Response to self-motion in waterstriders: visual discrimination between rotation and translation

Waterstriders (Gerris paludum) often try to maintain a nearly stationary position on a moving water surface. Passive motion is restricted to 3 degrees of freedom: yaw, longitudinal, and transverse displacement. They correct for passive rotation and translation by distinct behavioral sequences. The compensatory behavior is predominantly visually controlled.

Compound Eye Miniaturization in Lepidoptera: a comparative morphological analysis

Superposition and apposition compound eyes are commonly associated with moths and butterflies, respectively. However, recently intermediate eye designs, combining features of both apposition and superposition eyes were found in tiny insects. Here, we examine the eyes of 12 species of moth, ranging from 1.88 to 6.03 mm body size, by scanning and transmission electron microscopy. Correlations between body and eye sizes are discussed with regard to the eyes' functionality. Although all of the species shared an ommatidial organization characteristic of pterygote insects, three optical designs were found: (a) an apposition eye, (b) an eye resembling apposition eyes, but with a unique crystalline cone, and (c) an eye intermediate in structure between apposition and superposition eyes. Our comparisons also revealed a new type of basal matrix for the Lepidoptera. The results show that in most of the examined compound eyes (with the exception of the apposition eye of Micropterix aruncella), a clear distinction between apposition and superposition eyes is not feasible. Due to functional morphological constraints as a consequence of miniaturization, evolutionary transformations from superposition into apposition optics may have occurred several times independently in various ‘microlepidopteran’ taxa. The Phyllonorycter medicaginella eye appears to illustrate this evolutionary scenario best.     

N2 fixation in phototrophs: adaptation to a specialized way of life

Phototrophic diazotrophs include the photosynthetic green and purple bacteria, the heliobacteria, many cyanobacteria and the unusual chlorophyll-containing rhizobia that are found in the stem nodules of Aeschynomene spp. In this review, which concentrates on cyanobacteria, the interrelations between photosynthesis and N₂ fixation are discussed. Photosynthesis can, in theory, directly provide the ATP and reductant needed to support N₂ fixation but the link between these two processes is usually indirect, mediated through accumulated carbon reserves. In cyanobacteria, which possess an oxygenic photosynthesis, this serves to separate the O₂ that is produced by photosynthesis from the O₂-sensitive nitrogenase. However, in certain circumstances, oxygenic photosynthesis and N₂ fixation coexist. Under these conditions, respiratory consumption of photosynthetically generated O₂ may have an important role in minimizing O₂-damage to nitrogenase.     

Eye evolution at high resolution: The neuron as a unit of homology

Based on differences in morphology, photoreceptor-type usage and lens composition it has been proposed that complex eyes have evolved independently many times. The remarkable observation that different eye types rely on a conserved network of genes (including Pax6/eyeless) for their formation has led to the revised proposal that disparate complex eye types have evolved from a shared and simpler prototype. Did this ancestral eye already contain the neural circuitry required for image processing? And what were the evolutionary events that led to the formation of complex visual systems, such as those found in vertebrates and insects? The recent identification of unexpected cell-type homologies between neurons in the vertebrate and Drosophila visual systems has led to two proposed models for the evolution of complex visual systems from a simple prototype. The first, as an extension of the finding that the neurons of the vertebrate retina share homologies with both insect (rhabdomeric) and vertebrate (ciliary) photoreceptor cell types, suggests that the vertebrate retina is a composite structure, made up of neurons that have evolved from two spatially separate ancestral photoreceptor populations. The second model, based largely on the conserved role for the Vsx homeobox genes in photoreceptor-target neuron development, suggests that the last common ancestor of vertebrates and flies already possessed a relatively sophisticated visual system that contained a mixture of rhabdomeric and ciliary photoreceptors as well as their first- and second-order target neurons. The vertebrate retina and fly visual system would have subsequently evolved by elaborating on this ancestral neural circuit. Here we present evidence for these two cell-type homology-based models and discuss their implications.     

