A framework for understanding post-detection deception in predator-prey interactions

Predators and prey exist in persistent conflict that often hinges on deception-the transmission of misleading or manipulative signals-as a means for survival. Deceptive traits are widespread across taxa and sensory systems, representing an evolutionarily successful and common strategy. Moreover, the highly conserved nature of the major sensory systems often extends these traits past single species predator-prey interactions toward a broader set of perceivers. As such, deceptive traits can provide a unique window into the capabilities, constraints and commonalities across divergent and phylogenetically-related perceivers. Researchers have studied deceptive traits for centuries, but a unified framework for categorizing different types of post-detection deception in predator-prey conflict still holds potential to inform future research. We suggest that deceptive traits can be distinguished by their effect on object formation processes. Perceptual objects are composed of physical attributes (what) and spatial (where) information. Deceptive traits that operate after object formation can therefore influence the perception and processing of either or both of these axes. We build upon previous work using a perceiver perspective approach to delineate deceptive traits by whether they closely match the sensory information of another object or create a discrepancy between perception and reality by exploiting the sensory shortcuts and perceptual biases of their perceiver. We then further divide this second category, sensory illusions, into traits that distort object characteristics along either the what or where axes, and those that create the perception of whole novel objects, integrating the what/where axes. Using predator-prey examples, we detail each step in this framework and propose future avenues for research. We suggest that this framework will help organize the many forms of deceptive traits and help generate predictions about selective forces that have driven animal form and behavior across evolutionary time.

Testing bird-driven diurnal trade-offs of the moon moth's anti-bat tail

Traits are often caught in a dynamic tension of countervailing evolutionary pressures. Trade-offs can be imposed by predators evolutionarily curtailing the conspicuousness of a sexually selected trait, or acting in opposition to another natural selection pressure, for instance, a different predator with a divergent hunting strategy. Some moon moths (Saturniidae) have long hindwing tails that thwart echolocating bat attacks at night, allowing the moth to escape. These long tails may come at a cost, however, if they make the moth's roosting form more conspicuous to visually foraging predators during the day. To test this potential trade-off, we offered wild-caught Carolina wrens (Thryothorus ludovicianus) pastry dough models with real Actias luna wings that were either intact or had tails experimentally removed. We video recorded wrens foraging on models and found that moth models with tails did not experience increased detection and attack by birds. Thus, this elaborate trait, while obvious to human observers, does not seem to come at a cost of increased avian predator attention. The evolution of long hindwing tails, likely driven by echolocating predators at night, does not seem to be limited by opposing diurnal constraints. This study demonstrates the importance of testing presumed trade-offs and provides hypotheses for future testing.

Hidden phylogenomic signal helps elucidate arsenurine silkmoth phylogeny and the evolution of body size and wing shape trade-offs

One of the key objectives in biological research is understanding how evolutionary processes have produced Earth's diversity. A critical step towards revealing these processes is an investigation of evolutionary tradeoffs - that is, the opposing pressures of multiple selective forces. For millennia, nocturnal moths have had to balance successful flight, as they search for mates or host plants, with evading bat predators. However, the potential for evolutionary trade-offs between wing shape and body size are poorly understood. In this study, we used phylogenomics and geometric morphometrics to examine the evolution of wing shape in the wild silkmoth subfamily Arsenurinae (Saturniidae) and evaluate potential evolutionary relationships between body size and wing shape. The phylogeny was inferred based on 782 loci from target capture data of 42 arsenurine species representing all 10 recognized genera. After detecting in our data one of the most vexing problems in phylogenetic inference - a region of a tree that possesses short branches and no "support" for relationships (i.e., a polytomy), we looked for hidden phylogenomic signal (i.e., inspecting differing phylogenetic inferences, alternative support values, quartets, and phylogenetic networks) to better illuminate the most probable generic relationships within the subfamily. We found there are putative evolutionary trade-offs between wing shape, body size, and the interaction of fore- and hindwing shape. Namely, body size tends to decrease with increasing hindwing length but increases as forewing shape becomes more complex. Additionally, the type of hindwing (i.e., tail or no tail) a lineage possesses has a significant effect on the complexity of forewing shape. We outline possible selective forces driving the complex hindwing shapes that make Arsenurinae, and silkmoths as a whole, so charismatic.

