Ontogenetic colour change in Oreophryne ezra (Anura: Microhylidae) reflects an unusual shift from conspicuousness to crypsis but not in toxicity

Ontogenetic colour change (OCC) may signal a switch in defensive strategies across development. Commonly, juveniles use cryptic colours and transition to conspicuous coloration as adults. Extensive theoretical and empirical work suggest such a transition is more likely than the converse. Oreophryne ezra, a newly discovered frog from New Guinea, however, undergoes OCC that belies expectations. We investigated the notion juveniles are aposematic while the adults use crypsis. We quantified the extent of conspicuousness of O. ezra across life stages using spectrophotometry and models of avian vision; and analysed skin extracts for the presence of toxic alkaloids. As predicted, the juvenile colour patterns were estimated to be conspicuous to likely predators against the frogs natural viewing backgrounds, while adults consistently fell below the threshold of discriminability. However, we discovered no alkaloids in either juveniles or adults. This suggests the juveniles use alternative defensive chemicals, or the colour pattern has an alternative origin – to which we offer the hypothesis that juvenile frogs may be Batesian mimics of a synoptic species of weevil. This study highlights the potential for this system, and others like it, to inform our understanding of the adaptive significance of OCC and the selective drivers for different anti-predatory strategies

Defence mitigation by predators of chemically defended prey integrated over the predation sequence and across biological levels with a focus on cardiotonic steroids

Predator–prey interactions have long served as models for the investigation of adaptation and fitness in natural environments. Anti-predator defences such as mimicry and camouflage provide some of the best examples of evolution. Predators, in turn, have evolved sensory systems, cognitive abilities and physiological resistance to prey defences. In contrast to prey defences which have been reviewed extensively, the evolution of predator counter-strategies has received less attention. To gain a comprehensive view of how prey defences can influence the evolution of predator counter-strategies, it is essential to investigate how and when selection can operate. In this review we evaluate how predators overcome prey defences during (i) encounter, (ii) detection, (iii) identification, (iv) approach, (v) subjugation, and (vi) consumption. We focus on prey that are protected by cardiotonic steroids (CTS)—defensive compounds that are found in a wide range of taxa, and that have a specific physiological target. In this system, coevolution is well characterized between specialist insect herbivores and their host plants but evidence for coevolution between CTS-defended prey and their predators has received less attention. Using the predation sequence framework, we organize 574 studies reporting predators overcoming CTS defences, integrate these counter-strategies across biological levels of organization, and discuss the costs and benefits of attacking CTS-defended prey. We show that distinct lineages of predators have evolved dissecting behaviour, changes in perception of risk and of taste perception, and target-site insensitivity. We draw attention to biochemical, hormonal and microbiological strategies that have yet to be investigated as predator counter-adaptations to CTS defences. We show that the predation sequence framework will be useful for organizing future studies of chemically mediated systems and coevolution

Defence mitigation by predators of chemically defended prey integrated over the predation sequence and across biological levels with a focus on cardiotonic steroids

Predator–prey interactions have long served as models for the investigation of adaptation and fitness in natural environments. Anti-predator defences such as mimicry and camouflage provide some of the best examples of evolution. Predators, in turn, have evolved sensory systems, cognitive abilities and physiological resistance to prey defences. In contrast to prey defences which have been reviewed extensively, the evolution of predator counter-strategies has received less attention. To gain a comprehensive view of how prey defences can influence the evolution of predator counter-strategies, it is essential to investigate how and when selection can operate. In this review we evaluate how predators overcome prey defences during (i) encounter, (ii) detection, (iii) identification, (iv) approach, (v) subjugation, and (vi) consumption. We focus on prey that are protected by cardiotonic steroids (CTS)—defensive compounds that are found in a wide range of taxa, and that have a specific physiological target. In this system, coevolution is well characterized between specialist insect herbivores and their host plants but evidence for coevolution between CTS-defended prey and their predators has received less attention. Using the predation sequence framework, we organize 574 studies reporting predators overcoming CTS defences, integrate these counter-strategies across biological levels of organization, and discuss the costs and benefits of attacking CTS-defended prey. We show that distinct lineages of predators have evolved dissecting behaviour, changes in perception of risk and of taste perception, and target-site insensitivity. We draw attention to biochemical, hormonal and microbiological strategies that have yet to be investigated as predator counter-adaptations to CTS defences. We show that the predation sequence framework will be useful for organizing future studies of chemically mediated systems and coevolution

