Behavioral snake mimicry in breeding tits

Many animals mimic the behavior or the appearance of venomous snakes.When humans or other potential predators place their hand near the nest of tits belonging to the family Paridae(and a few other species),the incubating female performs a hissing display that mimics the inhalation hiss of a viper or another snake.They hiss vigorously while lunging their head forward and shaking their wings and tail,repeating this behavior several times.The structure of the hiss in tits is similar to that of the inhalation hiss of a snake,providing evidence of significant convergence of the mimic toward the model.The behavior of individual females is repeatable among tri als.Individuals that flew away from their nest box only performed the hissing display on 6%of later trials,when present at their box,whereas individuals that did not fly away hissed on 28% of occasions,consistent with great tits Parus major either cautiously flying away or staying put on their nest while actively defending it.Individuals that flew away produced fewer chicks than individuals that stayed and hissed.The hissing display was more common when snakes were more abundant:1)When breeding late during the season;2)when breeding at sites with more snakes;and 3)when breeding in subtropical and tropical China with a higher abundance of snakes than in Denmark with a lower abundance.The frequency of nest predation was higher in sites with no snakes,and the frequency of predation increased with decreasing frequency of hissing display.These findings are consistent with expectations for frequency-dependent selection acting on snake mimicry.     

Does defensive posture increase mimetic fidelity of caterpillars with eyespots to their putative snake models？

Organisms often evolve behaviours that increase or reinforce the protection from predators afforded by their morpho- logical defences. For example, mimetic animals may adopt postures or locomotory behaviours that emulate a characteristic fea- ture of their model to increase predator deception. Caterpillars with eyespots are thought to mimic snakes, and when threatened many of these caterpillars adopt a posture that appears to enhance this resemblance. Herein we evaluate the quantitative strength of evidence of behavioural mimicry in the caterpillars of 14 species by comparing how closely a series of putative snake-mimicking caterpillars resemble snakes while at rest and when threatened. Specifically, we quantified the head morphology and eye position of a range of snake species, as well as the shape of the apparent head （i.e. anterior body segments） and position of eyespots in caterpillars resting or in their defensive posture. This allowed us to objectively examine evidence for an increased resemblance to either snakes generally, or to Viperidae snakes specifically, upon adopting the defensive posture. Widening the anterior body segments during the defensive posture typically made caterpillars appear more viper-like as opposed to more snake-like in general. Enhanced resemblance to vipers upon mounting the defensive posture was apparent only from the dorsal view. Laterally, caterpillars more closely resembled snakes in the resting posture and shifting to the defensive posture instead reduced mimetic fidelity, Overall we found evidence for behavioural mimicry in all 14 species examined. We highlight that objectively quantifying mimetic fidelity can help identify key features involved in deception .     

Generalization of predator recognition:Velvet geckos display anti-predator behaviours in response to chemicals from non-dangerous elapid snakes

<正> Many prey species detect chemical cues from predators and modify their behaviours in ways that reduce their risk ofpredation. Theory predicts that prey should modify their anti-predator responses according to the degree of threat posed by thepredator. That is, prey should show the strongest responses to chemicals of highly dangerous prey, but should ignore or respondweakly to chemicals from non-dangerous predators. However, if anti-predator behaviours are not costly, and predators are rarelyencountered, prey may exhibit generalised antipredator behaviours to dangerous and non-dangerous predators. In Australia, mostelapid snakes eat lizards, and are therefore potentially dangerous to lizard prey. Recently, we found that the nocturnal velvetgecko Oedura lesueurii responds to chemicals from dangerous and non-dangerous elapid snakes, suggesting that it displays generalisedanti-predator behaviours to chemicals from elapid snakes. To explore the generality of this result, we videotaped the behaviourof velvet geckos in the presence of chemical cues from two small elapid snakes that rarely consume geckos: the nocturnalgolden-crowned snake Cacophis squamulosus and the diurnal marsh snake Hemiaspis signata. We also videotaped geckos in trialsinvolving unscented cards (controls) and cologne-scented cards (pungency controls). In trials involving Cacophis and Hemiaspischemicals, 50% and 63% of geckos spent long time periods ( 3 min) freezing whilst pressed flat against the substrate, respectively.Over half the geckos tested exhibited anti-predator behaviours (tail waving, tail vibration, running) in response to Cacophis(67%) or Hemiaspis (63%) chemicals. These behaviours were not observed in control or pungency control trials. Our resultssupport the idea that the velvet gecko displays generalised anti-predator responses to chemical cues from elapid snakes.Generalised responses to predator chemicals may be common in prey species that co-occur with multiple, ecologically similar,dangerous predators [Current Zoology 56 (3): 337-342, 2010].     

