Potential targets aimed at by spitting cobras when deterring predators from attacking

When threatened, spitting cobras eject venom towards the face of an aggressor. To uncover the relevant cues used by cobras for face recognition we determined how often artificial targets equipped with or without eyes elicited spitting behavior. In addition, we measured whether and how target shape and size influenced the spitting behavior of cobras. Results show that oval- and round-shaped targets were most effective, while triangles with the same surface area as oval ‘face like’ targets hardly elicited spitting. The likelihood of spitting depended on neither the presence, the spatial arrangement (horizontal or vertical) nor the surface texture (shiny or matt) of glass eyes. Most likely, cobras do not specifically aim at the eyes of an offender but at the center of the body part closest to them. As this is usually the face of an animal, this strategy will result in at least one eye of the offender being hit most of the time.     

Spitting cobras adjust their venom distribution to target distance

If threatened by a human, spitting cobras defend themselves by ejecting their venom toward the face of the antagonist. Circulating head movements of the cobra ensure that the venom is distributed over the face. To assure an optimal distribution of the venom, the amplitudes of head movements should decrease with increasing target distance. To find out whether cobras (Naja pallida and N. nigricollis) adjust their spitting behavior according to target distance we induced spitting from different distances and analyzed their spitting patterns. Our results show that the spray pattern of spiting cobras is not fixed. Instead the snake matches its venom distribution to the size of the target independent of target distance.     

Cover-seeking behavior in red spitting cobras (Naja mossambica pallida): Effects of tactile cues and darkness

Eleven red spitting cobras, Naja mossambica pallida, used clear Plexiglas hiding boxes as frequently as they used dark ones in a successive discrimination paradigm (experiment 1), which indicated that thigmotaxic cues can satisfy the cover-seeking needs of the snakes. In simultaneous discrimination tests, however, dark places were always preferred by the snakes (experiments II, III). Therefore, although thigmotaxic cues are sufficient, these plus darkness constitute a more favorable alternative for N m pallida. The husbandry advantages associated with clear hiding boxes, together with their sufficiency for the snakes, argue strongly for their use in many captive environments.     

The phylogeny of cobras inferred from mitochondrial DNA sequences: evolution of venom spitting and the phylogeography of the African spitting cobras (Serpentes: Elapidae: Naja nigricollis complex)

We use phylogenetic analysis of 1333 bp of mitochondrial DNA sequence to investigate the phylogeny and historical biogeography of the cobra-like elapid snakes, with special reference to the evolution of spitting and the phylogeography of the African spitting cobras, a radiation widespread in open vegetational formations throughout sub-Saharan Africa. Our results suggest that spitting adaptations appear to have evolved three times in cobras, but alternative scenarios cannot be rejected. The Asiatic Naja are monophyletic and originate from a single colonization of Asia from Africa. The radiation of the African spitting Naja appears to date back to the early Miocene and many speciation events in the group predate the Pliocene expansion of grasslands and the radiation of large grazing mammals in Africa. The cladogenic events in this complex appear to have been triggered by both ecological changes and tectonic events associated with the formation and expansion of the African Rift Valley. Taxonomically, our data confirm the inclusion of Boulengerina and Paranaja within Naja, and reveal a clade of African rainforest cobras including N. melanoleuca, Paranaja multifasciata and Boulengerina that constitutes the sister clade of the African open-formation non-spitting cobras. Naja nigricollis is polyphyletic, and we therefore recognize N. nigricincta as a separate species, more closely related to N. ashei and N. mossambica than to N. nigricollis.     

