We have recently welcomed two new Associate Editors to the board: Jacob Allgeier and Andrew Park. Find out more about them and their research interests.
University of Michigan, USA
Jake is an ecosystem ecologist who focuses on understanding the controls on food-web production in coastal tropical ecosystems (coral reefs, seagrass beds, and mangroves) from both top-down and bottom-up perspectives. An overarching goal of his research is to understand how humans are changing these processes to inform conservation of the many services these ecosystems provide, such as fisheries and carbon sequestration. website
Keywords: Ecosystem ecology, community ecology, experimentation, field ecology, statistics, movement studies, isotope ecology, aquatic, marine, coastal, coral reefs, mangroves, seagrass beds
Odum School of Ecology, University of Georgia, USA
Andrew develops theory to explain and predict population and evolutionary biology of host-parasite interactions. He is particularly interested in the causes and consequences of parasite specificity and how natural assemblages of animal species impact the fitness of parasites. His research spans biological scales including within-host parasite dynamics, population and community ecology, and macroecology, and his research approach blends modelling and data analysis. website
Keywords: host-parasite ecology and evolution, population & community ecology, macroecology, modelling, data analysis, terrestrial
See the full Journal of Animal Ecology Editorial Board here.
Following the success of last year’s Rainbow Research blog series, we are once again inviting contributions from LGBTQ+ ecologists and evolutionary biologists for a series of blog posts across the British Ecological Society journals to celebrate UK Pride Month this June.
The series aims to promote visibility and inclusion of researchers from the LGBTQ+ community with posts and videos promoting them and their research. Each post will be connected to a theme represented by one of the colours shown in the Progress Pride (a.k.a. Intersectional) Flag.
The themes are:
Red – Life Orange – Healing Yellow – Sunlight Green – Nature Blue – Harmony Purple – Spirit White/Pink/Blue – Transgender Pride Black/Brown – LGBTQ2S+ Indigenous Peoples and People of Colour
Posts can link to any of these themes, whether the theme connects to your research or your identity/ies.
We’d be delighted if you would like to write a post or…
In this post, Kate shares her #StoryBehindThePaper.
Ecological communities can be depicted as networks in which species are connected by interactions. These ecological networks have far-from-random structures, which may not only hide information about the natural history of the system represented but can also affect how resistant ecological communities are to different types of perturbations.
Using computer simulations to investigate how resistant plant-pollinator and plant-herbivore networks are to the loss of species, we sought to understand which properties of these systems affect their resistance.
We found that, because plant-pollinator interactions benefit both plants and insects – as opposed to herbivory, which only benefits insects – pollination networks undergo long and frequent co-extinction cascades and are less resistant than herbivory networks.
On the other hand, pollination networks benefit from containing species that have many interactions, as well as from their structure. This gives them interaction flexibility, allowing pollinators to rewire their interactions to new plants and hence escape co-extinction. Whereas the structure of herbivory networks limits the interaction flexibility of insect herbivores.
We have thus shown how, for two types of high-biodiversity plant-insect assemblages, their natural history and network structures contribute to their resilience to extinctions.
I very much enjoyed the coding challenge – since this was my first experience with this level of modelling – and designing the different scenarios for each of the questions.
One surprising discovery in this research was finding that rewiring can have a negative (even if small) effect on the robustness of antagonistic networks with theoretical structures. Because we didn’t find the same negative effect for herbivory networks, this suggests that the empiric structure of antagonistic systems could act as a buffer against co-extinction cascades.
Read the winning paper and all of those shortlisted for the 2021 award (free for a limited time) in this Virtual Issue.
This work marked a milestone in Kate’s PhD thesis, which was awarded in January 2019 by the University of Bristol, UK. At the time of the manuscript’s submission, Kate was a second-year postdoc at the University of Sao Paulo, Brazil and, even if working on different systems and approaches, has broadly continued with this research. She is currently looking for different structural patterns across networks of several interaction types and exploring how they influence the spread of effects across species.
This International Women’s Day, Journal of Animal Ecology’s Editors reflect on the path to improving the representation of women within our editorial board, and invite you to discuss how we, as a journal, may continue to support gender diversity overall.
