Non-predatory Species Research Articles

Расчет поступления ртути при употреблении дикой рыбы населением Вологодской области

The mercury content in the muscle tissue of roach and perch from the reservoirs of the Vologda region of the Russian Federation varies from 0,001 to 1,57 mg/kg of raw mass. Using the recommendations of the FAO/WHO, the safe amount of local fish in the diet of the population of the Vologda region is calculated: for adults — 309–1989 kg/week, depending on the type; for children — 83–525 g per week, depending on the type of fish and the age of the child. Using the recommendations of the US EPA, the safe amount of local fish in the diet of the population of the Vologda region is calculated: for adults— 182–350 kg/week, depending on the type; for children— 42–129 g per week, depending on the type of fish and the age of the child. The number of predatory fish in the diet of the population should be two times less than peaceful fish. It was found that the mercury content exceeds the normative levels in place in the Russian Federation (≥ 0,3 μg/g and ≥ 0,6 μg/g, respectively) in 6 % of the fish from non-predatory species and 8 % from predatory fish species. For children of school and preschool age, the proportion of perch that is recommended to be excluded from consumption is 60 and 51 %, respectively; the share of roach is 32 and 18 %, respectively. For the health of the adult population, it may be unsafe to eat more than 30 % of the studied perch and 4 % of the studied roach. English version of the article is available at URL: https://panor.ru/articles/calculation-of-mercury-intake-from-the-consumption-of-wild-fish-by-the-population-of-the-vologda-region/80552.html

Metabarcoding of canopy arthropods reveals negative impacts of forestry insecticides on community structure across multiple taxa

Abstract Insecticides used to combat outbreaks of forest defoliators can adversely affect non‐target arthropods. Forestry insecticides typically suppress Lepidoptera larvae which are the cornerstone of the canopy community of deciduous oak forests. The abrupt removal of this dominant component of the food web could have far‐reaching implications for forest ecosystems, yet it is rarely investigated in practice owing to several methodological shortcomings. The taxonomic impediment and the biased nature of arthropod sampling techniques particularly impede the assessment of insecticide impacts on diverse communities. To tackle this issue, we propose an experimental approach combining sampling by pyrethrum knockdown and species determination via DNA metabarcoding, using community subsampling to derive estimates of species abundances. We applied this protocol to investigate the short‐term effects of the insecticides diflubenzuron (DFB) and Bacillus thuringiensis var. kurstaki (BTK) on canopy‐dwelling arthropod communities in German oak woodlands. Our approach allowed us to detect most of the diversity and integrate species abundances in our analyses. By classifying arthropod species into assemblages based on their expected sensitivity rather than coarse taxonomic groupings, we could unveil substantial effects of DFB across multiple taxa 5 weeks after application. Although strong effects on single species appear related to direct toxicity, substantial impacts of DFB on parasitoids and xylophagous beetles suggest that anti‐defoliator treatments can have previously unsuspected indirect effects on some components of forest arthropod communities. The impacts of BTK on community structure were consistent with that of DFB though much weaker. Synthesis and applications. Comparing diversity patterns in the arthropod communities of sprayed and unsprayed oak canopies, our results show that selective insecticides can alter species diversity in presumably non‐sensitive taxa. Even though the ecological significance of these impacts has yet to be assessed in an operational setting, their existence calls for increased regulatory scrutiny on indirect effects. As community approaches become more attainable with the rapid development of DNA metabarcoding, we suggest the inclusion of community‐level end points as regulatory requirements for the approval of forest‐use insecticides.

