The evolution of brain neuron numbers in amniotes.

SignificanceThe evolution of brain processing capacity has traditionally been inferred from data on brain size. However, similarly sized brains of distantly related species can differ in the number and distribution of neurons, their basic computational units. Therefore, a finer-grained approach is needed to reveal the evolutionary paths to increased cognitive capacity. Using a new, comprehensive dataset, we analyzed brain cellular composition across amniotes. Compared to reptiles, mammals and birds have dramatically increased neuron numbers in the telencephalon and cerebellum, which are brain parts associated with higher cognition. Astoundingly, a phylogenetic analysis suggests that as few as four major changes in neuron-brain scaling in over 300 million years of evolution pave the way to intelligence in endothermic land vertebrates.

Animals evoking fear in the Cradle of Humankind: snakes, scorpions, and large carnivores.

Theories explain the presence of fears and specific phobias elicited by animals in contemporary WEIRD (Western, educated, industrialized, rich, and democratic) populations by their evolutionary past in Africa. Nevertheless, empirical data about fears of animals in the Cradle of Humankind are still fragmentary. To fill this gap, we examined which local animals are perceived as the most frightening by Somali people, who inhabit a markedly similar environment and the region where humans have evolved. We asked 236 raters to rank 42 stimuli according to their elicited fear. The stimuli were standardized pictures of species representing the local fauna. The results showed that the most frightening animals were snakes, scorpions, the centipede, and large carnivores (cheetahs and hyenas). These were followed up by lizards and spiders. Unlike in Europe, spiders represent less salient stimuli than scorpions for Somali respondents in this study. This conforms to the hypothesis suggesting that fear of spiders was extended or redirected from other chelicerates.

Measuring fear evoked by the scariest animal: Czech versions of the Spider Questionnaire and Spider Phobia Beliefs Questionnaire.

BACKGROUND: Although tiny in size and mostly harmless, spiders evoke exceptional fear in a significant part of the population and arachnophobia is one of the most common anxiety disorders with prevalence 2.7-6.1%. Two standard measures have been widely used to reliably assess the emotional and cognitive component of spider fear, the Spider Questionnaire (SPQ) and Spider Phobia Beliefs Questionnaire (SBQ). We aimed to develop and validate their Czech translations, describe distribution of spider fear in the Czech population, and analyse its association with disgust propensity and other sociodemographic characteristics. METHODS: In Phase 1, we developed Czech translations of both questionnaires using a back-translation procedure and then tested their psychometric properties against their English versions in a counterbalanced experimental design using the Mann-Whitney U test and two-sided t-test. In Phase 2, we analysed scores on the Czech SPQ and SBQ on a larger sample. We evaluated the effects of age, gender, level of education, biology background, and association with the assessments of snake fear (i.e. the Snake Questionnaire, SNAQ) and disgust propensity (i.e. the Disgust Scale-Revised, DS-R) using a Spearman correlation, redundancy analysis, and general linear models. RESULTS: We have demonstrated that the Czech SPQ and SBQ are equivalent to their originals and show excellent test-retest reliability (SPQ: 0.93; SBQ: 0.87-0.90). In total, 398 (10.3%) out of 3863 subjects reached the cut-off point for potential spider phobia. In addition, SPQ and SBQ scores were highly correlated (0.73-0.79), significantly more than with the SNAQ (0.21-0.32) or the DS-R (0.36-0.40). Two multivariate statistical methods revealed a significant association between the gender, age, level of education, biology background, or disgust propensity and the SPQ scores. CONCLUSION: The Czech SPQ and SBQ may produce reliable and valid assessments of spider fear, but they must be further psychometrically tested considering the limitation of this study before wider use. We corroborate previous findings that fear of spiders is significantly associated with sociodemographic variables, such as gender, age, or education, as well as with the individual level of disgust propensity.

Cytogenetically Elusive Sex Chromosomes in Scincoidean Lizards.

