There are 10 known populations of Acacia anomala occurring in two small disjunct groups some 30 km apart. The Chittering populations reproduce sexually whereas the Kalamunda populations appear to reproduce almost exclusively by vegetative multiplication. The level and distribution of genetic variation were studied at 15 allozyme loci. Two loci were monomorphic in all populations. In the Chittering populations the mean number of alleles per locus was 2.0 and the expected panmictic heterozygosity (genetic diversity) 0.209. In the Kalamunda populations the mean number of alleles per locus was 1.15 and the expected panmictic heterozygosity 0.079, although the observed heterozygosity of 0.150 was only marginally less than the Chittering populations (0.177). These data support the contention that the Chittering populations are primarily outcrossing whereas the Kalamunda populations are clonal, with each population consisting of individuals with identical and, in three of the four populations, heterozygous, multilocus genotypes. The level of genetic diversity within the Chittering populations is high for plants in general even though most populations are relatively smsll and isolated. It is proposed that either the length of time these populations have been reduced in size and isolated is insufficient for genetic diversity to be reduced or the genetic system of this species is adapted to small population conditions. Strategies for the adequate conservation of the genetic resources of Acacia anomala are discussed.

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Hybridization between two chromosomally distinct subspecies of the grasshopper Caledia captiva results in a high incidence of novel chromosomal rearrangements among the backcross progeny. Rearrangements are restricted to those chromosomes derived from the F1 hybrid parent. Chromosomal involvement is nonrandom with the same rearrangement occurring repeatedly in different backcrosses. A single individual can also generate an array of different rearrangements among its offspring. Several of the rearrangements have also been found in natural populations. The nonrandom and recurrent nature of these chromosomal mutations at high frequencies provides a plausible explanation for the establishment and fixation of chromosomal rearrangements in natural populations.

A temporal analysis of the chromosomal structure of the hybrid zone in the grasshopper Caledia captive has revealed that, over a period of six generations, the position of the zone has remained unchanged when assessed in terms of chromosomal frequencies. In complete contrast however, chromosomal genotypic frequencies have changed dramatically and asymmetrically over the same period. The frequencies of chromosomal heterozygotes have been significantly reduced on one side of the zone accompanied by increases in the frequencies of homozygous metacentric chromosomes. These asymmetrical genotypic changes are also reflected in a complete reversal of the patterns of gametic disequilibria (Tr2) across the zone. It is proposed that undirectional selection has favoured a metacentric karyotype on one side of the zone during a major climatic change.The structure of the hybrid zone involves two major and independent features. First, as a secondary consequence of hybridisation, recombinational change in F1 hybrids disrupts the internal organisation within chromosomes. This results in the production of inviable F2 and backcross progeny and hence, explains the structure of the zone in terms of the sharp change in chromosomal frequencies. Secondly, the asymmetrical nature of the gametic disequilibria between chromosomes represents the direction of selection which favours an acrocentric Torresian karyotype in dry years and a metacentric Moreton karyotype during mesic years. Variation in both chromosome structure and embryonic weight is associated with the predictability of the environment. The acrocentric Torresian karyotype and its associated larger embryos are correlated with a univoltine life history in drier, unpredictable habitats. A similar pattern exists within the Moreton subspecies in the form of a chromosomal dine in S.E. Australia. At the southern limit of this dine the karyotype is totally acrocentric, the life history is univoltine and the embryos are the same weight as the Torresian.It is speculated that variation in chromosomal structure, in terms of the relationship between centromeres and telomeres, may provide a mechanism for altering cellular phenotype through changes in such factors as replication patterns or chromatin packaging which may act quite independently of the informational content of the chromosome.

Mating system parameters of the rare and endangered species Banksia brownii were estimated for two populations using both the mixed mating and effective selfing models. Estimates of outcrossing rate were similar in both populations for both models (mixed mating t Pop. 1=0.68, Pop. 2=0.75; effective selfing t Pop. 1=0.65, Pop. 2=0.73) and were among the lowest reported for undisturbed Banksia populations. Banksia brownii is killed by fire and the high level of selfing found may be associated with this trait. Multilocus and minimum variance mean i estimates were similar and the covariance of selfing with gene fixation (D) was not significantly different from zero indicating that populations were not structured and that most of the inbreeding was the result of self-fertilisation. The absence of structure was attributed to gene dispersal through pollen disperse by birds, and selection against inbred seed. It is suggested that several entire, large populations of this species together with habitat sufficient to support pollinators be reserved to conserve this species.