The Simulation of the dynamics of 137Cs accumulation by freshwater fish

The study aimed to simulate the dynamics of 137Cs accumulation by freshwater fish under conditions of hypothetical radioactive contamination of water reservoirs in different seasons. The subject of research is the regularities of 137Cs accumulation by non-predatory fish species in eutrophic and oligotrophic water bodies. The dynamics of the 137Cs content in freshwater fish was calculated according to the content of radionuclides in water masses. The results of modeling the volumetric activity of 137Cs in water masses were used as an input parameter for the radionuclide accumulation in fish model. The fish organism was represented in the form of 3 independent related only by the balance equation; seasonal changes in the fish feeding intensity were taken into account in the modeling. The parameter that takes into account the contribution of the feeding intensity to the process of 137Cs intake into the fish organism has been determined. The features of the dynamics of 137Cs accumulation in eutrophic and oligotrophic water bodies fish are analyzed for cases of a hypothetical accidental input of 137Cs into ecosystems at the beginning of different periods of the annual life cycle of fish: 1st - from 1 to 31 March; 2nd - from 1 to 30 April; 3rd - from May 1 to September 19; 4th - from September 20 to October 19; 5th - from October 20 to November 30; 6th (freeze-up period) - from December 1 to February 28. The study has found that for a eutrophic water body the highest levels of 137Cs content in peaceful fish will be formed in the case of 137Cs entering ecosystems in spring (options 1–3). The maximum levels of 137Cs content in fish will be observed in the contamination period mentioned in option 3. Under hypothetical pollution in the autumn-winter period (options 4–6), the levels of 137Cs in peaceful fish will be approximately 2 times lower than in the case of pollution of the reservoir in spring. It has been found that the maximum value of the specific activity of 137Cs in fish from an oligotrophic water reservoir is not related to the season of pollution. However, the levels of fish pollution in the oligotrophic reservoir will be 1.5–2 times higher than those of the eutrophic one in options 1–3 and 3–4 times higher in options 4–6 . In the event of an emergency density of 137Cs fallout at the level of 4 kBq /m2 on the surface of different types of closed water reservoirs, its specific activity in peaceful fish will exceed the currently established permissible levels of fish products contamination. If the fallout density is twice as low (2kBq/ m2), the accumulation levels 137Cs by fishes of eutrophic water bodies will exceed the permissible standards in case of emergency inflows in spring. For oligotrophic water reservoirs, the guaranteed non-excess of the established standards in fish products is possible if the 137Cs fallout density is under 0.5 kBq /m2. Key words: fish, modeling, 137Cs, specific activity, hypothetical pollution, reservoirs of different trophic status.

1243Quantitative risk-benefit assessment of fish and seafood consumption scenarios to support recommendations

Abstract Background Fish/seafood consumption has health benefits, namely due to its omega-3 fatty acids levels and risks due to methylmercury contamination. This study aims to quantify the health impact of hypothetical scenarios of fish/seafood consumption through a risk-benefit assessment and provide support for recommendations, using Portuguese food consumption data. Methods We used data from the National Food, Nutrition and Physical Activity Survey 2015-2016 (n = 5811) to estimate the mean exposure to methylmercury and EPA+DHA in the current and alternative scenarios. Alternative scenarios were modelled using probabilistic approaches to reflect substitutions from the current consumption in the type of fish/seafood (predatory vs low-mercury species) or its frequency (1-7x/week). The overall scenarios’ impact was quantified using Disability-Adjusted Life Years (DALYs). Results About 14% of the Portuguese population exceeds the methylmercury tolerable weekly intake, and this prevalence is higher among small children (36.6%). Nevertheless, if the fish/seafood consumption increased to once a day, ≈11450 DALYs could be prevented each year. However, such a scenario would result in higher risk for pregnant women (1398 extra DALYs). Moreover, excluding predatory species consumption resulted in small but significant health gains (-1078 DALYs). Conclusions For the general population, the maximum health gains are obtained by consuming fish/seafood up to 7x/week, but among children and pregnant women, the frequency should be limited to 3-5x/week. All population should preferably choose non-predatory species. Key messages Daily fish consumption results in the highest overall populational health gain, but children and pregnant women need to limit it to 3-5x/week, due to methylmercury exposure.

