The potential utility of carotenoid-based coloration as a biomonitor of environmental change

© 2020 British Ornithologists' Union In the past 30 years, carotenoid-based animal signals have been an intense focus of research because they can potentially broadcast an honest reflection of individual reproductive potential. Our understanding of the underpinning physiological functions of carotenoid compounds is still emerging, however. Here, we argue that wildlife researchers and managers interested in assessing the impact of environmental quality on animal populations should be taking advantage of the signalling function of carotenoid-based morphological traits. Using birds as a model taxonomic group, we build our argument by first reviewing the strong evidence that the expression of avian carotenoid displays provides an integrated measure of a multitude of diet- and health-related parameters. We then present evidence that human-induced rapid environmental change (HIREC) impacts the expression of carotenoid signals across different critical periods of a bird’s lifetime. Finally, we argue that variation in signal expression across individuals, populations and species could be quantified relatively easily at a global scale by incorporating such measurements into widespread bird ringing activities. Monitoring the expression of carotenoid-based coloration could help to identify how the environmental factors linked to HIREC can affect avian populations and allow for potentially detrimental effects on biodiversity to be detected prior to demographic change

Tissue structure contributes to the production of a colored skin display in the Common Myna

Spectral data of colored and white eye patch tissues in mynas

Tissue structure contributes to the production of a colored skin display in the Common Myna

Spectral data of colored and white eye patch tissues in mynas

Eat yourself sexy: how selective macronutrient intake influences the expression of a visual signal in common mynas

These datasets and programs were analyzed in the manuscript 'Eat yourself sexy: how selective macronutrient intake influences the expression of a visual signal in common myna'. Producing colored signals often requires consuming dietary carotenoid pigments. Evidence that food deprivation can reduce coloration, however, raises the question of whether other dietary nutrients contribute to signal coloration, and furthermore, whether individuals can voluntarily select food combinations to achieve optimal coloration. We created a two-way factorial design to manipulate macronutrient and carotenoid access in common mynas (Acridotheres tristis) and measured eye patch coloration as a function of the food combinations individuals selected. Mynas had access to either water or carotenoid-supplemented water and could either eat a standard captive diet or choose freely between three nutritionally defined pellets (protein, lipid or carbohydrate). Mynas supplemented with both carotenoids and macronutrient pellets had higher color scores than control birds. Male coloration tended to respond more to nutritional manipulation than females, with color scores improving in macronutrient- and carotenoid-supplemented individuals compared with controls. All mynas consuming carotenoids had higher levels of plasma carotenoids, but only males showed a significant increase by the end of the experiment. Dietary carotenoids and macronutrient intake consumed in combination tended to increase plasma carotenoid concentrations the most. These results demonstrate for the first time that consuming specific combinations of macronutrients along with carotenoids contributes to optimizing a colorful signal, and point to sex-specific nutritional strategies. Our findings improve our knowledge of how diet choices affect signal expression and, by extension, how nutritionally impoverished diets, such as those consumed by birds in cities, might affect sexual selection processes and, ultimately, population dynamics

Data from: Tasting novel foods and selecting nutrient content in a highly successful ecological invader, the common myna

Invasion success is dependent on the ability of a species to discover and exploit novel food resources. Within this context, individuals must be willing to taste novel foods. They must also be capable of evaluating the nutritional content of new foods, and selecting their relative intake in order to fulfil their nutritional needs. Whereas the former capacity is well studied, little is known about the latter capacity. First, using the common myna as a model avian invader species, we quantified the willingness of mynas to taste novel foods relative to familiar ones. Mynas readily tasted high protein (HP) novel foods and consumed them in higher quantities compared to a familiar food. Data showed that at three different levels – mixes, ingredients and macronutrients – intake could not be explained by a random model. In experiment 2, we confirmed that mynas were making their selection based on protein (P) content rather than a selection for novelty per se. When given the choice of three equally unfamiliar foods, mynas again ate disproportionately from the high protein relative to high lipid and high carbohydrate foods. Analysis revealed that mynas consumed amounts of protein that were closer to the ones in their natural diet. Finally, in experiment 3, we measured inter-individual variation in innovation and exploration propensities, and examined associations with inter-individual variation in consumption of specific macronutrients. This analysis revealed that individuals that selected HP pellets were more exploratory and individuals that selected HC pellets were quicker to solve the innovative foraging task. These findings indicate that not only the willingness to taste novel foods, but also the capacity to evaluate their nutritional content, might be central to the myna's substantial ecological success

