Predation on invasive cane toads (Rhinella marina) by native Australian rodents

© 2014, Springer-Verlag Berlin Heidelberg. The success of an invasive species can be reduced by biotic resistance from the native fauna. For example, an invader that is eaten by native predators is less likely to thrive than one that is invulnerable. The ability of invasive cane toads (Rhinella marina) to spread through Australia has been attributed to the toad’s potent defensive chemicals that can be fatal if ingested by native snakes, lizards, marsupials and crocodiles. However, several taxa of native insects and birds are resistant to cane toad toxins. If native rodents are also capable of eating toads (as suggested by anecdotal reports), these large, abundant and voracious predators might reduce toad numbers. Our field observations and laboratory trials confirm that native rodents (Melomys burtoni, Rattus colletti and Rattus tunneyi) readily kill and consume cane toads (especially small toads), and are not overtly affected by toad toxins. Captive rodents did not decrease their consumption of toads over successive trials, and ate toads even when alternative food types were available. In combination with anecdotal reports, our data suggest that rodents (both native and invasive) are predators of cane toads in Australia. Despite concerns about the decline of rodents following the invasion of toads, our data suggest that the species we studied are not threatened by toads as toxic prey, and no specific conservation actions are required to ensure their persistence

Learning, evolvability and exploratory behaviour: extending the evolutionary reach of learning

Traditional accounts of the role of learning in evolution have concentrated upon its capacity as a source of fitness to individuals. In this paper I use a case study from invasive species biology—the role of conditioned taste aversion in mitigating the impact of cane toads on the native species of Northern Australia—to highlight a role for learning beyond this—as a source of evolvability to populations. This has two benefits. First, it highlights an otherwise under-appreciated role for learning in evolution that does not rely on social learning as an inheritance channel nor “special” evolutionary processes such as genetic accommodation (both of which many are skeptical about). Second, and more significantly, it makes clear important and interesting parallels between learning and exploratory behaviour in development. These parallels motivate the applicability of results from existing research into learning and learning evolution to our understanding the evolution of evolvability more generally.23 page(s

Phylogenetic evidence for the invasion of a commercialized European Phasmarhabditis hermaphrodita lineage into North America and New Zealand

Biological control (biocontrol) as a component of pest management strategies reduces reliance on synthetic chemicals, and seemingly offers a natural approach that minimizes environmental impact. However, introducing a new organism to new environments as a classical biocontrol agent can have broad and unanticipated biodiversity effects and conservation consequences. Nematodes are currently used in a variety of commercial biocontrol applications, including the use of Phasmarhabditis hermaphrodita as an agent targeting pest slug and snail species. This species was originally discovered in Germany, and is generally thought to have European origins. P. hermaphrodita is sold under the trade name Nemaslug®, and is available only in European markets. However, this nematode species was discovered in New Zealand and the western United States, though its specific origins remained unclear. In this study, we analyzed 45 nematode strains representing eight different Phasmarhabditis species, collected from nine countries around the world. A segment of nematode mitochondrial DNA (mtDNA) was sequenced and subjected to phylogenetic analyses. Our mtDNA phylogenies were overall consistent with previous analyses based on nuclear ribosomal RNA (rRNA) loci. The recently discovered P. hermaphrodita strains in New Zealand and the United States had mtDNA haplotypes nearly identical to that of Nemaslug®, and these were placed together in an intraspecific monophyletic clade with high support in maximum likelihood and Bayesian analyses. We also examined bacteria that co-cultured with the nematode strains isolated in Oregon, USA, by analyzing 16S rRNA sequences. Eight different bacterial genera were found to associate with these nematodes, though Moraxella osloensis, the bacteria species used in the Nemaslug® formulation, was not detected. This study provided evidence that nematodes deriving from the Nemaslug® biocontrol product have invaded countries where its use is prohibited by regulatory agencies and not commercially available

Reproduction and embryo viability of a range-limited tropical freshwater fish exposed to fluctuating hypoxia