Stimulus control of predatory behaviour in red spitting cobras (Naja mossambica pallida) and prairie rattlesnakes (Crotalus v. viridis)

Two experiments examined the responses of red spitting cobras (Naja mossambica pallida) to stimulus properties of rodent prey. In experiment 1 cobras exhibited elevated rates of tongue flicking (RTF) and trail-following behaviour after striking mice and after 15-s presentations of visual-chemical-thermal cues arising from mice held just out of striking range. Disturbance with a clean snake hook did not produce similar effects. In experiment 2 these cobras were compared with prairie rattlesnakes (Crotalus v. viridis). All snakes were exposed to five stimulus conditions in their home cages: (1) 3 s of disturbance (D) with a clean snake hook; (2) 15 s of D; (3) 3 s inspection of a live mouse held out of striking range (NS); (4) 15 s of NS; and (5) a presentation of a live mouse inside striking range (S). The snakes always struck in the latter condition, usually within 3 s. Rattlesnakes exhibited elevated RTF only after S, whereas cobras did so after 15 s of both NS and S. The performance of rattlesnakes was consistent with the assumption that these animals are ambushers; that of cobras was consistent with the assumption that these animals are active hunters which will chase and catch visually detected prey.     

Regulation and Non-Toxicity of the Spit from the Pale Spitting Spider Scytodes Pallida (Araneae: Scytodidae)

The pale spitting spider Scytodes pallida (Aranae: Scytodidae) has a unique habit of spitting a glue‐like and possibly toxic substance at its prey to render them immobile prior to envenomation. Quantitative behavioural studies involving the spit, a first for S. pallida, demonstrate that the spider regulates its spit expenditure when offered prey of variable sizes and struggling intensities. This behaviour interestingly mirrors the regulation of venom expenditure according to prey sizes and difficulties exhibited in other non‐spitting spiders. The spit, however, did not appear to have any toxic effects on different prey types exposed to the spit, opposing the long‐standing belief that the spit from scytodids can poison prey.     

Snake venomics of African spitting cobras: toxin composition and assessment of congeneric cross-reactivity of the pan-African EchiTAb-Plus-ICP antivenom by antivenomics and neutralization approaches

Venomic analysis of the venoms of Naja nigricollis, N. katiensis, N. nubiae, N. mossambica, and N. pallida revealed similar compositional trends. The high content of cytotoxins and PLA(2)s may account for the extensive tissue necrosis characteristic of the envenomings by these species. The high abundance of a type I α-neurotoxin in N. nubiae may be responsible for the high lethal toxicity of this venom (in rodents). The ability of EchiTAb-Plus-ICP antivenom to immunodeplete and neutralize the venoms of African spitting cobras was assessed by antivenomics and neutralization tests. It partially immunodepleted 3FTx and PLA(2)s and completely immunodepleted SVMPs and CRISPs in all venoms. The antivenom neutralized the dermonecrotic and PLA(2) activities of all African Naja venoms, whereas lethality was eliminated in the venoms of N. nigricollis, N. mossambica, and N. pallida but not in those of N. nubiae and N. katiensis. The lack of neutralization of lethality of N. nubiae venom may be of medical relevance only in relatively populous areas of the Saharan region. The impaired activity of EchiTAb-Plus-ICP against N. katiensis may not represent a major concern. This species is sympatric with N. nigricollis in many regions of Africa, although very few bites have been attributed to it.     

The ghost of a recent invasion in the reduced feeding rates of spitting cobras during the dry season in a rainforest region of tropical Africa?

Two species of cobras (Naja melanoleuca and Naja nigricollis) are known to occur in south eastern Nigeria, where much of the pristine rainforest surface has been felled in the last thirty years, and where the actual landscape is generally constituted by a mosaic of farmlands, plantations, suburban areas, with a few remnant forest fragments. In this region, Naja nigricollis is currently extending its range, especially by exploiting recently deforested areas. Based on the known general distribution range of this species and on the available literature data, it appears that Naja nigricollis has been colonizing the forested region of south eastern Nigeria, starting from the relatively arid savannas of central Nigeria, where this species aestivates during the driest months. In the forest region, however, snakes do not need to aestivate during the dry season. Nevertheless, whereas Naja melanoleuca has a foraging activity extended all-the-year round, Naja nigricollis reduces feeding rates during the dry months, although it does not suspend above-ground activity in these months. I suggest that rainforest spitting cobras suspend feeding during the dry months because their behaviour is just a ‘ghost’ of their recent past, when they were ‘normal’ spitting cobras of dry savana regions, which were thus constrained to aestivate during the dry season as it is the rule in this species in central and northern Nigeria. The ‘gost-of-the-past hypothesis’ seems to fit well with the ‘invading’ presence of Naja nigricollis in Nigerian areas where they were reported as rare or, even, absent, up to a few decades ago. Other hypotheses are discussed, and rejected.     

