Michael Hodda

The role of global trade and transport network topology in the human-mediated dispersal of alien species

More people and goods are moving further and more frequently via many different trade and transport networks under current trends of globalisation. These networks can play a major role in the unintended introduction of exotic species to new locations. With the continuing rise in global trade, more research attention is being focused on the role of networks in the spread of invasive species. This represents an emerging field of research in invasion science and the substantial knowledge being generated within other disciplines can provide ecologists with new tools with which to study invasions. For the first time, we synthesise studies from several perspectives, approaches and disciplines to derive the fundamental characteristics of network topology determining the likelihood of spread of organisms via trade and transport networks. These characteristics can be used to identify critical points of vulnerability within these networks and enable the development of more effective strategies to prevent invasions.

Impacts of inundation and drought on eukaryote biodiversity in semi-arid floodplain soils

Floodplain ecosystems are characterized by alternating wet and dry phases and periodic inundation defines their ecological character. Climate change, river regulation and the construction of levees have substantially altered natural flooding and drying regimes worldwide with uncertain effects on key biotic groups. In southern Australia, we hypothesized that soil eukaryotic communities in climate change affected areas of a semi‐arid floodplain would transition towards comprising mainly dry‐soil specialist species with increasing drought severity. Here, we used 18S rRNA amplicon pyrosequencing to measure the eukaryote community composition in soils that had been depleted of water to varying degrees to confirm that reproducible transitional changes occur in eukaryotic biodiversity on this floodplain. Interflood community structures (3 years post‐flood) were dominated by persistent rather than either aquatic or dry‐specialist organisms. Only 2% of taxa were unique to dry locations by 8 years post‐flood, and 10% were restricted to wet locations (inundated a year to 2 weeks post‐flood). Almost half (48%) of the total soil biota were detected in both these environments. The discovery of a large suite of organisms able to survive nearly a decade of drought, and up to a year submerged supports the concept of inherent resilience of Australian semi‐arid floodplain soil communities under increasing pressure from climatic induced changes in water availability.

Neodolichodorus australis n.sp. (Nematoda: Dolichodoridae) on carrot in Australia

Neodolichodorus australis n.sp. is described from Australia. It was associated with damage to a carrot crop at Narrandera, NSW. This is the first time the genus has been recorded on carrot or damaging an economic crop. At least three other species are known from Australia, mostly from native vegetation, and another from sand dune vegetation in New Zealand. Neodolichodorus australis n.sp. is characterised by seven transverse striae on the head, stylet 120–128 μm long, external transverse striae crossing the inner lateral field completely, posterior vulva (V=55–59%), one refractive element near the vagina, phasmid anterior to anus and short tail in adult females, (c>60, c′<1 ), spicules 43–48 μ long, protrusible gubernaculum 18–20 μm long with accessory piece, and spines around the posterior edge of the medial bursal lobe. An identification key to all species currently in the genus is included.

A review of current knowledge on particular taxonomic features of the Australasian nematode fauna, with special emphasis on plant feeders.

Geographic isolation and relatively recent arrivals of agricultural materials from the rest of the world have given Australia, New Zealand and Papua New Guinea a plant-associated nematode fauna substantially different from other countries. Although many of the major cosmopolitan species of plant-pathogenic nematodes are now present, several remain absent, particularly those with more restricted host, geographic or ecological ranges. There is a substantial indigenous plant-feeding native fauna associated with the native vegetation, but this is concentrated in a few families and genera, and few native species have become pathogenic to recently introduced commercial crops. Grasslands of both native and introduced species, as well as coastal habitats (dunes, beaches and mangroves) have been widely studied. Many plant-feeding and free-living nematodes from these habitats are from cosmopolitan taxa, but there are also endemic species and genera. Notable are the many species from otherwise terrestrial taxa in the coastal habitats. Geographic isolation has played a substantial role in evolution and radiation of many of the new taxa, as well as perhaps in the lack of many plant-parasitic nematode taxa.

Survey of fungi and nematodes associated with root and stolon diseases of white clover in the subtropical dairy region of Australia

A survey of 12 white clover-based dairy pastures on the north coast of New South Wales and south-eastern Queensland, Australia, detected 65 species of fungi and 6 nematode species. The fungi included species of Fusarium, Gliocladium, Codinaea, Alternaria, Colletotrichum, Drechslera, Rhizoctonia, Phoma, Pythium, Phytophthora, Penicillium, Rhizopus and Trichoderma from roots and stolons of white clover. Fungal rots of roots and stolons were most severe during the summer months (November and January samples), while root-knot symptoms caused by plant parasitic nematodes were more severe in June. Sedentary endoparasitic nematodes Meloidogyne trifoliophila, Heterodera trifolii and the ectoparasitic nematode Helicotylenchus dihystera were the numerically dominant nematodes in the region. Other nematode species, including Pratylenchus, Xiphinema and Tylenchorhynchus, were present at lower frequencies and principal component analysis indicated that these were less important as white clover pathogens. Meloidogyne trifoliophila was detected for the first time in Australia and was present at all sites. Many of the fungi and nematodes found are common pathogens of white clover. These pathogens are likely to be contributing to the poor seedling performance, growth and persistence of white clover typical in dairy pastures of the subtropical east coast of Australia.

