Population cytology of the genus Phaulacridium

Abstract

SUMMARYTen of the 27 populations of Phaulacridium marginale collected from South Island, New Zealand, during the 1973 meiotic season were polymorphic for extra heterochromatin. This was present either as B chromosomes or as supernumerary segments on the shortest autosomes. In some populations both polymorphisms were present simultaneously, sometimes at high frequencies. Three different types of B chromosome were seen; large telocentric, small telocentric and small metacentric isochromosomes though only one type was seen in any one population. Segments on the telocentric S and chromosomes were located distally. On the S11 chromosome, however, the extra segment was present as a short arm, thus making the chromosome submetacentric. This latter situation is similar to that in the related speciesPh. vittatum. The frequency of B's in the OM population appeared to be stable over years and there was no indication of any meiotic " drive" or " drag" in the males. The frequency of occurrence of B chromosomes in a population correlated negatively with annual rainfall (low B frequencies in regions of high rainfall). Neither type of extra heterochromatin had any significant effect on either mean cell chiasma frequency or on log variance of this metric. Possible synergism between B's and segments is discussed from the preliminary analysis of the OM population. The probable origins and age of the polymorphisms are discussed in detail.

A cytogenetic analysis in Psophus stridulus (L.) (Orthoptera: Acrididae): B-chromosomes and abnormal spermatid nuclei

“…The similarities in terms of the condensation cycle, the size and pycnotic properties of the X chromosome and some Bs of orthopteroid species have led to the suggestion that the Bs are derived from the X chromosome (Rothfels 1950;Henderson, 1961;Jackson & Cheung, 1967;Hewitt & John, 1972;Westerman, 1975). Gallagher et al (1973) provide further evidence for this suggestion in M.…”

“…In some cases heterochromatic associations between Bs and sex chromosomes have been observed during the first meiotic prophase (Nur, 1963;Westerman, 1975;Henriques-Gil et al, 1982). Jackson and Cheung (1967) observed these associations up to metaphase I and together with additional evidence also proposed the Bs to be derived from the X in Phaulacridium vittatum.…”

The taxonomy, distribution and origins of two species of Phaulacridium (Orthoptera: Acrididae) in the South Island of New Zealand

“…Once again they are very similar to those seen in the closely related Australian species P. vittatum and P. nanum. However when the meiotic recombination level in males is determined, highly significant differences between the two species can be shown for both mean cell chiasma frequency and its log variance (Westerman, 1974). A comparison of mean cell chiasma frequencies between populations within species shows no significant differences, in marked contrast to the comparison of the mean values between the two species ( P .…”

“…In addition to the similarity of the basic karyotypes in the two species, populations of both have also been shown to be polymorphic for B-chromosomes and supernumererary heterochromatic segments on the smaller autosomes (see Westerman & Fontana, 1973;Westerman, 1974Westerman, , 1975a. The Bs and segments are also virtually identical in morphology and in their effect on meiotic recombination.…”

“…Over the last 10 years, an intensive study has been made of the occurrence and role of polymorphisms for supernumerary heterochromatin in populations of P. marginale (Westerman & Fontana, 1973;Westerman, 1974Westerman, , 1975aWesterman, , b, 1977. These studies have necessitated frequent and widespread field collections on both North and South Islands and it has become increasingly apparent that in one area of South Island two distinct species of Phaulacridium are present.…”