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The gut microbial communities of mammals provide numerous benefits to their hosts. However, given the recent development of the microbiome field, we still lack a thorough understanding of the variety of ecological and evolutionary factors that structure these communities across species. Metabarcoding is a powerful technique that allows for multiple microbial ecology questions to be investigated simultaneously. Here, we employed DNA metabarcoding techniques, predictive metagenomics, and culture-dependent techniques to inventory the gut microbial communities of several species of rodent collected from the same environment that employ different natural feeding strategies [granivorous pocket mice (Chaetodipus penicillatus); granivorous kangaroo rats (Dipodomys merriami); herbivorous woodrats (Neotoma albigula); omnivorous cactus mice (Peromyscus eremicus); and insectivorous grasshopper mice (Onychomys torridus)]. Of particular interest were shifts in gut microbial communities in rodent species with herbivorous and insectivorous diets, given the high amounts of indigestible fibers and chitinous exoskeleton in these diets, respectively. We found that herbivorous woodrats harbored the greatest microbial diversity. Granivorous pocket mice and kangaroo rats had the highest abundances of the genus Ruminococcus and highest predicted abundances of genes related to the digestion of fiber, representing potential adaptations in these species to the fiber content of seeds and the limitations to digestion given their small body size. Insectivorous grasshopper mice exhibited the greatest inter-individual variation in the membership of their microbiomes, and also exhibited the highest predicted abundances of chitin-degrading genes. Culture-based approaches identified 178 microbial isolates (primarily Bacillus and Enterococcus), with some capable of degrading cellulose and chitin. We observed several instances of strain-level diversity in these metabolic capabilities across isolates, somewhat highlighting the limitations and hidden diversity underlying DNA metabarcoding techniques. However, these methods offer power in allowing the investigation of several questions concurrently, thus enhancing our understanding of gut microbial ecology., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology.)

Voltage-gated sodium channel Na V 1.8 regulates transmission of pain signals to the brain. While Na V 1.8 has the potential to serve as a drug target, the molecular mechanisms that shape Na V 1.8 gating are not completely understood, particularly mechanisms that couple activation to inactivation. Interactions between toxin producing animals and their predators provide a novel approach for investigating Na V structure-function relationships. Arizona bark scorpions produce Na + channel toxins that initiate pain signaling. However, in predatory grasshopper mice, toxins inhibit Na V 1.8 currents and block pain signals. A screen of synthetic peptide toxins predicted from bark scorpion venom showed that peptide NaTx36 inhibited Na + current recorded from a recombinant grasshopper mouse Na V 1.8 channel (OtNa V 1.8). Toxin NaTx36 hyperpolarized OtNa V 1.8 activation, steady-state fast inactivation, and slow inactivation. Mutagenesis revealed that the first gating charge in the domain I (DI) S4 voltage sensor and an acidic amino acid (E) in the DII SS2 - S6 pore loop are critical for the inhibitory effects of NaTx36. Computational modeling showed that a DI S1 - S2 asparagine (N) stabilizes the NaTx36 - OtNa V 1.8 complex while residues in the DI S3 - S4 linker and S4 voltage sensor form electrostatic interactions that allow a toxin glutamine (Q) to contact the first S4 gating charge. Surprisingly, the models predicted that NaTx36 contacts amino acids in the DII S5 - SS1 pore loop instead of the SS2 - S6 loop; the DII SS2 - S6 loop motif (QVSE) alters the conformation of the DII S5 - SS1 pore loop, enhancing allosteric interactions between toxin and the DII S5 - SS1 pore loop. Few toxins have been identified that modify Na V 1.8 gating. Moreover, few toxins have been described that modify sodium channel gating via the DI S4 voltage sensor. Thus, NaTx36 and OtNa V 1.8 provide tools for investigating the structure-activity relationship between channel activation and inactivation gating, and the connection to alternative pain phenotypes., Competing Interests: TE-A was employed by Amsaal Venom Farm after data was collected for this project. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 George, Lopez-Mateos, Abd El-Aziz, Xiao, Kline, Bao, Raza, Stockand, Cummins, Fornelli, Rowe, Yarov-Yarovoy and Rowe.)

