Why do curly tail lizards (genus Leiocephalus) curl their tails? An assessment of displays toward conspecifics and predators

Animal display behaviors are used to convey specific messages to other animals, including potential mates, rivals, and predators. However, because these different types of interactions can be mediated by a single behavioral display, or conversely, multiple signals can be used to convey one specific message, interpretation of any particular behavioral display can be difficult. Leiocephalus lizards (i.e., curly tails) provide an excellent opportunity to study the use of display behaviors across multiple contexts. Previous research has demonstrated that the use of tail curling in these lizards is associated with predation risk, but less is known regarding the use of this behavior in social interactions with conspecifics. The goal of this study was to determine the extent to which tail curling display behavior is used to mediate both social and predatory interactions in two species, Leiocephalus barahonensis and L. carinatus. We found that in lizards of both species, tail curling was used in interactions with both conspecifics and potential (human) predators. However, tail curl intensity did not differ between lizards involved in social encounters and solitary lizards, although L. barahonensis lizards performed more headbobs during social than non‐social observations. Further, L. carinatus lizards exhibited greater intensity of tail curling upon fleeing from a human predator than during observations in which individuals interacted with conspecifics, and lizards that exhibited tighter tail curls fled from predators for a longer distance. Finally, tail curl intensity was not correlated with headbob displays in either species, suggesting that these two components of display communicate different information. Our results suggest that tail curling displays, while consistently a component of interactions with potential predators, are not a necessary component of social interactions. These data contribute to a more complete understanding of how and why visual signals evolve for use in communication across multiple contexts.     

Comparison of LDH-B4 allozymes of macrourids (Teleostei: Gadiformes) by electrophoresis and peptide mapping

The heart-type lactate dehydrogenase (LDH-_B4) homologs of two species of Nezumia and eight species of Coryphaenoides are isomobile on two commonly used electrophoretic buffer systems. To test the hypothesis that the homologs possess the same primary structures, the allozymes from N. bairdii and four species of Coryphaenoides were purified by affinity chromatography on an oxamate aminohexyl Sepharose column and digested with trypsin. The resulting peptide mixtures were then mapped using reversed-phase high-performance liquid chromatography. The peptide maps of the enzyme homologs indicate that the overall similarity of the homologs is high, but unique peptides in each species indicate that the allozymes are not identical in primary structure.     

Viscoelastic properties of passive skeletal muscle in compression—Cyclic behaviour

Skeletal muscle relaxation behaviour in compression has been previously reported, but the anisotropic behaviour at higher loading rates remains poorly understood. In this paper, uniaxial unconfined cyclic compression tests were performed on fresh porcine muscle samples at various fibre orientations to determine muscle viscoelastic behaviour. Mean compression level of 25% was applied and cycles of 2% and 10% amplitude were performed at 0.2–80 Hz. Under cycles of low frequency and amplitude, linear viscoelastic cyclic relaxation was observed. Fibre/cross-fibre results were qualitatively similar, but the cross-fibre direction was stiffer (ratio of 1.2). In higher amplitude tests nonlinear viscoelastic behaviour with a frequency dependent increase in the stress cycles amplitude was found (factor of 4.1 from 0.2 to 80 Hz).The predictive capability of an anisotropic quasi-linear viscoelastic model previously fitted to stress-relaxation data from similar tissue samples was investigated. Good qualitative results were obtained for low amplitude cycles but differences were observed in the stress cycle amplitudes (errors of 7.5% and 31.8%, respectively, in the fibre/cross-fibre directions). At higher amplitudes significant qualitative and quantitative differences were evident. A nonlinear model formulation was therefore developed which provided a good fit and predictions to high amplitude low frequency cyclic tests performed in the fibre/cross-fibre directions. However, this model gave a poorer fit to high frequency cyclic tests and to relaxation tests. Neither model adequately predicts the stiffness increase observed at frequencies above 5 Hz.Together with data previously presented, the experimental data presented here provide a unique dataset for validation of future constitutive models for skeletal muscle in compression.     

LuxS quorum sensing: more than just a numbers game

Quorum sensing is a process of bacterial cell-to-cell communication involving the production and detection of extracellular signaling molecules called autoinducers. Quorum sensing allows populations of bacteria to collectively control gene expression, and thus synchronize group behavior. Processes controlled by quorum sensing are typically ones that are unproductive unless many bacteria act together. Most autoinducers enable intraspecies communication; however, a recently discovered autoinducer AI-2 has been proposed to serve as a 'universal signal' for interspecies communication. Studies suggest that AI-2 encodes information in addition to specifics about cell number.     

Plant disease resistance genes: recent insights and potential applications

Plant disease resistance genes (R genes) encode proteins that detect pathogens. R genes have been used in resistance breeding programs for decades, with varying degrees of success. Recent molecular research on R proteins and downstream signal transduction networks has provided exciting insights, which will enhance the use of R genes for disease control. Definition of conserved structural motifs in R proteins has facilitated the cloning of useful R genes, including several that are functional in multiple crop species and/or provide resistance to a relatively wide range of pathogens. Numerous signal transduction components in the defense network have been defined, and several are being exploited as switches by which resistance can be activated against diverse pathogens.     

Activation of CD74 inhibits migration of human mesenchymal stem cells

Therapeutic administration of mesenchymal stem cells (MSCs) by systemic delivery utilizes the innate ability of the cells to home to damaged tissues, but it can be an inefficient process due to a limited knowledge of cellular cues that regulate migration and homing. Our lab recently discovered that a potent pro-inflammatory cytokine, macrophage migration inhibitory factor (MIF), inhibits MSC migration. Because MIF may act on multiple cellular targets, an activating antibody (CD74Ab) was employed in this study to examine the effect of one MIF receptor, CD74 (major histocompatibility complex class II-associated invariant chain), on MSC motility. CD74 activation inhibits in a dose-dependent manner up to 90% of in vitro migration of MSCs at 40 μg/ml CD74Ab (p?<?0.001), with consistent effects observed among three MSC donor preparations. A blocking peptide from the C-terminus of CD74 eliminates the effect of CD74Ab on MSCs. This suggests that MIF may act on MSCs, at least in part, through CD74. Late-passage MSCs exhibit less chemokinesis than those at passage 2. However, MSCs remain responsive to CD74 activation during ex vivo expansion: MSC migration is inhibited ～2-fold in the presence of 5 µg/ml CD74Ab at passage 9 vs. ～3-fold at passage 2 (p?<?0.001). Consistent with this result, there were no significant differences in CD74 expression at all tested passages or after CD74Ab exposure. Targeting CD74 to regulate migration and homing potentially may be a useful strategy to improve the efficacy of a variety of MSC therapies, including those that require ex vivo expansion.