Rapid adaptation in a fast-changing world: Emerging insights from insect genomics

Many researchers have questioned the ability of biota to adapt to rapid anthropogenic environmental shifts. Here, we synthesize emerging genomic evidence for rapid insect evolution in response to human pressure. These new data reveal diverse genomic mechanisms (single locus, polygenic, structural shifts; introgression) underpinning rapid adaptive responses to a variety of anthropogenic selective pressures. While the effects of some human impacts (e.g. pollution; pesticides) have been previously documented, here we highlight startling new evidence for rapid evolutionary responses to additional anthropogenic processes such as deforestation. These recent findings indicate that diverse insect assemblages can indeed respond dynamically to major anthropogenic evolutionary challenges. Our synthesis also emphasizes the critical roles of genomic architecture, standing variation and gene flow in maintaining future adaptive potential. Broadly, it is clear that genomic approaches are essential for predicting, monitoring and responding to ongoing anthropogenic biodiversity shifts in a fast-changing world.     

Special relationship between sterols and oxygen: Were sterols an adaptation to aerobic life?

A fascinating link between sterols and molecular oxygen (O₂) has been a common thread running through the fundamental work of Konrad Bloch, who elucidated the biosynthetic pathway for cholesterol, to recent work supporting a role of sterols in the sensing of O₂. Synthesis of sterols by eukaryotes is an O₂-intensive process. In this review, we argue that increased levels of O₂ in the atmosphere not only made the evolution of sterols possible, but that these sterols may in turn have provided the eukaryote with an early defence mechanism against O₂. The idea that nature crafted sterols as a feedback loop to adapt to, or help protect against, the hazards of O₂ is novel and enticing. We marshal several lines of evidence to support this thesis: (1) coincidence of atmospheric O₂ and sterol evolution; (2) sterols regulate O₂ entry into eukaryotic cells and organelles; (3) sterols act as O₂ sensors across eukaryotic life; (4) sterols serve as a primitive cellular defence against O₂ (including reactive oxygen species). Therefore, sterols may have evolved in eukaryotes partially as an adaptive response to the rise of terrestrial O₂, rather than merely as a consequence of it.     

The eyes of a patrolling butterfly: visual field and eye structure in the Orange Sulphur, Colias eurytheme (Lepidoptera, Pieridae)

Sensory information plays a critical role in determining an animal's behavior on both proximate and evolutionary timescales. Butterflies, like many other insects, use vision extensively over their lifetimes, and yet relatively little work has been published to date on their visual capabilities. We describe the visual system of a pierid butterfly, Colias eurytheme, with the ultimate goal of better understanding its role in shaping the behavior of this animal. We made several measurements: visual field dimensions, eye surface area, interommatidial angle (Deltaphi), facet diameter (D), and eye parameter (p). C. eurytheme had a large visual field and considerable regional variation in visual acuity, as inferred by Deltaphi and D. When compared to females, males had larger eye surface areas, smaller Deltaphi, and larger D in all regions except ventrally. Both sexes had proportionally large eye surface areas compared to other butterflies. Minimum p in males was small, indicating that some regions of their eyes may operate close to the diffraction limit. Finally, we found that both eye surface area and D scaled positively, but with negative allometry to body size. We discuss the relevance of these visual characteristics to the biology and behavior of C. eurytheme.     

Genetic differentiation in life history between Daphnia galeata populations: an adaptation to local predation regimes?

Species of the water flea Daphnia exhibit constitutive as wellas phenotypically inducible anti-predator defence strategies,involving life history, morphological and behavioural traits.We explored the hypothesis of genetic differentiation in anti-predatordefence strategies using Daphnia clones originating from twodifferent water bodies: Tjeukemeer (the Netherlands) and FishPond (Belgium). Both water bodies are inhabited by zooplanktivorousfish. In contrast to Tjeukemeer, Fish Pond is also inhabitedby larvae of the phantom midge Chaoborus. The life history responsesof the two sets of clones to kairomones from fish (Perca), tokairomones from Chaoborus, and to a mixture of both were compared.Clones from Tjeukemeer and Fish Pond showed strong responsesto the presence of fish kairomone, with reductions in adultand neonate body length, in age at first reproduction and inthe total number of neonates produced during the first threeadult instars. Responses to Chaoborus kairomone were much lesspronounced, although there was a tendency towards an increasein the number of neonates in the first brood. Significant inter-populationgenetic differences were found for all the investigated traits.However, there was no indication for genetic adaptation of theFish Pond clones to negative size-selective predation by Chaoborus.Compared to Tjeukemeer clones, Fish Pond clones had a lowersize at first reproduction, produced smaller neonates and produceda higher number of neonates in their first brood. This suggestsadaptation to positive rather than to negative size selectivepredation. Genetic differences between populations were observedmainly for constitutive life history traits, rather than forphenotypic shifts in response to the presence of predator kairomones.     