Importance: Reducing physician occupational distress requires understanding workplace mistreatment, its relationship to occupational well-being, and how mistreatment differentially impacts physicians of diverse identities., Objectives: To assess the prevalence and sources of mistreatment among physicians and associations between mistreatment, occupational well-being, and physicians' perceptions of protective workplace systems., Design, Setting, and Participants: This survey study was administered in September and October 2020 to physicians at a large academic medical center. Statistical analysis was performed from May 2021 to February 2022., Main Outcomes and Measures: Primary measures were the Professional Fulfillment Index, a measure of intent to leave, and the Mistreatment, Protection, and Respect Measure (MPR). Main outcomes were the prevalence and sources of mistreatment. Secondary outcomes were the associations of mistreatment and perceptions of protective workplace systems with occupational well-being., Results: Of 1909 medical staff invited, 1505 (78.8%) completed the survey. Among respondents, 735 (48.8%) were women, 627 (47.1%) were men, and 143 (9.5%) did not share gender identity or chose "other"; 12 (0.8%) identified as African American or Black, 392 (26%) as Asian, 10 (0.7%) as multiracial, 736 (48.9%) as White, 63 (4.2%) as other, and 292 (19.4%) did not share race or ethnicity. Of the 1397 respondents who answered mistreatment questions, 327 (23.4%) reported experiencing mistreatment in the last 12 months. Patients and visitors were the most common source of mistreatment, reported by 232 physicians (16.6%). Women were more than twice as likely as men to experience mistreatment (31% [224 women] vs 15% [92 men]). On a scale of 0 to 10, mistreatment was associated with a 1.13 point increase in burnout (95% CI, 0.89 to 1.36), a 0.99-point decrease in professional fulfillment (95% CI, -1.24 to -0.73), and 129% higher odds of moderate or greater intent to leave (odds ratio, 2.29; 95% CI, 1.75 to 2.99). When compared with a perception that protective workplace systems are in place "to a very great extent," a perception that there are no protective workplace systems was associated with a 2.41-point increase in burnout (95% CI, 1.80 to 3.02), a 2.81-point lower professional fulfillment score (95% CI, -3.44 to -2.18), and 711% higher odds of intending to leave (odds ratio, 8.11; 95% CI, 3.67 to 18.35)., Conclusions and Relevance: This survey study found that mistreatment was common among physicians, varied by gender, and was associated with occupational distress. Patients and visitors were the most frequent source, and perceptions of protective workplace systems were associated with better occupational well-being. These findings suggest that health care organizations should prioritize reducing workplace mistreatment.

Pain, though unpleasant, is adaptive in calling an animal's attention to potential tissue damage. A long list of animals representing diverse taxa possess venom-mediated, pain-inducing bites or stings that work by co-opting the pain-sensing pathways of potential enemies. Typically, such venoms include toxins that cause tissue damage or disrupt neuronal activity, rendering painful stings honest indicators of harm. But could pain alone be sufficient for deterring a hungry predator? Some venomologists have argued "no"; predators, in the absence of injury, would "see through" the bluff of a painful but otherwise benign sting or bite. Because most algogenic venoms are also toxic (although not vice versa), it has been difficult to disentangle the relative contributions of each component to predator deterrence. Southern grasshopper mice (Onychomys torridus) are voracious predators of arthropods, feeding on a diversity of scorpion species whose stings vary in painfulness, including painful Arizona bark scorpions (Centruroides sculpturatus) and essentially painless stripe-tailed scorpions (Paravaejovis spinigerus) . Moreover, southern grasshopper mice have evolved resistance to the lethal toxins in bark scorpion venom, rendering a sting from these scorpions painful but harmless. Results from a series of laboratory experiments demonstrate that painful stings matter. Grasshopper mice preferred to prey on stripe-tailed scorpions rather than bark scorpions when both species could sting; the preference disappeared when each species had their stingers blocked. A painful sting therefore appears necessary for a scorpion to deter a hungry grasshopper mouse, but it may not always be sufficient: after first attacking and consuming a painless stripe-tailed scorpion, many grasshopper mice went on to attack, kill, and eat a bark scorpion even when the scorpion was capable of stinging. Defensive venoms that result in tissue damage or neurological dysfunction may, thus, be required to condition greater aversion than venoms causing pain alone.