Color variation in signal crayfish Pacifastacus leniusculus

External coloration in animals depends on the interaction of several different factors including the genetics and epigenetics processes that underlie the color expression,the mechanisms of color perception,and the general mechanisms controlling color evolution and function.Among all,camouflages from predators and conspicuousness are of particular interest because pose animal to choose between opposite adjustment in coloration.The external coloration of crustaceans is mainly due to the accumulation of carotenoids in the exoskeleton and the epidermal layer,and the trade-off between camouflage and communication had led to a variety of responses,involving signal partitioning,spectral sensibility,changing coloration,or signaling behavior.Here,we used digital images to explore intrapopulation variability of the external coloration of Pacifastacus leniusculus among body regions within an individual and between sexes.We found that 1)ventral coloration of claws are more saturated and brilliant than upper parts,2)males express a more saturated and brightness coloration than females,especially on the lower portion of claws,3)color intensity and brightness increases with size differently in different body regions,and 4)brightness is more variable in males than in females.All the above patterns support the hypothesis that color in this species could be the result of a compromise between camouflage from predators and conspicuousness for communication.The results of this study suggest that carotenoid might have something to do with intraspecific communication and perform more complex functions than that of a simple pigment.     

Optic tecta I superficial inter neurons detect motion in larval zebrafish

Detection of moving objects is an essential skill for animals to hunt prey,recognize conspecifics and avoid predators.The zebrafish,as a vertebrate model,primarily uses its elaborate visual system to distinguish moving objects against background scenes.The optic tectum(OT)receives and integrates inputs from various types of retinal ganglion cells(RGCs),including direction-selective(DS)RGCs and size-selective RGCs,and is required for both prey capture and predator avoidance.However,it remains largely unknown how motion information is processed within the OT.Here we performed in vivo whole-cell recording and calcium imaging to investigate the role of superficial interneurons(SINs),a specific type of optic tecta I neurons,in motion detection of larval zebrafish.SINs mainly receive excitatory synaptic inputs,exhibit transient ON-or OFF-type of responses evoked by light flashes,and possess a large receptive field(RF).One fifth of SINs are DS and classified into two subsets with separate preferred directions.Furthermore,SINs show size-dependent responses to moving dots.They are efficiently activated by moving objects but not static ones,capable of showing sustained responses to moving objects and having less visual adaptation than periventricular neurons(PVNs),the principal tecta I cells.Behaviorally,ablation of SINs impairs prey capture,which requires local motion detection,but not global looming-evoked escape.Finally,starvation enhances the gain of SINs'motion responses while maintaining their size tuning and DS.These results indicate that SINs serve as a motion detector for sensing and localizing sized moving objects in the visual field.     