Role of arrowworm Sagitta elegans (Chaetognatha) in plankton communities of the western Bering Sea

Arrowworm Saggita elegans is one of the important and abundant species in zooplankton communities of the western Bering Sea. Interannual variability of their biomass is considered on the data of long-term surveys conducted in 1986–2018, the species production is determined for the Anadyr-Navarin region and deep-water basin in 2008–2018, and the total production of zooplankton communities is calculated for 2008, 2015, and 2018. In the modern period, the biomass of S. elegans has significantly decreased compared to 1990–2000s, with exception of the shallow areas where it is relatively stable. The last decade included two periods with different oceanographic regime: the cold years (2007–2013) and the warm ones (2014–2018), but S. elegans did not demonstrate rapid response to such change of abiotic factors. However, the water circulation patterns in the upper layer were important for them and determined their transport and accumulation. For example, the high abundance and production of arrowworms in the deep-water area in 2008 and in the Anadyr-Navarin region in 2011 were conditioned by their transport and accumulation in these areas. S. elegans are predators, preying mainly upon copepods, so their impact on structure and production of zooplankton community is determined by significant grazing estimated at 50–100 % of Copepoda production or even more. The total production of zooplankton communities was higher in «warm» 2015 and 2018 than in «cold» 2008. The arrowworm production decreased in these warm years but production of non-predatory species (basically small- and medium-sized copepods) increased sharply because of their rapid response to temperature changes realized in high growth rate under higher temperature. Thus, the role of S. elegans in formation of the community production becomes lower in conditions favorable for high growth rate of non-predatory species.

Ueno’s brown frog Rana uenoi indiscriminately ceases calling in the presence of daytime birds

Animals need to recognise predators to assess threats and adjust their behaviour accordingly. Acoustic cues produced to attract mates may also be intercepted by predators, and signallers can use both visual and acoustic cues to detect predators and initiate escape or defensive behaviours. Here, to test whether Ueno’s brown frogs (Rana uenoi) advertising during daytime are able to visually and aurally recognize predatory birds, we monitored calling activity at 27 active breeding sites where birds were also known to occur. Based on visual and aural observations, frogs were significantly less likely to be calling when birds were present than when absent. However, we failed to determine whether male R. uenoi distinguished among predator and non-predator species, responding to the presence of all bird species with cessation of calling. While daytime calling activity decreased in the presence of birds, the maximum egg clutch count per site used as a proxy for reproductive output was unaffected by daytime presence of birds. Our results suggest that R. uenoi uses visual cues to detect disturbances, but that its ability to visually assess the risks posed by individual species is minimal.

Reaction to allospecific death and to an unanimated gorilla infant in wild western gorillas: insights into death recognition and prolonged maternal carrying.

It is still unclear to what extent animals possess knowledge of death. Primates display a large variety and often contradictory behaviors toward conspecific corpses, particularly those of infants (e.g., prolonged carrying and care). This study reports on reactions in a wild, habituated western gorilla group (Gorilla gorilla, 11-13 individuals) in the Central African Republic to an unanimated conspecific infant, and to an allospecific corpse. Individuals' reactions were compared to their usual behavior using both continuous focal animal sampling and 10-min instantaneous scan sampling. In the first observation, an infant gorilla fell out of a tree and looked dead. The mother retrieved it and remained unusually close to another adult female, until the infant started to move again, almost 1 h later. Cases of infants regaining consciousness after almost-fatal accidents may act as positive reinforcement for continued carrying by mothers, which might be socially learned. In the second case, three immature gorillas reacted to a dead red river hog. For 20min they stared at the corpse from tree branches above, while chest beating, defecating, and urinating several times. They showed fear and did not approach the corpse. These observations show that non-predatory species, such as gorillas, may be able to acquire and develop some knowledge about death even though they do not kill other vertebrates.

Dietary intake of arsenic, cadmium, mercury and lead by the population of Catalonia, Spain: Analysis of the temporal trend

In 2017, a monitoring study was conducted in Catalonia (Spain) to analyse, in widely consumed foodstuffs, the concentrations of arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb), as well as those of inorganic As (InAs) and methylmercury (MeHg). Health risks were estimated for various population groups, classified according to age. A continued reduction of dietary exposure to these elements was observed when comparing the results from the current and previous studies performed during the last 17 years. This reduction would be associated to a decrease of As, Cd, Hg and Pb concentrations in food, as well as by changes in dietary habits. None of the adult groups exceeded the safety threshold established by the EFSA, but toddlers, infants and children exceeded the PTWI for Cd and MeHg. The greatest intake of Cd and MeHg corresponded to infants, being due to the consumption of cuttlefish and hake. The consumption of these species should be reduced to two or three weekly portions, being combined with the intake of other non-predator species. Anyhow, the current results indicate that is necessary to conduct further periodical surveys, paying special attention to the trend in the intake of Cd and MeHg.