Noise distracts foraging bats

Predators frequently must detect and localize their prey in challenging environments. Noisy environments have been prevalent across the evolutionary history of predator–prey relationships, but now with increasing anthropogenic activities noise is becoming a more prominent feature of many landscapes. Here, we use the gleaning pallid bat, Antrozous pallidus, to investigate the mechanism by which noise disrupts hunting behaviour. Noise can primarily function to mask—obscure by spectrally overlapping a cue of interest, or distract—occupy an animal's attentional or other cognitive resources. Using band-limited white noise treatments that either overlapped the frequencies of a prey cue or did not overlap this cue, we find evidence that distraction is a primary driver of reduced hunting efficacy in an acoustically mediated predator. Under exposure to both noise types successful prey localization declined by half, search time nearly tripled, and bats used 25% more sonar pulses than when hunting in ambient conditions. Overall, the pallid bat does not seem capable of compensating for environmental noise. These findings have implications for mitigation strategies, specifically the importance of reducing sources of noise on the landscape rather than attempting to reduce the bandwidth of anthropogenic noise.

Fireflies thwart bat attack with multisensory warnings

Many defended animals prevent attacks by displaying warning signals that are highly conspicuous to their predators. We hypothesized that bioluminescing fireflies, widely known for their vibrant courtship signals, also advertise their noxiousness to echolocating bats. To test this postulate, we pit naïve big brown bats (Eptesicus fuscus) against chemically defended fireflies (Photinus pyralis) to examine whether and how these beetles transmit salient warnings to bats. We demonstrate that these nocturnal predators learn to avoid noxious fireflies using either vision or echolocation and that bats learn faster when integrating information from both sensory streams-providing fundamental evidence that multisensory integration increases the efficacy of warning signals in a natural predator-prey system. Our findings add support for a warning signal origin of firefly bioluminescence and suggest that bat predation may have driven evolution of firefly bioluminescence.

The evolution of anti-bat sensory illusions in moths

Prey transmit sensory illusions to redirect predatory strikes, creating a discrepancy between what a predator perceives and reality. We use the acoustic arms race between bats and moths to investigate the evolution and function of a sensory illusion. The spinning hindwing tails of silk moths (Saturniidae) divert bat attack by reflecting sonar to create a misleading echoic target. We characterized geometric morphometrics of moth hindwings across silk moths, mapped these traits onto a new, robust phylogeny, and found that elaborated hindwing structures have converged on four adaptive shape peaks. To test the mechanism underlying these anti-bat traits, we pit bats against three species of silk moths with experimentally altered hindwings that created a representative gradient of ancestral and extant hindwing shapes. High-speed videography of battles reveals that moths with longer hindwings and tails more successfully divert bat attack. We postulate that sensory illusions are widespread and are underappreciated drivers of diversity across systems.

Use of coronary Palmaz-Schatz stent in the percutaneous treatment of vertebral artery stenoses

A case of chronic vertebrobasilar insufficiency due to severe stenoses at the origins of both vertebral arteries was treated with percutaneous transluminal angioplasty and coronary Palmaz-Schatz stents. Use of stents led to a better angiographic result than angioplasty alone. The patient is improved 8 mo later.

Multiple sclerosis mimicking primary brain tumor

Surgical biopsy specimens of multiple sclerosis plaques have been only infrequently reported, and the scanty descriptions of these specimens have generally emphasized the inflammatory nature of the lesion. We present surgical specimens from four patients with multiple sclerosis on whom biopsies were performed because of clinical features mimicking brain tumor. Both general pathologists and neuropathologists involved with these cases experienced difficulty in arriving at the correct diagnosis. In all four cases, the lesions were remarkably uniform in microscopic appearance, consisting of monotonous sheets of gemistocytic astroglia interspersed by numerous foamy macrophages. In sections stained with hematoxylin-eosin, the most helpful diagnostic features were the even distribution of the foamy macrophages and the absence of associated necrosis. In each case, the diagnosis was confirmed with special stains that disclosed total destruction of myelin sheaths with relative preservation of axons. Significant inflammatory infiltration was present in only one of five biopsy specimens.