Mucuna pruriens Linn. seed extract pretreatment protects against cardiorespiratory and neuromuscular depressant effects of Naja sputatrix (Javan spitting cobra) venom in rats

Mucuna pruriens has been used by native Nigerians as a prophylactic for snakebite. The protective effects of M. pruriens seed extract (MPE) were investigated against the pharmacological actions of N. sputatrix (Javan spitting cobra) venom in rats. The results showed that MPE-pretreatment protected against cardiorespiratory and, to a lesser extent, neuromuscular depressant effects of N. sputatrix venom. These may be explained at least in part by the neutralisation of the cobra venom toxins by anti-MPE antibodies elicited by the MPE pretreatment.     

A spitting image: specializations in archerfish eyes for vision at the interface between air and water

Archerfish are famous for spitting jets of water to capture terrestrial insects, a task that not only requires oral dexterity, but also the ability to detect small camouflaged prey against a visually complex background of overhanging foliage. Because detection of olfactory, auditory and tactile cues is diminished at air–water interfaces, archerfish must depend almost entirely on visual cues to mediate their sensory interactions with the aerial world. During spitting, their eyes remain below the water''s surface and must adapt to the optical demands of both aquatic and aerial fields of view. These challenges suggest that archerfish eyes may be specially adapted to life at the interface between air and water. Using microspectrophotometry to characterize the spectral absorbance of photoreceptors, we find that archerfish have differentially tuned their rods and cones across their retina, correlated with spectral differences in aquatic and aerial fields of view. Spatial resolving power also differs for aquatic and aerial fields of view with maximum visual resolution (6.9 cycles per degree) aligned with their preferred spitting angle. These measurements provide insight into the functional significance of intraretinal variability in archerfish and infer intraretinal variability may be expected among surface fishes or vertebrates where different fields of view vary markedly.     

Cultural Modulation of Face and Gaze Scanning in Young Children

Previous research has demonstrated that the way human adults look at others’ faces is modulated by their cultural background, but very little is known about how such a culture-specific pattern of face gaze develops. The current study investigated the role of cultural background on the development of face scanning in young children between the ages of 1 and 7 years, and its modulation by the eye gaze direction of the face. British and Japanese participants’ eye movements were recorded while they observed faces moving their eyes towards or away from the participants. British children fixated more on the mouth whereas Japanese children fixated more on the eyes, replicating the results with adult participants. No cultural differences were observed in the differential responses to direct and averted gaze. The results suggest that different patterns of face scanning exist between different cultures from the first years of life, but differential scanning of direct and averted gaze associated with different cultural norms develop later in life.     

The performance of the muscles involved in spitting by the Archerfish Toxotes

The Archerfish Toxotes knocks aerial insects into the water by spitting at them. Spitting has been filmed and the excess pressure in the orobranchial cavity is estimated from the muzzle velocity as 7.2 kN m⁻². A dissection of the head shows that the adductor arcus palatini and geniohyoideus are most likely to be involved in spitting. From measurements made of these muscles, it is calculated that stresses up to at least 210 kN m⁻² must act in them during spitting. Further, it appears from the calculations that these muscles must shorten at rates of 2.4-3.0 muscle lengths sec⁻¹, which seems unlikely at such high stresses. It is possible that a catapult mechanism may be involved.     

Geographical differentiation and cryptic diversity in the monocled cobra,Naja kaouthia (Elapidae), from Thailand

