Evidence of a joint control of chiasma formation in spermatocytes and oocytes of a grasshopper

Abstract

Frequency of chiasmata was studied in male and female full-sibs belonging to nine genetically different families from the grasshopper Eyprepocnemis plorans. Mean cell chiasma frequency was always higher in spermatocytes than in oocytes. Furthermore, a positive correlation between both parameters in the families studied was observed. It is concluded that chiasma formation in both sexes is under a single genetic controlling system, chiasma sex differences being a reflection of a differential response of such control to the differing conditions of spermatocytes and oocytes. INTRODUCTIONDifferences in chiasma frequency between sexes seem to be a widespread phenomenon in animals since they have been observed in species from different taxonomic groups such as planarians (Pastor and Callan, 1952;Jones and Croft, 1989), grasshoppers (Cano and Santos, 1990 and referen-ces therein), urodele amphibians (Callan and Perry, 1977), marsupials (Bennett eta!., 1986; Hayman et a!., 1988) and eutherian mammals (Dunn and Bennett, 1967; Andersson and Sandberg, 1984).Information about this point is more scarce in plants. However sex differences in chiasma frequency have also been established in several plants, including Lilium and Friti!laria (Fogwill, 1958); Tulbaghia (Vosa, 1972); maize (Rhoades, 1978); some species of Allium (Gohil and Kaul, 1980); and Pinus radiata (Moran et a!., 1983).A more fundamental question which emerges from these findings, is whether such differences are indicative of separate meiotic controls in the two sexes or, on the contrary, they represent the response of a joint control to differing conditions in each sex (see Davies and Jones, 1974). In this paper we study this topic by comparing male and female chiasma frequency in full sibs belonging to nine genetically different families from the grasshopper Eyprepocnemis plorans. MATERIAL AND METHODSGravid Eyprepocnemisplorans females were collected in different natural populations and maintained in the laboratory in order to obtain pods. After 30 days at room temperature, pods were kept for at least 45 more days at 4°C and then incubated at 33°C until eclosion of the eggs. The individuals obtained from each female pod (a "family") were considered to be full-sibs since they correspond to the insemination of a single male (Lopez, 1987). Each family was maintained separately in 50 1 cages. Fifteen days after the appearance of adult males, testes were fixed in acetic-alcohol 1:3. Squash preparations of the fixed material were stained with acetic-orcein.Squash preparations of oocyte first metaphases were made using the method of Perry and Jones (1974) as modified by Henriques-Gil eta!., (1986

Histone H3 lysine 9 acetylation pattern suggests that X and B chromosomes are silenced during entire male meiosis in a grasshopper

“…In grasshoppers, the analysis of female meiosis is technically difficult, especially for prophase I oocytes. In those at metaphase I, however, Santos and Cano (1990) observed in E. plorans that autosomal and sex bivalents are indistinguishable in this respect. So, testing this hypothesis in grasshoppers is currently not affordable.…”

Occurrence of differential meiotic associations and additional chromosomes in the embryo-sac mother cells of Allium roylei Stearn

“…The two meiocytes, despite having same genetic constitution, differ in their micro-environment like space, temperature and alignment. Pastor and Callan (1952) and Santos and Cano (1990) also held similar view for explaining chiasma frquency differences in the two sex cells of genetically distinct lines of Dendrocoleum lacteum and Eyprepocnemis plorans, respectively. Sex-dependent developmental processes during premeiotic interphase are known to effect meiotic behaviour of chromosomes in A. tuberosum (Gohil and Kaul 1981).…”