What drives the evolution of body size in ectotherms? A global analysis across the amphibian tree of life

Aim

The emergence of large-scale patterns of animal body size is the central expectation of a wide range of (macro)ecological and evolutionary hypotheses. The drivers shaping these patterns include climate (e.g. Bergmann's rule), resource availability (e.g. ‘resource rule’), biogeographic settings and niche partitioning (e.g. adaptive radiation). However, these hypotheses often make opposing predictions about the trajectories of body size evolution. Therefore, whether underlying drivers of body size evolution can be identified remains an open question. Here, we employ the most comprehensive global dataset of body size in amphibians, to address multiple hypotheses that predict patterns of body size evolution based on climatic factors, ecology and biogeographic settings to identify underlying drivers and their generality across lineages.

Location

Global.

Time Period

Present.

Major Taxa Studied

Amphibians.

Methods

Using a global dataset spanning 7270 (>87% of) species of Anura, Caudata and Gymnophiona, we employed phylogenetic Bayesian modelling to test the roles of climate, resource availability, insularity, elevation, habitat use and diel activity on body size.

Results

Only climate and elevation drive body size patterns, and these processes are order-specific. Seasonality in precipitation and in temperature predict body size clines in anurans, whereas caecilian body size increases with aridity. However, neither of these drivers explained variation in salamander body size. In both anurans and caecilians, size increases with elevational range and with midpoint elevation in caecilians only. No effects of mean temperature, resource abundance, insularity, time of activity or habitat use were found.

Main Conclusions

Precipitation and temperature seasonality are the dominant climatic drivers of body size variation in amphibians overall. Bergmann's rule is consistently rejected, and so are other alternative hypotheses. We suggest that the rationale sustaining existing macroecological rules of body size is unrealistic in amphibians and discuss our findings in the context of the emerging hypothesis that climate change can drive body size shifts.     

Ultraviolet and carotenoid‐based coloration in the viviparous lizard Zootoca vivipara (Squamata: Lacertidae) in relation to age,sex, and morphology

Lizards display structural and pigment‐based colorations, and their visual system is sensitive to wavelengths of 300–700 nm. However, few studies in squamate reptiles have quantified interindividual colour variation that includes the structural ultraviolet (UV) component (300–400 nm). In the present study, we investigated variability of a ventral UV/yellow–red ornamentation in the common lizard Zootoca vivipara, including an analysis of spatial distribution, as well as sex and age differences. We also investigated whether the expression of coloration is related to body size and condition. Our analyses revealed two distinct patches: a gular patch with a strong UV reflectance and a belly patch with a dominant yellow–red reflectance. Males displayed a less saturated throat coloration with higher UV chroma and UV hue, and had a redder but duller belly coloration than females. Yearlings had less elaborate ornaments than adults, although they already displayed a yellow–red sexual dichromatism on the belly. UV sexual dichromatism was only apparent in adults as a result of a weaker UV reflectance in females, suggesting potential fitness costs of a bright UV coloration in that sex. Different colour traits were related to body size in both sexes, as well as to body condition in males. We discuss the potential evolutionary scenarios leading to the maintenance of this ornament in common lizards. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 128–141.     

Variability in Avian Eggshell Colour: A Comparative Study of Museum Eggshells

Background

The exceptional diversity of coloration found in avian eggshells has long fascinated biologists and inspired a broad range of adaptive hypotheses to explain its evolution. Three main impediments to understanding the variability of eggshell appearance are: (1) the reliable quantification of the variation in eggshell colours; (2) its perception by birds themselves, and (3) its relation to avian phylogeny. Here we use an extensive museum collection to address these problems directly, and to test how diversity in eggshell coloration is distributed among different phylogenetic levels of the class Aves.

Methodology and Results

Spectrophotometric data on eggshell coloration were collected from a taxonomically representative sample of 251 bird species to determine the change in reflectance across different wavelengths and the taxonomic level where the variation resides. As many hypotheses for the evolution of eggshell coloration assume that egg colours provide a communication signal for an avian receiver, we also modelled reflectance spectra of shell coloration for the avian visual system. We found that a majority of species have eggs with similar background colour (long wavelengths) but that striking differences are just as likely to occur between congeners as between members of different families. The region of greatest variability in eggshell colour among closely related species coincided with the medium-wavelength sensitive region around 500 nm.