In 2007, Journal of Animal Ecology was in a period of growth. Submissions had increased greatly over the preceding years and our editorial board consisted of 43 expert ecologists covering a range of specialties within the diverse animal ecology field. Over the next seven years, growth continued, with submission numbers rising from just under 800 in 2007 to just over 1000 in 2014. And the board kept up; increasing to 64 individuals. Things were looking good. That was until we turned our attention to the balance of male and female editors.
Some of the faces that have made up your journal editorial board
In 2014, just 14.1% of our editors (Senior and Associate) were female. This was actually an improvement on the 4.7% in 2007 but nowhere near representative or balanced enough. Clearly, something had to be done if the journal was going to reflect, not only society at large, but also the diversity of ecologists who may submit manuscripts to the journal.
It was at around this time that active efforts to increase gender diversity began to ramp up. When approaching people to join the board, and through our open calls, the journal made a conscious effort to approach and support more women whose scientific expertise were (and still are) an asset to the journal. A further seven years later, in 2021, 44 of our 95 editors were female, and today, there are 87 expert researchers on Journal of Animal Ecology’s board; 43 of them are women. That’s 49%. Finally, near something that reflects our society – both the British Ecological Society, where current membership data shows 55% female, 42% male, 1% non-binary, 2% prefer not to say and 1% prefer to self-describe; and beyond.
Former Executive Editor, Ken Wilson was largely responsible for leading the charge to increase the representation of women on the board, of course with enthusiastic support by the rest of the editorial team and the BES:
This is one of the things I am most proud of from my time as Executive Editor, but it wasn’t without its detractors because although we managed to achieve gender parity, in the process we also had to lose a number of excellent long-serving (male) Associate Editors who had been with us for the maximum nine years. Hopefully, the current Senior Editors can continue to diversify the editorial board even further.
Importantly, we note that in the above we have referred to female and male, women and men, but we fully recognise the fact that there are multiple dimensions within and beyond gender diversity. Like the rest of the BES, Journal of Animal Ecology is committed to promoting a community of ecologists which is as diverse as possible. We are pleased with where we are as a journal but believe there is more to be done so that our editorial board, and our authors, reflect the incredible diversity of ecologists working on the ecology of animals in every corner of the world.
We remain all ears regarding how members of the BES, our authors, and ecologists more broadly would like us to continue improving. Please do not hesitate to get in touch at firstname.lastname@example.org.
Journal of Animal Ecology Senior Editors: Jean-Michel Gaillard, Darren Evans, Lesley Lancaster and Nate Sanders
Editorial Office: Emilie Aimé and Kirsty Scandrett
Each year Journal of Animal Ecology awards the Elton Prize to the best Research Article in the journal by an early career researcher. Today we present the shortlisted papers for this year’s award, based on the 2021 (90th) volume of the journal.
The winner will be selected in the coming weeks so follow the blog and watch this space for future announcements!
This month we are pleased to welcome two new Associate Editors to the board: Marlène Gamelon and Ainhoa Magrach. Find out more about them and their research interests.
Laboratoire de Biométrie et Biologie Evolutive (LBBE), CNRS – Université Lyon, France
Marlène is a population ecologist interested in understanding how biotic, abiotic and anthropogenic (e.g. harvesting) factors influence natural populations. She uses modelling approaches to study how these factors shape phenotypic traits, demographic rates and population growth rate. Her work thus combines evolution and demography. Her research primarily relies on individual long-term monitoring of natural populations of birds and mammals, with implications in conservation and management. Marlène’s other research topics include life-history trade-offs and life-history strategies. website
Keywords: Population ecology, population dynamics, demography, life history theory, longitudinal data, natural populations
Basque Centre for Climate Change, Spain
Ainhoa is a community ecologist whose research focuses on the impact of global change (e.g. selective logging, forest fragmentation, climate change or agricultural intensification) on biodiversity, ecosystem functioning and ecosystem services. She is interested in basic research on the mechanisms that allow biodiversity to be maintained, as well as on more applied research questions focusing on how to use ecological theory to develop sustainable agricultural practices. Ainhoa has worked across temperate and tropical systems around the world, and across spatial scales, from local to global. website
Keywords: Community ecology, modeling, empirical data collection, terrestrial
See the full Journal of Animal Ecology Editorial Board here.
How do rapid changes in the world around us affect the risk of emerging diseases in people and wildlife? Olivier Restif, Lucinda Kirkpatrick, Sandra Telfer, David Redding, Harriet Bartlett, Orly Razgour, Greg Albery, and Sophie Vanwambeke report on their thematic session presented at the Ecology Across Borders event held in Liverpool, December 2021.
