Natasha L. Wiggins

Effects of Two Plant Secondary Metabolites, Cineole and Gallic Acid, on Nightly Feeding Patterns of the Common Brushtail Possum

We investigated effects of two plant secondary metabolites (PSMs), cineole and gallic acid, on the nightly feeding behavior of the common brushtail possum (Trichosurus vulpecula), a generalist folivore. We tested whether possums altered their feeding behavior in response to increasing levels of cineole, a dietary terpene. Possums were fed artificial diets containing three levels of cineole; zero (basal diet), medium (6.8% of total dry matter, DM), and high (15.3% DM). In another experiment, we introduced gallic acid, a dietary phenolic, into the diets. Possums were offered a Choice PSM diet (cineole and gallic acid diets simultaneously) or a No-Choice PSM diet (containing either cineole or gallic acid). Detoxification products of cineole and gallic acid were examined in urine to determine that different detoxification pathways were utilized in the elimination of each compound. With increasing cineole levels, possums ate less, had smaller feeding bouts, and had a lower rate of intake, but did not extend their total nightly feeding time. Possums offered the Choice PSM diet, compared with the No-Choice diets, ate more, had larger feeding bouts, and tended to increase their rate of intake. Results from the urinary analysis indicated that gallic acid and cineole were not involved in competing detoxification pathways in brushtail possums. There was also a significant sex effect: females ate more overall, ate more per feeding bout, and ate at a higher rate than males. These results indicate that PSMs not only constrain overall intake, but that possums alter their feeding behavior in response to them. Altered feeding patterns may reduce the negative influence of PSMs on intake.

Quantitative trait loci for key defensive compounds affecting herbivory of eucalypts in Australia

* Formylated phloroglucinols (FPCs) are key defensive compounds that influence herbivory by mammals and arthropods in eucalypts. However, the genetic architecture underlying variation in their levels remains poorly understood. * Quantitative trait loci (QTL) analysis for the concentrations of two major FPCs, sideroxylonal A and macrocarpal G, was conducted using juvenile leaves from 112 clonally duplicated progenies from an outcross F2 of Eucalyptus globulus. * Two unlinked QTL were located for macrocarpal, while another unlinked QTL was located for sideroxylonal. The sideroxylonal QTL collocated with one for total sideroxylonal previously reported using adult Eucalyptus nitens foliage, providing independent validation in a different evolutionary lineage and a different ontogenetic stage. * Given the potential widespread occurrence of these QTL, their ontogenetic stability, and their impact on a range of dependent herbivores, it is possible that they have extended phenotypic effects in the Australian forest landscape.

The success of GPS collar deployments on mammals in Australia

Global Positioning System (GPS) wildlife telemetry collars are being used increasingly to understand the movement patterns of wild mammals. However, there are few published studies on which to gauge their general utility and success. This paper highlights issues faced by some of the first researchers to use GPS technology for terrestrial mammal tracking in Australia. Our collated data cover 24 studies where GPS collars were used in 280 deployments on 13 species, including dingoes or other wild dogs (Canis lupus dingo and hybrids), cats (Felis catus), foxes (Vulpes vulpes), kangaroos (Macropus giganteus), koalas (Phascolarctos cinereus), livestock guardian dogs (C. l. familiaris), pademelons (Thylogale billardierii), possums (Trichosurus cunninghami), quolls (Dasyurus geoffroii and D. maculatus), wallabies (Macropus rufogriseus and Petrogale lateralis), and wombats (Vombatus ursinus). Common problems encountered were associated with collar design, the GPS, VHF and timed-release components, and unforseen costs in retrieving and refurbishing collars. We discuss the implications of collar failures for research programs and animal welfare, and suggest how these could be avoided or improved. Our intention is to provide constructive advice so that researchers and manufacturers can make informed decisions about using this technology, and maximise the many benefits of GPS while reducing the risks.

Behavioral Responses of a Generalist Mammalian Folivore to the Physiological Constraints of a Chemically Defended Diet