The lizards of the species-rich clade Scincoidea including cordylids, gerrhosaurids, skinks, and xantusiids, show an almost cosmopolitan geographical distribution and a remarkable ecological and morphological divergence. However, previous studies revealed limited variability in cytogenetic traits. The sex determination mode was revealed only in a handful of gerrhosaurid, skink, and xantusiid species, which demonstrated either ZZ/ZW or XX/XY sex chromosomes. In this study, we explored the karyotypes of six species of skinks, two species of cordylids, and one gerrhosaurid. We applied conventional and molecular cytogenetic methods, including C-banding, fluorescence in situ hybridization with probes specific for telomeric motifs and rDNA loci, and comparative genomic hybridization. The diploid chromosome numbers are rather conserved among these species, but the chromosome morphology, the presence of interstitial telomeric sequences, and the topology of rDNA loci vary significantly. Notably, XX/XY sex chromosomes were identified only in Tiliqua scincoides, where, in contrast to the X chromosome, the Y chromosome lacks accumulations of rDNA loci. We confirm that within the lizards of the scincoidean clade, sex chromosomes remained in a generally poor stage of differentiation.

Determinate growth is predominant and likely ancestral in squamate reptiles.

Body growth is typically thought to be indeterminate in ectothermic vertebrates. Indeed, until recently, this growth pattern was considered to be ubiquitous in ectotherms. Our recent observations of a complete growth plate cartilage (GPC) resorption, a reliable indicator of arrested skeletal growth, in many species of lizards clearly reject the ubiquity of indeterminate growth in reptiles and raise the question about the ancestral state of the growth pattern. Using X-ray micro-computed tomography (µCT), here we examined GPCs of long bones in three basally branching clades of squamate reptiles, namely in Gekkota, Scincoidea and Lacertoidea. A complete loss of GPC, indicating skeletal growth arrest, was the predominant finding. Using a dataset of 164 species representing all major clades of lizards and the tuataras, we traced the evolution of determinate growth on the phylogenetic tree of Lepidosauria. The reconstruction of character states suggests that determinate growth is ancestral for the squamate reptiles (Squamata) and remains common in the majority of lizard lineages, while extended (potentially indeterminate) adult growth evolved several times within squamates. Although traditionally associated with endotherms, determinate growth is coupled with ectothermy in this lineage. These findings combined with existing literature suggest that determinate growth predominates in both extant and extinct amniotes.

Comparing developmental stability in unisexual and bisexual rock lizards of the genus Darevskia.

Parthenogenetic species are usually considered to be short-lived due to the accumulation of adverse mutations, lack of genetic variability, and inability to adapt to changing environment. If so, one may expect that the phenotype of clonal organisms may reflect such genetic and/or environmental stress. To test this hypothesis, we compared the developmental stability of bisexual and parthenogenetic lizards of the genus Darevskia. We assessed asymmetries in three meristic traits: ventral, preanal, and supratemporal scales. Our results suggest that the amount of ventral and preanal asymmetries is significantly higher in clones compared with their maternal, but not paternal, progenitor species. However, it is questionable, whether this is a consequence of clonality, as it may be considered a mild form of outbreeding depression as well. Moreover, most ventral asymmetries were found in the bisexual species Darevskia valentini. We suggest that greater differences in asymmetry levels among bisexuals may be, for instance, a consequence of the population size: the smaller the population, the higher the inbreeding and the developmental instability. On the basis of the traits examined in this study, the parthenogens do not seem to be of significantly poorer quality.

A gyroscopic advantage: phylogenetic patterns of compensatory movements in frogs.

Head and eye compensatory movements known as vestibulo-ocular and vestibulo-cervical reflexes are essential to stay orientated in space while moving. We have used a previously developed methodology focused on the detailed mathematical description of head compensatory movements in frogs without the need for any surgical procedures on the examined specimens. Our comparative study comprising 35 species of frogs from different phylogenetic backgrounds revealed species-specific head compensatory abilities ensuring gaze stabilization. Moreover, we found a strong phylogenetic signal highlighting the great ability of compensatory head movements in families of Pyxicephalidae and Rhacophoridae from the Natatanura group. By contrast, families of Dendrobatidae and Microhylidae exhibited only poor or no head compensatory movements. Contrary to our expectation, the results did not corroborate an ecomorphological hypothesis anticipating a close relationship between ecological parameters and the head compensatory movements. We did not find any positive association between more complex (3D structured, arboreal or aquatic) habitats or more saltatory behavior and elevated abilities of head compensatory movements. Moreover, we found compensatory movements in most basal Archeobatrachia, giving an indication of common ancestry of these abilities in frogs that are variously pronounced in particular families. We hypothesize that the uncovered proper gaze stabilization during locomotion provided by the higher head compensatory abilities can improve or even enable visual perception of the prey. We interpret this completely novel finding as a possible gyroscopic advantage in a foraging context. We discuss putative consequences of such advanced neuromotor skills for diversification and ecological success of the Natatanura group.