Sexual deception： Coevolution or inescapable exploitation？

Sexual deception involves the mimicry of another species＇ sexual signals in order to exploit behavioural routines linked to those signals. Known sexually deceptive systems use visual, acoustic or olfactory mimicry to exploit insects for preda- tion, cleptoparasitism and pollination. It is predicted that where sexual deception inflicts a cost on the receiver, a coevolutionary arms race could result in the evolution of discriminating receivers and increasingly refined mimicry. We constructed a conceptual model to understand the importance of trade-offs in the coevolution of sexually deceptive mimic and receiver. Four components examined were： the cost of mimicry, the cost to receiver for being fooled, the density of mimics and the relative magnitude of a mimicry-independent component of fitness. The model predicts that the exploitation of non-discriminating receivers by accurate signal mimicry will evolve as an evolutionary stable strategy under a wide range of the parameter space explored. This is due to the difficulty in minimising the costs of being fooled without incurring the cost of falsely rejecting real mating opportunities. In the model, the evolution of deception is impeded when mimicry imposes substantial costs for both sides of the arms race. Olfac- tory signals that are potentially cheap to produce are therefore likely to be more vulnerable to exploitation than expensive visual ornaments     

Do animal eyespots really mimic eyes？

The diversity of anti-predator adaptations in the natural world has long been an active area of research in evolutionary and behavioural biology. A common visually-obvious feature found on prey are ＇eyespots＇, being approximately circular mark- ings often with concentric rings and conspicuous colours. These are found on a range of animals, especially adult and larval Lepidoptera and fish. One of the most widespread functions of eyespots seems to be to intimidate or startle predators： delaying, preventing or halting an attack. However, while the fact that they can influence predators in this way is tmcuntroversial, the mechanism（s） behind why they are effective is debated. Traditionally, they have been assumed to work by mimicking the eyes of the predator＇s own enemies, and much research in this field is conducted under the implicit or explicit assumption that this theory is correct. However, eyespots might work simply by being highly salient stimuli that promote sensory overload, biases, or neo- phobic reactions in predators. A range of recent studies has aimed to test these alternatives. Here, we critically evaluate this work and what it tells us about the mechanisms underlying eyespot function. We conclude that although eye mimicry is plausible, there remains a lack of evidence to support it and most observations are at least equally consistent with alternative mechanisms. Finally we also discuss how the debate can be resolved     

Receptor variability-driven evolution of snake toxins

Three-finger toxins(TFTs) are well-recognized nonenzymatic venom proteins found in snakes. However,although TFTs exhibit accelerated evolution, the drivers of this evolution remain poorly understood.The structural complexes between long-chainα-neurotoxins, a subfamily of TFTs, and their nicotinic acetylcholine receptor targets have been determined in previous research, providing an opportunity to address such questions. In the current study, we observed several previously identified positively selected sites(PSSs) and the highly variable C-terminal loop of these toxins at the toxin/receptor interface. Of interest, analysis of the molecular adaptation of the toxin-recognition regions in the corresponding receptors provided no statistical evidence for positive selection. However, these regions accumulated abundant amino acid variations in the receptors from the prey of snakes, suggesting that accelerated substitution of TFTs could be a consequence of adaptation to these variations. To the best of our knowledge, this atypical evolution, initially discovered in scorpions, is reported in snake toxins for the first time and may be applicable for the evolution of toxins from other venomous animals.     

An uneasy alliance:a nesting association between aggressive ants and equally fierce social wasps

Although the Neotropical territorially dominant arboreal ant Azteca chartifex Forel is very aggressive towards any intruder,its populous colonies tolerate the close presence of the fierce polistine wasp Polybia rejecta(F.).In French Guiana,83.33%of the 48 P.rejecta nests recorded were found side by side with those of A.chartifex.This nesting association results in mutual protection from predators(i.e.,the wasps protected from army ants;the ants protected from birds).We conducted field studies,laboratorybased behavioral experiments and chemical analyses to elucidate the mechanisms allowing the persistence of this association.Due to differences in the cuticular profiles of the two species,we eliminated the possibility of chemical mimicry.Also,analyses of the carton nests did not reveal traces of marking on the envelopes.Because ant forager flows were not perturbed by extracts from the wasps’Dufour’s and venom glands,we rejected any hypothetical action of repulsive chemicals.Nevertheless,we noted that the wasps"scraped"the surface of the upper part of their nest envelope using their mandibles,likely removing the ants'scent trails,and an experiment showed that ant foragers were perturbed by the removal of their scent trails.This leads us to use the term"erasure hypothesis."Thus,this nesting association persists thanks to a relative tolerance by the ants towards wasp presence and the behavior of the wasps that allows them to"contain"their associated ants through the elimination of their scent trails,direct attacks,"wing-buzzing"behavior and ejecting the ants.     

