The fluid mechanics of arthropod sniffing in turbulent odor plumes

Many arthropods capture odorant molecules from the environment using antennae or antennules bearing arrays of chemosensory hairs. The penetration of odorant-carrying water or air into the spaces between these chemosensory hairs depends on the speed at which they are moved through the surrounding fluid. Therefore, antennule flicking by crustaceans and wing fanning by insects can have a profound impact on the odorant encounter rates of the chemosensory sensilla they bear; flicking and fanning are examples of sniffing. Odors are dispersed in the environment by turbulent wind or water currents. On the scale of an antenna or antennule, an odor plume is not a diffuse cloud but rather is a series of fine filaments of scent swirling in odor-free water. The spatiotemporal pattern of these filaments depends on distance from the odor source. The physical interaction of a hair-bearing arthropod antennule with the surrounding fluid affects the temporal patterns of odor concentration an animal intercepts when it sniffs in a turbulent odor plume.     

Effects of odor flux and pulse rate on chemosensory tracking in turbulent odor plumes by the blue crab, Callinectes sapidus

The ability of animals to track through chemical plumes is often related to properties of evanescent odor bursts and to small-scale mixing process that determine burst properties. However, odor plumes contain variation over a range of scales, and little is known about how variation in the properties of the odor signal on the scale of one to several seconds affects foraging performance. We examined how flux and pulse rate interact to modulate the search behavior of blue crabs, Callinectes sapidus, locating odor sources in controlled flume flows. Experimental treatments consisted of continuous plumes and plumes with discrete odor pulses at intervals of 2.5 s and 4 s at two fluxes. Crabs experienced diminished search success and reduced search efficiency as flux decreased and the inter-pulse interval lengthened. There often were significant interactions between flux and pulse length, and neither property completely determined search behavior. Thus, over the time span of several seconds, the blue crab chemosensory system is not a simple flux detector. The sensitivity of blue crabs to inter-pulse intervals in the range of several seconds indicates that larger-scale mixing processes, which create odor variation on comparable scales, may exert a significant impact on foraging success in nature.     

Mechanisms of Salmonella pathogenesis in animal models

Animal models play an important role in understanding the mechanisms of bacterial pathogenesis. Here we review the recent studies of Salmonella infection in various animal models. Although mice are a classic animal model for Salmonella, mice do not normally get diarrhea, raising the question of how well the model represents normal human infection. However, pre-treatment of mice with oral streptomycin, which apparently reduces the normal microbiota, leads to an inflammatory diarrheal response upon oral infection with Salmonella. This has led to a re-evaluation of the role of various Salmonella virulence factors in colonization of the intestine and induction of diarrhea. Indeed, it is now clear that Salmonella purposefully induces inflammation, which leads to the production of both carbon sources and terminal electron acceptors by the host that allow Salmonella to outgrow the normal intestinal microbiota. Overall use of this modified mouse model provides a more nuanced understanding of Salmonella intestinal infection in the context of the microbiota with implications for the ability to predict human risk.     

The neural mechanisms of long distance animal navigation

Animal navigation is a complex process involving the integration of many sources of specialized sensory information for navigation in near and far space. Our understanding of the neurobiological underpinnings of near-space navigation is well-developed, whereas the neural mechanisms of long-distance navigation are just beginning to be unraveled. One crucial question for future research is whether the near space concepts of place cells, head direction cells, and maps in the entorhinal cortex scale up to animals navigating over very long distances and whether they are related to the map and compass concepts of long-distance navigation.     

Distinguishing social from nonsocial navigation in moving animal groups

Many animals, such as migrating shoals of fish, navigate in groups. Knowing the mechanisms involved in animal navigation is important when it comes to explaining navigation accuracy, dispersal patterns, population and evolutionary dynamics, and consequently, the design of conservation strategies. When navigating toward a common target, animals could interact socially by sharing available information directly or indirectly, or each individual could navigate by itself and aggregations may not disperse because all animals are moving toward the same target. Here we present an analysis technique that uses individual movement trajectories to determine the extent to which individuals in navigating groups interact socially, given knowledge of their target. The basic idea of our approach is that the movement directions of individuals arise from a combination of responses to the environment and to other individuals. We estimate the relative importance of these responses, distinguishing between social and nonsocial interactions. We develop and test our method, using simulated groups, and we demonstrate its applicability to empirical data in a case study on groups of guppies moving toward shelter in a tank. Our approach is generic and can be extended to different scenarios of animal group movement.     