Despite its exceptional impact, the COVID-19 pandemic is only the latest in a long list of emerging infectious diseases that have jumped from wildlife to humans. Most zoonotic pathogens have coevolved with their animal reservoirs over millennia, causing little harm until they come into contact with a new host species that happens to be more vulnerable. Although we have long been familiar with some “repeat offenders” (e.g. influenza, plague, brucellosis), the list of emerging zoonotic pathogens has grown steadily in the past 40 years.
In response to this challenge, epidemiologists, veterinarians, ecologists and social scientists amongst others have joined forces under the “One Health” banner. Crossing traditional disciplinary barriers, this approach investigates the spread of pathogens in different species and their environment, whilst also looking for ecological and social factors that may facilitate spillover between host species. Because humans interact and interfere with ecosystems all around the world, One Health seeks to uncover which social and economic activities are making humans, wildlife and domesticated animals vulnerable to zoonotic diseases.
At the same time, our interactions with nature through land use are central to our response to other man-made challenges we face: climate change, biodiversity loss and food security. For instance, The UK government has recently announced plans to pay farmers to rewild large areas of land and restore floodplains, sparking debate about the country’s ability to produce more food to reduce its reliance on food imports.
Around the world, we are seeing two opposing trends: deforestation and ecosystem degradation due to agricultural expansion in some regions, and reforestation and nature reserve creation in others. How do these rapid changes affect the risk of emerging diseases in people, livestock and wildlife? Will pathogens disappear with their hosts as natural habitats disappear, or will frequent contacts between species in patchwork landscapes increase zoonotic spillover? And can ecologists come up with environmental policies and strategies that benefits human, animal and ecosystem health?
These are some of the questions addressed by an international panel of scientists last December in Liverpool, at the Ecology Across Borders conference co-organised by the British Ecological Society and the Société Française d’Ecologie et Evolution. Chaired by Dr Lucinda Kirkpatrick (University of Antwerp) and Dr Olivier Restif (University of Cambridge), our thematic session — entitled “Impact of land use on emerging diseases: a One Health perspective” — featured six talks by British, Belgian and American ecologists and was sponsored by BES Publishing and environmental consulting company ADAS.
Providing important conceptual background, Dr. David Redding (UCL) argued that the relation between biodiversity and zoonotic risk is complex and may differ according to the spatial scale and ecological context studied. In a recent study using data collected around the world, Redding and colleagues found that reservoir hosts of zoonotic pathogens were more abundant in human-modified landscapes, even though overall biodiversity was reduced.
Yet patterns of association between zoonotic pathogens and environmental variables are distorted by biases in research effort, as Dr. Orly Razgour (University of Exeter) discussed, by presenting a systematic review of the impacts of land use changes on zoonotic diseases. Dr. Razgour highlighted important gaps in published research, for example, a dearth of studies assessing the effect of agricultural practices on wildlife hosts of zoonotic pathogens. Whereas in contrast, urbanisation is mostly discussed in the context of rodent and carnivore hosts, but rarely livestock.
Tackling the question of wildlife pathogens in urban environments, Dr Gregory Albery (Georgetown University) explained that, whilst data suggests that urban-adapted mammals have more zoonotic pathogens, this is largely driven by sampling biases. Known reservoir species are tested more often than other species, particularly in proximity to human populations. Therefore, It is vital that future empirical studies be designed to correct those biases so that risk factors of zoonotic spillover can be unraveled.
A compelling case study assessing zoonotic risk across anthropogenic landscapes was presented by Dr. Sandra Telfer (Aberdeen University), who focused on leptospirosis (an environmentally transmitted bacterial disease carried by rodents) in Madagascar. Dr. Telfer showed how the abundance of different host species and the prevalence of different pathogenic species varied with land use in urban and rural regions. Mirroring earlier findings on mosquito-borne diseases, leptospira prevalence in small mammals was greater in irrigated rice fields, leading to higher infection exposure for rural workers, which could create a trade-off between economic development and public health.