Tissue structure contributes to the production of a coloured skin display in the Common Myna

© The Author(s) 2020. Conspicuous coloured displays from ultraviolet to bright red have been documented in many species throughout the animal kingdom. These colours often occur as sexual signals and can be incorporated into different types of integuments (e.g. scales, feathers, skin). Two main mechanisms are known to produce coloured integuments: pigmentation and tissue structure. Although pigmental and structural coloration are separate mechanisms and can occur independently, some coloured displays might emerge from a combination of both. Here, we demonstrate, using biochemical, optical and morphological methodologies, that the yellow coloration of the skin located around the eye of Common (Indian) Mynas (Acridotheres tristis) is produced by both light-reflecting nanostructures and light-absorbing carotenoid pigments. Our analysis confirms that nanostructured collagen in the avian dermis work in combination with carotenoid pigments to produce vivid integumentary colours. Identifying the mechanisms behind the production of a coloured signal provides a basis for predicting how a signal’s function might be influenced by environmental factors such as fledgling nutrition

Data for experiments 1, 2 and 3.

Data collected on captive birds. Dataset 1 = Experiment 1: total amount of foods, ingredients, and nutrients consumed over 3 days. Mix 1 = Dog pellet (DP), Mix 2 = Dog pellet and Wombaroo (W), Mix 3 = Dog pellet + Wombaroo + Eggs & Biscuits (EB). P = protein, L = lipid, and C = carbohydrate. Dataset 2 = Experiment 2: total amount of artificial pellets consumed over 3 days. P = protein, L = lipid, and C = carbohydrate. Dataset 3 = Experiment 3: behavioural data for innovation test (innovation score = latency to solve - latency to first contact task) and exploration test (exploration score = PC1 scores from variables compiled in PCA)

Reintroducing rewilding to restoration – a search for novelty

Rewilding is emerging as a major issue in conservation. However, there are currently a dozen definitions of rewilding that include Pleistocene rewilding, island rewilding, trophic rewilding, functional rewilding and passive rewilding, and these remain fuzzy, lack clarity and, hence, hinder scientific discourse. Based on current definitions, it is unclear how the interventions described under the rewilding umbrella differ from those framed within the long-standing term 'restoration'. Even projects held up as iconic rewilding endeavours invariably began as restoration projects (e.g., Oostvaaderplassen; Pleistocene Park; the return of wolves to Yellowstone, etc.). Similarly, rewilding organisations (e.g., Rewilding Europe) typically began with a restoration focus. Scientific discourse requires precise language. The fuzziness of existing definitions of rewilding and lack of distinction from restoration practices means that scientific messages cannot be transferred accurately to a policy or practice framework. We suggest that the utility of 'rewilding' as a term is obsolete, and hence recommend scientists and practitioners use 'restoration' instead233255259MWH and MJS are funded by the Australia-Africa Universities Network - Partnership Research & Development Fund 201

Reintroducing rewilding to restoration – Rejecting the search for novelty

Rewilding is emerging as a major issue in conservation. However, there are currently a dozen definitions of rewilding that include Pleistocene rewilding, island rewilding, trophic rewilding, functional rewilding and passive rewilding, and these remain fuzzy, lack clarity and, hence, hinder scientific discourse. Based on current definitions, it is unclear how the interventions described under the rewilding umbrella differ from those framed within the long-standing term ‘restoration’. Even projects held up as iconic rewilding endeavours invariably began as restoration projects (e.g., Oostvaaderplassen; Pleistocene Park; the return of wolves to Yellowstone, etc.). Similarly, rewilding organisations (e.g., Rewilding Europe) typically began with a restoration focus. Scientific discourse requires precise language. The fuzziness of existing definitions of rewilding and lack of distinction from restoration practices means that scientific messages cannot be transferred accurately to a policy or practice framework. We suggest that the utility of ‘rewilding’ as a term is obsolete, and hence recommend scientists and practitioners use ‘restoration’ instead