Cue specificity of predator-induced phenotype in a marine snail: is a crab just a crab?

A wide range of taxa have been shown to display inducible, phenotypically plastic responses to known predators. Most studies of inducible defenses include only known predators but not non-predatory species in experimental designs, precluding tests of specificity for these responses. We tested the specificity of predator-induced defenses in the marine snail Nucella lamellosa, when exposed to chemical cues from potential crab predators as well as more distantly related non-predatory crabs that co-occur with this snail. Surprisingly, all crabs tested, even those that are not predators, triggered the common induced response of a reduction of soft-tissue mass relative to control animals, likely reflecting a reduction in snail feeding activity. In contrast, only N. lamellosa’s major predator, Cancer productus, triggered the production of a thicker apertural lip. Increased thickening of the apertural lip may be an adaptive response specific to C. productus, which uses shell-breaking at the apertural lip (i.e., shell-peeling) as their main form of attack. Apertural lip thickening appeared to be due to reallocation of shell material (i.e., a change in shell shape) rather than an increase in shell deposition. Our findings demonstrate the importance of determining the specificity of cues triggering inducible responses in prey, and the mechanisms that underlie these plastic responses, as the responses to general versus specific cues may limit the adaptive value of an inducible defense.

Mobbing of the top predator: a correlation between avian community richness and the number of mobbing species

Mobbing is an anti-predator strategy initiated by one or more members of prey species aiming at driving away a predator that is not undertaking an attack. Because of a continuous dispute as to whether mobbing of a top predator may indicate species richness, we tested the correlation between the number of species engaging in mobbing and avian community richness. In the boreal forest of central Norway, we conducted a series of 83 bird census trials in 2014 and 2015. Each census trial consisted of two 5-min phases. In the first phase an ordinary point count was performed as a control; in the immediately following second phase either a stuffed Eagle Owl or Capercaillie female decoy was presented to study mobbing of a top avian predator and non-predatory species. Mobbing was more likely to occur, and the number of species that engaged in mobbing was higher, in habitats richer of bird species. Our study showed that the cumulative effects of being mobbed increase with richness of the local avian community. We did not find any support for the notion that mobbing is triggered by mobbing activity of the two most active and abundant species. No support was provided for an assertion that using an owl decoy would result in higher number of detected species during a census. Our study urges the need for identification and quantification of costs of mobbing for an avian predator.

MERCURY CONTENT IN MUSCLE TISSUE OF EUROPEAN GRAYLING (THYMALLUS THYMALLUS (L.)) IN THE RIVERS OF THE VOLOGDA REGION

The article presents information about the mercury content in the muscle tissue of the European grayling Thymallus thymallus (L.) in 11 rivers of the Vologda region (Tagazhma, Vozhega, Votcha, Kostyuga, Tiksna, Sheben’ga, Pyrnug, Zemtsovka, Yurmanga, Bol’shaya Rechka and Yontala) for the period of 2011–2015. The average content of toxicant ranged from 0,04 mg/kg in individuals of the river Sheben’ga up to 0,21 mg/kg in the rivers Yurmanga and Bol’shaya Rechka. Four fish noted an excess of the permissible level of sanitary and hygienic standards (SanPiN 2.3.2.1078-01. 2.3.2.) for non-predatory fish species (0,3 mg/kg). Young grayling contains an average of 0,06–0,10 mg/kg mercury in muscle tissue, individuals five to six years old contain 0,26 and 0,27 mg/kg, respectively. A comparison of the level of mercury concentration in the muscle tissue of European grayling with that of other fish species showed that the Hg content does not go beyond the revealed background values for water bodies of the Vologda region.