Mechanisms of lipid peroxide formation in animal tissues

1. Homogenates of rat liver, spleen, heart and kidney form lipid peroxides when incubated in vitro and actively catalyse peroxide formation in emulsions of linoleic acid or linolenic acid. 2. In liver, catalytic activity is distributed throughout the nuclear, mitochondrial and microsomal fractions and is present in the 100000g supernatant. Activity is weak in the nuclear fraction. 3. Dilute (0·5%, w/v) homogenates catalyse peroxidation over the range pH5·0–8·0 but concentrated (5%, w/v) homogenates inhibit peroxidation and destroy peroxide if the solution is more alkaline than pH7·0. 4. Ascorbic acid increases the rate of peroxidation of unsaturated fatty acids catalysed by whole homogenates of liver, heart, kidney and spleen at pH6·0 but not at pH7·4. 5. Catalysis of peroxidation of unsaturated fatty acids by the mitochondrial and microsomal fractions of liver is inhibited by ascorbic acid at pH7·4 but the activity of the supernatant fraction is enhanced. 6. Inorganic iron or ferritin are active catalysts in the presence of ascorbic acid. 7. Lipid peroxide formation in linoleic acid or linolenic acid emulsions catalysed by tissue homogenates is partially inhibited by EDTA but stimulated by o-phenanthroline. 8. Cysteine or glutathione (1mm) inhibits peroxide formation catalysed by whole homogenates, mitochondria or haemoprotein. Inhibition increases with increase of pH.     

Mechanisms of cryoprotection in freezing tolerant animal systems

The theoretical mechanisms of freezing protection afforded by the natural occurrence of glycerol in an adult, freezing-tolerant insect have been considered in light of recent findings. While unequivocal identification of the specific site or sites of action of glycerol is yet obscured in a maze of interactions, it is apparent that a multicellular system (organism) that naturally possesses glycerol in high, nonlethal concentrations, that can maintain activity in the presence of tissue ice, that can survive frequent and prolonged freeze-thaw encounters, and finally, that can regulate cryoprotectant levels in the presence of changing environmental conditions should be a major focus of future studies.The carabid beetle, Pterostichus brevicornis has been found to regulate glycerol levels in response to fluctuating ambient temperatures even while frozen. Hemolymph freezing points and whole-body supercooling points correlated well with changes in glycerol. Freezing and supercooling points decreased 0.9 ° C per 4 g/100 ml increase in glycerol.An interpretation of the data accumulated on insect studies and integrated with data from other multicellular systems supports the theory that a single site of freezing concept as applied to considerations of cryoprotection and cryoinjury may not be realistic. Each level of events occurring during the freezing process in glycerolated and nonglycerolated animal systems has been discussed. There appears little room for speculative separation and isolation of the site of action for the events of freezing (and thawing) represent a continuum with changes in each parameter directly dependent upon the entire sequence.     

Mechanisms of microRNA-mediated gene regulation in animal cells

MicroRNAs are a large family of regulatory molecules found in all multicellular organisms. Even though their functions are only beginning to be understood, it is evident that microRNAs have important roles in a wide range of biological processes, including developmental timing, growth control, and differentiation. Indeed, recent bioinformatic and experimental evidence suggests that a remarkably large proportion of genes (>30%) are subject to microRNA-mediated regulation. Although it is clear that microRNAs function by suppressing protein production from targeted mRNAs, there is, at present, no consensus about how such downregulation is accomplished. In this review, I describe the evidence that there are multiple mechanisms of microRNA-mediated repression and discuss the possible connections between these mechanisms.     

Controlling airborne cues to study small animal navigation

Small animals such as nematodes and insects analyze airborne chemical cues to infer the direction of favorable and noxious locations. In these animals, the study of navigational behavior evoked by airborne cues has been limited by the difficulty of precisely controlling stimuli. We present a system that can be used to deliver gaseous stimuli in defined spatial and temporal patterns to freely moving small animals. We used this apparatus, in combination with machine-vision algorithms, to assess and quantify navigational decision making of Drosophila melanogaster larvae in response to ethyl acetate (a volatile attractant) and carbon dioxide (a gaseous repellant).     

A method to eliminate odor from recirculating air in the animal house.

A new method to eliminate odors from air recirculating in an animal house is described. The new system consists of an ozonizer and titania silica ozone decomposition catalyst in the terminal of a recirculating ventilation system. The principle underlying the elimination of odors is the oxidative reaction of malodorous components on the surface of the catalyst caused by coupling with ozonolysis. This method appeared superior in terms of its durability, efficiency and lack of resistance to air flow.     

Mechanisms and implications of animal flight maneuverability

Accelerations and directional changes of flying animals derivefrom interactions between aerodynamic force production and theinertial resistance of the body to translation and rotation.Anatomical and allometric features of body design thus mediatethe rapidity of aerial maneuvers. Both translational and rotationalresponsiveness of the body to applied force decrease with increasedtotal mass. For flying vertebrates, contributions of the relativelyheavy wings to whole-body rotational inertia are substantial,whereas the relatively light wings of many insect taxa suggestthat rotational inertia is dominated by the contributions ofbody segments. In some circumstances, inertial features of wingdesign may be as significant as are their aerodynamic propertiesin influencing the rapidity of body rotations. Stability inflight requires force and moment balances that are usually attainedvia bilateral symmetry in wingbeat kinematics, whereas bodyroll and yaw derive from bilaterally asymmetric movements ofboth axial and appendicular structures. In many flying vertebrates,use of the tail facilitates the generation of aerodynamic torquesand substantially enhances quickness of body rotation. Geometricalconstraints on wingbeat kinematics may limit total force productionand thus accelerational capacity in certain behavioral circumstances.Unitary limits to animal flight performance and maneuverabilityare unlikely, however, given varied and context-specific interactionsamong anatomical, biomechanical, and energetic features of design.     