Human evaluation of amphibian species: a comparison of disgust and beauty.

Animals can evoke a wide range of emotions helping us to choose a quick and appropriate reaction towards them: approach or avoidance in general. This work has focused on disgust evoked by amphibians in humans as well as perceived beauty. Due to the high morphological variability of recent amphibian taxa, we examined humans' cognitive categorisation of 101 amphibian photos and the effect of stimuli characteristics on disgust evaluation or beauty perception of individual groups/species. We also explored how respondents' characteristics, e.g. gender, age and disgust sensitivity (DS-R) influence the disgust and beauty evaluation of picture stimuli on a 7-point Likert scale. The scores of disgust and beauty evaluation were strongly negatively correlated, representing the opposite ends of a single axis, further referred to as the index of preference. The most preferred amphibians belonged to anurans, whereas the least preferred ones were mostly worm-like, legless and small-eyed caecilians. Additional analyses of morphologically diverse anurans showed that species with a round body shape, short forelegs, small eyes, warts, pink and grey colouration, or dark and dull colouration were perceived as disgusting or ugly. The effect of gender and age were only marginal; however, people with higher disgust sensitivity rated amphibians as more disgusting and less beautiful, which might support the hypothesis of a possible disgust involvement in animal fears and phobias. This topic has implications not only for the nature conservation decisions of globally endangered amphibians but also for understanding the evolution of disgust and its generalisation to harmless animals.

Beauty ranking of mammalian species kept in the Prague Zoo: does beauty of animals increase the respondents' willingness to protect them?

Aesthetic preferences for animals correspond with the species' presence in the worldwide zoos and influence the conservation priorities. Here, we investigated the relationship between the willingness of respondents to protect mammals and some attributed characteristics such as their aesthetic beauty. Further, several methodological aspects of measuring mammalian beauty were assessed. Animal beauty was associated not only with the respondents' willingness to protect the species but also with its attributed dangerousness and usefulness. We found that the most preferred animals were carnivores and ungulates, whilst smaller species of rodents and afrosoricids were unpopular. The main characteristics determining that an animal will be ranked as beautiful were complex fur pattern and body shape. We demonstrated that the position of mammalian species along the 'beauty' axis is surprisingly stable, no matter the form (illustrations vs photographs), context of stimulus presentation (several number of stimuli per family vs one randomly selected species per family), or the method of beauty evaluation (relative order vs Likert's scale).

Sex allocation and secondary sex ratio in Cuban boa (Chilabothrus angulifer): mother's body size affects the ratio between sons and daughters.

Secondary sex ratios of animals with genetically determined sex may considerably deviate from equality. These deviations may be attributed to several proximate and ultimate factors. Sex ratio theory explains some of them as strategic decisions of mothers improving their fitness by selective investment in sons or daughters, e.g. local resource competition hypothesis (LRC) suggests that philopatric females tend to produce litters with male-biased sex ratios to avoid future competition with their daughters. Until now, only little attention has been paid to examine predictions of sex ratio theory in snakes possessing genetic sex determination and exhibiting large variance in allocation of maternal investment. Cuban boa is an endemic viviparous snake producing large-bodied newborns (∼200 g). Extremely high maternal investment in each offspring increases importance of sex allocation. In a captive colony, we collected breeding records of 42 mothers, 62 litters and 306 newborns and examined secondary sex ratios (SR) and sexual size dimorphism (SSD) of newborns. None of the examined morphometric traits of neonates appeared sexually dimorphic. The sex ratio was slightly male biased (174 males versus 132 females) and litter sex ratio significantly decreased with female snout-vent length. We interpret this relationship as an additional support for LRC as competition between mothers and daughters increases with similarity of body sizes between competing snakes.

Strong support for Rensch's rule in an American clade of lizards (Teiidae and Gymnophtalmidae) and a paradox of the largest tejus.

Rensch's rule predicts an allometric relationship between male and female body size stating that the sexual size dimorphism (SSD) increases with body size in male-larger taxa and decreases in female-larger taxa in groups of related species. It means that the relationship between the male and female body size is hyperallometric, i.e., the allometric exponent of this relationship exceeds the unity. We explored the relationship between the male and female body size in a New World clade of lizards consisting of sister families Teiidae and Gymnophthalmidae, which exhibit a great variation in both their adult body sizes and SSD. All our estimates of the reduced major axis regression slopes ranged from 1.067 to 1.229 and clearly followed a pattern consistent with the Rensch's rule. Despite a clear general trend, giant species from the subfamily Tupinambinae show paradoxically only poor SSD. The cases of extreme male-larger SSD were found in species of moderate body size belonging to the genera Ameiva and Cnemidophorus. The abovementioned deviations from the hyperallometric relationship between the male and female body size are surprising and require further examination.

