Zsolt Bálint

Phylogeny and palaeoecology of Polyommatus blue butterflies show Beringia was a climate-regulated gateway to the New World

Transcontinental dispersals by organisms usually represent improbable events that constitute a major challenge for biogeographers. By integrating molecular phylogeny, historical biogeography and palaeoecology, we test a bold hypothesis proposed by Vladimir Nabokov regarding the origin of Neotropical Polyommatus blue butterflies, and show that Beringia has served as a biological corridor for the dispersal of these insects from Asia into the New World. We present a novel method to estimate ancestral temperature tolerances using distribution range limits of extant organisms, and find that climatic conditions in Beringia acted as a decisive filter in determining which taxa crossed into the New World during five separate invasions over the past 11 Myr. Our results reveal a marked effect of the Miocene–Pleistocene global cooling, and demonstrate that palaeoclimatic conditions left a strong signal on the ecology of present-day taxa in the New World. The phylogenetic conservatism in thermal tolerances that we have identified may permit the reconstruction of the palaeoecology of ancestral organisms, especially mobile taxa that can easily escape from hostile environments rather than adapt to them.

Microstructures and nanostructures of high Andean Penaincisalia lycaenid butterfly scales (Lepidoptera: Lycaenidae): descriptions and interpretations

The scales of one high Andean eumaeine lycaenid butterfly species with pale dorsal coloration and four species with vivid dorsal colour were investigated using field emission scanning electron microscopy. The micro‐ and nanostructures are illustrated, described, measured, and interpreted. The vivid colours in the species are caused by a pepper‐pot nanostructure of Urania‐type scales. This nanostructure is a three‐dimensional lattice within the body of the individual scale. The scales of the non‐vivid orange species are lacking this nanostructure and the surfaces of their scales show high microstructure irregularities. This absence of vivid colour may be correlated with thermal regulation. The irregularity of the scale microstructures suggests a heavy environmental pressure on the populations sampled. Previously unknown structural variations of Urania‐type scales are also described. The existence of closed scale microcell structures, explained as an apomorphic character in the tribe Eumaeini, most probably evolved independently several times. It is hypothesized that scale micro‐ and nanostructure modifications develop syntopically within a population, which in turn can lead to rapid diversification.

Substance specific chemical sensing with pristine and modified photonic nanoarchitectures occurring in blue butterfly wing scales

Butterfly wing scales containing photonic nanoarchitectures act as chemically selective sensors due to their color change when mixing vapors in the atmosphere. Based on butterfly vision, we built a model for efficient characterization of the spectral changes in different atmospheres. The spectral shift is vapor specific and proportional with the vapor concentration. Results were compared to standard principal component analysis. The modification of the chemical properties of the scale surface by the deposition of 5 nm of Al(2)O(3) significantly alters the character of the optical response. This is proof of the possibility to purposefully tune the selectivity of such sensors.

Selective Optical Gas Sensors Using Butterfly Wing Scales Nanostructures

Photonic crystals are periodic dielectric nanocomposites, which have photonic band gaps that forbid the propagation of light within certain frequency ranges. This property enables one to manipulate light with amazing facility. Such nanoarchitectures frequently occur in living organism like butterflies and beetles. Butterfly scales are particularly well suited to be used as optical gas sensors as their nanoarchitecture is an open sponge-like type, composed of chitin and air. The open nanoarchitecure allows fast gas exchange. The spectral change of the reflected light depends on the composition of the ambient atmosphere and also on the wing nanostructure. In this work we show the results of recent measurements on nine Polyommatine species with dorsal blue coloration. Their color is generated by similar pepper-pot type nanoarchitectures which exhibit species specific characteristics, associated with species specific color. Experiments were carried out changing the concentration and nature of test vapors while monitoring the spectral variations in time. Proper data processing results gas-selective and concentration dependent signals. Our work shows a way to a prospective integrated biological - optical sensor combining light-weight and low power consuming with environmental friendly production.

Color changes upon cooling of lepidoptera scales containing photonic nanoarchitectures

Photonic crystal type nanoarchitectures have an important advantage over conventional displays: they do not fade under solar illumination; on the contrary, more intense illumination generates more intense color. We present a simple method based on cooling in ambient air - to observe the color change of several butterfly wings colored by various photonic nanoarchitectures. The color change can be attributed to the condensation of atmospheric humidity in the nanocavities of the photonic nanoarchitecture. The effects were investigated by controlled cooling combined with the in-situ measurement of the changes in the reflectivity spectra. For certain species the reflectivity maximum (color) has almost completely disappeared. A correlation was also found between the openness of the nanostructure and the time of the color change. Cooling experiments, using thin copper wires showed that color alteration could be limited to millimeters; this may offer a possible alternative for display technology.