Studies of venom variability have advanced from describing the mechanisms of action and relative potency of medically important toxins to understanding the ecological and evolutionary causes of the variability itself. While most studies have focused on differences in venoms among taxa, populations, or age-classes, there may be intersexual effects as well. Striped bark scorpions (Centruroides vittatus) provide a good model for examining sex differences in venom composition and efficacy, as this species exhibits dramatic sexual dimorphism in both size and defensive behavior; when threatened by an enemy, larger, slower females stand and fight while smaller, fleeter males prefer to run. We here add evidence suggesting that male and female C. vittatus indeed have different defensive propensities; when threatened via an electrical stimulus, females were more likely to sting than were males. We reasoned that intersexual differences in defensive phenotypes would select for venoms with different functions in the two sexes; female venoms should be effective at predator deterrence, whereas male venoms, less utilized defensively, might be better suited to capturing prey or courting females. This rationale led to our predictions that females would inject more venom and/or possess more painful venom than males. We were wrong. While females do inject more venom than males in a defensive sting, females are also larger; when adjusted for body size, male and female C. vittatus commit equal masses of venom in a sting to a potential enemy. Additionally, house mice (Mus musculus) find an injection of male venom more irritating than an equal amount of female venom, likely because male venom contains more of the toxins that induce pain. Taken together, our results suggest that identifying the ultimate causes of venom variability will, as we move beyond adaptive storytelling, be hard-won., (© The Author 2016. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oup.com.)

FeCo nanoparticles (4 ± 1 nm), encapsulated by SiO2, were synthesized with and without a 2% (atomic ratio) vanadium doping. The impact from the presence of vanadium, an additive often used in the bulk to alter both physical and mechanical properties, on the nanomagnetism was probed by element-specific X-ray spectroscopy and magnetometry techniques. While the nanostructure was unaffected by the addition of 2% vanadium, the temperature dependent magnetic properties were altered significantly, such as the increased coercivity and an exchange bias field shift.

A Quick Guide on grasshopper mice which, contrary to the great majority of mouse species, are obligate carnivores., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Recent studies question the effectiveness of a traditional university curriculum in helping students improve their critical thinking and scientific literacy. We developed an introductory, general education (gen ed) science course to overcome both deficiencies. The course, titled Foundations of Science, differs from most gen ed science offerings in that it is interdisciplinary; emphasizes the nature of science along with, rather than primarily, the findings of science; incorporates case studies, such as the vaccine-autism controversy; teaches the basics of argumentation and logical fallacies; contrasts science with pseudoscience; and addresses psychological factors that might otherwise lead students to reject scientific ideas they find uncomfortable. Using a pretest versus posttest design, we show that students who completed the experimental course significantly improved their critical-thinking skills and were more willing to engage scientific theories the general public finds controversial (e.g., evolution), while students who completed a traditional gen ed science course did not. Our results demonstrate that a gen ed science course emphasizing the process and application of science rather than just scientific facts can lead to improved critical thinking and scientific literacy., (© 2015 M. P. Rowe, B. M. Gillespie, et al. CBE—Life Sciences Education © 2015 The American Society for Cell Biology. This article is distributed by The American Society for Cell Biology under license from the author(s). It is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).)

The integration of superparamagnetic core/shell nanoparticles into devices and other nanoscale technological applications requires a detailed understanding of how the intimate contact between core and shell nanophases affects the magnetism. We report how, for single-domain FeCo nanoparticles, an FeCo phase unique to the nanoscale with silica shells of increasing thicknesses spontaneously formed interfacial metal silicates between the core and shell (such as Fe2SiO4 and Co2SiO4) and altered the overall magnetism of the nanomaterial significantly. The influence of this previously overlooked phenomenon on magnetic properties is reported. Evidence of these metal silicate interfacial layers was observed by X-ray absorption spectroscopy (XAS) collected over the L3,2 absorption edges of Fe and X-ray photoelectron spectra (XPS) collected over the 2p transitions of Fe and Co. Through the correlation of magnetometry and XPS data, the evolution of nanoparticle magnetic anisotropy is shown to increase with the metal silicate.