The evolution of an annual life cycle in killifish: adaptation to ephemeral aquatic environments through embryonic diapause

An annual life cycle is characterized by growth, maturity, and reproduction condensed into a single, short season favourable to development, with production of embryos (seeds, cysts, or eggs) capable of surviving harsh conditions which juveniles or adults cannot tolerate. More typically associated with plants in desert environments, or temperate‐zone insects exposed to freezing winters, the evolution of an annual life cycle in vertebrates is fairly novel. Killifish, small sexually dimorphic fishes in the Order Cyprinodontiformes, have adapted to seasonally ephemeral water bodies across much of Africa and South America through the independent evolution of an annual life history. These annual killifish produce hardy desiccation‐resistant eggs that undergo diapause (developmental arrest) and remain buried in the soil for long periods when fish have perished due to the drying of their habitat. Killifish are found in aquatic habitats that span a continuum from permanent and stable to seasonal and variable, thus providing a useful system in which to piece together the evolutionary history of this life cycle using natural comparative variation. I first review adaptations for life in ephemeral aquatic environments in killifish, with particular emphasis on the evolution of embryonic diapause. I then bring together available evidence from a variety of approaches and provide a scenario for how this annual life cycle evolved. There are a number of features within Aplocheiloidei killifish including their inhabitation of marginal or edge aquatic habitat, their small size and rapid attainment of maturity, and egg properties that make them particularly well suited to the colonization of ephemeral waters.     

Conjugation in Hyalophysa chattoni Bradbury (Apostomatida): An adaptation to a symbiotic life cycle

Hyalophysa chattoni, borne as an encysted phoront on a crustacean's exoskeleton, metamorphoses to the trophont during the host's premolt. After the molt within 15 min to 2 h conjugants with food vacuoles appear in the exuvium, swimming along with the trophonts. Starvation in other ciliates usually precedes conjugation, but food vacuoles in conjugants do not preclude starvation. Only after ingestion and dehydration of vacuoles ceases, does digestion of exuvial fluid begin. Conjugants resorb their feeding apparatus as they fuse. A single imperforate membrane from each partner forms the junction membrane. In a reproductive cyst conjugants divide synchronously, but now the junction membrane is interrupted by pores and channels. After the last division the daughters undergo meiosis – two meiotic divisions and one mitotic division yielding two prokarya as they simultaneously differentiate into tomites. After fertilization, pairs separate and the synkaryon divides once into a macronuclear anlage and a micronucleus. Exconjugants leave the cyst and seek a host. The parental macronucleus remains active until the phoront stage when the anlage develops. Owing to random association of micronuclei during meiosis, Hyalophysa's exconjugants are more genetically diverse than exconjugants from conventional patterns of conjugation.     

Higher vitellogenin concentrations in honey bee workers may be an adaptation to life in temperate climates

The honey bee originated in tropical Africa and later dispersed to northern Europe. It has been suggested that a higher hemolymph storage capacity for the glycolipoprotein vitellogenin evolved in temperate regions, and that the trait constitutes an adaptation to a strongly seasonal environment. We have investigated whether the relative vitellogenin levels of European and African honey bees are in accordance with this hypothesis. Our data indicate that European workers have a higher set-point concentration for vitellogenin compared to their African origin. Considered together with available life history information and physiological data, the results lend support to the view that “winter bees”, a longlived honey bee worker caste that survives winter in temperate regions, evolved through an increase in the worker bees’ capacity for vitellogenin accumulation. Received 20 September 2004; revised 25 March 2005; accepted 13 April 2005.     