The role of diverse land uses (beyond land cover) in generating complex patterns of zoonotic risk was illustrated by Dr. Sophie Vanwambeke (UCLouvain), in relation to tick-borne diseases. Dr. Vanwambeke highlighted the importance of distinguishing between hazard (presence of infectious vectors), exposure (contacts with hazard) and management capacity (detecting and controlling outbreaks). For example, even though ticks are more abundant in forests, landscape fragmentation and human activities have shifted the burden of exposure into open terrain.
Following on the theme of rural interfaces for zoonotic spillover, Harriet Bartlett (University of Cambridge) compared the risk factors across livestock farming systems. Although intensive livestock farming is often blamed for amplifying the risk of zoonotic pathogens (e.g., avian influenza virus) Barlett argued that it provides other benefits. In particular, intensive livestock production tends to have higher yields, which could reduce the total land required to meet a set level of demand. This could allow for widespread sparing of land for nature whilst decreasing the interface between wildlife, livestock and humans. Barlett highlighted key knowledge shortfalls that must be bridged before we can determine which types of systems carry the least risk.
Whilst there is no simple solution to reduce spillover risk through one-size-fits-all land use policies, our thematic session advocated an integrated approach that is mindful of people’s health, biodiversity and food security. The study and management of zoonotic risk has a key role to play in the development of a truly transdisciplinary Planetary Health movement, which integrates a “One Health” perspective into the research and management of human impacts on the environment and life on Earth.
Find out more about Ecology Across Borders 2021, the British Ecological Society’s joint Annual Meeting with the French Society for Ecology and Evolution (SFE²).
Dani Davis of Florida State University sheds light on the story behind her winning Capturing Ecology award photograph, and the complex and mysterious abilities of spider that acts like a cat.
Animals that can change their colour never cease to amaze; from dazzling cuttlefish to disappearing chameleons, these creatures captivate our interest. However, these more well-known species may be welcoming a new member to the colour-changing club, an emerald-green spider known as the green lynx (Peucetia viridans). Green lynx spiders seem to share in the ability to camouflage into their background by matching the colour of the flower on which they sit and wait to catch prey, but how and when these spiders change their colours is not well understood.
Late summer is a captivating time to walk through the forest in the green lynx’s native range, stretching across the southern United States and into Mexico. Plants are particularly stunning at this time; tall inflorescences shoot up to attract visitors, bright green leaves of pitcher plants abound, and a sea of yellows, white, and purples dot the landscape. It’s during this time of year when the green lynx spider is most apparent. The spiders are up high on vegetation, feeding on the pollinators that are actively visiting during this time. Looking around at spiders on different plant species, one begins to notice something strange. It appears that the adult spiders are blending into their plant backgrounds by changing their body colours.
Finding adult spiders in the field during summer is surprisingly easy. To us humans, the spiders are quite conspicuous. Their propensity to sit at the tops of plants, either holding tightly to flowering spikes, often hanging upside down, or nestled among the flower tops, makes them easy to spot. Deriving their common name from their hunting style, the green lynx is an active hunter, either pouncing on pollinators or chasing down a host of general insects that happen to cross the spider’s path. When the unlucky insect attracts the green lynx’s attention, the spider pounces on its prey, quickly injecting it with a potent venom capable of subduing large and cumbersome prey.
The spiders all share the same green body with little white chevrons running down their backs, but many have slightly different colours expressed on the sides and top of their abdomens. Their voracious appetite and the ability to change colour to match their plant background would be helpful for them to either hide from predators or their prey. This ability has been noted in natural history observations and the spider literature but has not been well studied and is far from being understood.
The ability to change colour is relatively rare in spiders. It has been noted that some orb weavers and at least six species of crab spiders may change their colour in response to their flower background. The green lynx could add another species to this small list of colour-changing spiders, but more work is needed to confirm this. A study from Robertson et al. (1994) noted that pregnant green lynx spiders might change their colour to match green, purple, and white background over 16 days. But very little is known about the how the spiders shift from their basic green and white colours to match the complex colour patterns found in flowers.
In research conducted at Florida State University under the direction of Dr. Tom Miller, we have been investigating to what extent there is colour variation in the green lynx, along with its ability to colour change with both observational and manipulative studies in the lab. First off, we need to assess whether green lynx spiders match their flower backgrounds in the field, we collected 38 spiders from the Apalachicola National Forest in Florida. These spiders were collected from three distinct colour backgrounds: purple flowers (Liatris spicata), white flowers (Eupatorium altissimum), and bright green leaves (Sarracenia flava), taken back to the lab, and photographed.
