Andrew R. Parker

Water capture by a desert beetle

Some beetles in the Namib Desert collect drinking water from fog-laden wind on their backs. We show here that these large droplets form by virtue of the insects bumpy surface, which consists of alternating hydrophobic, wax-coated and hydrophilic, non-waxy regions. The design of this fog-collecting structure can be reproduced cheaply on a commercial scale and may find application in water-trapping tent and building coverings, for example, or in water condensers and engines.

Biomimetics of photonic nanostructures

Biomimetics is the extraction of good design from nature. One approach to optical biomimetics focuses on the use of conventional engineering methods to make direct analogues of the reflectors and anti-reflectors found in nature. However, recent collaborations between biologists, physicists, engineers, chemists and materials scientists have ventured beyond experiments that merely mimic what happens in nature, leading to a thriving new area of research involving biomimetics through cell culture. In this new approach, the nanoengineering efficiency of living cells is harnessed and natural organisms such as diatoms and viruses are used to make nanostructures that could have commercial applications.

515 million years of structural colour

Structures that cause colour or provide antireflection have been found in both living and extinct animals in a diversity of forms, including mirror-reflective and diffractive devices. An overview of this diversity is presented here, and behavioural and evolutionary implications are introduced.

Structural colour: Opal analogue discovered in a weevil

Beetles in dimly lit tropical forests often display structural colours, but in direct sunlight only part of the insect can be seen from any direction — it appears as a spot of light because multilayer reflectors on its rounded surface act like mirrors. Here we describe a beetle, Pachyrhynchus argus, found in forests in northeastern Queensland, Australia, that has a metallic coloration that is visible from any direction owing to a photonic crystal structure analogous to that of opal. To our knowledge, this is the first recorded example of an opal-type structure in an animal.

Aphrodite's iridescence

The most intense colours displayed in nature result from either multilayer reflectors or linear diffraction gratings1,2,3. Here we investigate the spectacular iridescence of a spine (notoseta) from the sea mouse Aphrodita sp. (Polychaeta: Aphroditidae). The spine normally appears to be deep red in colour, but when light is incident perpendicular to the axis of the spine, different colours are seen as stripes running parallel to the axis of the spine; over a range of smaller incident angles, the complete visible spectrum is reflected with a reflectivity of 100% to the human eye. The simple structure responsible for this effect is a remarkable example of photonic engineering by a living organism.

Colour in Burgess Shale animals and the effect of light on evolution in the Cambrian

Diffraction gratings are reported from external surfaces of the hard, protective parts of Wiwaxia corrugata, Canadia spinosa and Marrella splendens from the Burgess Shale (Middle Cambrian (515 million years), British Columbia). As a consequence, these animals would have displayed iridescence in their natural environment: Cambrian animals have previously been accurately reconstructed in black and white only. A diversity of extant marine animals inhabiting a similar depth to the Burgess Shale fauna possess functional diffraction gratings. The Cambrian is a unique period in the history of animal life where predatory lifestyles and eyes capable of producing visual images were evolving rapidly. The discovery of colour in Cambrian animals prompts a new hypothesis on the initiation of the ‘Big Bang’ in animal evolution which occurred during the Cambrian: light was introduced into the behavioural systems of metazoan animals for the first time. This introduction, of what was to become generally the most powerful stimulus in metazoan behavioural systems, would have triggered turbulence in metazoan evolution.

Solar–absorber antireflector on the eye of an Eocene fly (45 Ma)

Antireflection structures on eyes potentially increase visual efficiency through increased photon capture for a given stimulus condition. We report an unusual surface grating on the compound eyes of an Eocene dolichopodid dipteran (45 Ma) known only from Baltic amber. By measuring the reflective properties of a flat model of this grating constructed from material of appropriate refractive index we show that this lsquo;fly eye grating’ is an efficient antireflector of white light at angles up to 60 °, and a relatively good antireflector for angles beyond 60 °. We calculate that such a grating would be particularly useful on a curved corneal surface as it would increase the transmission of incident light through the cornea compared with a smooth surface. This structure is also reported on the curved regions of the corneas of at least two extant dipterans. We argue that this grating probably derives from the previously described moth eye antireflection structure, which we also report here to occur in a silverfish, a ‘primitive’ insect. The fly eye grating is a more efficient antireflector than the moth eye structure only at angles greater than about 10 ° from the surface normal. A comparable antireflector is employed on solar absorbers.

Discovery of Functional Iridescence and Its Coevolution with Eyes in the Phylogeny of Ostracoda (Crustacea)

Highly efficient iridescence caused by natural diffraction gratings is reported for the first time in the Crustacea. Iridescence presumably began as an epiphenomenon, but has evolved to include a courtship function in at least some myodocopid Ostracoda (Crustacea). Ostracod iridescence apparently preceded the evolution, and is probably a precursor, of cypridinid (Myodocopida) bioluminescence. By tracing the development of light reception and display, myodocopid evolution, in part at least, is revealed. Therefore, light appears to be the main stimulus to myodocopid evolution. The myodocopid lateral eye probably evolved at a similar point in time as iridescence, possibly to detect iridescence. The graduations by which the ostracod compound eye has developed are suggested. These findings challenge current theories which demand a single evolution of the compound eye.

A hearing and vestibular phenotyping pipeline to identify mouse mutants with hearing impairment

We describe a protocol for the production of mice carrying N-ethyl-N-nitrosourea (ENU) mutations and their screening for auditory and vestibular phenotypes. In comparison with the procedures describing individual phenotyping tests, this protocol integrates a set of tests for the comprehensive determination of the causes of hearing loss. It comprises a primary screen of relatively simple auditory and vestibular tests. A variety of secondary phenotyping protocols are also described for further investigating the deaf and vestibular mutants identified in the primary screen. The screen can be applied to potentially thousands of mutant mice, produced either by ENU or other mutagenesis approaches. Primary screening protocols take no longer than a few minutes, apart from ABR testing which takes upto 3.5 h per mouse. These protocols have been applied for the identification of mouse models of human deafness and are a key component for investigating the genes and genetic pathways involved in hereditary deafness.

A geological history of reflecting optics

Optical reflectors in animals are diverse and ancient. The first image-forming eye appeared around 543 million years ago. This introduced vision as a selection pressure in the evolution of animals, and consequently the evolution of adapted optical devices. The earliest known optical reflectors—diffraction gratings—are 515 Myr old. The subsequent fossil record preserves multilayer reflectors, including liquid crystals and mirrors, ‘white’ and ‘blue’ scattering structures, antireflective surfaces and the very latest addition to optical physics—photonic crystals. The aim of this article is to reveal the diversity of reflecting optics in nature, introducing the first appearance of some reflector types as they appear in the fossil record as it stands (which includes many new records) and backdating others in geological time through evolutionary analyses. This article also reveals the commercial potential for these optical devices, in terms of lessons from their nano-level designs and the possible emulation of their engineering processes—molecular self-assembly.