Mammalian herbivores, particularly browsers and folivores, encounter and consume a range of plant chemical defenses [plant secondary metabolites (PSMs)] on a regular basis. The physiological regulation of PSM ingestion and the resulting behavioral responses of mammalian herbivores directly affect their feeding decisions and the subsequent foraging strategies that they adopt. Generalist mammalian herbivores are hypothesized to consume a generalized diet because of physiological limitations of their detoxification systems. The consumption of a generalized diet is proposed to enable toxin (PSM) dilution through the use of multiple detoxification pathways. We tested the predictions of the detoxification–limitation hypothesis by offering two chemically different plant species, Eucalyptus regnans and E. globulus, to a generalist mammalian folivore, the common brushtail possum (Trichosurus vulpecula), as single- and mixed-species diets. By feeding more efficiently, brushtail possums benefited more, through increased intake, on the mixed-species diet than on either of the single-species diets. We argue that frequently switching between chemically diverse foliage reduces the physiological constraints imposed by a PSM-rich diet and enables more efficient feeding. The behavioral responses of brushtail possums were consistent with the proposed physiological constraints of a chemically defended diet, offering support for predictions of the detoxification–limitation hypothesis. We suggest that feeding behavior of herbivores may be a useful indicator of the physiological constraints imposed by a chemically defended diet.

A Two-Phase Model for Smoothly Joining Disparate Growth Phases in the Macropodid Thylogale billardierii

Generally, sigmoid curves are used to describe the growth of animals over their lifetime. However, because growth rates often differ over an animals lifetime a single curve may not accurately capture the growth. Broken-stick models constrained to pass through a common point have been proposed to describe the different growth phases, but these are often unsatisfactory because essentially there are still two functions that describe the lifetime growth. To provide a single, converged model to age animals with disparate growth phases we developed a smoothly joining two-phase nonlinear function (SJ2P), tailored to provide a more accurate description of lifetime growth of the macropod, the Tasmanian pademelon Thylogale billardierii. The model consists of the Verhulst logistic function, which describes pouch-phase growth – joining smoothly to the Brody function, which describes post-pouch growth. Results from the model demonstrate that male pademelons grew faster and bigger than females. Our approach provides a practical means of ageing wild pademelons for life history studies but given the high variability of the data used to parametrise the second growth phase of the model, the accuracy of ageing of post-weaned animals is low: accuracy might be improved with collection of longitudinal growth data. This study provides a unique, first robust method that can be used to characterise growth over the lifespan of pademelons. The development of this method is relevant to collecting age-specific vital rates from commonly used wildlife management practices to provide crucial insights into the demographic behaviour of animal populations.

Hungry grouse in a warming world: emerging risks from plant chemical defenses and climate change

Conservation and management of habitat is central to the conservation of grouse. Identifying thresholds of biotic and abiotic risks that may reduce habitat quality is therefore a component of habitat management of grouse. We propose that dietary phytochemicals, specifically plant secondary metabolites (PSMs), represent an ecological risk to grouse, which are not often considered in the management of grouse. Most species of grouse consume PSMs, which have negative consequences at some concentration. Moreover, several studies provide evidence that the risks posed by PSMs will likely increase under projected climate change scenarios. We discuss potential risks of PSMs for grouse and propose theoretical models, which can be used to test current and future physiological, behavioural and ecological risks of PSMs. We propose that dose-response thresholds can be used to predict and monitor the synergistic risks of PSMs and climate change for grouse. We further suggest that identifying dose-response thresholds to PSMs is needed in the management of vertebrate herbivores in general.

Scent Chemicals of the Brushtail Possum, Trichosurus vulpecula

The common brushtail possum (Trichosurus vulpecula) is the most widespread browsing marsupial in Australia, where it occupies woodland, agricultural, and urban environments. Following its introduction into New Zealand in the 19th century it has become a major feral pest, threatening native forests. The adaptability of the possum is thought to be due in part to its social organization, in which chemical communication is important. Possums have cloacal glands and exhibit related marking behavior. This study sought to characterize the chemicals involved in scent marking. Swabs were taken of the cloacal region of 15 possums (5 females, 10 males) from north-eastern Tasmania and analyzed by gas chromatography–mass spectrometry. There was a large number of compounds present, including 81 branched and unbranched, and saturated and unsaturated, fatty acids (C4–C15) and alcohols (C6–C26); 27 esters of 2,6- and 2,7-dimethyloctanol; 29 esters of formic acid; 39 sulfur compounds including S8 and a series of dialkyl disulfides, trisulfides, and tetrasulfides (C4–C10); and several alkylglycerol ethers. Many of these cloacal compounds are new to biology. There was considerable individual variability in the relative amounts of compounds found, and no evident sex differences, although the study was not designed to test this. This pattern suggests that these compounds may be acting collectively as a signature mixture of semiochemicals, carrying information on the individual, its kinship, and physiological and social status. This is the first detailed description of putative semiochemicals in any marsupial species.