Mutualisms in a changing world: an evolutionary perspective

Ecology Letters (2010) 13: 1459-1474 ABSTRACT: There is growing concern that rapid environmental degradation threatens mutualistic interactions. Because mutualisms can bind species to a common fate, mutualism breakdown has the potential to expand and accelerate effects of global change on biodiversity loss and ecosystem disruption. The current focus on the ecological dynamics of mutualism under global change has skirted fundamental evolutionary issues. Here, we develop an evolutionary perspective on mutualism breakdown to complement the ecological perspective, by focusing on three processes: (1) shifts from mutualism to antagonism, (2) switches to novel partners and (3) mutualism abandonment. We then identify the evolutionary factors that may make particular classes of mutualisms especially susceptible or resistant to breakdown and discuss how communities harbouring mutualisms may be affected by these evolutionary responses. We propose a template for evolutionary research on mutualism resilience and identify conservation approaches that may help conserve targeted mutualisms in the face of environmental change.     

Optogenetic manipulation of neural activity in C. elegans: From synapse to circuits and behaviour

The emerging field of optogenetics allows for optical activation or inhibition of excitable cells. In 2005, optogenetic proteins were expressed in the nematode Caenorhabditis elegans for the first time. Since then, C. elegans has served as a powerful platform upon which to conduct optogenetic investigations of synaptic function, circuit dynamics and the neuronal basis of behaviour. The C. elegans nervous system, consisting of 302 neurons, whose connectivity and morphology has been mapped completely, drives a rich repertoire of behaviours that are quantifiable by video microscopy. This model organism's compact nervous system, quantifiable behaviour, genetic tractability and optical accessibility make it especially amenable to optogenetic interrogation. Channelrhodopsin‐2 (ChR2), halorhodopsin (NpHR/Halo) and other common optogenetic proteins have all been expressed in C. elegans. Moreover, recent advances leveraging molecular genetics and patterned light illumination have now made it possible to target photoactivation and inhibition to single cells and to do so in worms as they behave freely. Here, we describe techniques and methods for optogenetic manipulation in C. elegans. We review recent work using optogenetics and C. elegans for neuroscience investigations at the level of synapses, circuits and behaviour.     

Lobula plate and ocellar interneurons converge onto a cluster of descending neurons leading to neck and leg motor neuropil in Calliphora erythrocephala

Summary In the fly, Calliphora erythrocephala, a cluster of three Y-shaped descending neurons (DNOVS 1–3) receives ocellar interneuron and vertical cell (VS4–9) terminals. Synaptic connections to one of them (DNOVS 1) are described. In addition, three types of small lobula plate vertical cell (sVS) and one type of contralateral horizontal neuron (Hc) terminate at DNOVS 1, as do two forms of ascending neurons derived from thoracic ganglia. A contralateral neuron, with terminals in the opposite lobula plate, arises at the DNOVS cluster and is thought to provide heterolateral interaction between the VS4–9 output of one side to the VS4–9 dendrites of the other. DNOVS 2 and 3 extend through pro-, meso-, and metathoracic ganglia, branching ipsilaterally within their tract and into the inner margin of leg motor neuropil of each ganglion. DNOVS 1 terminates as a stubby ending in the dorsal prothoracic ganglion onto the main dendritic trunks of neck muscle motor neurons. Convergence of VS and ocellar interneurons to DNOVS 1 comprises a second pathway from the visual system to the neck motor, the other being carried by motor neurons arising in the brain. Their significance for saccadic head movement and the stabilization of the retinal image is discussed.     

Cyclomorphosis in Daphnia: an adaptation to avoid invertebrate predation

Seasonal morphological changes in three Daphnia species were followed over a two-year period in two lakes that differ in invertebrate and fish pressure. Whereas the morphology of D. hyalina, the biggest of the three species, varied little from season to season, D. cucullata, the smallest, exhibited the most pronounced seasonal changes in head height/carapace length ratio. The pattern of seasonal changes of body proportions was similar in all size classes and isometric growth of the head was reported for D. cucullata. Unlike the head, tail spine length/carapace length ratio almost did not vary seasonally. Strong negative allometry of tail spine growth was observed. These results are consistent with the hypothesis that helmets and tail spines provide protection against invertebrates in the two smallest, thus most endangered species.     

