A cytotaxonomic study of the pusilla group of species in the genus Austroicetes Uv. (Orthoptera: Acrididae).

Abstract

Cytological study of the members of the pusilla group has shown that the "inland race" of A. pusilla (Walk.) differs in several constant chromosomal features from the other races and must be regarded as a distinct species; this has been described as A. interioris, sp. nov. The alleged "intergradation" between the two forms is to be ascribed to overlap in phenotypic characters and not to inter­ breeding, the "intermediates" being always cytologically typical of one or other species. Certain phenotypic characters are fully diagnostic when present, but a small proportion of individuals in eastern Australia and a much larger proportion in South Australia and Western Australia cannot be determined with certainty on the phenotype. A. nullarborensis Key differs cytologically from both the other species.

The taxonomy and distribution of the three species is discussed. A. pusilla and A. interioris cannot be regarded as species in statu nascendi, and their inter­ relations induce scepticism in regard to claims to have ·recognized introgressive hybridization in various groups of animals by classical taxonomic methods. The bearing of the new information on the phylogeny of the group is indicated.