Environmental regulation of life history phenology in Arabidopsis thaliana

The seasonal timing of plant development is regulated by environmental cues. Flowering time is influenced by the temperature and photoperiod experienced during vegetative growth, while germination timing is affected by temperatures during seed maturation and after dispersal. The timing of each developmental transition also determines seasonal conditions experienced during subsequent life stages, however the significance and stability of these interactions are not well understood. This work aimed to further an understanding of the environmental regulation of plant phenology by creating a multi-stage life history model based on Arabidopsis thaliana. Laboratory and field studies were used to inform predictive models of seed development and seed dormancy. The time required to complete seed development was mainly affected by temperature, and was therefore sensitive to seasonal flowering time. Mean daily temperatures at the end of seed maturation had the greatest influence on rates of primary dormancy loss, and post-dispersal temperatures determined rates of secondary dormancy induction. Germination probabilities were predicted by modelling frequencies of primary and secondary dormancy within the seed population. This revealed an abrupt switch from low to high germination when mean daily temperatures exceeded 14°C. Thermoinhibition was also predicted at high temperatures due to rapid secondary dormancy induction. Combining models with a previously described model of flowering time provided a framework for investigating the effects of perturbations on entire life history phenology. Seed set timing in spring and winter annuals was consistently predicted to coincide with mean daily temperatures of 14°C in locations across Northern Europe, resulting in the production of both dormant and non-dormant offspring. Phenotypic plasticity at each growth phase also served to buffer against modest perturbations in germination date, flowering date, and climate in order to maintain these specific dispersal conditions. This result was interpreted as evidence for a robust bet-hedging germination strategy

Massive over-representation of solute-binding proteins (SBPs) from the tripartite tricarboxylate transporter (TTT) family in the genome of the α-proteobacterium Rhodoplanes sp. Z2-YC6860.

Lineage-specific expansion (LSE) of protein families is a widespread phenomenon in many eukaryotic genomes, but is generally more limited in bacterial genomes. Here, we report the presence of 434 genes encoding solute-binding proteins (SBPs) from the tripartite tricarboxylate transporter (TTT) family, within the 8.2 Mb genome of the α-proteobacterium Rhodoplanes sp. Z2-YC6860, a gene family over-representation of unprecedented abundance in prokaryotes. Representing over 6 % of the total number of coding sequences, the SBP genes are distributed across the whole genome but are found rarely in low-GC islands, where the gene density for this family is much lower. This observation, and the much higher sequence identity between the 434 Rhodoplanes TTT SBPs compared with the average identity between homologues from different species, is indicative of a key role for LSE in the expansion. The TTT SBP genes were found in the vicinity of genes encoding membrane components of transport systems from different families, as well as regulatory proteins such as histidine-kinases and transcription factors, indicating a broad range of functions around the sensing, response and transport of organic compounds. A smaller expansion of TTT SBPs is known in some species of the β-proteobacteria Bordetella and we observed similar expansions in other β-proteobacterial lineages, including members of the genus Comamonas and the industrial biotechnology organism Cupriavidus necator, indicating that strong environmental selection can drive SBP duplication and specialisation from multiple evolutionary starting points

A Miniature Animal-Computer Interface for Use with Free-Flying Moths

Although the neurophysiological basis of insect flight control has been studied extensively and successfully in animals attached to rigid tethers, these conditions disrupt the natural feedback between the subject's intentions, sensory input, and motor output. Understanding how individual control algorithms are integrated at a behavioral level requires acquisition and modification of biopotentials in completely untethered, free-flying animals. Herein, I present and test a miniaturized animal-computer interface for use with freely-flying Manduca sexta hawkmoths. This device is capable of simultaneously acquiring two independent biopotential signals, applying electrical neuromuscular stimulation, and correlating collected and applied signals with behavioral data from high-speed videography. Application of this device may offer substantial insight into how insects fly and, by replicating these mechanisms, facilitate wider application of micro air vehicles through improved flight efficiency, stability, and maneuverability

Integrated piezoresistive sensors for atomic force-guided scanning Hall probe microscopy

We report the development of an advanced sensor for atomic force-guided scanning Hall probe microscopy whereby both a high mobility heterostructure Hall effect magnetic sensor and an n-Al0.4Ga0.6As piezoresistive displacement sensor have been integrated in a single III-V semiconductor cantilever. This allows simple operation in high-vacuum/variable-temperature environments and enables very high magnetic and topographic resolution to be achieved simultaneously. Scans of magnetic induction and topography of a number of samples are presented to illustrate the sensor performance at 300 and 77 K. (C) 2003 American Institute of Physics

Neuromuscular and biomechanical compensation for wing asymmetry in insect hovering flight

SUMMARY Wing damage is common in flying insects and has been studied using a variety of approaches to assess its biomechanical and fitness consequences. Results of these studies range from strong to nil effect among the variety of species, fitness measurements and damage modes studied, suggesting that not all damage modes are equal and that insects may be well adapted to compensate for some types of damage. Here, we examine the biomechanical and neuromuscular means by which flying insects compensate for asymmetric wing damage, which is expected to produce asymmetric flight forces and torques and thus destabilize the animal in addition to reducing its total wing size. We measured the kinematic and neuromuscular responses of hawkmoths (Manduca sexta) hovering in free flight with asymmetrically damaged wings via high-speed videography and extracellular neuromuscular activity recordings. The animals responded to asymmetric wing damage with asymmetric changes to wing stroke amplitude sufficient to restore symmetry in lift production. These asymmetries in stroke amplitude were significantly correlated with bilateral asymmetries in the timing of activation of the dorsal ventral muscle among and within trials. Correspondingly, the magnitude of wing asymmetry was significantly, although non-linearly, correlated with the magnitude of the neuromuscular response among individuals. The strongly non-linear nature of the relationship suggests that active neural compensation for asymmetric wing damage may only be necessary above a threshold (>12% asymmetry in wing second moment of area in this case) below which passive mechanisms may be adequate to maintain flight stability

Neuromuscular control of free-flight yaw turns in the hawkmoth Manduca sexta

SUMMARY The biomechanical properties of an animal’s locomotor structures profoundly influence the relationship between neuromuscular inputs and body movements. In particular, passive stability properties are of interest as they may offer a non-neural mechanism for simplifying control of locomotion. Here, we hypothesized that a passive stability property of animal flight, flapping counter-torque (FCT), allows hawkmoths to control planar yaw turns in a damping-dominated framework that makes rotational velocity directly proportional to neuromuscular activity. This contrasts with a more familiar inertia-dominated framework where acceleration is proportional to force and neuromuscular activity. To test our hypothesis, we collected flight muscle activation timing, yaw velocity and acceleration data from freely flying hawkmoths engaged in planar yaw turns. Statistical models built from these data then allowed us to infer the degree to which the moths inhabit either damping- or inertia-dominated control domains. Contrary to our hypothesis, a combined model corresponding to inertia-dominated control of yaw but including substantial damping effects best linked the neuromuscular and kinematic data. This result shows the importance of including passive stability properties in neuromechanical models of flight control and reveals possible trade-offs between manoeuvrability and stability derived from damping