Parallel invasions produce heterogenous patterns of life history adaptation: rapid divergence in an invasive insect

Biotic invasions provide a natural experiment in evolution: when invasive species colonize new ranges, they may evolve new clines in traits in response to environmental gradients. Yet it is not clear how rapidly such patterns can evolve and whether they are consistent between regions. We compare four populations of the invasive cabbage white butterfly (Pieris rapae) from North America and Japan, independently colonized by P. rapae 150 years ago and 300 years ago, respectively. On each continent, we employed a northern and southern population to compare the effects of latitude on body mass, development rate and immune function. For each population, we used a split‐sibling family design in which siblings were reared at either warm (26.7 °C) or cool (20 °C) temperatures to determine reaction norms for each trait. Latitudinal patterns in development time were similar between the two continents. In contrast, there were strong geographical differences in reaction norms for body size, but no consistent effects of latitude; there were no detectable effects of latitude or continent on immune function. These results imply that some life history traits respond consistently to selection along climatic gradients, whereas other traits may respond to local environmental factors, or not at all.     

Responses to a warming world: Integrating life history,immune investment,and pathogen resistance in a model insect species

Environmental temperature has important effects on the physiology and life history of ectothermic animals, including investment in the immune system and the infectious capacity of pathogens. Numerous studies have examined individual components of these complex systems, but little is known about how they integrate when animals are exposed to different temperatures. Here, we use the Indian meal moth (Plodia interpunctella) to understand how immune investment and disease resistance react and potentially trade‐off with other life‐history traits. We recorded life‐history (development time, survival, fecundity, and body size) and immunity (hemocyte counts, phenoloxidase activity) measures and tested resistance to bacterial (E. coli) and viral (Plodia interpunctella granulosis virus) infection at five temperatures (20–30°C). While development time, lifespan, and size decreased with temperature as expected, moths exhibited different reproductive strategies in response to small changes in temperature. At cooler temperatures, oviposition rates were low but tended to increase toward the end of life, whereas warmer temperatures promoted initially high oviposition rates that rapidly declined after the first few days of adult life. Although warmer temperatures were associated with strong investment in early reproduction, there was no evidence of an associated trade‐off with immune investment. Phenoloxidase activity increased most at cooler temperatures before plateauing, while hemocyte counts increased linearly with temperature. Resistance to bacterial challenge displayed a complex pattern, whereas survival after a viral challenge increased with rearing temperature. These results demonstrate that different immune system components and different pathogens can respond in distinct ways to changes in temperature. Overall, these data highlight the scope for significant changes in immunity, disease resistance, and host–parasite population dynamics to arise from small, biologically relevant changes to environmental temperature. In light of global warming, understanding these complex interactions is vital for predicting the potential impact of insect disease vectors and crop pests on public health and food security.     

SMS 2.0: an updated database to study the structural plasticity of short peptide fragments in non-redundant proteins

The function of a protein molecule is greatly influenced by its three-dimensional (3D) structure and therefore structure prediction will help identify its biological function. We have updated Sequence, Motif and Structure (SMS), the database of structurally rigid peptide fragments, by combining amino acid sequences and the corre-sponding 3D atomic coordinates of non-redundant (25%) and redundant (90%) protein chains available in the Protein Data Bank (PDB). SMS 2.0 provides information pertaining to the peptide fragments of length 5-14 resi-dues. The entire dataset is divided into three categories, namely, same sequence motifs having similar, intermedi-ate or dissimilar 3D structures. Further, options are provided to facilitate structural superposition using the pro-gram structural alignment of multiple proteins (STAMP) and the popular JAVA plug-in (Jmol) is deployed for visualization. In addition, functionalities are provided to search for the occurrences of the sequence motifs in other structural and sequence databases like PDB, Genome Database (GDB), Protein Information Resource (PIR) and Swiss-Prot. The updated database along with the search engine is available over the World Wide Web through the following URL http://cluster.physics.iisc.ernet.in/sms/.