Sexual dimorphism can result from sexual or ecological selective pressures, but the importance of alternative reproductive roles and trait compensation in generating phenotypic differences between the sexes is poorly understood. We evaluated morphological and behavioral sexual dimorphism in striped bark scorpions (Centruroides vittatus). We propose that reproductive roles have driven sexually dimorphic body mass in this species which produces sex differences in locomotor performance. Poor locomotor performance in the females (due to the burden of being gravid) favors compensatory aggression as part of an alternative defensive strategy, while male morphology is coadapted to support a sprinting-based defensive strategy. We tested the effects of sex and morphology on stinging and sprinting performance and characterized overall differences between the sexes in aggressiveness towards simulated threats. Greater body mass was associated with higher sting rates and slower sprinting within sexes, which explained the greater aggression of females (the heavier sex) and, along with longer legs in males, the improved sprint performance in males. These findings suggest females are aggressive to compensate for locomotor costs of reproduction while males possess longer legs to enhance sprinting for predator evasion and mate finding. Sexual dimorphism in the metasoma ("tail") was unrelated to stinging and sprinting performance and may best be explained by sexual selection.

Painful venoms are used to deter predators. Pain itself, however, can signal damage and thus serves an important adaptive function. Evolution to reduce general pain responses, although valuable for preying on venomous species, is rare, likely because it comes with the risk of reduced response to tissue damage. Bark scorpions capitalize on the protective pain pathway of predators by inflicting intensely painful stings. However, grasshopper mice regularly attack and consume bark scorpions, grooming only briefly when stung. Bark scorpion venom induces pain in many mammals (house mice, rats, humans) by activating the voltage-gated Na(+) channel Nav1.7, but has no effect on Nav1.8. Grasshopper mice Nav1.8 has amino acid variants that bind bark scorpion toxins and inhibit Na(+) currents, blocking action potential propagation and inducing analgesia. Thus, grasshopper mice have solved the predator-pain problem by using a toxin bound to a nontarget channel to block transmission of the pain signals the venom itself is initiating.

Background: Among scorpion species, the Buthidae produce the most deadly and painful venoms. However, little is known regarding the venom components that cause pain and their mechanism of action. Using a paw-licking assay (Mus musculus), this study compared the pain-inducing capabilities of venoms from two species of New World scorpion (Centruroides vittatus, C. exilicauda) belonging to the neurotoxin-producing family Buthidae with one species of non-neurotoxin producing scorpion (Vaejovis spinigerus) in the family Vaejovidae. A pain-inducing α-toxin (CvIV4) was isolated from the venom of C. vittatus and tested on five Na(+) channel isoforms., Principal Findings: C. vittatus and C. exilicauda venoms produced significantly more paw licking in Mus than V. spinigerus venom. CvIV4 produced paw licking in Mus equivalent to the effects of whole venom. CvIV4 slowed the fast inactivation of Na(v)1.7, a Na(+) channel expressed in peripheral pain-pathway neurons (nociceptors), but did not affect the Na(v)1.8-based sodium currents of these neurons. CvIV4 also slowed the fast inactivation of Na(v)1.2, Na(v)1.3 and Na(v)1.4. The effects of CvIV4 are similar to Old World α-toxins that target Na(v)1.7 (AahII, BmK MI, LqhIII, OD1), however the primary structure of CvIV4 is not similar to these toxins. Mutant Na(v)1.7 channels (D1586A and E1589Q, DIV S3-S4 linker) reduced but did not abolish the effects of CvIV4., Conclusions: This study: 1) agrees with anecdotal evidence suggesting that buthid venom is significantly more painful than non-neurotoxic venom; 2) demonstrates that New World buthids inflict painful stings via toxins that modulate Na(+) channels expressed in nociceptors; 3) reveals that Old and New World buthids employ similar mechanisms to produce pain. Old and New World α-toxins that target Na(v)1.7 have diverged in sequence, but the activity of these toxins is similar. Pain-inducing toxins may have evolved in a common ancestor. Alternatively, these toxins may be the product of convergent evolution.

