Adaptive colour change and background choice behaviour in peppered moth caterpillars is mediated by extraocular photoreception

Light sensing by tissues distinct from the eye occurs in diverse animal groups, enabling circadian control and phototactic behaviour. Extraocular photoreceptors may also facilitate rapid colour change in cephalopods and lizards, but little is known about the sensory system that mediates slow colour change in arthropods. We previously reported that slow colour change in twig-mimicking caterpillars of the peppered moth (Biston betularia) is a response to achromatic and chromatic visual cues. Here we show that the perception of these cues, and the resulting phenotypic responses, does not require ocular vision. Caterpillars with completely obscured ocelli remained capable of enhancing their crypsis by changing colour and choosing to rest on colour-matching twigs. A suite of visual genes, expressed across the larval integument, likely plays a key role in the mechanism. To our knowledge, this is the first evidence that extraocular colour sensing can mediate pigment-based colour change and behaviour in an arthropod

Extraocular photoreception and colour plasticity in caterpillars of the peppered moth, Biston betularia

Visual camouflage is a textbook example of natural selection, and a widespread strategy used by both predators and prey to avoid detection. Background matching, where the animal resembles the colour, brightness, and/ or pattern of the surrounding visual background is a common form of visual camouflage, and can occur through genetic polymorphism, behavioural background choice, or dynamic colour change. Dynamic colour change can occur very rapidly (milliseconds) or gradually, sometimes taking weeks to complete. Visual cues such as colour, brightness, and pattern, have been shown to elicit colour change, and in some colour-changing animals visual cues are sensed outside of the eye using extraocular photoreceptors (EOPs). Colour change research has been focused predominantly on rapid, chromatophore-based colour change, as observed in cephalopods. In contrast, little is known about the physiology and evolutionary origins of gradual colour change. To avoid predation in a wide range of environments, caterpillars of the peppered moth (Biston betularia) masquerade as twigs and gradually change colour to match them. This thesis investigates the colour-changing response in B. betularia larvae: the shape of the reaction norm to colour and brightness gradients; the use and molecular basis of extraocular photoreception; and whether B. betularia alter resting behaviour to maximise concealment. Through a series of artificial twig experiments, I found that B. betularia larvae respond to both colour and luminance cues to produce a continuous range of phenotypes, rather than being restricted to a brown/green polyphenism as previously reported. To test for the possibility of extraocular photoreception, I occluded the eyes (ocelli) of groups of larvae and compared responses to colour and luminance with non-blindfolded control larvae. There was no difference in the colour-changing response of blindfolded larvae compared to controls, and blindfolded larvae also rested on colours that better matched their own colour to the same extent as non-blindfolded controls. I next examined the potential for visual machinery in the larval dermis, finding expression of a suite of visual genes throughout dermal tissue in B. betularia larvae and adults. In larvae, this expression was generally much higher relative to head tissue than found for adults. This finding corroborates the morphological and behavioural evidence for dermal photoreceptors in B. betularia larvae. The final chapter is an attempt to examine the exclusivity of extraocular photoreception in B. betularia, and its evolutionary origins, through tissue-specific measurement of opsin expression in larvae and adults of a phylogenetically broad sample of Lepidoptera. Dermal opsin expression was found in other species, but depended on the gene (UV, blue, LW1, LW2) and developmental stage. Phylogenetic signal was found only for expression of LW1 in larvae, and LW2 in adults. Larval colouration strategy between species also appears to affect dermal opsin expression. The thesis provides strong evidence for a novel physiological phenomenon: extraocular colour photoreception in the dermis of an insect, used to mediate colour change and behavioural background choice. The observation that dermal opsin expression occurs in several other species suggests that EOPs may be widespread in the Lepidoptera. Future work should be directed at the challenging task of understanding the mechanism underlying this class of EOPs, and characterising their functional roles in other species

Colour change of twig-mimicking peppered moth larvae is a continuous reaction norm that increases camouflage against avian predators

Camouflage, and in particular background-matching, is one of the most commonanti-predator strategies observed in nature. Animals can improve their match to thecolour/pattern of their surroundings through background selection, and/or by plasticcolour change. Colour change can occur rapidly (a few seconds), or it may be slow,taking hours to days. Many studies have explored the cues and mechanisms behindrapid colour change, but there is a considerable lack of information about slow colourchange in the context of predation: the cues that initiate it, and the range of phenotypesthat are produced. Here we show that peppered moth (Biston betularia) larvae respondto colour and luminance of the twigs they rest on, and exhibit a continuous reactionnorm of phenotypes. When presented with a heterogeneous environment of mixed twigcolours, individual larvae specialise crypsis towards one colour rather than developingan intermediate colour. Flexible colour change in this species has likely evolved inassociation with wind dispersal and polyphagy, which result in caterpillars settling andfeeding in a diverse range of visual environments. This is the first example of visuallyinduced slow colour change in Lepidoptera that has been objectively quantified andmeasured from the visual perspective of natural predators