Predatory pollinator deception： Does the orchid mantis resemble a model species？

Cases of imperfect or non-model mimicry are common in plants and animals and challenge intuitive assumptions about the nature of directional selection on mimics. Many non-rewarding flower species do not mimic a particular species, but at- tract pollinators through ＇generalised food deception＇. Some predatory animals also attract pollinators by resembling flowers, perhaps the most well known, yet least well understood, is the orchid mantis Hymenopus coronatus. This praying mantis has been hypothesised to mimic a flower corolla and we have previously shown that it attracts and captures pollinating insects as prey. Predatory pollinator deception is relatively unstudied and whether this occurs through model mimicry or generalised food decep- tion in the orchid mantis is unknown. To test whether the orchid mantis mimics a specific model flower species we investigated similarities between its morphology and that of flowers in its natural habitat in peninsular Malaysia. Geometric morphometrics were used to compare the shape of mantis femoral lobes to flower petals. Physiological vision models were used to compare the colour of mantises and flowers from the perspective of bees, flies and birds. We did not find strong evidence for a specific model flower species for the orchid mantis. The mantis＇ colour and shape varied within the range of that exhibited by many flower pet- als rather than resembling one type in particular. We suggest that the orchid mantis resembles an average, or generalised flower-like stimulus. Thus predatory pollinator deception in the orchid mantis is likely to function as a form of generalised food deception, as opposed to model mimicry .     

Orientation of larval and juvenile horseshoe crabs Limulus polyphemus to visual cues: Effects of chemical odors

<正> Adult horseshoe crabs Limulus polyphemus have long served as models for the study of vision in marine arthropods.Yet,little is known about the ability of early life history stages to detect and respond to visual cues.We examined the visuallydirected movements of larvae and first stage juveniles to horizons containing dark visual targets of different sizes.The studytested the hypotheses that (1) larval and juvenile crabs can detect and respond to visual targets and (2) the direction of orientationvaries with the presence of chemical cues associated with settlement habitats.Orientation of larval and juvenile crabs torectangles subtending angles from 30-330° was tested in a circular arena containing water that either lacked estuarine chemicalcues (offshore water) or contained odors from aquatic vegetation or known predators.In the absence of chemical odors,larvaeoriented toward and juveniles moved away from dark horizons subtending angles 60°.When placed in water containingchemical odors from potential nursery habitats,including the seagrasses Halodule wrightii and Syringodium filiforme,crabsreversed their direction of orientation relative to their responses in offshore water.Odors from two known predators,themummichug Fundulus grandis and blue crab Callinectes sapidus,had no affect on the orientation of larvae.Yet,juvenilesresponded to both odors by moving toward the visual target.Results support the hypothesis that the visual orientation of larvaland juvenile horseshoe crabs changes upon exposure to habitat and predator cues and that the direction of the response undergoesan ontogenetic shift following metamorphosis     

Last decade update for three-finger toxins: Newly emerging structures and biological activities

Three-finger toxins(TFTs) comprise one of largest families of snake venom toxins. While they are principal to and the most toxic components of the venoms of the Elapidae snake family, their presence has also been detected in the venoms of snakes from other families. The first TFT, α-bungarotoxin, was discovered almost 50 years ago and has since been used widely as a specific marker of the α7 and muscle-type nicotinic acetylcholine receptors. To date, the number of TFT amino acid sequences deposited in the UniProt Knowledgebase free-access database is more than 700, and new members are being added constantly.Although structural variations among the TFTs are not numerous, several new structures have been discovered recently; these include the disulfide-bound dimers of TFTs and toxins with nonstandard pairing of disulfide bonds. New types of biological activities have also been demonstrated for the well-known TFTs, and research on this topic has become a hot topic of TFT studies. The classic TFTs α-bungarotoxin and α-cobratoxin, for example, have now been shown to inhibit ionotropic receptors of γ-aminobutyric acid, and some muscarinic toxins have been shown to interact with adrenoceptors. New, unexpected activities have been demonstrated for some TFTs as well, such as toxin interaction with interleukin or insulin receptors and even TFT-activated motility of sperm. This minireview provides a summarization of the data that has emerged in the last decade on the TFTs and their activities.     