Predators feeding on toxic prey may evolve physiological resistance to the preys' toxins. Grasshopper mice (Onychomys spp.) are voracious predators of scorpions in North American deserts. Two species of grasshopper mice (Onychomys torridus and Onychomys arenicola) are broadly sympatric with two species of potentially lethal bark scorpion (Centruroides exilicauda and Centruroides vittatus) in the Sonoran and Chihuahuan deserts, respectively. Bark scorpions produce toxins that selectively bind sodium (Na(+)) and potassium (K(+)) ion channels in vertebrate nerve and muscle tissue. We previously reported that grasshopper mice showed no effects of bark scorpion envenomation following natural stings. Here we conducted a series of toxicity tests to determine whether grasshopper mice have evolved resistance to bark scorpion neurotoxins. Five populations of grasshopper mice, either sympatric with or allopatric to bark scorpions, were injected with bark scorpion venom; LD50s were estimated for each population. All five populations of grasshopper mice demonstrated levels of venom resistance greater than that reported for non-resistant Mus musculus. Moreover, venom resistance in the mice showed intra- and interspecific variability that covaried with bark scorpion sympatry and allopatry, patterns consistent with the hypothesis that venom resistance in grasshopper mice is an adaptive response to feeding on their neurotoxic prey.

Ground squirrels (Spermophilus spp.) have evolved a battery of defences against the rattlesnakes (Crotalus spp.) that have preyed on them for millions of years. The distinctive behavioural reactions by these squirrels to rattlesnakes have recently been shown to include self-application of rattlesnake scent-squirrels apply scent by vigorously licking their fur after chewing on shed rattlesnake skins. Here, we present evidence that this behaviour is a novel antipredator defence founded on exploitation of a foreign scent. We tested three functional hypotheses for snake scent application--antipredator, conspecific deterrence and ectoparasite defence--by examining reactions to rattlesnake scent by rattlesnakes, ground squirrels and ectoparasites (fleas). Rattlesnakes were more attracted to ground squirrel scent than to ground squirrel scent mixed with rattlesnake scent or rattlesnake scent alone. However, ground squirrel behaviour and flea host choice were not affected by rattlesnake scent. Thus, ground squirrels can reduce the risk of rattlesnake predation by applying rattlesnake scent to their bodies, potentially as a form of olfactory camouflage. Opportunistic exploitation of heterospecific scents may be widespread; many species self-apply foreign odours, but few such cases have been demonstrated to serve in antipredator defence.

An investigation of the modulation of charge transport through thin films of n-octanethiolate monolayer-protected gold nanoparticles (MPN) induced by the sorption of organic vapors is presented. A model is derived that allows predictions of MPN-coated chemiresistor (CR) responses from vapor-film partition coefficients, and analyte densities and dielectric constants. Calibrations with vapors of 28 compounds collected from an array of CRs and a parallel thickness-shear-mode resonator are used to verify assumptions inherent in the model and to assess its performance. Results afford insights into the nature of the vapor-MPN interactions, including systematic variations in apparent film swelling efficiencies, and show that the model can predict CR responses typically to within 24%. Using CRs of different dimensions, vapor sensitivities are found to be virtually independent of the MPN film volume over a range of 104 (device-area x MPN layer thickness). Sensitivities vary inversely with analyte vapor pressure similarly for the two sensor types, but the CR sensor affords significantly greater signal-to-noise ratios, yielding calculated detection limits in the low-part-per-billion concentration range for several of the analytes tested. The implications of these results for implementing MPN-coated CR arrays as detectors in microanalytical systems are considered.