Flint, N ORCiD: 0000-0003-4331-4109Hypoxia can profoundly affect fish reproduction and larval development, but its effects on fish from tropical Australia are not well understood. In the present study, the effects of diel fluctuating hypoxia on reproduction and embryo viability were investigated for a range-limited tropical freshwater fish, namely the Utchee Creek rainbowfish (Melanotaenia utcheensis). The lethal level for adult rainbowfish after gradual oxygen depletion was ∼7% dissolved oxygen (DO) saturation. After 28 days, the reproductive success of adult fish exposed to fluctuating hypoxia treatments was measured by fecundity, gonad health, egg incubation time, egg and larval mortality, viability and size of hatching larvae. Reproduction was impaired in the lowest sublethal treatment (minimum 10% DO saturation each day). No ill effects of parental exposure to diel fluctuating hypoxia on embryos were identified, and minor differences in temperature between aquaria had a greater effect on embryos than parental hypoxia treatments. Similarly, no effects of embryonic exposure to diel fluctuating hypoxia were identified. Utchee Creek rainbowfish appear to be more hypoxia tolerant than temperate species, in keeping with their habitat in warm lowland streams, but they are still susceptible to the increasing frequency and intensity of hypoxia possible with increasing temperature and reduced flow as a result of climate change. © 2018 CSIRO

Embryos of eastern rainbowfish Melanotaenia splendida splendida (Peters, 1866) tolerate fluctuating hypoxia

Flint, N ORCiD: 0000-0003-4331-4109© CSIRO. Hypoxia can have profound sublethal effects on reproduction and embryonic development of some freshwater fish. In the present study, the effects of diel fluctuating hypoxia on embryo viability were investigated for the eastern rainbowfish Melanotaenia splendida splendida, a small-bodied species common in wetlands of tropical Queensland. After daily hypoxic exposure (minimum 5% saturation) from fertilisation until hatch, no effects were found on egg incubation time, egg and larval mortality, and viability and size of hatching larvae. Older life history stages of the species are vulnerable to this level of hypoxia. Embryos of phytolithophilic species are likely exposed to fluctuating dissolved oxygen saturations in their natural habitat, and hypoxia tolerance may be a requirement for fish species that spawn predominantly on submerged plant material

Embryos of eastern rainbowfish Melanotaenia splendida splendida (Peters, 1866) tolerate fluctuating hypoxia

© CSIRO. Hypoxia can have profound sublethal effects on reproduction and embryonic development of some freshwater fish. In the present study, the effects of diel fluctuating hypoxia on embryo viability were investigated for the eastern rainbowfish Melanotaenia splendida splendida, a small-bodied species common in wetlands of tropical Queensland. After daily hypoxic exposure (minimum 5% saturation) from fertilisation until hatch, no effects were found on egg incubation time, egg and larval mortality, and viability and size of hatching larvae. Older life history stages of the species are vulnerable to this level of hypoxia. Embryos of phytolithophilic species are likely exposed to fluctuating dissolved oxygen saturations in their natural habitat, and hypoxia tolerance may be a requirement for fish species that spawn predominantly on submerged plant material

Reproduction and embryo viability of a range-limited tropical freshwater fish exposed to fluctuating hypoxia

Hypoxia can profoundly affect fish reproduction and larval development, but its effects on fish from tropical Australia are not well understood. In the present study, the effects of diel fluctuating hypoxia on reproduction and embryo viability were investigated for a range-limited tropical freshwater fish, namely the Utchee Creek rainbowfish (Melanotaenia utcheensis). The lethal level for adult rainbowfish after gradual oxygen depletion was ∼7% dissolved oxygen (DO) saturation. After 28 days, the reproductive success of adult fish exposed to fluctuating hypoxia treatments was measured by fecundity, gonad health, egg incubation time, egg and larval mortality, viability and size of hatching larvae. Reproduction was impaired in the lowest sublethal treatment (minimum 10% DO saturation each day). No ill effects of parental exposure to diel fluctuating hypoxia on embryos were identified, and minor differences in temperature between aquaria had a greater effect on embryos than parental hypoxia treatments. Similarly, no effects of embryonic exposure to diel fluctuating hypoxia were identified. Utchee Creek rainbowfish appear to be more hypoxia tolerant than temperate species, in keeping with their habitat in warm lowland streams, but they are still susceptible to the increasing frequency and intensity of hypoxia possible with increasing temperature and reduced flow as a result of climate change. © 2018 CSIRO