Why is the tongue of blue-tongued skinks blue? Reflectance of lingual surface and its consequences for visual perception by conspecifics and predators.

Blue-tongued skinks of the genus Tiliqua (Scincidae) are characterized by their large blue melanin-pigmented tongues, often displayed during open-mouth threats, when the animal feels endangered. It is not clear whether this unusual coloration is a direct anti-predation adaptation or it may rather serve intraspecific communication, as ultraviolet-blue color is a frequent visual signal in a number of lizard species. We used spectrophotometry and visual modeling to compare blue tongues of Tiliqua gigas with tongues and skin coloration of other lizard species, and to examine their appearance through the eyes of both the conspecifics and avian predators. Our results show that (1) the tongue coloration is probably not substantially influenced by the amount of melanin in the skin, (2) lingual and oral tissues are UV-reflective in general, with blue colored tongues having chromatic qualities similar to UV-blue skin patches of other lizard species, (3) UV-blue tongues are more conspicuous than pink tongues, especially in the visual model of conspecifics. We hypothesize that blue tongues may possibly serve as a semantic (honest) signal analogous to UV-blue skin patches of other lizard species due to greater UV-bias in the vision of diurnal lizards. Regarding the social behavior and high aggressiveness in Tiliqua and their relatives, such signal might serve, e.g., in intraspecific long-distance communication between conspecifics in order to avoid aggression, and its anti-predation effect may only be a secondary function (exaptation).

Structural consistency of exploratory behaviour of sub-adult and adult spiny mice (Acomys cahirinus) in seven different tests.

The genus Acomys is of growing importance to many research fields. Previous research has shown that individuals differ when exploring new environments and that these behavioural strategies are consistent in time. In this study, we subjected 60 commensal Acomys cahirinus (37 males, 23 females) to a series of seven tests (free exploration, forced exploration under bright illumination, forced exploration under low illumination, hole board test, vertical activity test, elevated plus maze, and voluntary wheel running) to acquire independent behavioural traits and investigate whether and how personality develops in spiny mice. The full series of experiments was performed twice during ontogeny: once in the sub-adult stage (tested at 62-72 days of age) and once in the adult stage (102-112 days of age). We found that behaviour of the animals was repeatable both within (range of R values from 0.155 to 0.726) and across the two life-stages (0.238 to 0.563). While the structure of behaviour in adults was rather clear, it had not been fully crystalized in sub-adults, suggesting personality changes during maturation, even though some individual traits might be repeatable across ontogeny. Notably, the most consistent behavioural traits across the different tests were jumping and rearing, which are not commonly reported.

Social deprivation in maternal mouthbrooders Tropheus sp. "Caramba" (Teleostei: Cichlidae) decreases the success rate of reproduction and survival rate of fish fry.

Early offspring separation from mothers causes social deprivation. Mouthbrooding, when eggs and fry are incubated in the buccal cavity of the parent, is one of the reproductive strategies in fish. The mother is the incubating parent in African lake cichlids from the genus Tropheus. Many of these are produced in captivity and some producers use artificial incubators in which eggs are incubated separately from the mother. We hypothesized that this practice may dramatically modify the reproduction rate of fish individuals produced by the method of artificial incubation. The long-term experiment focused on Tropheus sp. "Caramba" had been carried out for 10 years when maternally incubated and separated individuals were compared. We found a negative effect of artificial egg and offspring incubation out of the mother's buccal cavity. The deprived females laid the same number of eggs as maternally incubated females, but most eggs were lost during the incubation. Moreover, the reproduction frequency was significantly lower in deprived females in comparison with those maternally incubated. This study should be perceived as preliminary. For this reason and with respect to welfare principles, we strongly recommend similarly designed experiments focused on other potentially sensitive fish mouthbrooders. Once the syndrome would be confirmed, we recommend avoiding artificial incubation of mouthbrooding fish in general.

Protecting isolated reptile populations outside their main area of distribution: a predictive model of the Dice snake, Natrixtessellata, distribution in the Czech Republic.

