Variation of shape and of discrete anatomical characters in the morabine grasshoppers

Abstract

Within the Morabinae (0rthoptera : Eumastacidae) there is some variation of discrete characters including the midgut diverticula, the ovariole count, and the number of eye stripes. The midgut diverticula, numbering 12, 15, 18, 20-24, and 36 are of systematic interest, and the eye stripes reflect the number of moults undergone. The ovariole count is almost constant within some species, but in others geographical clines are apparent. One of these has been followed in detail and the ovariole counts shown to be under genetic control with the high numbers of ovarioles dominant in reciprocal crosses between individuals having high ovariole counts and those having low counts. Twelve morphometric measurements were made on over 1450 adult morabine grasshoppers and on over 100 nymphs. The lengths of the subgenital plates of the adult males and the ovariole numbers of the adult females were analysed separately and the remaining 10 measurements were subjected to a canonical analysis to discover how many contrasts of form exist within the Morabinae and what the biological nature of these contrasts may be. Six biologically meaningful contrasts of form were found among the adults, including one which distinguishes between the broad groups of morabines with 12, 18, and 36 midgut diverticula. The patterns of growth of the nymphs were also studied morphometrically. Those females which will become adult in six instars begin to diverge from the males in the fourth instar whereas those which will become adult in seven instars do not diverge until the fifth.