Creating new evolutionary pathways through bioinvasion: the population genetics of brushtail possums in New Zealand

Rapid increases in global trade and human movement have created novel mixtures of organisms bringing with them the potential to rapidly accelerate the evolution of new forms. The common brushtail possum (Trichosurus vulpecula), introduced into New Zealand from Australia in the 19th century, is one such species having been sourced from multiple populations in its native range. Here, we combine microsatellite DNA- and GIS-based spatial data to show that T. vulpecula originating from at least two different Australian locations exhibit a population structure that is commensurate with their introduction history and which cannot be explained by landscape features alone. Most importantly, we identify a hybrid zone between the two subspecies which appears to function as a barrier to dispersal. When combined with previous genetic, morphological and captive studies, our data suggest that assortative mating between the two subspecies may operate at a behavioural or species recognition level rather than through fertilization, genetic incompatibility or developmental inhibition. Nevertheless, hybridization between the two subspecies of possum clearly occurs, creating the opportunity for novel genetic combinations that would not occur in their natural ranges and which is especially likely given that multiple contact zones occur in New Zealand. This discovery has implications for wildlife management in New Zealand because multiple contact zones are likely to influence the dispersal patterns of possums and because differential susceptibility to baiting with sodium fluoroacetate between possums of different origins may promote novel genetic forms

Data from: Creating new evolutionary pathways through bio-invasion: the population genetics of brushtail possums in New Zealand

Rapid increases in global trade and human movement have created novel mixtures of organisms bringing with them the potential to rapidly accelerate the evolution of new forms. The common brushtail possum (Trichosurus vulpecula), introduced into New Zealand from Australia in the 19th Century, is one such species having been sourced from multiple populations in its native range. Here, we combine microsatellite DNA and GIS-based spatial data to show that T.vulpecula originating from at least two different Australian locations exhibit a population structure that is commensurate with their introduction history and which cannot be explained by landscape features alone. Most importantly, we identify a hybrid zone between the two subspecies which appears to function as a barrier to dispersal. When combined with previous genetic, morphological and captive studies, our data suggest that assortative mating between the two subspecies may operate at a behavioural or species recognition level rather than through fertilization, genetic incompatibility, or developmental inhibition. Nevertheless, hybridization between the two subspecies of possum clearly occurs, creating the opportunity for novel genetic combinations that would not occur in their natural ranges and which is especially likely given that multiple contact zones occur in New Zealand. This discovery has implications for wildlife management in New Zealand because multiple contact zones are likely to influence the dispersal patterns of possums and because differential susceptibility to baiting with sodium fluoroacetate between possums of different origins, may promote novel genetic forms

possum_genotypes

possum_genotype

Trophic transfer of metals in a seagrass food web: Bioaccumulation of essential and non-essential metals

Metal concentrations are reported for a seagrass ecosystem receiving industrial inputs. δ13C and δ15N isotope ratios were used to establish trophic links. Copper concentrations (dry mass) ranged from<0.01 μg/g in fish species to 570 μg/g (μ=49 ± SD=90 μg/g) in the oyster Saccostrea glomerata. Zinc concentrations ranged from 0.6 μg/g in the seagrass Zostera capricorni to 10,800 μg/g in the mud oyster Ostrea angasi (μ=434 ± 1390 μg/g). Cadmium concentrations ranged from<0.01 μg/g in fish species to 268 μg/g in Ostrea angasi (μ=6 ± 25 μg/g). Lead concentrations ranged from<0.01 μg/g for most fish species to 20 μg/g in polychaetes (μ=2 ± 3 μg/g). Biomagnification of metals did not occur. Organisms that fed on particulate organic matter and benthic microalgae had higher metal concentrations than those that fed on detritus. Species physiology also played an important role in the bioaccumulation of metals.L. Schneider was financed by an International Postgraduate Research Scholarship (IPRS) funded by the Australian Government. All biological samples were collected by the NSW Office of Environment and Heritage using collection procedures approved under its state act. No conflict of interest is declared for this manuscript

The genetic signature left by the range expansion of red foxes in Australia is detectable after more than 80 years of population stability