Effect of the clover root-knot nematode (Meloidogyne trifoliophila) on growth of white clover

Root-infecting nematodes are common on white clover ( Trifolium repens ) in dairy pastures on the north coast of New South Wales and southeastern Queensland, Australia, where they are thought to contribute to poor growth and persistence. The nematode responsible for causing root-knot symptoms on white clover was identified as Meloidogyne trifoliophila , a species not previously recorded from Australia. M. trifoliophila failed to reproduce on any of the standard North Carolina hosts used to identify M. javanica , M. hapla , M. arenaria and M. incognita , but caused severe galling and exhibited a high rate of reproduction on white clover. PCR primers for these Meloidogyne species also failed to amplify DNA of M. trifoliophila . Identity was confirmed by morphological measurements and plant symptoms. In a glasshouse test, increasing initial nematode density within the range 0 to 10 000 per 500 ml pot led to reduced shoot and root growth, fewer nodules and more severe root-knot symptoms. A second pot test screened weed species as potential alternative hosts of M. trifoliophila . None of the eight grass species was galled but M. trifoliophila reproduced on two of the eight dicotyledon weeds, spear thistle ( Cirsium vulgare ) and pigweed ( Portulaca oleraceae ).

Prioritising plant-parasitic nematode species biosecurity risks using self organising maps

Abstract The biosecurity risks from many plant-parasitic nematode (PPN) species are poorly known and remain a major challenge for identifying potentially invasive species. A self organising map (SOM) was used to prioritise biosecurity risks from PPN to the whole of continental Australia as well as each of the states and the Northern Territory separately. The SOM used the recorded worldwide distributions of 250 systematically selected species from 43 genera, and identified 18 different countries spanning Asia, Africa, North and Central America, Europe and the Pacific with very similar PPN assemblages to Australia as a whole. Many of the species in these countries are not recorded in Australia, and therefore pose a biosecurity risk. Analysed separately, the states and territories were identified as forming five separate clusters, each with a different region of the world, and with different characteristic PPN. Many of the PPN found in the regions clustered with an Australian state have not been recorded from anywhere in Australia, and others have very restricted distributions within Australia, thus posing different biosecurity risks. The SOM analysis ranked the risks of the different PPN based on likelihoods of establishment. The rankings confirmed the risks from frequently quarantined PPN, but more importantly identified species, which upon further investigation could be new threats. This method can be used to identify previously overlooked species for more detailed risk assessments.

Keeping ‘one step ahead’ of invasive species: using an integrated framework to screen and target species for detailed biosecurity risk assessment

Predicting which species will become invasive in each country or region before they arrive is necessary to devise and implement measures for minimising the costs of biological invasions. Metaphorically, this is keeping one step ahead of invasive species. A structured and systematic approach for screening large numbers of species and identifying those likely to become invasive is proposed in this paper. The Pest Screening and Targeting (PeST) framework integrates heterogeneous information and data on species biogeography, biotic and abiotic factors to first determine a preliminary risk index, then uses this index to identify species for a second, more detailed, risk evaluation process to provide a final ranking. Using the PeST framework, 97 species of plant-parasitic nematodes were evaluated for their biosecurity risks to Australia. The species identified as greatest risks included both previously unrecognised and currently-recognised species. The former included Heterodera zeae, Meloidogyne graminicola, M. enterolobii, M. chitwoodi and Scutellonema bradys, while the latter included Bursaphelenchus xylophilus, Ditylenchus destructor, Globodera pallida, Heterodera glycines and H. filipjevi. Of the ten criteria used in the PeST framework, emerging pest status, pathogenicity, host range and species biogeography most strongly influenced overall risk. The PeST framework also identified species where research to fill in critical knowledge gaps will be most beneficial (e.g. Globodera tabacum, Heterodera cajani, H. filipjevi, Meloidogyne ethiopica, Pratylenchus fallax and P. sudanensis). Where data were available, the information and associated metadata gathered for the PeST framework can be used to guide biosecurity decision making; determine species which require pre border certification and target sampling at the borders.

First record of Meloidogyne trifoliophila in Australia.

Meloidogyne trifoliophila (Bernard and Eisenback) has been recorded for the first time in Australia on white clover (Trifolium repens L.) roots on the north coast of New South Wales and southern Queensland. Identification was based on morphological observations and a host differential test.

Orientation, reproduction and effect of spiral nematode (Helicotylenchus dihystera) on growth of white clover (cv. Haifa)

Helicotylenchus dihystera oriented towards white clover roots in an artificial growth medium and feeding was indicated by head penetration of the roots. In a glasshouse pot experiment, H. dihystera reproduced successfully on white clover with reproduction (Pf:Pi) falling from 7.4 to 3.2 as initial density rose from 10 to 500 nematodes per pot. There was no significant effect on plant growth, even at the highest initial density which was equivalent to the average density previously found in the field.