Conclusions

The majority of bird species share similar background eggshell colours, while the greatest variability among species aligns with differences along a red-brown to blue axis that most likely corresponds with variation in the presence and concentration of two tetrapyrrole pigments responsible for eggshell coloration. Additionally, our results confirm previous findings of temporal changes in museum collections, and this will be of particular concern for studies testing intraspecific hypotheses relating temporal patterns to adaptation of eggshell colour. We suggest that future studies investigating the phylogenetic association between the composition and concentration of eggshell pigments, and between the evolutionary drivers and functional impacts of eggshell colour variability will be most rewarding.     

Beyond latitude: Temperature,productivity and thermal niche conservatism drive global body size variation in Odonata

Aim

So far, latitudinal body size clines have been discussed primarily in the context of thermoregulation, sensu Bergmann. However, body size patterns are ambiguous in ectotherms, and this heterogeneity remains poorly understood. We tested whether Bergmann's rule and the resource availability rule, which states that energetic requirements determine species body size, apply to damselflies and dragonflies (Odonata). Furthermore, we hypothesized that the contrasting effects of thermoregulation and resource availability (e.g., productivity) can obscure the overall gradient in body size variation.

Location

Global.

Time period

Contemporary.

Major taxa studied

Odonata.

Methods

Using data for 43% of all odonate species described so far, we tested our hypotheses in phylogenetically and spatially comparative analyses at assemblage and species levels. For the distribution data, we integrated expert range maps and ecoregional ranges based on all available occurrence records. To distinguish between long-term and evolutionarily recent responses of environmental drivers in body size, we constructed a phylogenetically informed classification of all odonate species and decomposed the body size into its phylogenetic and specific components for our subset of species.

Results

We documented a weak positive relationship between body length and latitude but found strong and contrasting effects for temperature between dragonflies and damselflies and consistent positive effects for productivity that explained 35–57% of body size variation. Moreover, we showed a strong phylogenetic signal in sized-based thermoregulation that shaped the distribution of dragonflies, but not of damselflies.

Main conclusions

We concluded that temperature, productivity and conservatism in size-based thermoregulation synergistically determine the distribution of ectotherms, while the taxon-specific importance of these factors can lead to contrasting and weak latitude–size relationships. Our results reinforce the importance of body size as a determinant of species distributions and responses to climate change.     

Temperature,but Not Available Energy,Affects the Expression of a Sexually Selected Ultraviolet (UV) Colour Trait in Male European Green Lizards

Background

Colour signals are widely used in intraspecific communication and often linked to individual fitness. The development of some pigment-based (e.g. carotenoids) colours is often environment-dependent and costly for the signaller, however, for structural colours (e.g. ultraviolet [UV]) this topic is poorly understood, especially in terrestrial ectothermic vertebrates.

Methodology/Principal Findings

In a factorial experiment, we studied how available energy and time at elevated body temperature affects the annual expression of the nuptial throat colour patch in male European green lizards (Lacerta viridis) after hibernation and before mating season. In this species, there is a female preference for males with high throat UV reflectance, and males with high UV reflectance are more likely to win fights. We found that (i) while food shortage decreased lizards'' body condition, it did not affect colour development, and (ii) the available time for maintaining high body temperature affected the development of UV colour without affecting body condition or other colour traits.

Conclusions/Significance

Our results demonstrate that the expression of a sexually selected structural colour signal depends on the time at elevated body temperature affecting physiological performance but not on available energy gained from food per se in an ectothermic vertebrate. We suggest that the effect of high ambient temperature on UV colour in male L. viridis makes it an honest signal, because success in acquiring thermally favourable territories and/or effective behavioural thermoregulation can both be linked to individual quality.     

Environmental correlates of body size influence range size and extinction risk: A global study in rodents

Aim

Species-level traits, such as body and range sizes, are important correlates of extinction risk. However, both are often related and are driven by environmental factors. Here, we elucidated links between environmental factors, body size, range size and susceptibility to extinction, across the whole order of rodents.

Location

Global.

Time period

Current.

Major taxa studied

Rodents (order Rodentia).

Methods

We compiled an unprecedentedly large database of rodent morphology, phylogeny, range size, conservation status, global climate and normalized difference vegetation index (NDVI), comprising >86% of all described species. Using phylogenetic regressions, we initially explored the environmental factors driving body size. Next, we modelled the relationship between body size and range size. From this relationship, we computed and mapped (at the assemblage level) an index of relative range size, corresponding to the deviation from the expected range size of each species, given its body size. Finally, we tested whether relative range was correlated with the risk of extinction of the species derived from an assessment by the International Union for Conservation of Nature.