Marginal populations of animals are highly susceptible to environmental pressures associated with climatic changes. Understanding their distribution and ecological requirements is, thus, essential for the development of efficient conservation strategies. The dice snake, Natrixtessellata, is listed as critically endangered in the Czech Republic. In certain regions (Bohemia and Silesia), its populations are located beyond the northern border of the continuous range of the species, while the south Moravian populations are connected to it. Based on the statewide database of the Czech Nature Conservation Agency, we created a predictive model and determined key factors influencing the species distribution. The most relevant factors were: watercourses and bodies, average annual temperatures, altitude, slope inclination and precipitation seasonality. The model fits the presence records well and is applicable in both theory and practice of the species conservation - for example, focusing faunistic research to certain areas, critical analysis of controversial presence reports and as an input for species management in the form of repatriation and introduction.

Human emotional evaluation of ancestral and modern threats: fear, disgust, and anger.

Introduction: Animal and human ancestors developed complex physiological and behavioral response systems to cope with two types of threats: immediate physical harm from predators or conspecifics, triggering fear, and the risk of infections from parasites and pathogens leading to the evolution of the behavioral immune system with disgust as the key emotion. Integration of the evolutionary concepts of the fear module and behavioral immune systems has been infrequent, despite the significant survival advantages of disgust in various contexts. Studies comparing attention to ancestral and modern threats accompanied by fear have yielded ambiguous results and what qualifies as salient modern disgusting stimuli remains unclear. We do not know whether disgust or the behavioral immune system, as inherent aspects of human psychology, have adapted to safeguard us from pandemic risks or poisoning by modern toxic substances. Methods: To test these effects, we have developed a survey comprised of 60 short vignettes describing threats evoking fear and disgust belonging to one of the three main categories of threats: (1) ancestral (phylogenetic), (2) modern (ontogenetic), and (3) pandemics of airborne disease. Each vignette was evaluated on a 7-point Likert scale based on fear, disgust, and anger. In total, 660 respondents completed the survey. The data were analysed using a factor analysis and general linear model with the respondent as a random factor. Results: The results show that the strongest fear is triggered by modern threats (electricity, car accidents), while the highest disgust is evoked by ancient threats (body waste products, worms, etc.). Interestingly, disgust does not respond to modern threat stimuli such as toxic substances or radioactivity as these evoke mainly fear and anger. Finally, a distinct response pattern was found for pandemic threats, in which both fear (e.g., of disease and death) and disgust (e.g., of used face masks) are employed. Discussion: Our study offers valuable insights into the emotional responses to ancestral and modern threats and their adaptation to pandemic challenges. Ancestral threats are not always more powerful stimuli than adequate threats of the modern type, but they function specifically. Thus, snakes and heights as fear-inducing ancestral threats form separate factors in a multivariate analysis, whereas all ancestral disgust stimuli group together. The threat of a pandemic forms a specific category and people process it emotionally and cognitively. These insights contribute to our understanding of human psychology and behavior in an ever-changing world.

The first description of dermal armour in snakes.

Osteoderms, also called dermal armour, often play a role in predator defence. The presence of osteoderms is highly irregularly distributed across the squamate phylogeny and they have not been found in snakes. In this study, we searched for candidate snake species that would benefit from such armour to protect their body, focusing primarily on fossorial species with defensive tail displays. We examined the tail morphology of 27 snake species from different families using micro-computed tomography (µCT) and micro- radiography. We discovered dermal armour in four species of sand boas (Erycidae) that also feature enlarged and highly modified caudal vertebrae. This is the first description of dermal armour in snakes. Ancestral state reconstructions revealed that osteoderms likely evolved once or multiple times in Erycidae. We have not found osteoderms in any other examined snake species. Nevertheless, similar structures are known from unrelated squamate clades, such as gerrhosaurids and geckos. This supports the idea of underlying deep developmental homology. We propose the hypothesis that osteoderms protect sand boas like the "brigandine armour" of medieval warriors. We interpret it as another component of the sand boas' rich defence strategy.

Toward a reliable detection of arachnophobia: subjective, behavioral, and neurophysiological measures of fear response.