To get an accurate representation of the spiders’ colouration, we used a new method – the Colormesh pipeline – which begins by standardising the spider abdomens’ shapes using the geometric morphometrics software TPS Series. The software works by contouring all of the spider’s bodies to be the same shape through the placing of landmarks on the image around the abdomen. Then, each image is fit with an array of 1515 triangles that covered the body of the spider and measured for red, green, and blue colour values. These data are then used to investigate the specific, complex colour patterns for individual spiders and to correlate these patterns with the plant background on which the spider was found.
The results from the colour analysis show that there is significant variation in the green colouration, specifically between spiders collected on different backgrounds. Colour differs between spiders, primarily around the chevrons running down the spider’s abdomen, where the presence or absence of green colouration was noted. From this study of colour matching in the field, it is clear that the background flower colour affects the colour of the spider’s abdomen.
What is less clear, however, is how and when these spiders change their colour. We therefore wanted to see if spiders taken from a plant of one colour (purple, white, or green) could then change their colour to match a new background colour (purple, white, or green). Spiders were again collected from the Apalachicola National Forest and taken back to the lab. This was a full reciprocal experiment, with replicate spiders from each original background being placed into both their original and all possible novel backgrounds. These experimental spiders were then photographed at two weeks and four weeks to explore whether colour change occurred. The results from this study are still being explored and will hopefully shed more light on the potential ability of the green lynx to change their colour in response to the plant on which they sit.
The mystery of the green lynx’s cryptic colour-changing ability is far from solved. Though it has been shown that there is a definite difference between spider colouration on different plants in the field, mysteries still abound. It is still unknown how the spiders change their colour, what triggers may be associated with this, and whether this is an ability they can use to switch between different plants. The ecological implications are another area of interest in the natural communities where this spider thrives. The green lynx is a voracious predator of pollinators on the plants where they sit and wait for prey, so this camouflage ability of the lynx could negatively affect the plant if the spider a significant number of its pollinators.
It is still unknown whether the green lynx will be known as another species that can actively change their colour in a way that allows it to move from flower to flower. There is still plenty to be learned about this species and what their colourful appearances mean for their ecology and for the plants, pollinators, and predators in their communities. They’re a beautiful species with many secrets left to explore.
Natalia Cristina García del Museo Argentino de Ciencias Naturales nos lleva en un viaje al espacio y al centro de una pluma para explicar cómo la naturaleza crea colores ultra-reflectivos.
El título que elegí para este blog es un juego de palabras con una de mis historias favoritas de H.P. Lovecraft, El color del espacio, publicado originalmente en 1927. Me encanta encontrar pequeñas conexiones entre los temas que investigo y todo lo relacionado con la cultura popular, y cuando comencé a estudiar de la evolución del color en las aves, inmediatamente se me vino a la mente la historia de Lovecraft sobre un color nuevo y desconocido que llegó del espacio exterior. Debido a ciertas propiedades de los ojos de las aves, su percepción del color es bastante diferente a la nuestra, incluido el hecho de que muchas especies de aves pueden ver la luz ultravioleta, por lo que perciben colores que ningún ser humano ha visto jamás.
Otro aspecto que me fascina son los diferentes mecanismos involucrados en la elaboración de la coloración del plumaje, permitiendo que las aves produzcan una increíble variedad de tonalidades. Los plumajes azules, por ejemplo, son el resultado de la interacción de los rayos de luz con nanoestructuras dentro de las barbas de las plumas. Estas barbas contienen una estructura esponjosa, que consiste en burbujas de aire sumergidas en una matriz de queratina. Dada la forma en que estas burbujas están organizadas espacialmente, los rayos de luz de longitud de onda corta y muy corta son reflejados preferentemente por la superficie de la pluma, mientras que otras longitudes de onda son canceladas o absorbidas por una capa de melanina ubicada debajo de la matriz esponjosa. Me fascinó tanto la idea de que los colores se originaran en el nanoespacio dentro de la pluma, que ayudé a mi colega y amiga Ana Barreira a estudiar la coloración de la Tersina (Tersina viridis) para su tesis doctoral, como un proyecto paralelo mientras estaba haciendo mi propio doctorado. Este hermoso pájaro se puede encontrar posado en lo alto de los árboles de la selva atlántica en América del Sur. Dorsalmente, los machos de esta especie se ven azules o azul verdoso claro dependiendo de la posición relativa del observador y la fuente de luz.