South‐East Asia has an exceptionally high diversity of snakes, with more than 250 snake species currently recorded from Thailand. This diversity likely reflects the diverse range of geographical and climatic conditions under which they live, but the evolutionary history and population genetics of many snake species in South‐East Asia have been little investigated in comparison with morphological studies. Here, we investigated genetic variation in the monocled cobra, Naja kaouthia, Lesson, 1831, across its distribution range in Thailand using mitochondrial DNA (cytochrome b, control region) for ~100 individuals and the nuclear DNA gene (C‐mos) for a small subset. Using population genetic and phylogenetic methods, we show high levels of genetic variation between regional populations of this non‐spitting cobra, including the north‐eastern, north‐central and southern regions, in addition to a population on Pha‐ngan Island, 150 km offshore from the southern peninsula. Moreover, inclusion of the north‐eastern population renders N. kaouthia paraphyletic in relation to other regional Naja species. The north‐eastern population is therefore probably specifically distinct. Given that these cobras are otherwise undifferentiated based on colour and general appearance to the “typical” cobra type of this region, they would represent a cryptic species. As has been shown in other animal groups from Thailand, it is likely that the geographical characteristics and/or tectonic alteration of these regions have facilitated high levels of population divergence of N. kaouthia in this region. Our study highlights the need for dense sampling of snake populations to reveal their systematics, plan conservation and facilitate anti‐snake venom development.     

Changes in visual fields associated with web reduction in the spider family uloboridae

When visual fields of the primitive orb-weaver, Waitkera waitkerensis, are reconstructed using measurements taken from intact lenses and cross and longitudinal sections of the prosoma, they show that this species has complete visual surveillance, but that none of the visual fields of its eight eyes overlap. The more advanced orb-weaver, Uloborus glomosus, also has eight eyes, but each eye has a greater visual angle, giving this species a complex pattern of overlapping visual fields. Uloborids that spin reduced webs are characterized by reduction or loss of the four anterior eyes and other carapace modifications necessary for them to effectively monitor and manipulate their reduced webs. The eyes of these uloborids have greater visual angles than those of orb-weavers, resulting primarily from perimetric expansion of their retinal hemispheres. Additionally, the axes of their visual fields are more ventrally directed due to greater dorsal than ventral retinal expansion and to ventral redirection of the entire eye. Consequently, even though the anterior lateral eyes of the triangle-weaver Hyptiotes cavatus lack retinae, the species' six functional eyes permit complete visual surveillance and exhibit visual overlap. The single-line-weaver, Miagrammopes animotus, has lost its four anterior eyes, and with them much of the anterior vision and all of the visual overlap found in the other species. However, changes similar to those of H. cavatus permit this species to retain most if its dorsal and ventral visual surveillance. Thus, ocular changes act in consort to maintain relatively complete visual surveillance in the face of eye loss and other major carapace modifications necessary for the operation of reduced webs.     

The role of background movement in goldfish vision

In experiments described in the literature objects presented to restrained goldfish failed to induce eye movements like fixation and/or tracking. We show here that eye movements can be induced only if the background (visual surround) is not stationary relative to the fish but moving. We investigated the influence of background motion on eye movements in the range of angular velocities of 5–20° s⁻¹. The response to presentation of an object is a transient shift in mean horizontal eye position which lasts for some 10 s. If an object is presented in front of the fish the eyes move in a direction such that it is seen more or less symmetrically by both eyes. If it is presented at ±70° from the fish's long axis the eye on the side of the object moves in the direction that the object falls more centrally on its retina. During these object induced eye responses the typical optokinetic nystagmus of amplitude of some 5° with alternating fast and slow phases is maintained, and the eye velocity during the slow phase is not modified by presentation of the object. Presenting an object in front of stationary or moving backgrounds leads to transient suppression of respiration which shows habituation to repeated object presentations. Accepted: 14 April 2000     

The effect of eye movement on the control of arm movement to a target

Abstract

The purpose of this study was to investigate the effect of eye movement on the control of arm movement to a target. Healthy humans flexed the elbow to a stationary target in response to a start tone. Simultaneously, the subject moved the eyes to the target (saccade eye movement), visually tracked a laser point moving with the arm (smooth pursuit eye movement), or gazed at a stationary start point at the midline of the horizontal visual angle (non-eye movement—NEM). Arm movement onset was delayed when saccade eye movement accompanied it. The onset of an electromyographic burst in the biceps muscle and the onset of saccade eye movement were almost simultaneous when both the arm and the eyes moved to the target. Arm movement duration during smooth pursuit eye movement was significantly longer than that during saccade eye movement or NEM. In spite of these findings, amplitudes of motor-evoked potential in the biceps and triceps brachii muscles were not significantly different among the eye movement conditions. These findings indicate that eye movement certainly affects the temporal control of arm movement, but may not affect corticospinal excitability in the arm muscles during arm movement.     

