Molecular discrimination of Perna (Mollusca: Bivalvia) species using the polymerase chain reaction and species-specific mitochondrial primers

This work was prompted by the need to be able to identify the invasive mussel species, Perna viridis, in tropical Australian seas using techniques that do not rely solely on morphology. DNA-based molecular methods utilizing a polymerase chain reaction (PCR) approach were developed to distinguish unambiguously between the three species in the genus Perna. Target regions were portions of two mitochondrial genes, cox1 and nad4, and the intergenic spacer between these that occurs in at least two Perna species. Based on interspecific sequence comparisons of the nad4 gene, a conserved primer has been designed that can act as a forward primer in PCRs for any Perna species. Four reverse primers have also been designed, based on nad4 and intergenic spacer sequences, which yield species-specific products of different lengths when paired with the conserved forward primer. A further pair of primers has been designed that will amplify part of the cox1 gene of any Perna species, and possibly other molluscs, as a positive control to demonstrate that the PCR is working.

The distribution of Fasciola hepatica in Queensland, Australia, and the potential impact of introduced snail intermediate hosts

A survey was conducted to establish the distribution of the liver fluke, Fasciola hepatica, in the state of Queensland, Australia, and to evaluate the impact of the introduced snail intermediate hosts, Pseudosuccinia columella and Austropeplea viridis. Serum samples from a total of 5103 homebred cattle in 142 beef herds distributed throughout the state and 523 pooled milk samples from dairy herds from the state's major dairying regions were tested for antibodies to F. hepatica by ELISA. Snails were collected on infected properties around the limits of the F. hepatica distribution. F. hepatica infection was detected in 44 dairy herds and two beef herds. The distribution of infected herds indicates that F. hepatica is established only in southeast Queensland. The distribution there was patchy but the parasite was more widespread than suggested by an earlier survey. The predominant intermediate host species found along the northern limit of the distribution was P. columella. We conclude that the introduction of P. columella and A. viridis has not yet had a major impact on the distribution of F. hepatica in Queensland. However, the presence of P. columella, which is much more adaptable to tropical habitats than the native intermediate host, Austropeplea tomentosa, at the northern limit of the F. hepatica distribution suggests that there is potential for the parasite to expand its range.

Reproductive ecology of invasive Ochna serrulata (Ochnaceae) in south-eastern Queensland

We investigated aspects of the reproductive ecology of Ochna serrulata (Hochst.) Walp., an invasive plant in eastern Australia. O. serrulata drupes were similar in size to fleshy fruits of other local invasive plants, but showed some distinct differences in quality, with a very high pulp lipid content (32.8% of dry weight), and little sugar and water. Seeds were dispersed by figbirds, Sphecotheres viridis Vieillot, a locally abundant frugivore, and comprised between 10 and 50% of all non-Ficus spp. fruit consumed during October and November. The rate of removal of O. serrulata drupes was greater in bushland than suburban habitats, indicating that control in bushland habitats should be a priority, but also that suburban habitats are likely to act as significant seed sources for reinvasion of bushland. Germination occurred under all seed-processing treatments (with and without pulp, and figbird gut passage), suggesting that although frugivores are important for dispersal, they are not essential for germination. Recruitment of buried and surface-sown seed differed between greenhouse and field experiments, with minimal recruitment of surface-sown seed in the field. Seed persistence was low, particularly under field conditions, with 0.75% seed viability after 6 months and 0% at 12 months. This provides an opportunity to target control efforts in south-eastern Queensland in spring before fruit set, when there is predicted to be few viable seeds in the soil.

Comparative seed and dispersal ecology of three exotic subtropical Asparagus species

The genus Asparagus includes at least six invasive species in Australia. Asparagus aethiopicus and A. africanus are invasive in subtropical Australia, and a third species, A. virgatus is naturalized and demonstrates localized spread in south east Queensland. To better understand how the attributes of these species contribute to their invasiveness, we compared fruit and seed traits, germination, seedling emergence, seed survival, and time-to-maturity. We further investigated dispersal ecology of A. africanus, examining the diet of a local frugivore, the figbird (Sphecotheres viridis) and the effect of gut passage on seedling emergence. Overall, A. aethiopicus was superior in germination and emergence, with the highest mean germination (98.8%) and emergence (94.5%) under optimal conditions and higher emergence (mean of 73.3%) across all treatments. In contrast, A. africanus had the lowest germination under optimal conditions (71.7%) and low mean seedling emergence (49.5%), but had fruits with the highest relative yield (ratio of dry pulp to fruit fresh weight) that were favored by a local frugivore. Figbirds consumed large numbers of A. africanus fruits (~30% of all non-Ficus fruits), and seedling germination was not significantly affected by gut passage compared to unprocessed fruits. Asparagus virgatus germinated poorly under cool, light conditions (1.4%) despite a high optimum mean (95.0%) and had low mean performance across emergence treatments (36.3%). The species also had fruits with a low pulp return for frugivores. For all species, seed survival declined rapidly in the first 12 mo and fell to < 3.2% viability at 36 mo. On the basis of the traits considered, A. virgatus is unlikely to have the invasive potential of its congeners. Uniformly short seed survival times suggest that weed managers do not have to contend with a substantial persistent soil-stored seed bank, but frugivore-mediated dispersal beyond existing infestations will present a considerable management challenge.