Results

We found that, contrary to the expectations of Bergmann's rule, the body size of rodents was mostly influenced by variation in NDVI (rather than latitude/temperature). Body size, in turn, imposed a constraint on species range size, as evidenced by a triangular relationship that was segmented at the lower bound. The relative species range size derived from this relationship highlighted four geographical regions where rodents with small relative range were concentrated globally. We demonstrated that lower relative range size was associated with increased risk of extinction.

Main conclusions

Species that, given their body size, are distributed across ranges that are smaller than expected have elevated extinction risk. Therefore, investigating the relationships between environmental drivers, body size and range size might help to detect species that could become threatened in the near future.     

Comparison of multivariate methods for estimating soil total nitrogen with visible/near-infrared spectroscopy

Aims

This study aimed to compare stepwise multiple linear regression (SMLR), partial least squares regression (PLSR) and support vector machine regression (SVMR) for estimating soil total nitrogen (TN) contents with laboratory visible/near-infrared reflectance (Vis/NIR) of selected coarse and heterogeneous soils. Moreover, the effects of the first (1st) vs. second (2nd) derivative of spectral reflectance and the importance wavelengths were explored.

Methods

The TN contents and the Vis/NIR were measured in the laboratory. Several methods were employed for Vis/NIR data pre-processing. The SMLR, PLSR and SVMR models were calibrated and validated using independent datasets.

Results

Results showed that the SVMR and the PLSR models had similar performances, and better performances than the SMLR. The spectral bands near 1450, 1850, 2250, 2330 and 2430 nm in the PLSR model were important wavelengths. In addition, the 1st derivative was more appropriate than the 2nd derivative for spectral data pre-processing.

Conclusions

PLSR was the most suitable method for estimating TN contents in this study. SVMR may be a promising technique, and its potential needs to be further explored. Moreover, the future studies using outdoor and airborne/satellite hyperspectral data for estimating TN content are necessary for testing the findings.     

Seasonal Changes in Colour: A Comparison of Structural,Melanin- and Carotenoid-Based Plumage Colours

Background

Plumage coloration is important for bird communication, most notably in sexual signalling. Colour is often considered a good quality indicator, and the expression of exaggerated colours may depend on individual condition during moult. After moult, plumage coloration has been deemed fixed due to the fact that feathers are dead structures. Still, many plumage colours change after moult, although whether this affects signalling has not been sufficiently assessed.

Methodology/Principal Findings

We studied changes in coloration after moult in four passerine birds (robin, Erithacus rubecula; blackbird, Turdus merula; blue tit, Cyanistes caeruleus; and great tit, Parus major) displaying various coloration types (melanin-, carotenoid-based and structural). Birds were caught regularly during three years to measure plumage reflectance. We used models of avian colour vision to derive two variables, one describing chromatic and the other achromatic variation over the year that can be compared in magnitude among different colour types. All studied plumage patches but one (yellow breast of the blue tit) showed significant chromatic changes over the year, although these were smaller than for a typical dynamic trait (bill colour). Overall, structural colours showed a reduction in relative reflectance at shorter wavelengths, carotenoid-based colours the opposite pattern, while no general pattern was found for melanin-based colours. Achromatic changes were also common, but there were no consistent patterns of change for the different types of colours.

Conclusions/Significance

Changes of plumage coloration independent of moult are probably widespread; they should be perceivable by birds and have the potential to affect colour signalling.     

Range contractions and reduced body mass predicted for endemic skinks of the Cameroon Volcanic Line with future warming

Aim

The vulnerability of montane species to environmental change has been increasingly recognized in recent years. However, most of these species are regionally endemic with restricted distributions, limiting dispersal necessary for avoiding extinction. The outcome of threats posed for montane lizards is further complicated in species exhibiting mass–temperature relationships where body size increases with cooling temperatures, and thus with altitude, causing intraspecific physiological and behavioural differences. We aimed to identify areas suitable for montane endemic skinks of the Cameroon Volcanic Line (CVL) under current and future climates to reveal patterns of persistence and vulnerability based on an intersection of climate and body mass.