Lead-phase and red-stripe color morphs of red-backed salamanders Plethodon cinereus differ in hematological stress indices:A consequence of differential predation pressure?

<正> Throughout the animal kingdom there are species that have two or more phenotypic forms or 'morphs', and many ofthese are amphibians. In North America, the red-backed salamander Plethodon cinereus can have either a red dorsal stripe or nodorsal stripe (lead-phase form), and evidence to date indicates the lead-phase form incurs a greater number of attacks from predators.In a recent collection of 51 P. cinereus, blood smears of both color morphs (35 red-stripe, 16 lead-phase) were examined toobtain numbers of circulating leukocytes (via light microscopy), which can be used to indirectly estimate levels of stress hormonesin vertebrates via a 'hematological stress index', which is the ratio between the number of two leukocyte types (neutrophilsand lymphocytes). Our results showed that lead-phase salamanders tended to have greater numbers of circulating neutrophils andlower numbers of circulating lymphocytes than red-stripe morphs, leading to higher average neutrophil-lymphocyte ratios inlead-phase individuals. Since the salamanders were held (refrigerated) for 7 days before sampling, we cannot be certain if this effectis a stress reaction to the captivity or the normal level for this morph. However comparison with two sets of related salamandersthat were captured and sampled immediately indicates the red-stripe salamanders were either not stressed from the captivityat all, or their white blood cell distributions had returned to normal after 7 days of captivity. Taken together, our results indicatethat lead-phase forms of P. cinereus have higher stress levels than the red-stripe forms, which may be a consequence of theirhigher exposure to, and/or attacks from, predators. They may also indicate that the lead-phase form is less-suited to captivity thanthe red-stripe form of this species     

Preliminary Insights into the Habitat Preferences of the Centralian Bandy Bandy （Vermicella vermiformis）（Squamata： Elapidae） in Central Australia

Bandy Bandy’s（Vermicella spp.）are a striking,black-and-white ringed genus of small elapid snakes endemic to Australia.All taxa are burrowers and little is known of their biology and ecology.We investigated the habitat preferences of the only arid-dwelling species,the centralian bandy bandy（Vermicella vermiformis）,in the MacDonnell Ranges west of Alice Springs in the Northern Territory.Using systematic road-cruising,we encountered 16V.vermiformis over a 12 months period between 2009 and 2010.We used logistic regression to model the occurrence of the species against a range of different habitat variables collected at multiple scales.Despite the small sample size,V.vermiformis exhibited a clear preference for acacia shrubland habitats,with acacia variables present in all AICc ranked models in the 95%confidence set.The factors driving this association,together with the preference for habitat not burnt in the most recent wildfires,may be related to the abundance of their only known prey,blind snakes（Ramphotyphlops spp.）.     

A GIM-Based Biomimetic Learning Approach for Motion Generation of a Multi-Joint Robotic Fish

In this paper, we propose a biomimetic learning approach for motion generation of a multi-joint robotic fish. Based on a multi-joint robotic fish model, two basic Carangiform swimming patterns, namely ＂cruise＂ and ＂C sharp turning＂, are extracted as training samples from the observations of real fish swimming. A General Internal Model （GIM）, which is an imitation of Central Pattern Generator （CPG） in nerve systems, is adopted to learn and to regenerate coordinated fish behaviors. By virtue of the universal function approximation ability and the temporal/spatial scalabilities of GIM, the proposed learning approach is able to generate the same or similar fish swimming patterns by tuning two parameters. The learned swimming patterns are implemented on a multi-joint robotic fish in experiments. The experiment results verify the effectiveness of the biomimetic learning approach in generating and modifying locomotion patterns for the robotic fish.     

