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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Helgoland marine research 32 (1979), S. 466-475 
    ISSN: 1438-3888
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Tisbe clodiensis andT. holothuriae females and males were maintained at different densities, from sexual maturity to the extrusion of the first egg sac, in order to study the effect of crowding on the number of nauplii produced by the first egg sac. They were tested in pure cultures at densities of 1, 2, 4, 6 and 8 couples per 20 ml of sea water, and in mixed cultures (half of the individuals belonging to each of the two species) with 2, 4, 6 and 8 couples per 20 ml, without food limitation. At the highest crowding level, and forT. holothuriae only, the effect of daily renewal of the culture water was examined. The mean number of nauplii per female decreases with increased density. A significant linear regression of number of nauplii on number of couples was found. The regression slopes appear to be the same for both species, regardless of whether they are cultured singly or together. The daily renewal of water diminishes the effect of crowding. The possibility that a complex chemical compound, produced by the animals, which enables the latter to perceive and to react to crowding, is discussed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two new forms of the copepod genus Tisbe, one of which was found in the Lagoon of Venice near Chioggia (Italy), and the other in the port of Malta, have been studied. Although showing a striking resemblance in morphology, all attempts to cross representatives of the 2 populations have failed. They may, therefore, be considered as “sibling species”. Even on closer study, no qualitative structural differences between them were found. However, careful analysis of some biometrical traits revealed significant differences. A certain differentiation of another kind emerges from the comparison of the life-cycle and population dynamics. Under standard laboratory conditions the following main parameters have been considered: (1) survival; (2) mean and minimum generation time, T; (3) net reproduction rate, R 0; (4) intrinsic rate of natural increase, r m. The significance of the findings is discussed.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 30 (1975), S. 151-165 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Distribution and abundance of Tisbe species were studied throughout a period of 3 years at 3 stations in the Lagoon of Venice (Italy). At 2 other stations samples were taken occasionally, as also at the Lido station (open sea). Twelve species may be considered as common inhabitants of the lagoon, and 3 species appear to be occasional transients, compared to the 9 species found at the Lido. A comparison of the physical data shows that the stations were similar in temperature and salinity, but differed primarily in pH values, sediment characteristics, algal substratum and faunal benthic community. The fact that remarkable differences in species composition and distribution of Tisbe could be observed between the various parts of the lagoon and the lagoon and the open sea, indicates that temperature and salinity are not so important for species diversity as are biotic factors. A particularly strong difference existed between samples taken at the bottom and from pilings, which constitute a very special biotope for the benthic communities in the lagoon and seem to be a preferred habitat for T. lagunaris and T. cucumariae. The data suggest that there is a certain interaction between T. holothuriae and the other species. Whenever T. holothuriae was abundant, the other species were rare, but T. clodiensis, T. dobzhanskii (Stations 1 and 2) and Tisbe sp. (Station 3) attained high relative abundance whenever T. holothuriae decreased considerably in number. T. holothuriae represents certainly the hardiest species of the lagoon, displaying a great ability to cope with stress conditions, even those present in the interior lagoon where strong fluctuations in salinity, temperature, pH and oxygen prevail.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Genetica 45 (1975), S. 289-305 
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to determine the biotic selective factors affecting the fitness of genotypes in the polymorphic speciesT. clodiensis, five types of experimental populations were utilized: (1) Populations started with equal numbers of virgin females and males of the three genotypes (pp, pP, PP) at f(p)=f(P)=0.5 in Hardy-Weinberg proportions; (2) Populations started with equal numbers of heterozygous females and males; (3) Populations started with equal numbers of recessive homozygous females and dominant homozygous females, each fertilized by males of the same genotype; (4) Populations with virgin females and males of the three genotypes at f(p)=0.2, f(P)=0.8 in Hardy-Weinberg proportions; (5) One population as in (4) but with f(p)=0.7 and f(P)=0.3. The populations were sampled at about three weekly intervals in order to follow the gene frequencies for about fifteen generations. A comparison between group (3) and other groups suggests that interaction between genotypes may affect the survival of the genotypes concerned. Comparison of groups (1) and (2) seems to indicate that sexual selection is also involved. The estimated selective coefficients, which appear to vary in different periods and groups of populations, lead to the conclusion that fitness inT. clodiensis is a function of the genetic structure of the population as well as of the population density. The selection pressure is then determined by a great number of biotic components operating in different stages of the life cycle; and it seems reasonable to conclude that inT. clodiensis, at least under these experimental conditions, a frequency-dependent selective mechanism is involved.
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  • 5
    Publication Date: 1975-05-01
    Print ISSN: 0016-6707
    Electronic ISSN: 1573-6857
    Topics: Biology
    Published by Springer
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  • 6
    Publication Date: 1969-06-01
    Print ISSN: 0025-3162
    Electronic ISSN: 1432-1793
    Topics: Biology
    Published by Springer
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  • 7
    Publication Date: 1975-01-01
    Print ISSN: 0025-3162
    Electronic ISSN: 1432-1793
    Topics: Biology
    Published by Springer
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