The redlegged earth mite (Halotydeus destructor) and the blue oat mite (Penthaleus major) are major pests of pastures and crops in southern Australia. Reproductive modes, migration rates and levels of differentiation between populations were investigated using allozyme eleetrophoresis. Collections were made throughout Victoria and a sample was also obtained from Western Australia.Three enzyme loci were polymorphic in H. destructor (Mdh-1, Mdh-2 and Idh). Genotype frequencies of these loci did not differ between phenotypie males and females, providing no evidence for haplodiploidy. Allele frequencies were in Hardy-Weinberg equilibrium, indicating that H. destructor is diploid and sexual. This was confirmed via crosses between males and females. Allele frequencies differed between Victorian sites, although F statistics indicated little differentiation over all loci. A sample from Western Australia did not differ in allele frequencies from the Victorian sites. Four polymorphic loci were found in P. major (Mdh-1, Mdh-2, Idh and Gpi). Only a few mnltilocus genotypes occurred in a sample, indicating that P. major is parthenogenic. No male P. major were found in this study. A number of colour morphs were also identified and a genetic association between genital plate colour and clonal type was found in one population of P. major. Two different body colour morphs were associated with different clonal types.
Seed production characteristics of Eucalyptus regnans following self (S), outcross (O), (S+O ) and open
pollination were investigated as a contribution to understanding of breeding system control in this
species.
All five trees tested produced seed after self-pollination, although yield was reduced relative to
outcrossing. Isozyme analysis was used to determine paternity of individual seeds produced by polli-
nation with a 1 : 1 mixture of S and 0 pollens. Preferential outcrossing was demonstrated, with an
average of 81% of seeds being outcrosses. S and 0 seeds were also found within the same open-
pollinated capsules, confirming the experimental observation that receipt of outcross pollen does not per
se preclude self-fertilisation.
The independent probabilities of survival of S and 0 embryos, as determined from seed yield per
100 flowers after separate S and 0 pollination, accounted for much of the preferential outcrossing effect.
However, some trees produced more outcrosses than expected and competitive interaction of embryo
genotypes within a capsule cannot be discounted.
Following open pollination, samples from 15 trees averaged 16.7 ovules and 1.48 full seeds per
capsule, giving a mean seed : ovule ratio of 9.0%. The modal number of seeds per capsule was 1 and
the maximum 9, while 21% of capsules yielded no full seeds.
These observations and experiments suggest post-fertilisation control of the breeding system,
dependent upon both embryo genotype and maternal resource allocation.
Individual trees within a stand of Eucalyptus regnans were found to vary in fecundity and time of flowering. Allele frequencies at three enzyme loci were estimated for the outcross pollen pool taking these differences into account, and were found to vary with time. These frequencies were compared to those estimated using methods that assume allele frequencies in outcross pollen pools are constant throughout a flowering season. For times when the bulk of trees were in flower the allele frequencies estimated by all methods were similar, but early and late in the season they differed dependent on the genotypes of the trees in flower. The demonstrated temporal heterogeneity of allele frequencies did not have a major effect on single locus, maximum likelihood estimates of the level of outcrossing in this population.
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