Conspecific and heterospecific alarm substances induce behavioral responses in juvenile catfish Rhamdia quelen

ABSTRACT The recognition of chemical information indicating the presence of a predator is very important for prey survival. In this study we tested antipredator behavioral response of juvenile silver catfish (Rhamdia quelen) against predator odor released by two different potential predators, Hoplias malabaricus and the snake Helicops infrataeniatus, and alarm cues and disturbance cues released by conspecifics and by non-predator species, Megaleporinus obtusidens and Astyanax lacustris. We used juvenile catfish that were naive to predators. The trials consisted of a 10-min prestimulus and a 10-min post-stimulus observation period. The behavioral response displayed by silver catfish exposed to alarm cues comprised a decrease in shelter use and an increase in locomotion, and also a longer latency period before feeding. Our results showed that juvenile silver catfish can perceive chemical cues released by predators, heterospecifics and conspecifics.

Top predators negate the effect of mesopredators on prey physiology.

Summary Predation theory and empirical evidence suggest that top predators benefit the survival of resource prey through the suppression of mesopredators. However, whether such behavioural suppression can also affect the physiology of resource prey has yet to be examined.Using a three‐tier reef fish food web and intermittent‐flow respirometry, our study examined changes in the metabolic rate of resource prey exposed to combinations of mesopredator and top predator cues.Under experimental conditions, the mesopredator (dottyback, Pseudochromis fuscus) continuously foraged and attacked resource prey (juveniles of the damselfish Pomacentrus amboinensis) triggering an increase in prey O2 uptake by 38 ± 12·9% (mean ± SE). The visual stimulus of a top predator (coral trout, Plectropomus leopardus) restricted the foraging activity of the mesopredator, indirectly allowing resource prey to minimize stress and maintain routine O2 uptake. Although not as strong as the effect of the top predator, the sight of a large non‐predator species (thicklip wrasse, Hemigymnus melapterus) also reduced the impact of the mesopredator on prey metabolic rate.We conclude that lower trophic‐level species can benefit physiologically from the presence of top predators through the behavioural suppression that top predators impose on mesopredators. By minimizing the energy spent on mesopredator avoidance and the associated stress response to mesopredator attacks, prey may be able to invest more energy in foraging and growth, highlighting the importance of the indirect, non‐consumptive effects of top predators in marine food webs.

Communication about predator type by a bird using discrete, graded and combinatorial variation in alarm calls

Many animals use variation in their alarm calls to warn conspecifics about different predatory threats. Information about predators can be encoded by producing discrete types of alarm calls and/or through graded variation in a single call type (i.e. calling rate or note repetitions). Another way to encode predator information is to combine different types of calls or notes into longer structured sequences. However, few studies have examined how individuals use discrete, graded and combinatorial variation in alarm calls to denote specific risks. I investigated the acoustic structure and information content of alarm calls in Japanese great tits, Parus major minor, by exposing their nests to three predator species (snakes, crows and martens) and a nonpredator species (doves). Great tits produced acoustically discrete alarm calls for the different nest predators: ‘jar’ calls for snakes and ‘chicka’ calls for crows and martens. The adults further discriminated between crows and martens by altering the calling rate and note number of the ‘chicka’ calls. A total of 175 types of note combinations were observed in the ‘chicka’ calls, and the tits used these combination types differently for the crows and martens. These results provide the first demonstration that birds can encode information about predator type by using production specificity, graded features and note combinations of discrete alarm calls. Previous studies have shown that parent and nestling Japanese great tits can respond in different, adaptive ways to discrete alarm calls. However, further playback studies are required to determine whether and how conspecifics can extract predator information from graded and combinatorial variation in alarm calls.