Color Changes Upon Cooling of Lepidoptera Scales Containing Photonic Nanoarchitectures, and a Method for Identifying the Changes

Abstract The effects produced by the condensation of water vapor from the environment in the various intricate nanoarchitectures occurring in the wing scales of several Lepidoptera species were investigated by controlled cooling (from 23° C, room temperature to -5 to -10° C) combined with in situ measurements of changes in the reflectance spectra. It was determined that all photonic nanoarchitectures giving a reflectance maximum in the visible range and having an open nanostructure exhibited alteration of the position of the reflectance maximum associated with the photonic nanoarchitectures. The photonic nanoarchitectures with a closed structure exhibited little to no alteration in color. Similarly, control specimens colored by pigments did not exhibit a color change under the same conditions. Hence, this method can be used to identify species with open photonic nanoarchitectures in their scales. For certain species, an almost complete disappearance of the reflectance maximum was found. All specimens recovered their original colors following warming and drying. Cooling experiments using thin copper wires demonstrated that color alterations could be limited to a width of a millimeter or less. Dried museum specimens did not exhibit color changes when cooled in the absence of a heat sink due to the low heat capacity of the wings.

Living Photonic Crystals: Nanostructure of the Scales of Cyanophrys Remus Butterfly

The complex photonic crystal type nanoarchitectures found in the wing scales of the male butterfly Cyanophrys remus were investigated structurally by electron microscopy and optically by reflectance spectroscopy. Both the vivid metallic blue of the dorsal scales and the matt, pea-green coloration of the ventral scales are attributed to photonic crystal type structures composed of chitin and air. The dorsal scales are single crystalline, while the ventral ones contain a large number of randomly oriented micron size single crystalline grains of face centered cubic inverse opal. The remarkable complexity and efficiency of biologic photonic crystals may provide clues in designing artificial structures with similar parameters.

Changes in structural and pigmentary colours in response to cold stress in Polyommatus icarus butterflies

While numerous papers have investigated the effects of thermal stress on the pigmentary colours of butterfly wings, such studies regarding structural colours are mostly lacking, despite the important role they play in sexual communication. To gain insight into the possible differences between the responses of the two kinds of colouration, we investigated the effects of prolonged cold stress (cooling at 5 °C for up to 62 days) on the pupae of Polyommatus icarus butterflies. The wing surfaces coloured by photonic crystal-type nanoarchitectures (dorsal) and by pigments (ventral) showed markedly different behaviours. The ventral wing surfaces exhibited stress responses proportional in magnitude to the duration of cooling and showed the same trend for all individuals, irrespective of their sex. On the dorsal wing surface of the males, with blue structural colouration, a smaller magnitude response was found with much more pronounced individual variations, possibly revealing hidden genetic variations. Despite the typical, pigmented brown colour of the dorsal wing surface of the females, all cooled females exhibited a certain degree of blue colouration. UV-VIS spectroscopy, optical microscopy, and scanning and transmission electron microscopy were used to evaluate the magnitude and character of the changes induced by the prolonged cold stress.

Pretreated Butterfly Wings for Tuning the Selective Vapor Sensing

Photonic nanoarchitectures occurring in the scales of Blue butterflies are responsible for their vivid blue wing coloration. These nanoarchitectures are quasi-ordered nanocomposites which are constituted from a chitin matrix with embedded air holes. Therefore, they can act as chemically selective sensors due to their color changes when mixing volatile vapors in the surrounding atmosphere which condensate into the nanoarchitecture through capillary condensation. Using a home-built vapor-mixing setup, the spectral changes caused by the different air + vapor mixtures were efficiently characterized. It was found that the spectral shift is vapor-specific and proportional with the vapor concentration. We showed that the conformal modification of the scale surface by atomic layer deposition and by ethanol pretreatment can significantly alter the optical response and chemical selectivity, which points the way to the efficient production of sensor arrays based on the knowledge obtained through the investigation of modified butterfly wings.

Variability of the structural coloration in two butterfly species with different prezygotic mating strategies

Structural coloration variability was investigated in two Blue butterfly species that are common in Hungary. The males of Polyommatus icarus (Common Blue) and Plebejus argus (Silver-studded Blue) use their blue wing coloration for conspecific recognition. Despite living in the same type of habitat, these two species display differences in prezygotic mating strategy: the males of P. icarus are patrolling, while P. argus males have sedentary behavior. Therefore, the species-specific photonic nanoarchitecture, which is the source of the structural coloration, may have been subjected to different evolutionary effects. Despite the increasing interest in photonic nanoarchitectures of biological origin, there is a lack of studies focused on the biological variability of structural coloration that examine a statistically relevant number of individuals from the same species. To investigate possible structural color variation within the same species in populations separated by large geographical distances, climatic differences, or applied experimental conditions, one has to be able to compare these variations to the normal biological variability within a single population. The structural coloration of the four wings of 25 male individuals (100 samples for each species) was measured and compared using different light-collecting setups: perpendicular and with an integrating sphere. Significant differences were found in the near UV wavelength region that are perceptible by these polyommatine butterflies but are invisible to human observers. The differences are attributed to the differences in the photonic nanoarchitecture in the scales of these butterflies. Differences in the intensity of structural coloration were also observed and were tentatively attributed to the different prezygotic mating strategies of these insects. Despite the optical complexity of the scale covered butterfly wings, for sufficiently large sample batches, the averaged normal incidence measurements and the averaged measurements using an integrating sphere are in agreement.