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The selective action of different thermal ranges on two geographically isolated Asellus aquaticus (L.) populations (Holland and Southern Italy) is evaluated. Tolerance for high temperature (30°C) in individuals of the same population is inversely related to body-size. In addition, in both populations males exhibit a higher mortality than females, which have a consistently smaller size. In the southern population many individuals complete their biological cycle, whereas in the norther populations...
The maximum salinity tolerance of two freshwater Isopods, Asellus aquaticus (L.) and A. coxalis Dollf., to sodium chloride, phosphate and nitrate, has been tested in the laboratory. By means of short and medium term tests, it has been observed that these salts (above all phosphate) have a strong effect on the mortality of the two species. This demonstrates a low probability of survival of Asellus in environments which undergo natural, as well as cultural, eutrophication processes.
The different tolerance for high temperature (30°) among the young of two geographical races (Holland and Southern Italy) of Asellus aquaticus (L.) (Crust. Isop.) is evaluated. The young of the southern population exhibit a lower mortality rate than those of the northern population, which died before the 60th day of the experiment. The southern animals also exhibit an inverse relationship between mortality rate and body-size. In fact the survival rate of the young is greater than that of the adults....
The two species Asellus aquaticus and Asellus coxalis are distinguished by numerous characteristics relative to the biological cycle (longevity, birth and development rates, importance of intraspecific competition) and the trophic niche. We believe these differences to be due to the concomitant effect of: 1) different selective pressure due to a different evolutionary history, 2) modification by man of the biotope previously colonized by the species A. aquaticus alone, 3) occupation of the biotope...
Seasonal variations in brood size have been described in samples of Asellus aquaticus (L.) Crust. Isop.; the samples were caught monthly in a freshwater pool and kept in the laboratory, at constant tem perature and exposed to natural light. It was shown that: (1) the average number of larvae per deposition varies from about 35 (in summer) to about 50 (in winter); (2) when the brood size reaches maximum or minimum values, the mating frequency reaches minimum or maximum values respectively, reestablishing...
The existence of a form of "parental influence" has been established in two species of Asellus: aquaticus and coxalis. The presence of adults of the same species in the breeding jars of the young individuals halves the mortality; for the young coxalis it doubles the rate of development. The hypothesis is advanced that in the two biotopes studied the species coxalis is asserting itself to the detriment of aquaticus, on account of the greater importance that the "parental influence" has in this species....
A certain percentage (34%) of the females in wild populations of the freshwater Isopod Asellus aquaticus (L.) open their marsupia, and about 40% of their embryos are lost in the water. Such an ejection is due to the presence of dead embryos in the marsupium, and this presence is "perceived" by the mother, who gets rid of them operating a true counter-selection. It is possible to interpret the phenomenon as a kind of parental care, in that the female avoids to lose the whole progeny by the removal...
The action of 8-hydroxyquinoline citrate on cleavage mitosis of Asellus aquaticus L. (Crust Isop.) embryos is studied. An exact picture of chromosomal abberration, metaphase arrest, and a decrease of the transition rate between the different mitotic stages are the most evident effects of the substance. Finally the function of mitotic spindle inhibitor of 8-hydroxyquinoline is discussed.
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