Location

Cameroon Volcanic Line

Methods

We recorded occurrences and measured body mass in the field for two CVL-endemic skink species. We supplemented occurrences with online repository records. We projected current and future habitat suitability in the region by implementing bioclimatic species distribution models-based on occurrences. We tested for elevational variations in body mass, and integrated both occurrence and body mass information in a trait-based model to estimate current and future body mass.

Results

Projected currently suitable habitat for both species was limited to higher elevation regions, which are inhabited by numerous other threatened herpetofauna. We additionally detected Bergmann clines in body mass for both species. Given this variation in body mass, trait model projections covered slightly larger geographical ranges than bioclimatic estimates. Under future warming, both models project substantial contractions in suitable areas, potentially constraining species to mountain tops. Through the trait-based approach, we further detected potential warming-induced body mass reductions in projected suitable areas.

Main Conclusions

We demonstrate how combining occurrence records with species trait information in ecological modelling can reveal complementary trends for comprehensive warming impact assessments. Overall, challenges toward the persistence of CVL-endemic skinks should prompt urgent responses in national conservation management and local community engagement.     

Patterns in body size and melanism along a latitudinal cline in the wingless grasshopper,Phaulacridium vittatum

Aim We explore geographic variation in body size within the wingless grasshopper, Phaulacridium vittatum, along a latitudinal gradient, and ask whether melanism can help explain the existence of clinal variation. We test the hypotheses that both male and female grasshoppers will be larger and lighter in colour at lower latitudes, and that reflectance and size will be positively correlated, as predicted by biophysical theory. We then test the hypothesis that variability in size and reflectance is thermally driven, by assessing correlations with temperature and other climatic variables. Location Sixty‐one populations were sampled along the east coast of Australia between latitudes 27.63° S and 43.10° S, at elevations ranging from 10 to 2000 m a.s.l. Methods Average reflectance was used as a measure of melanism and femur length as an index of body size for 198 adult grasshoppers. Climate variables were generated by BIOCLIM for each collection locality. Hierarchical partitioning was used to identify those variables with the most independent influence on grasshopper size and reflectance. Results Overall, there was no simple relationship between size and latitude in P. vittatum. Female body size decreased significantly with latitude, while male body size was largest at intermediate latitudes. Rainfall was the most important climatic variable associated with body size of both males and females. Female body size was also associated with radiation seasonality and male body size with reflectance. The reflectance of females was not correlated with latitude or body size, while male reflectance was significantly higher at intermediate latitudes and positively correlated with body size. Analyses of climate variables showed no significant association with male reflectance, while female reflectance was significantly related to the mean temperature of the driest quarter. Main conclusions Geographic variation in the body size of the wingless grasshopper is best explained in terms of rainfall and radiation seasonality, rather than temperature. However, melanism is also a significant influence on body size in male grasshoppers, suggesting that thermal fitness does play a role in determining adaptive responses to local conditions in this sex.     

Functional implications of temperature‐correlated colour polymorphism in an iridescent,scarabaeine dung beetle

Abstract 1. In many Coleoptera, iridescent colouration is generated by exoskeleton ultra‐structure, within which multilayer interference reflects only certain wavelengths. Published work indicates that the colour polymorphism shown by some iridescent beetles is under genetic control. However, the present study suggests environmental involvement in the polymorphic southern African dung beetle, Gymnopleurus humanus Macleay. 2. At 24 study sites across a 1000‐km latitudinal temperature gradient, population samples of G. humanus were dominated by blue individuals in the cooler south, by cupreous individuals in the warmer north, and by locally co‐occurring blue, green and cupreous individuals in intermediate situations. 3. Using digital reflectance spectrophotometry, we measured wavelength intensity values across the visible spectrum (400–800 nm) and used the 70 measured specimens to estimate maximum reflectance from a further 3912 beetles. Differences in mean reflectance values between 24 populations were strongly correlated with average annual temperatures at study sites. 4. Much stronger correlations between mean reflectance values and average temperatures of the cool dry season months suggest that the cross‐climatic patterns may be related to interaction between breeding seasonality and development under different cooler temperatures. 5. Published evidence suggests that inherent physical properties of cholesteric liquid crystals and their responses to different thermal conditions could, potentially, generate the different exocuticle ultra‐structure responsible for different reflected colour wavelengths. Furthermore, colour polymorphism could be advantageous across a gradient from cooler to warmer climate as a result of the different thermal properties of different colours. 6. Given the correlation with temperature, it is predicted that the prevailing reflected colour balance in southern populations would shift in response to global climatic change.     