Adaptive colour change and background choice behaviour in peppered moth caterpillars is mediated by extraocular photoreception

Light sensing by tissues distinct from the eye occurs in diverse animal groups, enabling circadian control and phototactic behaviour. Extraocular photoreceptors may also facilitate rapid colour change in cephalopods and lizards, but little is known about the sensory system that mediates slow colour change in arthropods. We previously reported that slow colour change in twig-mimicking caterpillars of the peppered moth (Biston betularia) is a response to achromatic and chromatic visual cues. Here we show that the perception of these cues, and the resulting phenotypic responses, does not require ocular vision. Caterpillars with completely obscured ocelli remained capable of enhancing their crypsis by changing colour and choosing to rest on colour-matching twigs. A suite of visual genes, expressed across the larval integument, likely plays a key role in the mechanism. To our knowledge, this is the first evidence that extraocular colour sensing can mediate pigment-based colour change and behaviour in an arthropod

Adaptive colour change and background choice behaviour in peppered moth caterpillars is mediated by extraocular photoreception.

Light sensing by tissues distinct from the eye occurs in diverse animal groups, enabling circadian control and phototactic behaviour. Extraocular photoreceptors may also facilitate rapid colour change in cephalopods and lizards, but little is known about the sensory system that mediates slow colour change in arthropods. We previously reported that slow colour change in twig-mimicking caterpillars of the peppered moth (Biston betularia) is a response to achromatic and chromatic visual cues. Here we show that the perception of these cues, and the resulting phenotypic responses, does not require ocular vision. Caterpillars with completely obscured ocelli remained capable of enhancing their crypsis by changing colour and choosing to rest on colour-matching twigs. A suite of visual genes, expressed across the larval integument, likely plays a key role in the mechanism. To our knowledge, this is the first evidence that extraocular colour sensing can mediate pigment-based colour change and behaviour in an arthropod

Raw spectrophotometer files for luminance gradient experiment

Raw spectrophotometer files for luminance gradient experiment (black, greys and white dowels

Canker Development and Biocontrol Potential of CHV-1 Infected English Isolates of Cryphonectria parasitica Is Dependent on the Virus Concentration and the Compatibility of the Fungal Inoculums

Biological control of Cryphonectria parasitica fungus, causal agent of chestnut blight, by virus infection (hypovirulence) has been shown to be an effective control strategy against chestnut blight in Europe and some parts of North America. The most studied mycovirus is the Cryphonectria hypovirus 1 (CHV-1) type species of the Hypoviridae family. To efficiently provide biocontrol, the virus must be able to induce hypovirulence in its fungal host in chestnut trees. Here, two different CHV-1 subtype I virus strains (E-5 and L-18), gained by transmissions, were tested for their hypovirulence induction, biocontrol potential, and transmission between vegetatively compatible (VCG) and incompatible fungal isolate groups in sweet chestnut seedlings and branches. Both strains of CHV-1 showed great biocontrol potential and could protect trees by efficiently transmitting CHV-1 by hyphal anastomosis between fungal isolates of the same VCG and converting virulent to hypovirulent cankers. The hypovirulent effect was positively correlated with the virus concentration, tested by four different reverse-transcription PCRs, two end-point and two real-time methods, one of which represents a newly developed real-time PCR for the detection and quantification of CHV-1

Grundlagen des Ultraschall-Drahtbondens

Als Grundlage für die in den nachfolgenden Kapiteln beschriebenen Modelle und Methoden werden in diesem Kapitel zunächst der Ablauf eines Ultraschall-Drahtbondprozesses sowie die dafür notwendige Ultraschallerweichung („Ultrasonic Softening“) beschrieben. Anschließend werden Modelle für den piezoelektrischen Wandler vorgestellt, der zur Erzeugung der Ultraschallschwingung genutzt wird, und es wird eine Einführung in die Mehrzieloptimierung und Verhaltensanpassung inkl. einiger relevanter Vorarbeiten gegeben