Introduction: The administration of questionnaires presents an easy way of obtaining important knowledge about phobic patients. However, it is not well known how these subjective measurements correspond to the patient's objective condition. Our study aimed to compare scores on questionnaires and image evaluation to the objective measurements of the behavioral approach test (BAT) and the neurophysiological effect of spiders extracted from fMRI measurements. The objective was to explore how reliably subjective statements about spiders and physiological and behavioral parameters discriminate between phobics and non-phobics, and what are the best predictors of overall brain activation. Methods: Based on a clinical interview, 165 subjects were assigned to either a "phobic" or low-fear "control" group. Finally, 30 arachnophobic and 32 healthy control subjects (with low fear of spiders) participated in this study. They completed several questionnaires (SPQ, SNAQ, DS-R) and underwent a behavioral approach test (BAT) with a live tarantula. Then, they were measured in fMRI while watching blocks of pictures including spiders and snakes. Finally, the respondents rated all the visual stimuli according to perceived fear. We proposed the Spider Fear Index (SFI) as a value characterizing the level of spider fear, computed based on the fMRI measurements. We then treated this variable as the "neurophysiological effect of spiders" and examined its contribution to the respondents' fear ratings of the stimuli seen during the fMRI using the redundancy analysis (RDA). Results: The results for fear ranks revealed that the SFI, SNAQ, DS-R, and SPQ scores had a significant effect, while BAT and SPQ scores loaded in the same direction of the first multivariate axis. The SFI was strongly correlated with both SPQ and BAT scores in the pooled sample of arachnophobic and healthy control subjects. Discussion: Both SPQ and BAT scores have a high informative value about the subject's fear of spiders and together with subjective emotional evaluation of picture stimuli can be reliable predictors of spider phobia. These parameters provide easy and non-expensive but reliable measurement wherever more expensive devices such as magnetic resonance are not available. However, SFI still reflects individual variability within the phobic group, identifying individuals with higher brain activation, which may relate to more severe phobic reactions or other sources of fMRI signal variability.

Infectiousness of Asymptomatic Meriones shawi, Reservoir Host of Leishmania major.

Leishmaniases are neglected diseases caused by protozoans of the genus Leishmania that threaten millions of people worldwide. Cutaneous leishmaniasis (CL) caused by L. major is a typical zoonosis transmitted by phlebotomine sand flies and maintained in rodent reservoirs. The female sand fly was assumed to become infected by feeding on the skin lesion of the host, and the relative contribution of asymptomatic individuals to disease transmission was unknown. In this study, we infected 32 Meriones shawi, North African reservoirs, with a natural dose of L. major obtained from the gut of infected sand flies. Skin manifestations appeared in 90% of the animals, and xenodiagnosis with the proven vector Phlebotomus papatasi showed transmissibility in 67% of the rodents, and 45% were repeatedly infectious to sand flies. Notably, the analysis of 113 xenodiagnostic trials with 2189 sand flies showed no significant difference in the transmissibility of animals in the asymptomatic and symptomatic periods; asymptomatic animals were infectious several weeks before the appearance of skin lesions and several months after their healing. These results clearly confirm that skin lesions are not a prerequisite for vector infection in CL and that asymptomatic animals are an essential source of L. major infection. These data are important for modeling the epidemiology of CL caused by L. major.

Are vipers prototypic fear-evoking snakes? A cross-cultural comparison of Somalis and Czechs.

Snakes are known as highly fear-evoking animals, eliciting preferential attention and fast detection in humans. We examined the human fear response to snakes in the context of both current and evolutionary experiences, conducting our research in the cradle of humankind, the Horn of Africa. This region is characterized by the frequent occurrence of various snake species, including deadly venomous viperids (adders) and elapids (cobras and mambas). We conducted experiments in Somaliland and compared the results with data from Czech respondents to address the still unresolved questions: To which extent is human fear of snakes affected by evolutionary or current experience and local culture? Can people of both nationalities recognize venomous snakes as a category, or are they only afraid of certain species that are most dangerous in a given area? Are respondents of both nationalities equally afraid of deadly snakes from both families (Viperidae, Elapidae)? We employed a well-established picture-sorting approach, consisting of 48 snake species belonging to four distinct groups. Our results revealed significant agreement among Somali as well as Czech respondents. We found a highly significant effect of the stimulus on perceived fear in both populations. Vipers appeared to be the most salient stimuli in both populations, as they occupied the highest positions according to the reported level of subjectively perceived fear. The position of vipers strongly contrasts with the fear ranking of deadly venomous elapids, which were in lower positions. Fear scores of vipers were significantly higher in both populations, and their best predictor was the body width of the snake. The evolutionary, cultural, and cognitive aspects of this phenomenon are discussed.