Morphological variations in a widely distributed Eastern Asian passerine cannot be consistently explained by ecogeographic rules

Ecogeographic rules that describe quantitative relationships between morphologies and climate might help us predict how morphometrics of animals was shaped by local temperature or humidity. Although the ecogeographic rules had been widely tested in animals of Europe and North America, they had not been fully validated for species in regions that are less studied. Here, we investigate the morphometric variation of a widely distributed East Asian passerine, the vinous‐throated parrotbill (Sinosuthora webbiana), to test whether its morphological variation conforms to the prediction of Bergmann''s rule, Allen''s rules, and Gloger''s rule. We at first described the climatic niche of S. webbiana from occurrence records (n = 7838) and specimen records (n = 290). The results of analysis of covariance (ANCOVA) suggested that the plumage coloration of these parrotbills was darker in wetter/warmer environments following Gloger''s rule. However, their appendage size (culmen length, beak volume, tarsi length) was larger in colder environments, the opposite of the predictions of Allen''s rule. Similarly, their body size (wing length) was larger in warmer environments, the opposite of the predictions of Bergmann''s rule. Such disconformity to both Bergmann''s rule and Allen''s rule suggests that the evolution of morphological variations is likely governed by multiple selection forces rather than dominated by thermoregulation. Our results suggest that these ecogeographic rules should be validated prior to forecasting biological responses to climate change especially for species in less‐studied regions.     

Unveiling the environmental drivers of intraspecific body size variation in terrestrial vertebrates

Aim

Whether intraspecific spatial patterns in body size are generalizable across species remains contentious, as well as the mechanisms underlying these patterns. Here we test several hypotheses explaining within-species body size variation in terrestrial vertebrates including the heat balance, seasonality, resource availability and water conservation hypotheses for ectotherms, and the heat conservation, heat dissipation, starvation resistance and resource availability hypotheses for endotherms.

Location

Global.

Time period

1970–2016.

Major taxa studied

Amphibians, reptiles, birds and mammals.

Methods

We collected 235,905 body size records for 2,229 species (amphibians = 36; reptiles = 81; birds = 1,545; mammals = 567) and performed a phylogenetic meta-analysis of intraspecific correlations between body size and environmental variables. We further tested whether correlations differ between migratory and non-migratory bird and mammal species, and between thermoregulating and thermoconforming ectotherms.

Results

For bird species, smaller intraspecific body size was associated with higher mean and maximum temperatures and lower resource seasonality. Size–environment relationships followed a similar pattern in resident and migratory birds, but the effect of resource availability on body size was slightly positive only for non-migratory birds. For mammals, we found that intraspecific body size was smaller with lower resource availability and seasonality, with this pattern being more evident in sedentary than migratory species. No clear size–environment relationships were found for reptiles and amphibians.

Main conclusions

Within-species body size variation across endotherms is explained by disparate underlying mechanisms for birds and mammals. Heat conservation (Bergmann's rule) and heat dissipation are the dominant processes explaining biogeographic intraspecific body size variation in birds, whereas in mammals, body size clines are mostly explained by the starvation resistance and resource availability hypotheses. Our findings contribute to a better understanding of the mechanisms behind species adaptations to the environment across their geographic distributions.     

Thermal tolerance of tropical and temperate alpine plants suggests that ‘mountain passes are not higher in the tropics’

Aim

Tolerance of species to extreme temperatures largely determines their distribution and vulnerability to climate change. We examined thermal tolerance in tropical and temperate alpine plants, testing the hypotheses that: (a) temperate plants are resistant to more extreme temperatures and have an overall wider thermal tolerance breadth (TTB); (b) TTB in temperate plants is wider than TTB in tropical plants during the entire growing season; (c) resistance to frost and heat varies during the season in temperate plants but not in tropical plants; (d) TTB of a species predicts its latitudinal range.

Location

Tropical (Ecuador, Bolivia) and temperate (USA, Austria) mountains.

Time period

Four periods of the growing season (2014, 2016–2019).

Major taxa

Ninety-six vascular plant species.

Methods

We employed the electrolyte leakage method to estimate the temperature resistance, that is, the temperature at which 50% tissue injury (Lt50) occurs in leaves. We used phylogenetic linear mixed-effect models in a Bayesian framework to test for differences between the plant groups.