Más recientemente, nos interesamos en estudiar las plumas blancas en el lado ventral de los machos de Tersina. Las plumas blancas en muchas especies tienen una matriz de queratina y aire dentro de sus barbas, pero esta matriz carece de organización estructural, lo que lleva a una dispersión de luz independiente de la longitud de onda. Este podría haber sido el caso de las plumas blancas de la Tersina, pero supusimos que encontraríamos algo diferente. Hace más de una década, colegas de otro laboratorio compararon una pluma azul de un individuo normal de Chara Copetona (Cyanocitta stelleri) con una pluma blanca de un individuo amelanótico de la misma especie (un individuo que tuvo un plumaje de color normal y luego mudó a un plumaje completamente blanco). Descubrieron que las barbas de ambas plumas contenían la estructura esponjosa normal y bien formada que se esperaba que produjera una coloración azul. Sin embargo, la falta de melanina fue la clave de la coloración del individuo blanco. De manera análoga, imaginamos que las plumas blancas de la Tersina carecerían de melanina pero no diferirían drásticamente de las plumas azules en su nanoestructura.
Con colegas del Museo Argentino de Ciencias Naturales y del Departamento de Física de la Universidad de Buenos Aires, exploramos cómo la nanoestructura de las plumas se combina con otros elementos (pigmentos y forma de las barbas) en los plumajes de diferentes colores de la Tersina. Examinamos la morfología de las plumas de color azul verdoso de la espalda y las plumas blancas del vientre de esta especie, y medimos la reflectancia de luz de ambos tipos de plumas. Primero notamos que las plumas del vientre no son uniformemente blancas, sino que tienen un toque de color azul verdoso claro en sus puntas. Curiosamente, encontramos que ambos parches de plumaje tienen un pico de reflectancia de luz alrededor de 550 nm (percibido justamente como un tono azul verdoso por los humanos), pero este pico es mucho menos intenso en el vientre. Y, como esperábamos, encontramos que las barbas de las plumas azules y blancas tienen matrices esponjosas similares en sus puntas, en consonancia con sus espectros de reflectancia similares. ¿Por qué se ven tan diferentes entonces? Las principales diferencias entre las plumas azules y blancas no es la organización de la matriz esponjosa en si, sino su distribución (uniforme a través de las barbas de las plumas azules, reducidas hacia el raquis o eje central de la pluma en las plumas blancas) y la falta total de melanina en las plumas blancas.
Desde el punto de vista del desarrollo de un individuo, esto es interesante porque todavía no sabemos mucho sobre cómo las aves logran producir plumas de diferentes colores en sus cuerpos. Nuestros resultados contribuyen a la idea de que grandes diferencias de color, como entre azul y blanco, no requieren cambios drásticos en la nanoestructura interna que refleja la luz, sino que pueden lograrse mediante la regulación de la deposición de pigmentos y/o de la proporción de matriz esponjosa presente. Desde una perspectiva evolutiva, todavía estamos tratando de comprender si el color de las aves comunica información sobre su calidad individual a los competidores y posibles parejas y cómo lo hace. Una idea muy extendida es que la producción de colores brillantes y llamativos puede resultar costosa. Sin embargo, creo que ciertas líneas de evidencia desafían esta idea. Por ejemplo, sabemos que las plumas negras en algunas subespecies de Maluros (Malurus sp.) contienen altas cantidades de melanina enmascarando una nanoestructura que produciría la misma coloración azul que exhiben otras poblaciones de la misma especie. Esto me hace pensar, si la matriz esponjosa de las plumas es costosa de producir, ¿por qué “desperdiciarla” en plumas que terminarían luciendo blancas o negras por falta o exceso de melanina? Nuestros resultados, junto con otros estudios, señalan que el contenido de melanina puede cambiar rápidamente entre poblaciones, especies y parches de plumaje, lo que sugiere que estos pigmentos son clave para comprender la diversidad de colores observados en las aves, incluidas aquellas cuya producción se atribuye a nanoestructuras.
Natalia Cristina García from the Museo Argentino de Ciencias Naturales takes us on a journey into space and into the centre of a feather to explain how ultra-reflective colours are created by nature.