Charge-transfer-mediated olefin-selective sensing by use of chemiresistors (CR) coated with composite films of n-octanethiolate-monolayer-protected gold nanoparticles (C8-MPN) and each of several square-planar PtCl2(olefin)(pyridine) coordination complexes is described. Where the gas-phase olefin analyte differs from that initially coordinated to Pt, olefin substitution occurs and is accompanied by a persistent shift in the composite film resistance. Commensurate changes in film mass are also observed with a similarly coated thickness shear mode resonator. Regeneration is possible by exposure to the initially complexed olefin gas or vapor. If the olefin analyte is the same as that initially coordinated to Pt, then a reversible charge-transfer interaction occurs that is accompanied by a decrease in film resistance (increase in film mass), which recovers spontaneously after removal of the olefin from the atmosphere above the sensor. This behavior differs from that of MPN-coated CRs lacking such Pt complexes, which invariably yield resistance increases upon exposure to nonpolar vapors. Red shifts in the UV-vis absorbance spectra of the PtCl2(olefin)(pyridine) complexes in solution upon addition of free olefin support the hypothesis that Pt-olefin coordination in the composite films creates temporary low-resistance pathways that compete effectively with the concurrent increase in tunneling resistance associated with swelling-induced separation of C8-MPN cores. Structurally analogous non-olefins produce only increases in film resistance. Selective measurement of styrene, ethylene, 1-octene, and 1,3-butadiene is illustrated. Olefin detection limits are reduced as much as 23 000-fold by inclusion of the corresponding Pt complex in the CR interface film. Composite films suffer a gradual loss of selectivity from decomposition of the Pt-olefin complex, apparently facilitated by a Au-Pt charge transfer.

X-linked photopigment polymorphism produces six different color vision phenotypes in most species of New World monkey. In the subfamily Callitrichinae, the three M/L alleles underlying these different phenotypes are present at unequal frequencies suggesting that selective pressures other than heterozygous-advantage operate on these alleles. Earlier we investigated this hypothesis with functional substitution, a technique using a computer monitor to simulate colors as they would appear to humans with monkey visual pigments (Visual Neuroscience 21:217-222, 2004). The stimuli were derived from measurements of ecologically relevant fruit and foliage. We found that discrimination performance depended on the relative spectral positioning of the substituted M and L pigment pair. Here we have undertaken a systematic examination of two simulation parameters--test field luminance and stimulus duration. Discriminability of the fruit colors depended on which phenotype was simulated but only at short stimulus durations and/or low luminances. Under such conditions, phenotypes with the larger pigment peak separations performed better. At longer durations and higher luminances, differences in performance across different substitutions tended to disappear. The stimuli used in this experiment were analyzed with several color discrimination models. There was limited agreement among the predictions made by these models regarding the capabilities of animals with different pigment pairs and none predicted the dependence of discrimination on changes in luminance and stimulus duration.

Recent years have witnessed a growing interest in learning how colour vision has evolved. This trend has been fuelled by an enhanced understanding of the nature and extent of colour vision among contemporary species, by a deeper understanding of the paleontological record and by the application of new tools from molecular biology. This review provides an assessment of the progress in understanding the evolution of vertebrate colour vision. In so doing, we offer accounts of the evolution of three classes of mechanism important for colour vision--photopigment opsins, oil droplets and retinal organisation--and then examine details of how colour vision has evolved among mammals and, more specifically, among primates.

Most platyrrhine monkeys have a triallelic M/L opsin gene polymorphism that underlies significant individual variations in color vision. A survey of the frequencies of these polymorphic genes suggests that the three alleles occur with equal frequency among squirrel monkeys (subfamily Cebinae), but are not equally frequent in a number of species from the subfamily Callitrichinae. This departure from equal frequency in the Callitrichids should slightly increase the ratio of dichromats to trichromats in the population and significantly alter the relative representation of the three possible dichromatic and trichromatic phenotypes. A particular feature of the inequality is that it leads to a relative increase in the number of trichromats whose M/L pigments have the largest possible spectral separation. To assess whether these trichromatic phenotypes are equally well equipped to make relevant visual discriminations, psychophysical experiments were run on human observers. A technique involving the functional substitution of photopigments was used to simulate the discrimination between fruits among a background of leaves. The goal of the simulation was to reproduce in the cones of human observers excitations equivalent to those produced in monkey cones as the animals view fruit. Three different viewing conditions were examined involving variations in the relative luminances of fruit and leaves and the spectrum of the illuminant. In all cases, performance was best for simulated trichromacies including M/L pigments with the largest spectral separation. Thus, the inequality of opsin gene frequency in Callitrichid monkeys may reflect adaptive pressures.