Using spider web types as a substitute for assessing web-building spider biodiversity and the success of habitat restoration

Arthropods have been regarded as good indicators of habitat quality due to their sensitivity to changes in habitat state. However, there are many constraints to working with arthropods that make them inaccessible to land managers and most volunteer-driven initiatives. Our study examined a novel approach for detecting changes in web-building spider communities by focussing on the types of webs that spiders build rather than the spider itself. This method was cost-effective, easy-to-use, and importantly, we found a strong congruency between the diversity of web architecture and the diversity of web-building spider genera. The metrics derived from this method could distinguish differences in web-building communities among habitat types that represented a successional gradient, and thus we concluded that the method was useful for monitoring the progress of restoration. Many other applications for the method are possible such as environmental impact assessment and agricultural pest management, and we encourage development in these areas.15 page(s

Community-Friendly Methods for Monitoring Riverside Rehabilitation: A Case Study

Local community groups in their management of rehabilitation projects are often motivated by the goal of creating ecosystems that provide improved habitats for native species. It is important that community groups have the ability to monitor progress towards such a goal, to ensure their hard work and time has not been wasted. Indeed, government funding bodies now require the objectives of rehabilitation projects to be measured in terms of outcomes and reported as such. Terrestrial invertebrates have been recommended as bioindicators because of their abundance, importance in ecosystem function and their sensitivity to environmental change. However, monitoring invertebrates is often not feasible by community groups because of the high costs of both laboratory sorting and storage of specimens. Monitoring invertebrates also requires access to both specialist equipment and taxonomic expertise. Here we present the results of a project to develop indices that: (i) are cost-effective; (ii) limit and/or eliminate laboratory processing and the need for expert help; (iii) can be derived by community groups; (iv) based on processes that invertebrates are responsible for; and (v) are indicative of, and related to, successive stages of riparian rehabilitation. Several simple methods such as scoring insect leaf damage, measuring rates of seed removal by ants and assessing the diversity of web-building spiders (using features of their webs) were developed. These methods and indices were then compared to invertebrate taxa richness and abundance at the same sites estimated from traditional invertebrate sampling techniques such as yellow-pan and pit-fall traps. A set of the simpler methods were subsequently trialled at community attended workshops where we examine observer accuracy, precision and method 'useability'. Quantitative and semi-qualitative collected data from these workshops were used to further refine methods and a number of important outcomes were gained through post-workshop evaluations

The construction of small-scale, quasi-mechanistic spatial models of insect energetics in habitat restoration: A case study of beetles in Western Australia

Aim: The management and restoration of ecological processes mediated by biotic interactions is now broadly advocated and may be achieved by targeting restoration towards key agents. Although theoretically examined, a practical approach to incorporating the physiology and energetics of insects into restoration planning is poorly articulated. I aimed to provide a case study using the thermal biology and energetics of beetles to identify the distribution of habitat suitability in a large restoration landscape. Location: South-west Western Australia. Methods: I modelled the thermal performance of metabolic rates of thirteen Phyllococerus purpurascens, and twenty Colpochila “species 2,” measured repeatedly at seven temperatures between five and 40°C using flow-through respirometry. Thermal constraints were used to inform a species distribution model of each species at extremely high spatiotemporal resolution, projecting the physiological state of each species for every hour at 5″ resolution across a 152-km2 restoration landscape in south-western Australia to estimate the habitat suitability for beetles. Results: Both species’ metabolic rates increased exponentially to a critical point, followed by rapid decline, but the thermal tolerance thresholds were different for each species. Both had strikingly high-thermal tolerance relative to their nocturnal habits and local climatic conditions. The models of beetle prevalence estimated both species to be active and able to access the entire project area for all of the austral spring, summer and autumn. Main conclusions: The results reported here suggest ubiquitous habitat suitability for flower beetles in disturbed landscapes. Incorporation of similar mechanistic models for other species at high resolution offers potential insight into habitat suitability for a broad range of ectotherms