The effect of tocopherol and dimethyl sulfoxide on focal edema and lipid peroxidation induced by isocortical injection of ferrous chloride

Addition of iron salts to suspensions of subcellular organelles or polyunsaturated fatty acids results in the formation of oxidative free radicals with subsequent initiation of lipid peroxidation. Pretreatment of rats with anti-oxidants prevents peroxidation following isocortical ferrous chloride injection, and increases the rate of resolution of iron-induced focal edema. In this experiment, treatment of rats at the time of injection of 5 microliters of 100 mM FeCl2 with tocopherol and DMSO caused decreased formation of brain peroxidation at the injection site, as measured by formation of MDA. Tocopherol failed to change the quantity of tissue fluid accumulation. However, DMSO alone, or combined with tocopherol, hastened the resolution of brain edema. Tocopherol may terminate peroxidation reactions by donation of a phenolic hydrogen, forming a quinone of tocopherol. DMSO has many pharmacologic effects; however, inhibition of initiation reactions by scavenging hydroxyl radicals, and direct and indirect effects on focal edema accumulation may account for our observations.

Effects of antiperoxidants on FeCl2-induced lipid peroxidation and focal edema in rat brain

Head trauma with contusion or cortical laceration and hemorrhage causes focal edema with encephalomalacia and gliosis. Because cerebral hemorrhage ultimately results in deposition of heme compounds and iron into the neuropil, we injected an aqueous solution of iron salts to simulate the decompartmentalization of iron after trauma. We pretreated animals with saline or with 600 mg/kg alpha-tocopherol plus 5 ppm selenium added to the drinking water. Formation of lipid peroxidation products was significantly inhibited within the iron injection site in the antiperoxidant-pretreated rats at 30, 60, and 120 min after injection of iron into the isocortex. The antiperoxidants failed to prevent formation of focal brain edema at the injection site between 1 and 8 h after injection; however, significantly less edema was present in the alpha-tocopherol + selenium-pretreated animals 24 and 48 h after injection. The efficacy of antiperoxidants in preventing lipid peroxidation, and enhancing the resolution of ferrous-induced focal brain edema suggest that tocopherol + selenium administration caused free radical quenching and termination of lipid peroxidation, and increased membrane stabilization, an effect similar to the action of glucocorticoids.

Formation of malonaldehyde and focal brain edema induced by subpial injection of FeCl2 into rat isocortex

Subpial injection of iron salts or iron-containing blood products into rat isocortex induces recurrent epileptiform discharges coupled with cavitary necrosis and gliosis. Since aqueous iron or heme compounds cause formation of superoxide radicals and peroxidation of membrane lipids, we studied the rate of formation of malonaldehyde (MDA) after subpial injection of 5 microliters of various concentrations of FeCl2 and CoCl2. Injection of CoCl2 failed to alter isocortical MDA levels. However, significant formation of MDA occurred after injection of 25, 50 and 100 mM FeCl2 into rat isocortex. Formation of peak MDA levels of 13.4 +/- 1.0 nmol.mg protein-1 occurred at 15 in to 1 h after 100 mM FeCl2 injection; levels returned to equal control by 12 h. Tissue fluid accumulation occurred by 2 h after FeCl2 injection and persisted for 38 h. Histopathologic assessment using Nissl staining of tissue from the injection site showed loss of cellular staining, coagulation necrosis, and accumulation of macrophages and glial cells. Although these experiments showed the initiation of lipid peroxidation and formation of focal isocortical edema by injection of aqueous solutions of iron salts, we speculate that decompartmentalization of iron red blood cells after trauma, cerebral hemorrhage or infarction may be important in the propagation of tissue damage from such injuries.

Changes in [3H]lysine incorporation into protein in a seizure focus in rat isocortex

A focus of epileptiform discharge was induced in rat isocortex by subpial injection of 5 microliters of 100 mM FeCl3. Control animals were prepared with saline injections. Protein synthesis was estimated by uptake of [3H]lysine and its incorporation into protein at the site of iron injection, in the contralateral homotopic isocortex, and in the midline cerebellum. We found diminished uptake of [3H]lysine into all regions of rat brain in the interictal or nonseizing iron-injected animals, whereas the corrected rate of incorporation of [3H]lysine into protein was not significantly different from control rates. Actively seizing animals showed no inhibition of uptake of [3H]lysine, but [3H]lysine incorporation into protein relative to the uptake was significantly inhibited within the epileptic focus but not in the other areas examined. This decreased incorporation of amino acids into protein parallels that found in animals convulsing after electroshock or pentylenetetrazol injection.