Male threespine stickleback ( Gasterosteus aculeatus) use nuptial colors to attract mates and intimidate rivals. We quantified stickleback color and environmental lighting using methods independent of human perception to evaluate the information transmitted by male signals in a habitat where these signals are displayed. We also developed models of chromatic processing based on four cone photopigments (peak absorptions at 360, 445, 530, and 605 nm) characterized microspectrophotometrically in G. aculeatus and three other stickleback species. We show that a simple opponent mechanism receiving equally weighted inputs from cones with peak absorptions at 445 nm and 605 nm efficiently encodes variation in male throat colors. An orthogonal opponent mechanism-the difference between outputs of 530-nm cones and mean of outputs of 445- and 605-nm cones-produces a neural signal that could be used for species recognition and would be largely insensitive to variation in male throat color. We also show that threespine stickleback throats/photopigments are optimized for this coding scheme. These and other findings lead to testable hypotheses about the spectral processing mechanisms present in the threespine stickleback visual systems and the evolutionary interactions that have shaped this signal/receiver system.

Animal communication involves very dynamic processes that can generate new uses and functions for established communicative activities. In this article, the authors describe how an aposematic signal, the rattling sound of rattlesnakes (Crotalus viridis), has been exploited by 2 ecological associates of rattlesnakes: (a) California ground squirrels (Spermophilus beecheyi) use incidental acoustic cues in rattling sounds to assess the danger posed by the rattling snake, and (b) burrowing owls (Athene cunicularia) defend themselves against mammalian predators by mimicking the sound of rattling. The remarkable similarity between the burrowing owl's defensive hiss and the rattlesnake's rattling reflects both exaptation and adaptation. Such exploitation of the rattling sound has favored alternations in both the structure and the deployment of rattling by rattlesnakes.

We propose that the predator-prey relationship between California ground squirrels, Spermophilus beecheyi beecheyi, and northern Pacific rattlesnakes, Crotalus viridis oreganus, offers a compelling analogy with the well-studied case of intraspecific fighting and assessment. Because ground squirrels frequently place themselves at risk by harassing rattlesnakes, they stand to benefit from assessment strategies which serve to mediate risk. For example, larger and warmer snakes are more dangerous than smaller and cooler ones. These determinants of dangerousness covary with acoustic characteristics of the rattling sounds elicited by squirrel harassment. To determine whether squirrels use these acoustic cues regarding rattlesnake body size and body temperature, we played back rattling and control sounds to individuals in a population of free-living squirrels. The squirrels clearly associated rattling sounds with rattlesnakes and proved capable of assessing both determinants of rattlesnake dangerousness on the basis of acoustic cues. Several features of squirrel behaviour covaried with these acoustic cues, including tail flagging, bipedal posture, and hesitancy to reapproach the area where the rattle was heard. Many of these behavioural differences were sustained for up to 10 min postplayback. Copyright 1999 The Association for the Study of Animal Behaviour.

Adult California ground squirrels, Spermophilus beecheyi beecheyi, actively confront and harass northern Pacific rattlesnakes, Crotalus viridis oreganus, which are the principal predator of ground squirrel pups. In this report we examine the roles of risk (snake size) and context (location of encounter and squirrel reproductive category) in rattlesnake assessment by ground squirrels. In interpreting the results, we borrow heavily from the well-developed conceptual framework applied in the analogous case of intraspecific conflict. Large and small snakes were tethered near the home burrows of male ground squirrels, and maternal and nonmaternal female ground squirrels. Ground squirrels appeared to employ assessment strategies which served to mediate the level of risk associated with confronting larger snakes. The results suggest that ground squirrels exercise greater caution when dealing with large snakes and invest more in monitoring the snake from a safe distance. Maternal squirrels, which have more at stake reproductively, spent more time and effort in snake-directed activities than did squirrels from other reproductive categories. Mothers also differentiated more strongly between large and small snakes, perhaps reflecting the greater vulnerability of their pups to larger snakes. Finally, ground squirrels discriminated between snakes found close to their home burrow and those encountered further abroad. At the home burrow, squirrels monitored the snake from a closer distance, displayed a greater willingness to confront the snake, and escalated to more dangerous levels of harassment. This assessment strategy may reflect a higher payoff to squirrels that persist in driving snakes out of the home area, thereby reducing the risk of future ambush. Copyright 1999 The Association for the Study of Animal Behaviour.