Segregation and Recombination of a Multipartite Mitochondrial DNA in Populations of the Potato Cyst Nematode <Emphasis Type="Italic">Globodera pallida</Emphasis>

The discovery that the potato cyst nematode Globodera pallida has a multipartite mitochondrial DNA (mtDNA) composed, at least in part, of six small circular mtDNAs (scmtDNAs) raised a number of questions concerning the population-level processes that might act on such a complex genome. Here we report our observations on the distribution of some scmtDNAs among a sample of European and South American G. pallida populations. The occurrence of sequence variants of scmtDNA IV in population P4A from South America, and that particular sequence variants are common to the individuals within a single cyst, is described. Evidence for recombination of sequence variants of scmtDNA IV in P4A is also reported. The mosaic structure of P4A scmtDNA IV sequences was revealed using several detection methods and recombination breakpoints were independently detected by maximum likelihood and Bayesian MCMC methods. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users. [Reviewing Editor: Dr. Rafael Zardoya]     

Optimal Eye-Gaze Fixation Position for Face-Related Neural Responses

It is generally agreed that some features of a face, namely the eyes, are more salient than others as indexed by behavioral diagnosticity, gaze-fixation patterns and evoked-neural responses. However, because previous studies used unnatural stimuli, there is no evidence so far that the early encoding of a whole face in the human brain is based on the eyes or other facial features. To address this issue, scalp electroencephalogram (EEG) and eye gaze-fixations were recorded simultaneously in a gaze-contingent paradigm while observers viewed faces. We found that the N170 indexing the earliest face-sensitive response in the human brain was the largest when the fixation position is located around the nasion. Interestingly, for inverted faces, this optimal fixation position was more variable, but mainly clustered in the upper part of the visual field (around the mouth). These observations extend the findings of recent behavioral studies, suggesting that the early encoding of a face, as indexed by the N170, is not driven by the eyes per se, but rather arises from a general perceptual setting (upper-visual field advantage) coupled with the alignment of a face stimulus to a stored face template.     

Redescription of Naja siamensis (Serpentes: Elapidae), a widely overlooked spitting cobra from S.E. Asia: geographic variation, medical importance and designation of a neotype

The Indochinese spitting cobra, Naja siamensis Laurenti, 1768, is redescribed. In order to avoid future confusion with other Asiatic Naja species, and to fix this scientific name irrefutably, we designate a neotype for this species, and designate the same specimen as neotype for the junior synonym Naja naja isanensis Nutaphand, 1982. The pattern of geographic variation in this species is investigated by means of multivariate analysis of morphological characters. We summarize the literature concerning this species, with particular emphasis on separating information concerning N. siamensis from that relating to other Asiatic cobra species. This species is of considerable medical importance, and we present case histories of local envenoming and snake venom ophthalmia.     

Salient eyes deter conspecific nest intruders in wild jackdaws (Corvus monedula)

Animals often respond fearfully when encountering eyes or eye-like shapes. Although gaze aversion has been documented in mammals when avoiding group-member conflict, the importance of eye coloration during interactions between conspecifics has yet to be examined in non-primate species. Jackdaws (Corvus monedula) have near-white irides, which are conspicuous against their dark feathers and visible when seen from outside the cavities where they nest. Because jackdaws compete for nest sites, their conspicuous eyes may act as a warning signal to indicate that a nest is occupied and deter intrusions by conspecifics. We tested whether jackdaws’ pale irides serve as a deterrent to prospecting conspecifics by comparing prospectors’ behaviour towards nest-boxes displaying images with bright eyes (BEs) only, a jackdaw face with natural BEs, or a jackdaw face with dark eyes. The jackdaw face with BEs was most effective in deterring birds from making contact with nest-boxes, whereas both BE conditions reduced the amount of time jackdaws spent in proximity to the image. We suggest BEs in jackdaws may function to prevent conspecific competitors from approaching occupied nest sites.