Results

Temperate and tropical plants do not differ in their temperature resistance. The four hypotheses are rejected since: (a) temperate plants do not have significantly wider overall TTB compared to tropical plants, (b) TTB of temperate plants is wider than TTB of tropical plants only at the end of the temperate summer, (c) seasonal acclimation is observed in both plant groups, (d) the latitudinal range of the plants is not related to TTB.

Main conclusions

The lack of TTB differences between temperate and tropical alpine plants is consistent with trends observed in ectothermic animals, which suggests a general latitudinal pattern in high-elevation poikilotherm organisms. Limited acclimation capacity to cope with long freezing exposures restricts the occurrence of tropical alpine species to thermally aseasonal environments making them particularly vulnerable to climate change.     

Are long‐term widespread avian body size changes related to food availability? A test using contemporaneous changes in carotenoid‐based color

Recent changes in global climate have been linked with changes in animal body size. While declines in body size are commonly explained as an adaptive thermoregulatory response to climate warming, many species do not decline in size, and alternative explanations for size change exist. One possibility is that temporal changes in animal body size are driven by changes in environmental productivity and food availability. This hypothesis is difficult to test due to the lack of suitable estimates that go back in time. Here, we use an alternative, indirect, approach and assess whether continent‐wide changes over the previous 100 years in body size in 15 species of Australian birds are associated with changes in their yellow carotenoid‐based plumage coloration. This type of coloration is strongly affected by food availability because birds cannot synthesize carotenoids and need to ingest them, and because color expression depends on general body condition. We found significant continent‐wide intraspecific temporal changes in body size (wing length) and yellow carotenoid‐based color (plumage reflectance) for half the species. Direction and magnitude of changes were highly variable among species. Meta‐analysis indicated that neither body size nor yellow plumage color showed a consistent temporal trend and that changes in color were not correlated with changes in size over the past 100 years. We conclude that our data provide no evidence that broad‐scale variation in food availability is a general explanation for continent‐wide changes in body size in this group of species. The interspecific variability in temporal changes in size as well as color suggests that it might be unlikely that a single factor drives these changes, and more detailed studies of museum specimens and long‐term field studies are required to disentangle the processes involved.     

The reliability of achromatic displays is island-dependent in nocturnal Storm Petrels

Nocturnal birds rely on achromatic visual signals to assess rivals and potential mates, but variation in the expression of these displays has been understudied. Here we use UV-visible reflectance spectrometry to study colour variation and the potential signalling function of the dark brown chest and white rump plumage – a colour pattern conspicuously exhibited during twilight courtship displays – in nocturnal Mediterranean Storm Petrels Hydrobates pelagicus melitensis from three islands with different exposures to predation and human disturbance. Human activity may increase perceived predation risk and thus affect activity budgets and the physiological stress response, with possible consequences on the relationship between individual body condition and plumage coloration. We found that chest and especially rump feathers reflected in the ultraviolet (UV) but there was no evidence of sexual dichromatism. However, we found support for a male-specific signalling role of plumage coloration. Indeed, chest yellow–red chroma and rump UV chroma were positively related to body condition in males, but only in the two islands representing the poorer environmental conditions. Therefore, environmental variability can potentially modify the reliability of achromatic displays, with possible consequences on sexual selection patterns in a nocturnal bird.     

FReD: the floral reflectance database--a web portal for analyses of flower colour

Background

Flower colour is of great importance in various fields relating to floral biology and pollinator behaviour. However, subjective human judgements of flower colour may be inaccurate and are irrelevant to the ecology and vision of the flower''s pollinators. For precise, detailed information about the colours of flowers, a full reflectance spectrum for the flower of interest should be used rather than relying on such human assessments.

Methodology/Principal Findings

The Floral Reflectance Database (FReD) has been developed to make an extensive collection of such data available to researchers. It is freely available at http://www.reflectance.co.uk. The database allows users to download spectral reflectance data for flower species collected from all over the world. These could, for example, be used in modelling interactions between pollinator vision and plant signals, or analyses of flower colours in various habitats. The database contains functions for calculating flower colour loci according to widely-used models of bee colour space, reflectance graphs of the spectra and an option to search for flowers with similar colours in bee colour space.

Conclusions/Significance

The Floral Reflectance Database is a valuable new tool for researchers interested in the colours of flowers and their association with pollinator colour vision, containing raw spectral reflectance data for a large number of flower species.     