Mechanisms of disposal of bacterial lipopolysaccharides by animal hosts

Much of the very extensive literature describing the (bio)chemistry and biology of bacterial lipopolysaccharides (LPS, endotoxin) has dealt with the properties of these molecules as potent triggers of host responses. This brief review will focus on what has been learned recently about mechanisms by which the host can dispose of LPS and counter its often excessive stimulatory effects.     

Mechanisms of arthropod transmission of plant and animal viruses.

A majority of the plant-infecting viruses and many of the animal-infecting viruses are dependent upon arthropod vectors for transmission between hosts and/or as alternative hosts. The viruses have evolved specific associations with their vectors, and we are beginning to understand the underlying mechanisms that regulate the virus transmission process. A majority of plant viruses are carried on the cuticle lining of a vector's mouthparts or foregut. This initially appeared to be simple mechanical contamination, but it is now known to be a biologically complex interaction between specific virus proteins and as yet unidentified vector cuticle-associated compounds. Numerous other plant viruses and the majority of animal viruses are carried within the body of the vector. These viruses have evolved specific mechanisms to enable them to be transported through multiple tissues and to evade vector defenses. In response, vector species have evolved so that not all individuals within a species are susceptible to virus infection or can serve as a competent vector. Not only are the virus components of the transmission process being identified, but also the genetic and physiological components of the vectors which determine their ability to be used successfully by the virus are being elucidated. The mechanisms of arthropod-virus associations are many and complex, but common themes are beginning to emerge which may allow the development of novel strategies to ultimately control epidemics caused by arthropod-borne viruses.     

Mechanisms associated with cellular desiccation tolerance in the animal extremophile artemia

Using differential scanning calorimetry, we demonstrated the presence of biological glasses and measured the transition temperatures in dry encysted embryos (cysts) of the brine shrimp, Artemia franciscana. Cysts from the following three geographic locations were studied: San Francisco Bay (SFB); the Great Salt Lake, Utah (GSL); and the Mekong Delta, Vietnam (VN; these cysts were produced from previous sequential inoculations of SFB cysts into growth ponds). Values for the glass transition temperature, T(g), were highest in VN cysts. This study indicates that the composition and properties of these biological glasses can be altered by natural selection and thermal adaptation. To our knowledge, T(g) values for all three kinds of cysts were significantly higher than those for any other desiccation-tolerant animal system. To gain insight into the significance of T(g), we examined the thermal stability of these dry cysts at 80 °C. GSL cysts were the least tolerant, by far, with VN cysts being extremely tolerant and SFB cysts not far behind. Those results correlated with the thermal transition values. Also measured were alcohol-soluble carbohydrates, ~90% of which is the disaccharide trehalose, a known component of biological glasses. Amounts in the GSL cysts were significantly less than those in the other two kinds of cysts. Several stress proteins were measured in the three groups of cysts, with all of them being in lesser amounts in GSL cysts compared with the SFB and VN cysts. We interpret the data in terms of mechanisms involved with desiccation tolerance and thermal conditions at the sites of cyst collection.     

Mechanisms of cigarette smoke-induced COPD: insights from animal models

Cigarette smoke-induced animal models of chronic obstructive pulmonary disease support the protease-antiprotease hypothesis of emphysema, although which cells and proteases are the crucial actors remains controversial. Inhibition of either serine or metalloproteases produces significant protection against emphysema, but inhibition is invariably accompanied by decreases in the inflammatory response to cigarette smoke, suggesting that these inhibitors do more than just prevent matrix degradation. Direct anti-inflammatory interventions are also effective against the development of emphysema, as are antioxidant strategies; the latter again decrease smoke-induced inflammation. There is increasing evidence for autoimmunity, perhaps directed against matrix components, as a driving force in emphysema. There is intriguing but controversial animal model evidence that failure to repair/failure of lung maintenance also plays a role in the pathogenesis of emphysema. Cigarette smoke produces small airway remodeling in laboratory animals, possibly by direct induction of fibrogenic growth factors in the airway wall, and also produces pulmonary hypertension, at least in part through direct upregulation of vasoactive mediators in the intrapulmonary arteries. Smoke exposure causes goblet cell metaplasia and excess mucus production in the small airways and proximal trachea, but these changes are not good models of either chronic bronchitis or acute exacerbations. Emphysema, small airway remodeling, pulmonary hypertension, and mucus production appear to be at least partially independent processes that may require different therapeutic approaches.