Intercropping With Aromatic Plants Decreases Herbivore Abundance, Species Richness, and Shifts Arthropod Community Trophic Structure

ABSTRACT Habitat management is important for the regulation of arthropod community structures to reduce pest populations in orchard ecosystems, but there is limited information on how intercropping with aromatic plants regulates arthropod community structure at trophic levels. We selected four aromatic plants, Mentha canadensis L., Agerarum houstonianum Mill, Tagetes patula L., and Ocimum basilicum L., as intercrops in apple orchard to analyze the effects of intercropping on herbivore and predator abundance, species richness, and to measure the changes of trophic levels of the associated arthropod community. We found that intercropping with aromatic plants, compared with intercropping with natural herb vegetation, significantly reduced herbivore abundance and species richness by 25.62 and 11.6%, respectively. Intercropping significantly increased predator abundance and species richness by 18.78 and 15.6%, respectively, with predator abundance most notably affected during the flowering period of aromatic plants. Furthermore, herbivore abundance and species richness were strongly negatively correlated with predator species richness. Intercropping affected herbivore-predator dynamics, with an observed increase in the ratios of predator abundance and richness to herbivore abundance and richness. Our results indicate that intercropping with aromatic plants in apple orchards may play a role in the observed shift from a herbivore-dominated to a predator-dominated trophic structure, which is likely to have important flow-on effects on arthropod community structure.

Intercropping with aromatic plants hindered the occurrence of Aphis citricola in an apple orchard system by shifting predator–prey abundances

Abstract Enhancing biological control of pests through habitat management in agricultural systems has gained increasing attention. Three different aromatic plants, ageratum (Agerarum houstonianum Mill.), French marigold (Tagetes patula L.) and basil (Ocimum basilicum L.), were chosen as intercrops for apple orchards to evaluate the effects of intercropping on Aphis citricola Van der Goot and its local natural enemies in China. We found that compared with natural vegetation, A. citricola abundance was significantly decreased by 29.26%, 35.80% and 38.28% in plots intercropped with ageratum, French marigold and basil, respectively. The number of natural enemies of A. citricola in plots intercropped with T. patula and O. basilicum were significantly higher than in plots of natural vegetation. Equally important, intercropping affected the composition of natural enemies and the population dynamics of A. citricola and its natural enemies. Annual cumulative numbers of natural enemies were significantly negatively correlated with A. citricola annual cumulative individual numbers except for O. tantillus. Our results demonstrate that intercropping with aromatic plants could be an effective method for biological control of A. citricola in apple orchards.

Macropod habitat use and response to management interventions in an agricultural–forest mosaic in north-eastern Tasmania as inferred by scat surveys

Context Native pest herbivores often require population numbers to be controlled in landscape settings where agricultural, plantation forests and native forests are juxtaposed. The Tasmanian pademelon Thylogale billardierii and the red-necked wallaby Macropus rufogriseus rufogriseus are among the most abundant native pest herbivore species in Tasmania. Aims We aimed to determine the habitat use of pademelons and wallabies in response to (i) environmental and seasonal variation, and (ii) two different wildlife management interventions (shooting and fencing) in an agricultural–forest mosaic in north-eastern Tasmania. Methods Macropod abundance before and after shooting and fencing management interventions were estimated by changes in the rate of deposition of faecal pellets (scats per unit area per time interval) on an array of permanent transects that were stratified across three habitat types (agricultural land, plantation forest, and native forest). An experiment was also conducted to determine the endurance of fresh scats in the three habitats. Key results More than 90% of scats remained undecomposed for over five months, and more than 50% of scats remained undecomposed for over 11 months across the study site. Decomposition rates were significantly influenced by habitat type, specifically, highest in agricultural land and lowest in native forest for both species. Scat deposition rates showed that species abundance was influenced by habitat type and season. Macropod abundance was highest in agricultural land and lowest in native forest. Compared with summer and early autumn, pademelon scat abundance significantly decreased in late autumn and spring on agricultural land but showed no change for plantation forest or native forest. Wallaby scats showed similar seasonal trends for all three habitats, lower in late autumn and spring compared with summer and early autumn. Following each of the management interventions, macropod scat deposition rates decreased predominantly on agricultural land. This effect decreased with increasing distance from intervention loci. Conclusions We demonstrate that scat monitoring provides a useful survey technique for the assessment of macropod habitat use, and show that macropods select for agricultural habitats. Shooting and fencing interventions reduced the use of agricultural habitats, but this effect was localised. Implications A whole-landscape perspective is required when assessing the impacts of management interventions on pest populations. Results highlight the formidable challenges in controlling native herbivores in habitat mosaics, given the localised effects of management interventions and the importance of environmental and seasonal factors as drivers of habitat use.