Coat colour in marsupials: genetic variants at the ASIP locus determine grey and black fur of the brushtail possum

The possession of fur or hair is a defining characteristic of mammals and can occur in a variety of colours and patterns. While genetic determinants of coat colour are well described in eutherian 'placental' mammals, the other major mammalian infraclass, marsupials, is grossly understudied. The fur of the common brushtail possum (Trichosurus vulpecula), an iconic native mammal found throughout Australia and introduced into Aotearoa New Zealand, possesses two main colour morphs: grey and black. To identify genetic variants associated with coat colour, we performed a genome-wide association study (GWAS) with genotype by sequencing (GBS) data. Single nucleotide variants (SNVs) on chromosome 3, close to the agouti signalling protein (ASIP) gene that controls the temporal and spatial distribution of pigments in eutherian mammals, were identified. Fine-mapping identified a C>T variant at chr3:100483705 that results in a ASIP:p.Arg115Cys missense substitution, and animals homozygous for this variant have black fur. In addition to uncovering the first genetic determinant of coat colour in a natural marsupial population, comparative analysis of ASIP in divergent marsupial species identified the dasyurids as having accelerated evolution, reflecting their well described diversity of coat colour and pattern.

Rodent management in Aotearoa New Zealand: approaches and challenges to landscape-scale control

Aotearoa-New Zealand has only four rodent species, all introduced. In order of arrival, they are Pacific rat Rattus exulans, brown rat R. norvegicus, house mouse Mus musculus, and black rat R. rattus. Rodent management in New Zealand aims mainly to conserve indigenous biodiversity rather than to protect crops or manage diseases, as is usual elsewhere. We describe four major "regimes" and one major vision for rodent control in New Zealand to meet ecological restoration objectives. Current challenges for island eradications are for large islands that are remote or populated by people. Aerial 1080 is the only large-scale (tens of thousands of hectares) option for black rat control, but its application requires adjustment to counter subsequent rapid black rat repopulation. Unfenced "ecosanctuaries" (mean 720 ha) use ground-based traps and poisons to target mainly black rats and face constant reinvasion. Ecosanctuaries with mammal-resistant fences (up to 3500 ha) limit reinvasion and target more pest species and have enabled the return of previously extirpated taxa to the main islands. Predator Free 2050 aims to eradicate the rat species (but not mice) plus some other introduced mammals from New Zealand by 2050. This vision is not attainable with current tools, but research and experimental management is exploring techniques and technologies. The large scale (to 100 000 ha) at which black rats are now targeted for control to extremely low abundance seems to be unique to New Zealand.

Expression, purification and characterisation of the recombinant possum lipocalin vulpeculin

BACKGROUND

Lipocalins are a large family of proteins, which possess a highly conserved eight-stranded antiparallel beta-barrel structure as distinctive trait. This family includes Major Urinary Proteins (MUPs) from rats and mouse, studied for their role in urinary protein-mediated chemosignalling. Vulpeculin has been identified as the most abundant protein in the urine of the common brushtail possum, Trichosurus vulpecula. On the basis of high similarity with other MUPS, we hypothesised that vulpeculin might have a role in possum chemosignalling and investigated its stability and binding ability.

METHODS

We expressed and purified vulpeculin using an E.coli-based system and confirmed correct folding by circular dichroism (CD) spectroscopy. Thermal stability was studied by CD and binding properties were investigated using two optical probes N-phenyl-naphthylamine (NPN) and 8-anilino-1-naphthalene sulphonic acid (ANS).

RESULTS

CD revealed a secondary structure typical of a predominantly β-sheet protein, consistent with the beta barrel structure of the lipocalin family. Vulpeculin showed a high level of thermostability, as assessed by CD, exhibiting a small shift in the secondary structure even at 95 °C. Binding assays indicated that vulpeculin cannot accommodate the NPN ligand but can bind ANS.

CONCLUSION

The urinary secretion, high degree of sequence similarity with other lipocalins, its beta sheet structure assessed by CD and potential to bind hydrophobic ligands in the hydrophobic cavity or an external hydrophobic pocket, suggest vulpeculin may be involved in possum chemosignalling.

GENERAL SIGNIFICANCE

This work represents a first step towards the further investigation of the newly discovered lipocalin and its role in possum chemosignalling.

Has the introduction of two subspecies generated dispersal barriers among invasive possums in New Zealand?

