Karyotypes and Meiosis of the Morabine Grasshoppers Ii. The Genera Culmacris and Stiletta.

Abstract

The genus Culmacris contains no species having the primitive XO:XX sex chromosome mechanism, as found in the tribe Morabini. Two of its species have an XY:XX sex-chromosome mechanism, due to the acquisition of an X-autosome fusion (F18) early in the phylogeny of the genus. It also includes a number of taxa with X1X2Y:X1X1X2X2 sex-chromosome systems. It is proposed that this condition arose from the XY:XX one as a result of a single Y-autosome fusion (F19). The species and races of the X1X2Y section of the genus differ from one another karyotypically in respect of the size and shape of the X2 and Y chromosomes, which are especially variable; in some of them the CD autosome has undergone dissociation into separate C and D acrocentrics (D5, D7 and D8) and in one taxon the AB has also undergone dissociation (D6). This extensive karyotypic diversification contrasts with the relative morphological uniformity of this complex. The genus Stiletta contains two species with the primitive XO:XX mechanism. Both of these have a fusion between two small autosomes (F8), and one of them has an additional fusion between small autosomes (F9), giving rise to 2n = 13, the lowest chromosome number known in the Morabinae.