Polarization-difference imaging (PDI) was recently presented by us as a method of imaging through scattering media [Opt. Lett. 20, 608 (1995)]. Here, PDI is compared with conventional, polarizationblind imaging systems under a variety of conditions not previously studied. Through visual and numerical comparison of polarization-difference and polarization-sum images of metallic targets suspended in scattering media, target features initially visible in both types of images are shown to disappear in polarization-sum images as the scatterer concentration is increased, whereas these features remain visible in polarization-difference images. Target features producing an observed degree of linear polarization of less than 1% are visible in polarization-difference images. The ability of PDI to suppress partially polarized background variations selectively is demonstrated, and discrimination of target features on the basis of polarization information is discussed. Our results show that, when compared with conventional imaging, PDI yields a factor of 2-3 increase in the distance at which certain target features can be detected.

Many animals have visual systems that exploit the polarization of light, and some of these systems are thought to compute difference signals in parallel from arrays of photoreceptors optimally tuned to orthogonal polarizations. We hypothesize that such polarization-difference systems can improve the visibility of objects in scattering media by serving as common-mode rejection amplifiers that reduce the effects of background scattering and amplify the signal from targets whose polarization-difference magnitude is distinct from the background. We present experimental results obtained with a target in a highly scattering medium, demonstrating that a manmade polarization-difference system can render readily visible surface features invisible to conventional imaging.

The close apposition of the inner segments of the two cones that combine to form a double cone causes the pair of cone inner segments to guide light as a unitary structure whose transverse sections are roughly elliptical. Electron micrographs of the photoreceptors of a green sunfish (Lepomis cyanellus) retina provide evidence that the refractive index in the ellipsoid region of the inner segments of the double cones is higher in the center than at the perimeter. The hypothesis that the shape and refractive-index gradient could confer differential polarization sensitivity on double cones is examined with a two-dimensional waveguide model of a double-cone inner segment. The model has a dielectric constant that varies parabolically along the narrowest (x) dimension, leading to the index profile: n(x) = nmax[1-(x/x0)2]1/2, where nmax is the peak value of the index and x0 is a parameter specifying the rate at which the index decreases with increasing magnitude of x. A quantity, the polarization contrast, is introduced as a measure of the differential polarization sensitivity of adjacent receptors in the square mosaic of double cones in the sunfish retina. Polarization contrast is proportional to the relative difference in power absorbed by two double cones oriented with their shortest axes orthogonal to each other and stimulated by a field of uniform polarization. Polarization contrast is computed as a function of wavelength for appropriate values of nmax and x0. For normally incident light polarized parallel to one of the two axes of the double cones' cross sections, the polarization contrast is generally between 1% and 5% for wavelengths ranging from 550 to 750 nm. Over most of those wavelengths the polarization contrast of the graded-index-model double cone is approximately five times as large as that of a homogeneous-slab model of the same size and average refractive index. Additional benefits of a graded index, optical isolation of adjacent photoreceptors and antireflection at the photoreceptor entrance, are also discussed.

The past year has seen a growing public awareness of sexual harassment in the workplace. The question of what constitutes sexual harassment and how to recognize it has been debated in the news, the courts, and Congress. This HBR case study is less concerned with defining it than with examining what a manager should do about it. When Filmore Trust manager Jerry Tarkwell found out one of his employees was being sexually harassed on the job, he thought he knew exactly what to do. Following company policy, he immediately notified the bank's equal employment office. Then he called Jill McNair, the employee being harassed. Her response dumbfounded him. "You had no right to call EEO before talking to me," McNair said angrily. Do you have any idea what could happen to me and to my career if people find out about this?" Tarkwell didn't understand; McNair wasn't to blame. He believed the only person who should be worried was the harasser. Tarkwell tried to spell out the procedure for her. "All you have to do is write a letter and ..." McNair cut him off. "If this gets investigated by EEO, everyone in the building could be questioned. I'll probably get transferred, and then I won't have a chance at promotion. And who'd want to work with me? Every man in the company would be afraid I'd report him if he so much as opened a door for me."(ABSTRACT TRUNCATED AT 250 WORDS)