Cytological basis of the B chromosome accumulation mechanism in the grasshopper Heteracris littoralis (Ramb)

Abstract

An accumulation mechanism of the standard B chromosome of the grasshopper Heteracris littoralis has been studied in a natural population located in El Saler (Valencia) by two different methods: (i) the karyologica]l analysis of the offspring from wild females and (ii) cytological observations of male and female meiosis. The transmission rate of the accessory through females obtained from crosses (0.61) was slightly lower than that obtained from direct meiotic observations of secondary oocytes (0.71). The B chromosome is transmitted at a rate of about 05 through lB males, the value expected from mendelian segregation. The implications of these findings are discussed and the parasitic nature of the B is proposed.

Prevalence of B chromosomes in Orthoptera is associated with shape and number of A chromosomes

“…Female meiotic drive has been demonstrated in the grasshoppers Melanoplus femur-rubrum (Lucov and Nur 1973;Nur 1977), Myrmeleotettix maculatus (Hewitt 1973(Hewitt , 1976, Heteracris litoralis (Cano and Santos 1989), Omocestus burri (Santos et al 1993), and Eyprepocnemis plorans (Zurita et al 1998;Bakkali et al 2002). Three of these species show all A chromosomes acrocentric, but M. maculatus and O. burri have, like many Old World gomphocerines, three biarmed pairs arisen by the fixation of three centric fusions (see Table 4 Relationship between shape of Bs and shape of As Hewitt 1979), one of which probably involved the autosome carrying the histone genes, i.e.…”

Sex-dependent meiotic behaviour of B chromosomes in the grasshopper Eyprepocnemis plorans

“…Hewitt (1976) concluded that meiotic drive in Myrmeleotettix females was a consequence of spindle asymmetry with the B chromosome orientating towards the egg pole more often. Likewise, Cano and Santos (1988) observed in H. littoralis that in anaphase I cells one of the poles was more condensed than the other suggesting an asymmetric spindle in this species also.…”

“…Whatever mechanisms are involved, they do not affect the normal chromosomes which segregate identically in both sexes (except the X chromosome). In M. maculatus and FL littoralis the behaviour of B chromosomes in male and female meiosis is similar but, in the latter, Bs tend to migrate towards the egg pole due to an asymmetry of the spindle which makes more probable the localization of the B in the egg side than in the polar body side (Hewitt, 1976;Cano and Santos, 1988). The first meiotic division spindle of Eyprepocnemis may also be asymmetric since at late anaphase I and telophase I one pole is more condensed than the other (see figs 4 and 5), however the fact that Bs orientate in the equatorial plate indicates that there is no parallel with the cases of Myrmelotettix or Heteracris.…”

“…This is particularly so in the female where only one of the products of meiosis will form a functional gamete. For instance, in the grasshoppers Myrme!eotettix maculatus (Hewitt, 1973), Melanoplus femur-rubrum (Lucov and Nur, 1973) and Heteracris littoralis (Cano and Santos, 1988) Bs undergo a process of meiotic drive that increases the probability of inclusion in the egg. In these cases, the behaviour of Bs is probably not qualitatively different in males and females.…”

B chromosomes and Robertsonian fusions of <i>Dichroplus pratensis</i> (Acrididae): intraspecific support for the centromeric drive theory

“…For example, grasshoppers have typically asymmetric oocyte spindles and B chromosomes are known to drive during female meiosis in some species (Hewitt, 1979;Cano and Santos, 1989;Santos et al, 1993). Thus, D. pratensis, being polymorphic for Bs and Rb fusions is an exceptional model to test the centromeric drive theory as applied to B chromosomes.…”