Temperature‐driven color lightness and body size variation scale to local assemblages of European Odonata but are modified by propensity for dispersal

1. Previous macrophysiological studies suggested that temperature‐driven color lightness and body size variations strongly influence biogeographical patterns in ectotherms. However, these trait–environment relationships scale to local assemblages and the extent to which they can be modified by dispersal remains largely unexplored. We test whether the predictions of the thermal melanism hypothesis and the Bergmann's rule hold for local assemblages. We also assess whether these trait–environment relationships are more important for species adapted to less stable (lentic) habitats, due to their greater dispersal propensity compared to those adapted to stable (lotic) habitats.
2. We quantified the color lightness and body volume of 99 European dragon‐ and damselflies (Odonata) and combined these trait information with survey data for 518 local assemblages across Europe. Based on this continent‐wide yet spatially explicit dataset, we tested for effects temperature and precipitation on the color lightness and body volume of local assemblages and assessed differences in their relative importance and strength between lentic and lotic assemblages, while accounting for spatial and phylogenetic autocorrelation.
3. The color lightness of assemblages of odonates increased, and body size decreased with increasing temperature. Trait–environment relationships in the average and phylogenetic predicted component were equally important for assemblages of both habitat types but were stronger in lentic assemblages when accounting for phylogenetic autocorrelation.
4. Our results show that the mechanism underlying color lightness and body size variations scale to local assemblages, indicating their general importance. These mechanisms were of equal evolutionary significance for lentic and lotic species, but higher dispersal ability seems to enable lentic species to cope better with historical climatic changes. The documented differences between lentic and lotic assemblages also highlight the importance of integrating interactions of thermal adaptations with proxies of the dispersal ability of species into trait‐based models, for improving our understanding of climate‐driven biological responses.

     

UV-deprived coloration reduces success in mate acquisition in male sand lizards (Lacerta agilis)

Background

Recent work on animal signals has revealed a wide occurrence of UV signals in tetrapods, in particular birds, but also in lizards (and perhaps other Squamate reptiles). Our previous work on the Swedish sand lizard (Lacerta agilis) has verified, both in correlative selection analyses in the wild and with laboratory and field experiments, the importance of the green ‘badge’ on the body sides of adult males for securing mating opportunities, probably mostly through deterring rival males rather than attracting females. The role of UV in communication has, however, never been examined.

Methodology/Principal Findings

Here we show that when measured immediately after spring skin shedding, there is also signaling in the UV. By UV-depriving the signal (reflectance) with sun block chemicals fixated with permeable, harmless spray dressing, we show that males in the control group (spray dressing only) had significantly higher success in mate acquisition than UV-deprived males.

Conclusions/Significance

These results suggest that at least two colour traits in sand lizards, badge area and UV, contribute to rival deterrence and/or female choice on UV characters, which elevates success in mate acquisition in UV intact male sand lizards.     

Silica nanoparticles aid in structural leaf coloration in the Malaysian tropical rainforest understorey herb Mapania caudata

Background and Aims

Blue-green iridescence in the tropical rainforest understorey sedge Mapania caudata creates structural coloration in its leaves through a novel photonic mechanism. Known structures in plants producing iridescent blues consist of altered cellulose layering within cell walls and in special bodies, and thylakoid membranes in specialized plastids. This study was undertaken in order to determine the origin of leaf iridescence in this plant with particular attention to nano-scale components contributing to this coloration.

Methods

Adaxial walls of leaf epidermal cells were characterized using high-pressure-frozen freeze-substituted specimens, which retain their native dimensions during observations using transmission and scanning microscopy, accompanied by energy-dispersive X-ray spectroscopy to identify the role of biogenic silica in wall-based iridescence. Biogenic silica was experimentally removed using aqueous Na₂CO₃ and optical properties were compared using spectral reflectance.

Key Results and Conclusions

Blue iridescence is produced in the adaxial epidermal cell wall, which contains helicoid lamellae. The blue iridescence from cell surfaces is left-circularly polarized. The position of the silica granules is entrained by the helicoid microfibrillar layers, and granules accumulate at a uniform position within the helicoids, contributing to the structure that produces the blue iridescence, as part of the unit cell responsible for 2 ° Bragg scatter. Removal of silica from the walls eliminated the blue colour. Addition of silica nanoparticles on existing cellulosic lamellae is a novel mechanism for adding structural colour in organisms.