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Since 1969 systematic sampling has recorded the appearance in nature of a species, Asellus (Proasellus) coxalis Dollf., and its progressive increase in a biotope (Sarno River, Naples) previously occupied by the single species Asellus (Asellus) aquaticus (L). The two species are at present living in sympatry. It has been noted that both species undergo significant numerical variations in the various months of the year. The maximum peaks for coxalis fall in the two month period April-May and for aquaticus...
1) Two species of Asellus (aquaticus and coxalis) have been found in the natural state in sympatric conditions, though they are normally found in allopatric conditions. 2) An experimental laboratory study has been made of the competition between the two species. 3) The damage is mutual (statistically significant data). 4) The hypothesis is suggested that the two species are not evolving toward a sympatric life, but that coxalis is about to gain the upper hand over aquaticus; it is not unlikely that...
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...
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....
The main effects of monochromatic light on the development of newly born Asellus aquaticus (L.) are: a) the enormously prolonged time needed for the reaching of sexual differentiation; b) a significant reduction in the number of the differentiated individuals (at the 90th day); c) a great increase in mortality; d) an enlargement of the variations between minimum and maximum values of the time needed for sexual differentiation between individuals born during springtime and during autumn. It is supposed...
Esistenza di un polimorfismo enzimatico relativo alla fosfoglucomutasi in Asellus aquaticus (L). È descritto un polimorfismo enzimatico in Asellus aquaticus. Tale polimorfismo concerne la fosfoglucomutasi. I dati ottenuti sono in favore dell'ipotesi che il polimorfismo sia controllato da un singolo locus genico con due alleli codominanti (PGM e PGM).
È stato studiato il comportamento degli ibridi di F e F di due razze geografiche di Asellus aquaticus (L.) provenienti rispettivamente dall'Olanda e dal Sud Italia. Il carattere seguito è la velocità di sviluppo, significativamente diversa nelle due razze parentali; la determinazione è poligenica come è dimostrato dalla segregazione della F. E stata dimostrata l’importanza del tipo di determinazione genetica che limitando la plasticità del carattere fissa i «tempi» di sviluppo delle rispettive razze...
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