Population cytology of the genus Phaulacridium. II. Phaulacridium marginale (Walker); chiasma frequency studies from South Island, New Zealand

Population cytology of the genus Phaulacridium. IV. Phaulacridium marginale (Walker)--the North Island populations

Samples of Phaulacridium marginale were taken from the North Island of New Zealand, together with further samples from three South Island populations. Seven of the North Island populations were found to be polymorphic for a small telocentric B chromosome. In only one case was the B chromosome significantly associated with an increase chiasma frequency. All three South Island populations contained B chromosomes. Seven of the nine N.I. populations were also polymorphic for extra segments on the centric end of the S11 chromosome. In six of them this polymorphism co-existed with that for B'S. A new polymorphism was encountered in two populations. This was for a large block of heterochromatic material located at the centric end of one of the smaller medium-sized chromosomes which thus becomes acro- rather than telocentric. Tt would appear that the New Zealand grasshopper, Ph. marginale, is able to tolerate many different polymorphisms for extra heterochromatin. However, this ability is perhaps restricted to central populations. In this context, the high level of occurence of these polymorphisms in the North Island could be due to the better climatological conditions existing there compared to most of the South Island.

Population cytology of the genus Phaulacridium

Ten 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 super-numerary 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 S9 and S10 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 species Ph 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.