The cytogenetic structure of Tasmanian populations of Phaulacridium vittatum

Abstract

In 8 out of 20 Tasmanian populations of Phaulacridium vittatum from 0.3-11.0 percent of the males carried a single supernumerary chromosome. In such males the X and B univalents are both heteropycnotic at first prophase of male meiosis and associate with another in a non-homolgous manner in about two-thirds of the diplotene cells examined. In all 56 B-containing individuals studied, however, these associations lapse by first metaphase and the X and the B move at random with respect to one another at first anaphase. The supernumerary in this species is stable and only 5 of the 56 individuals with supernumeraries showed evidence of B-chromosome non-disjunction in the pre-meiotic mitoses. Since there was no other evidence for the loss or gain of supernumeraries in the male line it is clear that B-transmission is regular in the males of this species. There were significant differences between population with respect to mean cell chiasma frequency but there was no significant effect of the B-chromosome on this metric. Additionally a comparison of mean cell chiasma frequency in follicles with and without supernumeraries from a mosaic individual shows no significant difference.

FISH detection of ribosomal cistrons and assortment-distortion for X and B chromosomes in <i>Dichroplus pratensis</i> (Acrididae)

“…Due to their usual heterochromatic nature, B and X chromosomes in the grasshopper Metaleptea brevicornis tend to associate achiasmatically during male first prophase, although random association and non significant differences between meiotic substages were observed (Grieco and Bidau, 1999). Moreover, in other grasshopper species, such as Phaulacridium vittatum and Eyprepocnemis plorans, where significant associations between B and X have been observed, both elements either segregated randomly (John and Freeman, 1975) or preferentially to opposite poles independently of previous degree of association (Ló pez-Leó n et al, 1996). In D. pratensis however, the association between both univalents clearly followed a recurrent pattern by which, in all individuals, the maximum degree of association was attained during zygoteneearly pachytene.…”

B Chromosomes and Sex in Animals

“…The first result pointing in this direction was reported in the grasshopper Phaulacridium vit-tatum , where Jackson and Cheung [1967] claimed that X and B chromosomes show preferential migration to opposite poles during first meiotic division, in a natural population from Tasmania. However, John and Freeman [1975] analysed the same population, and other 7 B-carrying populations from Tasmania, and found that X and B segregated randomly in all 56 B-carrying males from the 8 populations. This clearly excluded this Tasmanian population as a case of preferential X-B segregation, bearing also in mind that all other populations analysed from continental Australia showed random X-B segregation [John and Freeman, 1974;Rowe and Westerman, 1974].…”

Achiasmate segregation of X and B univalents in males of the grasshopperEyprepocnemis plorans is independent of previous association

“…In addition, the same population may show different X-B segregation patterns over time. Thus, the preferential segregation to opposite poles reported by Jackson & Cheung (1967) in P. vittatum was not observed by John & Freeman (1975) in the same population. The same is illustrated by the Jete population of E. plorans, where the X and B univalents segregated randomly in a 1977 sample (Camacho et al 1980) but preferentially to opposite poles in the 1991 and 1992 samples reported here.…”