Reconstructing biological invasions from historical sources can provide insights into how they occur but are difficult to do when invasions are poorly documented. Genetic signatures left by invaders can also offer insights into invasion routes, points of origin and general biology but often present conclusions that are contradictory to expectations. Here, we test the ability of continental-wide microsatellite genotype data from 29 loci and 3122 samples to reconstruct the well-documented invasion of red foxes Vulpes vulpes from the United Kingdom into Australia over 150 years ago, an invasion that has led to the extinction of many native species. Our analysis reveals several key signals of invasion evident in Australian foxes. They display lower levels of diversity than foxes sampled from the UK, exhibit clines in diversity from the point of introduction (south-east Australia) to the edge of their range, and show strong evidence of allele surfing in westerly and north-easterly directions. These characteristics are consistent with a single point of origin followed by rapid expansion in westerly and north-easterly directions as suggested by historical records. We also find little genetic structure in foxes across Australia with only the vast Nullarbor Plains and Great Victoria Desert region presenting a detectable barrier to their dispersal. As such, no mainland region within the current range of foxes can be considered genetically isolated and therefore appropriate for localised eradication efforts. Overall, our analyses demonstrate the ability of comprehensive population genetic studies to reconstruct invasion histories even after more than 80 years since colonisation was stabilised.</p

Effects of hypoxia on habitat quality of pelagic planktivorous fishes in the northern Gulf of Mexico

To evaluate the impact of hypoxia (< 2 mg O₂ l⁻¹) on habitat quality of pelagic prey fishes in the northern Gulf of Mexico, we used a spatially explicit, bioenergetics-based growth rate potential (GRP) model to develop indices of habitat quality. Our focus was on the pelagic bay anchovy Anchoa mitchilli and Gulf menhaden Brevoortia patronus. Positive GRP was considered high-quality habitat (HQH) and negative GRP was considered low-quality habitat (LQH). Models used water temperature, dissolved oxygen (DO), zooplankton biomass, and phytoplankton concentration collected during the peak periods of hypoxia in 2003, 2004, and 2006 to estimate fish GRP. Results showed that hypoxic areas were always LQH. However, with respect to the entire water column, hypoxia had only a minor impact on overall habitat quality, with habitat quality being driven primarily by prey availability followed by water temperature. These results are in contrast to other ecosystems, such as the Chesapeake Bay, where hypoxia affects a larger fraction of the water column than in the Gulf of Mexico and has a significant impact on overall habitat quality. Differences in the effect of hypoxia on habitat quality between these 2 ecosystems suggest that the vertical extent of hypoxia relative to water column depth (i.e. hypoxic volume) is a fundamental consideration when evaluating the impacts of hypoxia on pelagic fish production.This is the publisher’s final pdf. The published article is copyrighted by Inter-Research and can be found at: http://www.int-res.com/journals/meps/meps-home/Keywords: Eutrophication, Food web, Dead zone, Non-point source pollution, Habitat suitabilityKeywords: Eutrophication, Food web, Dead zone, Non-point source pollution, Habitat suitabilit

Does hypoxia have population-level effects on coastal fish? Musings from the virtual world

Hypoxia is often associated with increasing nutrient loadings and has clear mortality effects on sessile organisms, but its population effects on mobile organisms in coastal environments are uncertain. The evidence for hypoxia having population level effects is laboratory experiments, many examples of localized effects in nature, a few population-level examples, fish kills, and intuition. Despite the perception by many people, none of these provide conclusive evidence of widespread population responses to hypoxia. We synthesize the results from seven ecological simulation models that examined how low dissolved oxygen (DO) affected fish at the individual, population, and community levels. These models represent a variety of species, simulate the dynamics at a range of temporal scales and spatial scales, and impose a variety of subsets of possible DO effects. Several patterns emerged from the accumulated results. First, predicted responses were large in simpler models, and small to large in more complex models. Second, while the main effects of increased hypoxia were generally small to moderate, there were instances of relatively large indirect effects and interaction effects. Indirect effects involved growth and mortality responses due to altered spatial distribution (rather than due directly to DO) and food web interactions. Interaction effects were larger responses to hypoxia when other factors were at certain levels (e.g., responses at low versus high fish densities). Interactions also occurred when the predicted responses were larger than would be expected by the sum of the separate effects. Third, accurate information on exposure and degree of avoidance of low DO were critical unknowns. Our interpretations should be viewed as suggestive rather than definitive. The patterns described were based on a collection of modeling results that were not designed to be compared to each other. A quick look at other models seems to confirm our patterns, or at minimum, does not contradict our patterns. Quantifying the effects of hypoxia on fish populations, whether large or small, is critical for effective management of coastal ecosystems and for cost-effective and efficient design of remediation actions. The potential for interaction and indirect effects complicates field study and management. Improving our predictions of the effects of hypoxia on fish populations and communities has moved from a computational issue to a biological issue. We seem to be making progress on monitoring and modeling movement behavior, but progress is slower in food web theory and empirical research and in quantifying interspecific interactions and habitat quality in terms of process rates that relate to population dynamics

Testing single-sample estimators of effective population size in genetically structured populations

This research was supported by Australian Research Council Grant DP0559363 to WBS and RAN