Many studies have shown how pigments and internal nanostructures generate color in nature. External surface structures can also influence appearance, such as by causing multiple scattering of light ...(structural absorption) to produce a velvety, super black appearance. Here we show that feathers from five species of birds of paradise (Aves: Paradisaeidae) structurally absorb incident light to produce extremely low-reflectance, super black plumages. Directional reflectance of these feathers (0.05-0.31%) approaches that of man-made ultra-absorbent materials. SEM, nano-CT, and ray-tracing simulations show that super black feathers have titled arrays of highly modified barbules, which cause more multiple scattering, resulting in more structural absorption, than normal black feathers. Super black feathers have an extreme directional reflectance bias and appear darkest when viewed from the distal direction. We hypothesize that structurally absorbing, super black plumage evolved through sensory bias to enhance the perceived brilliance of adjacent color patches during courtship display.
When a measure becomes a target, it often ceases to be a good measure – an effect familiar from the declining usefulness of standardized testing in schools. This economic principle also applies to ...mate choice and, perhaps surprisingly, pregnancy. Just as females screen potential mates under many metrics, human mothers unconsciously screen embryos for quality. ‘Examinees’ are under intense selection to improve test performance by exaggerating formerly ‘honest’ signals of quality. Examiners must change their screening criteria to maintain useful information (but cannot abandon old criteria unilaterally). By the resulting ‘proxy treadmill’, new honest indicators arise while old degraded indicators linger, resulting in trait elaboration and exaggeration. Hormone signals during pregnancy show extreme evolutionary escalation (akin to elaborate mating displays).
Mate choice by honest signaling is a classic explanation for elaborate traits in nature. Many researchers have: (i) observed deceptive signaling, and (ii) wondered how honest signals relate to trait elaboration.Honest signaling is analogous to high-stakes testing. Quality is hard to measure directly, so proxies (tests) are used. High-stakes testing causes ‘teaching to the test’ without improving educational outcomes.Embryo choice is another high-stakes test. Mothers select healthy embryos and terminate sub-par embryos automatically. Embryos are selected to pass maternal tests without improving their quality. The resulting arms race causes extreme and elaborate signals during pregnancy.We can better understand elaborate traits in nature if we interpret mate selection, and embryo choice, as a dynamic give-and-take between two parties with conflicting fitness interests.
Modern medicine has revolutionized family planning. Remarkably, women11Authors' note: Many people who make use of ART belong to the LGBTQ+ community. The authors note that, while the word “woman” is ...used in this article to describe pregnant people and those who produce ova, people of various gender identities could provide an ovum and/or gestate a pregnancy. can carry to term embryos with whom they share no genetic connection, a feat made possible through egg donation and/or gestational surrogacy. Our reproductive systems evolved to accommodate embryos that are 50% related to the carrier, not 0% related. Here, we apply evolutionary theory to explain how and why pregnancy is riskier with an unrelated embryo. When a woman gestates an unrelated embryo, she is significantly more likely to develop preeclampsia and other diseases above and beyond the known risks associated with advanced maternal age, IVF, multiple gestation, and subfertility. Such “allogeneic pregnancies” are riskier even in fertile, healthy, commercial surrogates and when the egg is donated by a young, healthy donor. We propose that unrelated embryos present a special immune challenge to the gestational carrier, because they have fewer matching genes to the maternal body—therefore exacerbating symptoms of evolutionary maternal-fetal conflict. Indeed, maternal risks seem lower when the embryo is more related to the carrier, e.g., if a sister donates the egg. Finally, we discuss microchimerism in egg donation pregnancies, whereby wholly foreign cells pass from mother to embryo and vice-versa. We conclude with several medical proposals. First, egg donors and surrogates should be informed of the increased health risks they would face. In considerations of risk, these young, fertile women should not be compared to older, infertile women undergoing IVF; the proper comparison group is other young, fertile women. Second, contrary to some medical advice, perhaps genetically-related egg donors and surrogates should be preferred, all else equal. An immunological matching scheme, like what is used for organ transplants, could improve surrogate pregnancy outcomes. Third, more research is needed on microchimerism, sperm exposure, and the long-term impacts of allogeneic pregnancies on maternal and child health.
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•Women can carry to term embryos to whom they are genetically unrelated, an evolutionary mismatch.•Pregnancy using an egg donor or gestational surrogate carries greater risks, i.e., when the embryo is unrelated to the carrier.•Hypertensive disorders and various placental pathologies are more likely in young and healthy carriers of unrelated embryos.•Surrogates and egg donors should be told of the increased risks they face compared to other similarly fertile, young women.•Evolutionary theory can inform future medical research in the field of assisted reproductive technology.