Antiperoxidant pretreatment and iron-induced epileptiform discharges in the rat: EEG and histopathologic studies

Iron causes formation of superoxide radicals resulting in peroxidation of membranous components of tissue. Hemosiderin deposition in human brain often accompanies chronic posttraumatic seizures induced by trauma. We injected an aqueous solution of iron salts, the principal metallic iron of whole blood, into rat isocortex. Serial electroencephalographic recording showed than 94% of untreated animals developed epileptiform discharges. Pretreatment with alpha-tocopherol and with 2 ppm selenium prevented development of iron-induced epileptiform activity in 72% of animals. Histopathologic assessment of serial sections stained with Nissl, hematoxylin and eosin, and prussian blue showed cavitation, neuronal pyknosis and loss, and astrogliosis in untreated animals. The site of iron injection in animals treated with antiperoxidants contained only an area of neuronal pyknosis. The efficacy of antioxidants in preventing development of iron-induced cavitation, gliosis, and epileptiform discharges suggests that peroxidative injury may be important in the development of experimental epilepsy induced by isocortical injection of ferrous chloride.

Dendritic alterations in rat isocortex within an iron-induced chronic epileptic focus

Ferrous chloride was injected into the rat isocortex in 5-microliters volumes as an aqueous solution with a concentration of 100 mM. Bursts of epileptiform discharges were sustained throughout the 6 weeks of observation. Nissl and Golgi-Cox stains showed gliosis and neuronal loss within the injection site. Neurons adjacent to the cavitory lesion showed deformity of dendrites, dendritic nodularity, loss of spines, and string-of-beads deformity. These changes are identical to those found in human epileptogenic foci.

A study of cyclic nucleotide metabolism and the histology of rat liver during 3'-methyl-4-dimethylamino-azobenzene carcinogenesis. II. Cyclic AMP metabolism

We have studied cAMP metabolism in rat livers undergoing carcinogenesis induced by dietary 3'-methyl-4-dimethylaminoazobenzene. A correlation between the biochemical and the histological changes described in the companion paper has been made. In this study, we saw 100% incidence of cholangiocarcinoma by 10 weeks. During weeks 1--10, the biochemistry of tumor-free areas of the livers only was studied; during weeks 11-13, the increased size of the tumors made possible a biochemical study of the tumor tissue as well as the non-tumor tissue, and a comparison between the two was made. Alterations in all parameters of cAMP metabolism were seen from the earliest stages of treatemnt. Most striking were those of adenylate cyclase activity which preceded and accompanied tumor formation, and were seen in both non-tumor and tumor tissue. In the first few weeks of treatment, small acidophilic glycogen-deficient hepatocytes appeared in the periportal areas of the liver lobules. During this time, there was an increase in maximal isoproterenol stimulation of adenylate cyclase and to a lesser extent in the basal activity of the enzyme; increases in phosphodiesterase activity were seen, and were greatest in weeks 1, 2; cAMP levels were diminished in weeks 1, 2 and slightly but not significantly elevated at week 3. From week 4 onwards an even smaller glycogen-deficient cell population appeared in perilobular areas amongst the acidophilic hepatocytes, and tumors began to appear elsewhere in the livers; at this time, there were further marked increases in the basal activity and isoproterenol responsiveness of adenylate cyclase, and the appearance of increased Gpp(NH)p responsiveness of the enzyme; the increase in phosphodiesterase activities seen at week 3 (smaller than that seen in weeks 1, 2) was sustained but did not further increase; cAMP levels were now significantly elevated also, but they did not rise steadily as did the activity of adenylate cyclase. There was a marked difference between the adenylate cyclase activities in non-tumor tissue from tumor-bearing and non-tumor-bearing livers in weeks 4--10, but there was no difference between the phosphodiesterase activities or cAMP levels in these two groups. Adenylate cyclase activity was extremely high in both non-tumor tissue of tumor-bearing livers from weeks 4--10 and tumors from weeks 11--13. Although phosphodiesterase activities were most elevated in the tumors, there were extremely high cyclic AMP levels in these tissues. The difference between the cAMP levels of tumor and non-tumor tissue was striking. Our findings are discussed with respect to the two-state model of carcinogenesis...