The introduction of species into new environments provides the opportunity for the evolution of new forms through admixture and novel selection pressures. The common brushtail possum, Trichosurus vulpecula vulpecula from the Australian mainland and T.v.fuliginosus from Tasmania, were introduced multiple times to New Zealand from Australia to become one of New Zealand’s most significant pests. Although derived from two subspecies, possums in New Zealand are generally considered to be a single entity. In a previous analysis, we showed that possums in the Hawkes Bay region of New Zealand appeared to consist of at least two overlapping populations. Here, we extend that analysis using a genotype-by-sequencing approach to examine the origins and population structure of those possums and compare their genetic diversity to animals sampled from Australia. We identify two populations of each subspecies in Hawkes Bay and provide clear evidence of a contact zone between them in which a hybrid form is evident. Our analysis of private alleles shows higher rates of dispersal into the contact zone than away from it, suggesting that the contact zone functions as a sink (and hence as a barrier) between the two subspecies. Given the widespread and overlapping distribution of the two subspecies across both large islands in New Zealand, it is possible that many such contact zones exist. These results suggest an opportunity for a more targeted approach to controlling this pest by recognising sub-specific differences and identifying the contact zones that may form between them.

Excluding mammalian predators increases bird densities and seed dispersal in fenced ecosanctuaries

Islands are epicenters of animal extinctions and population declines. These losses exacerbate biodiversity loss and disrupt ecological services in areas of high endemism. Island defaunation is primarily driven by invasive mammalian predators, and mammal eradications are reversing population declines for some island species. Invasive mammal eradications may also have the capacity to restore ecological interactions, along with the recovery of island fauna. Here we show that invasive mammal eradication in fenced ecosanctuaries results in higher rates of bird foraging on fruit, and higher bird-mediated seed dispersal, than in similar forests without mammal eradication. We further show that higher foraging and seed dispersal is related to higher densities of native bird species, after accounting for natural variation in fruit availability. For the many other systems globally that are under threat from invasive mammals, New Zealand's fenced ecosanctuary model offers a promising tool for restoring biodiversity and ecosystem services.

Responses of New Zealand forest birds to management of introduced mammals

Over the past 1000 years New Zealand has lost 40-50% of its bird species, and over half of these extinctions are attributable to predation by introduced mammals. Populations of many extant forest bird species continue to be depredated by mammals, especially rats, possums, and mustelids. The management history of New Zealand's forests over the past 50 years presents a unique opportunity because a varied program of mammalian predator control has created a replicated management experiment. We conducted a meta-analysis of population-level responses of forest birds to different levels of mammal control recorded across New Zealand. We collected data from 32 uniquely treated sites and 20 extant bird species representing a total of 247 population responses to 3 intensities of invasive mammal control (zero, low, and high). The treatments varied from eradication of invasive mammals via ground-based techniques to periodic suppression of mammals via aerially sown toxin. We modeled population-level responses of birds according to key life history attributes to determine the biological processes that influence species' responses to management. Large endemic species, such as the Kaka (Nestor meridionalis) and New Zealand Pigeon (Hemiphaga novaeseelandiae), responded positively at the population level to mammal control in 61 of 77 cases for species ≥20 g compared with 31 positive responses from 78 cases for species <20 g. The Fantail (Rhipidura fuliginosa) and Grey Warbler (Gerygone igata), both shallow endemic species, and 4 nonendemic species (Blackbird [Turdus merula], Chaffinch [Fringilla coelebs], Dunnock [Prunella modularis], and Silvereye [Zosterops lateralis]) that arrived in New Zealand in the last 200 years tended to have slight negative or neutral responses to mammal control (59 of 77 cases). Our results suggest that large, deeply endemic forest birds, especially cavity nesters, are most at risk of further decline in the absence of mammal control and, conversely suggest that 6 species apparently tolerate the presence of invasive mammals and may be sensitive to competition from larger endemic birds.

Management Policies for Invasive Alien Species: Addressing the Impacts Rather than the Species

Effective long-term management is needed to address the impacts of invasive alien species (IAS) that cannot be eradicated. We describe the fundamental characteristics of long-term management policies for IAS, diagnose a major shortcoming, and outline how to produce effective IAS management. Key international and transnational management policies conflate addressing IAS impacts with controlling IAS populations. This serious purpose–implementation gap can preclude the development of broader portfolios of interventions to tackle IAS impacts. We posit that IAS management strategies should directly address impacts via impact-based interventions, and we propose six criteria to inform the choice of these interventions. We review examples of interventions focused on tackling IAS impacts, including IAS control, which reveal the range of interventions available and their varying effectiveness in counteracting IAS impacts. As the impacts caused by IAS increase globally, stakeholders need to have access to a broader and more effective set of tools to respond.

Evaluating the effects of landscape structure on the recovery of an invasive vertebrate after population control

CONTEXT

Effective landscape control of invasive species is context-dependent due to the interplay between the landscape structure, local population dynamics, and metapopulation processes. We use a modelling approach incorporating these three elements to explore the drivers of recovery of populations of invasive species after control.

