The cytology and Feulgen-DNA microdensitometry of some New Zealand stick insect species (Phasmatodea:Phasmatidae)

Abstract

Since there is no cytogenetic record of the New Zealand Phasmatidae, the initial aim of this study was to describe the chromosome complements of the species examined. From a study of colchicine treated mitotic metaphases, a diploid chromosome number of 36 is established for both Micrarchus hystriculeus (?) and Clitarchus hookeri (?) and 38 for both Tectarchus diversus (?) and Argosarchus horridus (?). In these species the females have two X-chromosomes and the males one, the X being a large metacentric chromosome. "Pre-metaphase stretch" during prophase of male meiosis was observed in Clitarchus hookeri, Argosarchus horridus and Tectarchus diversus. Colchicine treated mitotic metaphases suggest the parthenogenetic Acanthoxyla intermedia (?) has a diploid chromosome number of either 38 or 39. The implications of this are discussed. The DNA content and area of haemocyte nuclei from some New Zealand stick insect species was determined by Feulgen microdensitometry. There is a significant positive linear correlation between nuclear area and DNA content in two of the seven haemocyte samples. Analysis of variance of haemocyte DNA measurements suggests there is no significant difference between Clitarchus hookeri ? and Tectarchus diversus ? but there is a significant difference between: (1) Acanthoxyla intermedia ? and Tectarchus diversus ? (2) Acanthoxyla intermedia ? and Clitarchus hookeri ?. The DNA content and area of sperm, interphase and metaphase testis nuclei was also determined by Feulgen microdensitometry. There is a significant positive linear correlation between nuclear area and DNA content in all sperm, interphase and metaphase samples. Analysis of variance suggests the variation between samples is greater than the variation between species and therefore it is not possible to conclude whether or not there are significant nuclear DNA differences between species. The possible reasons for the large variation between and within samples are discussed and modifications in experimental technique which could reduce this, and allow the detection of DNA differences between closely related species, are suggested. A review of the literature revealed that different authors use different experimental techniques and therefore a standard experimental procedure is put forward. Topics for future research are also suggested.