Cytological studies of the two-spotted spider mite Tetranychus urticae Koch (Tetranychidae, trombidiformes). I: Meiosis in eggs

Abstract

Meiosis in eggs of Tetranychus urticae Koch is described. The two maturation divisions result in (a) a haploid female pronucleus consisting of three karyomeres; -(b) a divided first polar body in which the chromosomes change into karyomeres; -(c) a second polar body, entering a new mitosis which is blocked in metaphase. Irradiation of adult females produced chromosome fragments in the meiotic divisions. The fragments behave as intact chromosomes which proves that during meiosis a diffuse kinetochore is present. The meiotic divisions show the cytologically characteristic features of an inverted meiosis. The presence of such a meiosis is corroborated by observations on eggs heterozygous for chromosome mutations. In both maturation divisions the chromosomes are orientated equatorially. It is suggested that the equatorial orientation is brought about by chiasmata having terminalized to both ends of the dyads. It is argued that in organisms with holokinetic chromosomes during meiosis an axial orientation of the bivalents does not necessarily imply a normal meiosis but can also imply an inverted meiosis.

Cytological studies of the two-spotted spider mite Tetranychus urticae Koch (tetranychidae, trombidiformes) II. Meiosis in growing oocytes

“…It may be assumed that sister chromatids are paired when repulsion takes place during diplotene. The latter two assumptions are in agreement with the general theories about spindle fibre attachment of chromosomes (Luykx, 1970;Bajer and Molr-Bajer, 1972) and do not conflict with the situation during first anaphase (Feiertag-Koppen, 1976). Nordenskirld (1962) and John & Lewis (1965) suppose that in holokinetic chromosomes, in case of two or more chiasmata, terminalization takes place by moving of the chiasmata away from each other, irrespective of their position relative to the ends.…”

“…The second metaphase is characterized by secondary pairing of the homologous chromatids in the equatorial plane (Fig. It may be asked whether this material is identical to the small Feulgen-negative grains found in the equatorial plane during meiotic telophases (Feiertag-Koppen, 1976). The coccid system is considered as the general case of an inverted meiosis in organisms with holokinetic chromosomes, the chiasmata of which have completely disappeared at first metaphase (Hughes-Schrader, 1948).…”

“…Adult females of Tetranychus urticae Koch were collected from a wild type strain (strain Sambucus) which was cultured as described before (Feiertag-Koppen, 1976).…”

“…The interpretation of the inverted meiosis referring to the distinction between a preand post-reductional meiosis is appficable only to the non-crossover parts of the chromosomes (Battaglia & Boyes, 1955). Cytological investigations on eggs of Tetranychus urticae Koch have demonstrated the occurrence of an inverted meiosis as well as the presence of terminal connections between the disjoining chromatids in first anaphase (Feiertag-Koppen, 1976). Cytological investigations on eggs of Tetranychus urticae Koch have demonstrated the occurrence of an inverted meiosis as well as the presence of terminal connections between the disjoining chromatids in first anaphase (Feiertag-Koppen, 1976).…”

Specialization in the behaviour of chromosomes on the meiotic spindle

“…Even more complex movements at diakinesis and pro-metaphase I, as a preparation for metaphase orientation, are proposed by Feiertag-Koppen (1976, 1981 for Tetranychus urticae, which has very small chromosomes. (b) The second type with usually rather small chromosomes ( Fig.…”