In samples of Macrobiotus hufelandi found near Andalo (Trento) the sex-ratio changes in different places of the same rock (from 1:1 to 1:4). The caryological examination of the spanandric population (sex-ratio = 1:4) shows that many animals have 12 chromosomes in the mitoses and 6 bivalents in the meiotic prophase, as in the appenninic populations, but most of the females have 18 chromosomes in the mitoses and the same number of univalents in the ovarian eggs. Therefore in some sites of the rock...
The chromosome morphology and number in somatic and germinal mitoses were studied in some species of Macrobiotus. Most of these species (M. areolatus, M. coronifer, M. harmsworthi, M. hufelandii and bisexual biotype of M. richtersi) have 2n = 12 chromosomes, but in two acquatic species with similar morphology (M. dispar and M. pullari) 2n = 10 chromosomes are found. The chromosome number in males and females of M. areolatus and M. richtersi is the same. In the ripening oocytes and in the first blastomeres...
A sample of Hypsibius oberhaeuseri without males was found near Trento.The karyologic examination found that this sample is a tetraploid biotype (4n = 24) reproducing with an ameiotic parthenogenesis. Some quantitative inquiries about the tetraploid biotype and the two others (diploid and triploid) indicate that the somatic size increases with the ploidy. The presence of three biotypes in H. oberhaeuseri demonstrates that some species of Tardigrada have a high level of complexity.
In a bisexual population of Macrobiotus richtersi from Pisa the chromosomal set is 2n = 12 and n = 6. It is also shown that in the same species, but in a different geographical territory (Modena), is present a parthenogenetic triploid (3n = 18) biotype. This kind of parthenogenesis is ameiotic. In the organs of the triploid individuals the number of cells is similar to that of the diploid population.
Bisexual and unisexual (without males) biotypes are found in the Tardigrade Hypsibius oberhaeuseri. The caryological analysis shows a chromosome number 2n = 12 and n = 6 in the bisexual biotype, while in the biotype without males there are 18 chromosomes in the mitosis and 18 univalents in the maturative division. Therefore a biotype of H. oberhaeuseri is triploid with an ameiotic parthenogenesis.
The chromosome number in M. hufelandii is 2 n = 12 and n = 6 as in two other species of Macrobiotus (M. richtersi from Pisa and M. harmsworthi). The results differ from previous data which have stated 2 n = 14 in M. hufelandii females. It is supposed that at least two sibling species are included in M. hufelandii.
In the Tardigrades the number of the storage cells, of the cells of the Malpighian tubules and of the 3rd ventral ganglion, varies. In the last case the swinging of the cell number, being not related to the growth, is due to a renewal of cells. Therefore the Tardigrades have not a constant cell number in spite of a trend towards a secondary numerical constancy of some tissues, e.g. of the nervous tissue.
In four species of Macrobiotus (M. areolatus, M. hufelandii, M. intermédius and M. richtersi) with bisexual populations the sex ratio is about 1 : 1. In two of these species (M. hufelandii and M. richtersi) were found some samples without males, probably parthenogenetic. The bisexual populations of Macrobiotus show a sexual dimorphism, females being bigger than male animals.
Four populations with a different sex ratio of the tardigrade Macrobiotus hufelandi are recognized in an alpine valley. This difference is due to the presence of three biotypes (diploid, triploid and tetraploid biotype). Ameiotic thelitokous parthenogenesis is present in the triploid and tetraploid biotypes, while the diploid biotype is bisexual. Two types of eggs, probably related to the biotypes, are identified by morphologic analysis of egg shell.
Having found no males during three years of breeding in Macrobiotus dispar the parthenogenesis has been demonstrated. The karyological examination has shown that M. dispar has a diploid meiotic and chiasmatic parthenogenesis and the restitutive process takes place at the beginning of the 2nd oocyte division.
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