactic swimming ever occurs. Rheotaxis is a gradual, adaptive behavior: the higher the velocity of the current, the stronger the degree of the rheotactic response, as demonstrated by the increasing significance of the polar distribution of the tracks. Beyond 500 μm/s the water flow is so strong that it affects the locomotion of U. setigera continuously and strongly inducing this species to perform a new behavioral pattern, the Fast Backward Bidimensional Swimming. Under stressing water currents it reacts at first by creeping along straighter trajectories and then with faster locomotion, in such a way that its reaction is to a certain extent proportional to the drag of the currents. the rheotaxis of U. setigera is discussed as an adaptive response.     

The Interface Between Air and Water: A Perturbation Source Eliciting Adaptive Behaviour in Ciliates

ABSTRACT Interference with the water-air interface, both direct (by contact with a flat, rigid surface) and indirect (by inducing a meniscus) caused the ciliated protozoa we investigated to actively collect in the water column or on the substrate directly under the area of altered surface tension. A crowding effect is observed in this "rest area" reaching plateau values within one hour after onset of the experiment. The simple experimental procedures described here induced analogous behaviour in both Paramecium caudatum (a swimmer) and Oxytricha bifaria (a crawler). The ciliates seem in this reaction to be seeking a refuge from vibrations transmitted by the free interface. Our discovery is discussed in its implications for the adaptive biology and ecology of these micro-organisms.     

Mating-Type Dependent Cell Pairing in Oxytricha hymenostoma. III. Chromatin Mixing After Macronuclear Fusion*

SYNOPSIS. Mating-type dependent cell pairing in Oxytricha hymenostoma was studied by both light autoradiography and transmission electron microscopy. The process results in the macronuclear bodies of the 2 partners fusing completely with each other 2 by 2. In each fusion the 2 chromatin masses, easily distinguishable from each other for the first 6 h of the pairing, progressively intermingled and underwent a sort of rearrangement so that they eventually acquired a uniform pattern. The possible mechanisms regulating macronuclear fusion and DNA amount in the daughter cells are discussed.     

Mating-Type Dependent Cell Pairing in Oxytricha hymenostoma: Macronuclear Fusion and Lack of Meiosis

SYNOPSIS In a hologamy-like process observed in Oxytricha hymenostoma , 2 cells belonging to complementary mating types fused and appeared to contribute equally to the macronuclei of the organism resulting from the fusion. The process was characterized by the absence of micronuclear division and by fusion of the macronuclei of the 2 partners. True conjugation involving micronuclear meiosis was not observed in O. hymenostoma. The biologic significance and the possible adaptive role of the hologamy-like process are discussed.     

Substrates Determine Spatial Distribution of Oxytricha bifaria (Ciliata Hypotrichida)

The extent to which a particular substrate (scratched glass) affects the distribution of a population ( Oxytricha bifaria ) that settled on it was measured, yielding the following results: (1) the species distinguishes among substrates slightly differing in the quality of their superficial scratches (average dimensions of 2, 2.8, 3.5, 6.5, 17 and 25 μm, respectively); (2) it "chooses" the preferred substrate by adopting specific differential behaviors; and (3) population cell density conditions its overall distribution.