Bachelor groups in primate multilevel society facilitate gene flow across fragmented habitats

In the face of ongoing habitat fragmentation,many primate species have experienced reduced gene flow resulting in a reduction of genetic diversity,population bottlenecks,and inbreeding depression,including golden snub-nosed monkeys Rhinopithecus roxellana.Golden snub-nosed monkeys live in a multilevel society composed of several 1 male harem units that aggregate to form a cohesive breeding band,which is followed by one or more bachelor groups composed of juvenile,subadult,and adult male members.In this research,we examine the continuous landscape resistance surface,the genetic diversity and patterns of gene flow among 4 isolated breeding bands and 1 all-male band in the Qinling Mountains,China.Landscape surface modeling suggested that human activities and ecological factors severely limit the movement of individuals among breeding bands.Although these conditions are expected to result in reduced gene flow,reduced genetic diversity,and an increased opportunity for a genetic bottleneck,based on population genetic analyses of 13 microsatellite loci from 188 individuals inhabiting 4 isolated breeding bands and 1 all-male band,we found high levels of genetic diversity but low levels of genetic divergence,as well as high rates of gene flow between males residing in the all-male band and each of the 4 breeding bands.Our results indicate that the movement of bachelor males across the landscape,along with their association with several different breeding bands,appears to provide a mechanism for promoting gene flows and maintaining genetic diversity that may counteract the otherwise isolating effects of habitat fragmentation.     

Humidity and seasonality drives body size patterns in males of the bush cricket Isophya rizeensis Sevgili, 2003 （Orthoptera： Tettigoniidae： Phaneropterinae）

Two primary patterns of body size variation have been recorded in ectotherms in relation to latitudinal/altitudinal shifts. In some, body size increases with increasing latitude/altitude whereas, in others, body size decreases with increasing latitude/altitude. This clinal variation is generally assumed to be caused by local adaptation to environmental conditions however the selective variable（s） （temperature, humidity, diet quality, etc.） is still heavily debated. Here we investigate geographic variation in body size of dark and pale color morphs of males of the bush-cricket lsophya rizeensis collected from 15 locations along an elevation gradient ranging from 350 to 2 500 m. Using an information theoretical approach we evaluate the relative support of four different hypotheses （the temperature size rule, the moisture gradient hypothesis, the seasonal constraint hypothesis, and the primary productivity hypothesis） explaining body size variation along the altitudinal gradient. Body size variation in pale color morphs showed a curvilinear relationship with altitude while dark color morphs showed no variation in body size. Body size variation in pale color morphs was highly correlated with precipitation and temperature seasonality values thus giving strong support for the moisture gradient and seasonal constraint hypothesis. Our results reinforce the importance of gradients in humidity and seasonality over temperature in the creation of altitudinal body size clines and the role of selection for resistance to stress factors in the establishment of these clines. Whether a body size cline is observed or not might also depend on the phenotypic properties of the individuals, like coloration.     

The group size effect and synchronization of vigilance in the Tibetan wild ass

Vigilance behavior is considered as an effective strategy for prey species to detect predators.An individual benefits from living in a group by reducing the time spent being vigilant without affecting the probability of detecting a predator.However,the mechanism producing a decrease in vigilance with increasing group size is unclear.Many models of vigilance assume that group members scan independently of one another.Yet in recent studies,the other 2 patterns of vigilance,coordination and synchronization,were reported in some species.In 2 summers(2018 and 2019),we studied the group-size effect on vigilance and foraging of Tibetan wild ass in Chang Tang Nature Reserve of Tibet.We also tested whether individuals scan the environment independently,tend to coordinate their scans,or tend to synchronize their vigilance.The results showed that individuals decreased the time spent on vigilance with increasing group size,while increased the time spent foraging.Group members scanned the environment at the same time more frequently and there was a positive correlation between group members'behaviors,indicating that Tibetan wild asses tend to synchronize their vigilance.