Morphometric Differentiation in the Viatica Group of Morabine Grasshoppers (Orthoptera, Eumastacidae)

Abstract

Atchley, W. R., and J. Cheney (Depts. of Biology and Statistics, Texas Tech Univ., Lubbock, Texas, 79409, and Dept. of Genetics, Univ. of Melbourne, Parkville, Victoria, Australia). 1974. Morphometric differentiation in the Viatica group of morabine grasshoppers (Orthoptera, Eumastacidae). Syst. Zool. 23:400-415.-Morphometric differentiation in 10 egg guide characters was examined in 13 chromosomal races and species within the Viatica group of morabine grasshoppers. Considerable divergence was found to have occurred among races within each provisional species and among the various provisional species. The extent of multivariate phenetic overlap among races within a species ranges from 28% between the 2n = 19 and 2n = 17 races of viatica to 13% among the three races of P24. The interracial relationships among the taxa as reflected by canonical variate analyses of the 13 taxa and of the 8 taxa (races pooled) generally gave close correspondence to the known genetic and geographic affinities among the taxa. Factor analysis of the pooled data followed by analysis of variance and a posteriori testing of the factor scores provided evidence of intertaxa differentiation in the shape of the egg guide. Again, a close correspondence between phenetic variation, genetic divergence and ecogeographic separation was noted. Finally, the extent of multivariate phenetic overlap was found to decrease as a function of phylogenetic distance with the phylogenetically most primitive races having the greatest overlap with the other taxa and the most derived forms being phenetically the most discrete. [Morphometric differentiation; multivariate statistics; speciation; morabine grasshoppers.] The Viatica group of morabine grasshoppers (Orthoptera, Eumastacidae) is a cluster of morphologically very uniform species and races occurring in southeastern Australia (Fig. 1). Since these insects are wingless, they exhibit very low vagility and tend to form local colonies between which migration occurs only rarely. The members of the Viatica group have been the subject of critical cytogenetic studies by White and co-workers (White, Carson, and Cheney, 1964; White, et al., 1967; White, et al., 1969; White, 1968 and 1970) who have shown these species to be of considerable importance in speciation theory. According to the interpretation of White, et al. (1967) and White (1968) genetic divergence among several of the included taxa has been achieved by a mechanism which they have referred to as stasipatric speciation. Most of the taxa in this species group, which cannot be assigned to any of the four described genera of Morabinae, are at present taxonomically undescribed. Therefore, most of the taxa are designated with P (for provisional species) and an alphanumerical code, these being the symbols used in the Australian National Insect Collection, Canberra. The morphological uniformity among the provisional species of the Viatica group belies the fact that several have become differentiated into two or more races by combinations of translocations, pericentric inversions and other gross chromosomal rearrangements. In all, 13 distinct taxa are known in the Viatica group and are included in this report. In spite of the considerable evidence available on cytogenetic and ecogeographic separation in these forms, critical studies on morphometric divergence have until recently been lacking. Blackith and Blackith (1969) examined morphometric shape variation in the Viatica group species, but their study was not concerned with measuring