The title I chose for this blog is a word play with one of my favourite stories by H. P. Lovecraft, The colour out of space, originally published in 1927. I love finding small connections between the topics I research and anything pop-culture related, and when I first approached the study of colour evolution in birds, Lovecraft’s story about a new, unknown colour that arrived from outer space immediately came to my mind. Due to certain properties of birds’ eyes, their colour perception is quite different from ours, including the fact that many bird species can see ultraviolet light, thus perceiving colours no human has ever seen.
Another fact that fascinates me is the very different mechanisms that can be involved in the elaboration of plumage colouration, allowing birds to produce an incredible variety of hues. Blue plumages, for example, result from the interaction of rays of light with nanostructures inside the feather barbs. These barbs contain a spongy matrix, consisting of air bubbles immersed in a keratin matrix. Given the way these bubbles are spatially organised, light rays of short and very short wavelength are preferentially reflected by the feather surface, while other wavelengths are cancelled or absorbed by a layer of melanin pigments located below the spongy matrix.
I loved the idea of colours originating in the nano-space within the feather so much that I helped my colleague and friend Ana Barreira to study the colouration of the Swallow Tanager (Tersina viridis) for her PhD thesis, as a side project while I was doing my own PhD. This beautiful passerine can be found perching high in the trees of the Atlantic rainforest in South America. Dorsally, males of this species look either blue or light greenish-blue depending on the relative position of the observer and the light source.
More recently, we became curious about the white feathers in the ventral side of male swallow tanagers. White feathers in many species have a matrix of keratin and air within their barbs, but this matrix lacks any structural organisation, leading to a wavelength-independent scattering of light. This could have been the case of the white feathers of the swallow tanager, but we predicted we would find something different. More than a decade ago, colleagues from another lab compared a blue feather of a normal individual of Stellar’s Jay with a white feather from an amelanotic individual (an individual that had normal coloured plumage and then molted into an entire white plumage) of the same species. They found that the barbs of both feathers contained the expected normal, well-formed spongy structure that would produce a blue colouration. However, the lack of melanin was the key to the white colouration of the white individual. In an analogous way, we imagined the white feathers of the swallow tanager would lack melanin but would not differ dramatically in nanostructure from blue feathers.
With colleagues from the Museo Argentino de Ciencias Naturales and the Physics Department of the Universidad de Buenos Aires, we explored how feather nanostructure is combined with other elements (pigments and barb shape) in differently coloured plumage patches of the Swallow Tanager. We looked into the morphology of the greenish-blue feathers from the bird’s back and the white feathers from the belly, and measured light reflectance from both types of feathers. We first noticed that belly feathers are not uniformly white, but have a hint of light greenish blue colouration in their tips. Interestingly, we found that both plumage patches have a light reflectance peak around 550 nm (perceived as a greenish blue hue by humans), but this is much less intense in the belly. And, as we expected, we found that the barbs of both blue and white feathers have similar spongy matrices at their tips, consistent with their similar reflectance spectra. Why do they look so different then? The main differences between blue and white feathers was not the organization itself of the spongy matrix but its distribution (uniform across the barbs of blue feathers, reduced towards the rachis or central stem of the feather in the white feathers) and the lack of melanin pigments in the white feathers.
From a developmental point of view, this is interesting because we still do not know much about how birds manage to produce differently coloured feathers in their bodies. Our results contribute to the idea that drastic colour differences such as blue versus white do not require drastic changes in the internal nanostructures from which light is reflected, but instead these may be achieved through the regulation of pigment deposition and/or of the proportion of spongy matrix present. From an evolutionary perspective, we are still trying to understand if and how birds communicate information about their individual quality to competitors and potential mates. A widespread idea is that bright, conspicuous colours may be costly to produce. However, I think certain lines of evidence challenge this idea. For instance, we know that black feathers in some fairy-wren subspecies contain high quantities of melanin masking a nano-structure that would produce the same blue coloration exhibited by other populations of the same species. This makes me think, if feather nano-structure is costly to produce, why “waste” it in feathers that would end up looking white or black due to a lack or an excess of melanin? Our results, together with other studies, point at melanin content as rapidly changing between populations, species and plumage patches, suggesting that these pigments are key to understanding the diversity of colours observed in birds, including those whose production is attributed to nanostructures.