Brilliantly-colored birds are a model system for research into evolution and sexual selection. Red, orange, and yellow carotenoid-colored plumages have been considered honest signals of condition; ...however, sex differences in feather pigments and microstructures are not well understood. Here, we show that microstructures, rather than carotenoid pigments, seem to be a major driver of male-female color differences in the social, sexually-dimorphic tanager genus Ramphocelus. We comprehensively quantified feather (i) color (using spectrophotometry), (ii) pigments (using liquid chromatography-mass spectrometry (LC-MS)), and (iii) microstructures (using scanning electron microscopy (SEM) and finite-difference time-domain (FDTD) optical modeling). Males have significantly more saturated color patches than females. However, our exploratory analysis of pigments suggested that males and females have concordant carotenoid pigment profiles across all species (MCMCglmm model, female:male ratio = 0.95). Male, but not female, feathers have elaborate microstructures which amplify color appearance. Oblong, expanded feather barbs in males enhance color saturation (for the same amount of pigment) by increasing the transmission of optical power through the feather. Dihedral barbules (vertically-angled, strap-shaped barbules) in males reduce total reflectance to generate "super black" and "velvet red" plumage. Melanin in females explains some, but not all, of the male-female plumage differences. Our results suggest that a widely cited index of honesty, carotenoid pigments, cannot fully explain male appearance. We propose that males are selected to evolve amplifiers-in this case, microstructures that enhance appearance-that are not necessarily themselves linked to quality.
When a measure becomes a target, it ceases to be a good measure. For example, when standardized test scores in education become targets, teachers may start "teaching to the test," leading to ...breakdown of the relationship between the measure - test performance - and the underlying goal - quality education. Similar phenomena have been named and described across a broad range of contexts, such as economics, academia, machine learning, and ecology. Yet it remains unclear whether these phenomena bear only superficial similarities, or if they derive from some fundamental unifying mechanism. Here, we propose such a unifying mechanism, which we label
. We first review illustrative examples and their labels, such as the "cobra effect," "Goodhart's law," and "Campbell's law." Second, we identify central prerequisites and constraints of proxy failure, noting that it is often only a partial failure or
. We argue that whenever incentivization or selection is based on an imperfect proxy measure of the underlying goal, a pressure arises that tends to make the proxy a worse approximation of the goal. Third, we develop this perspective for three concrete contexts, namely neuroscience, economics, and ecology, highlighting similarities and differences. Fourth, we outline consequences of proxy failure, suggesting it is key to understanding the structure and evolution of goal-oriented systems. Our account draws on a broad range of disciplines, but we can only scratch the surface within each. We thus hope the present account elicits a collaborative enterprise, entailing both critical discussion as well as extensions in contexts we have missed.
Sustainable cities depend on urban forests. City trees-pillars of urban forests-improve our health, clean the air, store CO
, and cool local temperatures. Comparatively less is known about city tree ...communities as ecosystems, particularly regarding spatial composition, species diversity, tree health, and the abundance of introduced species. Here, we assembled and standardized a new dataset of
= 5,660,237 trees from 63 of the largest US cities with detailed information on location, health, species, and whether a species is introduced or naturally occurring (i.e., "native"). We further designed new tools to analyze spatial clustering and the abundance of introduced species. We show that trees significantly cluster by species in 98% of cities, potentially increasing pest vulnerability (even in species-diverse cities). Further, introduced species significantly homogenize tree communities across cities, while naturally occurring trees (i.e., "native" trees) comprise 0.51-87.4% (median = 45.6%) of city tree populations. Introduced species are more common in drier cities, and climate also shapes tree species diversity across urban forests. Parks have greater tree species diversity than urban settings. Compared to past work which focused on canopy cover and species richness, we show the importance of analyzing spatial composition and introduced species in urban ecosystems (and we develop new tools and datasets to do so). Future work could analyze city trees alongside sociodemographic variables or bird, insect, and plant diversity (e.g., from citizen-science initiatives). With these tools, we may evaluate existing city trees in new, nuanced ways and design future plantings to maximize resistance to pests and climate change. We depend on city trees.
Structurally assisted super black in colourful peacock spiders McCoy, Dakota E; McCoy, Victoria E; Mandsberg, Nikolaj K ...