OBJECTIVES

We aim to improve our understanding of the factors influencing the landscape-level control of invasive species.

METHODS

We focus on the case study of invasive brushtail possum (Trichosurus vulpecula) control in New Zealand. We assess how 13 covariates describing the landscape, patch, and population features influence the time of population recovery to a management density threshold of two possums/ha. We demonstrate the effects of those covariates on population recovery under three scenarios of population growth: logistic growth, strong Allee effects, and weak Allee effects.

RESULTS

Recovery times were rapid regardless of the simulated population dynamics (average recovery time < 2 years), although populations experiencing Allee effects took longer to recover than those growing logistically. Our results indicate that habitat availability and patch area play a key role in reducing times to recovery after control, and this relationship is consistent across the three simulated scenarios.

CONCLUSIONS

The control of invasive possum populations in patchy landscapes would benefit from a patch-level management approach (considering each patch as an independent management unit), whereas simple landscapes would be better controlled by taking a landscape-level view (the landscape as the management unit). Future research should test the predictions of our models with empirical data to refine control operations.

Multi-scale dynamic maps for the management of invading and established wildlife populations: brushtail possums in New Zealand

Context The abundance and distribution of mammalian species often change in response to environmental variability, losses or gains in suitable habitat and, in the case of pest species, control programs. Consequently, conventional distribution maps rapidly become out of date and fail to provide useful information for wildlife managers. For invasive brushtail possum populations in New Zealand, the main causes of change are control programs by central and local government agencies, and post-control recovery through recolonisation and in situ recruitment. Managers need to know current, and likely future, possum population levels relative to control targets to help assess success at preventing the spread of disease or for protecting indigenous species. Information on the outcomes of government-funded possum control needs to be readily available to members of the general public interested in issues such as conservation, disease management and animal welfare. Aims To produce dynamic, scalable maps of the current and predicted future distribution and abundance of possums in New Zealand, taking into account changes due to control, and to use recent visualisation technology to make this information accessible to managers and the general public for assessing control strategies at multiple spatial scales. Methods We updated an existing individual-based spatial model of possum population dynamics, extending it to represent all individuals in a national population of up to 40 million. In addition, we created a prototype interface for interactive web-based presentation of the model’s predictions. Key results The improved capability of the new model for assessing possum management at local-to-national scales provided for real-time, mapped updates and forecasts of the distribution and abundance of possums in New Zealand. The versatility of this platform was illustrated using scenarios for current and emerging issues in New Zealand. These are hypothetical incursions of possums, reinvasion of large areas cleared of possums, and impacts on animal welfare of national-scale management of possums as vectors of bovine tuberculosis (TB). Conclusions The new individual-based spatial model for possum populations in New Zealand demonstrated the utility of combining models of wildlife population dynamics with high-speed computing capability to provide up-to-date, easily accessible information on a species’ distribution and abundance. Applications include predictions for future changes in response to incursions, reinvasion and large-scale possum control. Similar models can be used for other species for which there are suitable demographic data, typically pest species, harvested species or species with a high conservation value. Implications Models such as the spatial model for possums in New Zealand can provide platforms for (1) real-time visualisation of wildlife distribution and abundance, (2) reporting and assessing progress towards achieving management goals at multiple scales, (3) use as a decision-support tool to scope potential changes in wildlife populations or simulate the outcomes of alternative management strategies, and (4) making information about pest control publicly available.

Valuing conservation benefits of disease control in wildlife: A choice experiment approach to bovine tuberculosis management in New Zealand's native forests

We assess the non-monetary environmental benefits that accrue incidentally in New Zealand (NZ) from pest management conducted primarily to control an animal disease, bovine tuberculosis (TB). TB is an infectious disease that is one of the world's most serious animal health problems and, in many parts of the developing world, still a major mortality risk for humans. The incidence of TB in New Zealand (NZ) farmed livestock has been reduced progressively over the last 20 years, largely due to extensive and sustained population control of the main wildlife reservoir of disease, the introduced brushtail possum. Possums are also major pests that threaten indigenous forest biodiversity, and so extensive possum control for TB mitigation also incidental benefits conservation, but the extent and public value of this benefit has yet to be quantified. We conducted a choice experiment survey of the NZ public in an effort to value the native forest biodiversity benefits of TB-related possum control. We find strong public support for conservation outcomes consequent to TB-possum control in public native forests. The public place substantial value on the most observable biodiversity benefits of TB possum control, such as improved forest canopies and presence of native birds. The benefits, costs and values of TB-possum control are discussed in relation to the future directives of NZ's TB control programme, which is headed toward first regional and then national level disease eradication.