Proceedings - Royal Society. Biological sciences/Proceedings - Royal Society. Biological Sciences,
05/2019, Letnik:
286, Številka:
1902
Journal Article
Recenzirano
Odprti dostop
Male peacock spiders ( Maratus, Salticidae) compete to attract female mates using elaborate, sexually selected displays. They evolved both brilliant colour and velvety black. Here, we use scanning ...electron microscopy, hyperspectral imaging and finite-difference time-domain optical modelling to investigate the deep black surfaces of peacock spiders. We found that super black regions reflect less than 0.5% of light (for a 30° collection angle) in Maratus speciosus (0.44%) and Maratus karrie (0.35%) owing to microscale structures. Both species evolved unusually high, tightly packed cuticular bumps (microlens arrays), and M. karrie has an additional dense covering of black brush-like scales atop the cuticle. Our optical models show that the radius and height of spider microlenses achieve a balance between (i) decreased surface reflectance and (ii) enhanced melanin absorption (through multiple scattering, diffraction out of the acceptance cone of female eyes and increased path length of light through absorbing melanin pigments). The birds of paradise (Paradiseidae), ecological analogues of peacock spiders, also evolved super black near bright colour patches. Super black locally eliminates white specular highlights, reference points used to calibrate colour perception, making nearby colours appear brighter, even luminous, to vertebrates. We propose that this pre-existing, qualitative sensory experience-'sensory bias'-is also found in spiders, leading to the convergent evolution of super black for mating displays in jumping spiders.
Personality traits are important because they can affect individual survival as well as how a population may respond to environmental change. How these traits arise, whether they are maintained ...throughout ontogeny, and how environmental factors differentially affect them throughout life is poorly understood. Understanding these pathways is important for determining the function and evolution of animal personality. We examined the development of two commonly studied personality traits, boldness and docility, in a long-term study of yellow-bellied marmots, Marmota flaviventris. Using data collected between 2002 and 2011, we quantified the repeatability within three age groups (juveniles, yearlings and adults), the correlation between age classes, and the behavioural syndromes of these two traits within the three life stages. We quantified boldness through flight initiation distance (FID) tests, and we quantified docility through marmots' response to being trapped. We found that boldness was repeatable only in yearlings, but docility was repeatable in all age classes. We also found that juvenile docility predicted later docility. We also found no behavioural syndrome between boldness and docility in any life stage. This suggests an adaptive hypothesis: that these personality traits develop independently and at potentially age-appropriate times. Thus, the development of personality traits may facilitate animal's coping with age-dependent requirements and constraints.
•We examined the development of two personality traits, boldness and docility, in yellow-bellied marmots.•Boldness was not a personality trait in juveniles, but was in yearlings and adults.•Docility was a personality trait in each age class.•Juvenile docility levels predicted older levels of docility.•There was no behavioural syndrome between docility and boldness in any age class.
•Living creatures use micro- and nano-scale structures to manipulate light (e.g., for antireflection, maximal reflection, iridescent coloration, and efficient photosynthesis).•Optical simulations can ...help explore the frontier of micro- and nano-scale biodiversity, gain insights into colorful signals and sexual selection, identify evolutionary innovations across environments, and guide the design of new technologies inspired by natural structures.•The finite-difference time-domain (FDTD) method is a powerful numerical modeling technique to study how light interacts with materials, allowing researchers to obtain reflection, transmission, diffraction, absorption, and more.•FDTD is a good choice of method for researchers who wish to simulate a naturalistic broadband light source, study complicated structures that cannot easily be analyzed through analytical optical theory alone, conduct parameter sweeps over structures of interest, and test potential bio-inspired applications.•FDTD is often used in conjunction with experimental techniques to probe how organisms’ structures produce a variety of optical effects, and the workflow is accessible to researchers from many different backgrounds.
Light influences most ecosystems on earth, from sun-dappled forests to bioluminescent creatures in the ocean deep. Biologists have long studied nano- and micro-scale organismal adaptations to manipulate light using ever-more sophisticated microscopy, spectroscopy, and other analytical equipment. In combination with experimental tools, simulations of light interacting with objects can help researchers determine the impact of observed structures and explore how variations affect optical function. In particular, the finite-difference time-domain (FDTD) method is widely used throughout the nanophotonics community to efficiently simulate light interacting with a variety of materials and optical devices. More recently, FDTD has been used to characterize optical adaptations in nature, such as camouflage in fish and other organisms, colors in sexually-selected birds and spiders, and photosynthetic efficiency in plants. FDTD is also common in bioengineering, as the design of biologically-inspired engineered structures can be guided and optimized through FDTD simulations. Parameter sweeps are a particularly useful application of FDTD, which allows researchers to explore a range of variables and modifications in natural and synthetic systems (e.g., to investigate the optical effects of changing the sizes, shape, or refractive indices of a structure). Here, we review the use of FDTD simulations in biology and present a brief methods primer tailored for life scientists, with a focus on the commercially available software Lumerical FDTD. We give special attention to whether FDTD is the right tool to use, how experimental techniques are used to acquire and import the structures of interest, and how their optical properties such as refractive index and absorption are obtained. This primer is intended to help researchers understand FDTD, implement the method to model optical effects, and learn about the benefits and limitations of this tool. Altogether, FDTD is well-suited to (i) characterize optical adaptations and (ii) provide mechanistic explanations; by doing so, it helps (iii) make conclusions about evolutionary theory and (iv) inspire new technologies based on natural structures.
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