Hunted hunters? Effect of group size on predation risk and growth in the Australian subsocial crab spider Diaea ergandros

A reduced predation risk is considered to be a major adaptive advantage of sociality. While most studies are concerned with non-predatory prey species, group-living predators are likely to face similar threats from higher-order predators. We studied the relationship between group size and predation risk in the subsocial crab spider Diaea ergandros by testing predictions from theoretical models including attack abatement as well as the formation of protective retreats. In a field survey, we found predatory clubionid spiders in 35 % of the D. ergandros nests and as predicted, nest size did not correlate with predator presence. In a subsequent laboratory experiment, we observed survival probability, nest construction activity and feeding behaviour including weight development between groups of different sizes as well as in the absence or presence of a predator. Large groups had an advantage in terms of survival and growth compared to smaller groups or single individuals. They also built significantly larger nests than smaller groups, supporting the idea of protective retreat formation being an adaptive benefit to group living. Even though clubionids did attack D. ergandros, they did not significantly affect overall mortality of D. ergandros. The feeding experiment showed that spiders fed on a larger proportion of flies in the presence of a predator. However, these groups gained significantly less weight compared to the control groups, indicating that the potential predators not only act as predators but also as food competitors, constituting a twofold cost for D. ergandros.

Adaptive forgetting in Iberian green frog tadpoles (Pelophylax perezi): Learned irrelevance and latent inhibition may avoid predator misidentification.

Predator recognition often requires learning by prey individuals. Iberian green frog tadpoles (Pelophylax perezi) have the ability to learn to recognize new potential predators when their chemical cues are found paired with conspecific alarm cues. However, a random pairing of alarm cues and chemical stimuli of a nonpredator might later induce costly antipredator responses to nondangerous species. Here, we studied the potential existence in this frog species of two phenomena (learned irrelevance and latent inhibition) that could help tadpoles to avoid these nonadaptive responses to chemical cues of nonpredator species. Our results showed that, when tadpoles experienced a random pattern of presence of alarm cues alone or predator cues alone over the 4 days before or after the simultaneous detection of these two cues paired, no learned association was formed. These results showed the existence of an effect of learned irrelevance on learning in Iberian green frog tadpoles. Also, tadpoles clearly inhibited the formation of a learning association between predator and alarm cues after a 4-day period during which they had been exposed to the predator cues alone. This result showed the existence of an effect of latent inhibition on learning about cues related to increased predation risk. Thus, both learned irrelevance and latent inhibition, rather than being considered to be failed predator recognition, can rather be seen as adaptive ways for dealing with conflicting information and as strategies to avoid learning irrelevant information and costly antipredatory responses to nonpredatory stimuli.

Incubating females use dynamic risk assessment to evaluate the risk posed by different predators

Uncertainty poses a substantial problem for animals, making it is essential for individuals to anticipate changes in their environment to select suitable behavioral strategies. In nest-building species where parents care for dependent young, predation is a major cause of reproductive failure. However, because parents generally have inadequate information about nest predation risks, attaining information about predation hazards increases their likelihood of making informed, optimal decisions. Risk assessment should therefore be widespread, particularly in incubating parents of species that breed in cavities or closed nests, which have limited information about predator presence. This study experimentally investigated the dynamic risk assessment in incubating female brown thornbill (Acanthiza pusilla), a long-lived Australian passerine, which builds closed dome nests in dense vegetation. When the females were exposed to the calls of a nest predator, a predator of adults, and a nonpredatory species, they reacted most strongly to the predator of adults’ calls, by looking out of the nest for longest. Females significantly increased their level of alertness on hearing calls of both predator species and maintained their higher level of alertness after the simulated predator presence ended. Females in nests with a high degree of visual cover, and therefore a larger information deficit, reacted more strongly to predator calls than females in more open nests. Moreover, poorly concealed nests had a higher probability of being predated. These results show that incubating female thornbills use dynamic risk assessment and base their response on who is at risk and the degree of information deficit.

Comparison of nest defence behaviour between two associate passerines

Nest predation is one of the most important factors limiting reproductive success, and antipredator behaviour can significantly reduce the loss of avian broods. I carried out field experiments on two sympatric passerines: the barred warbler and the red-backed shrike. Many authors have described the protective nature of nesting association between these species. However, we have little knowledge about the true nature of the relationships between associates. I examined (1) whether barred warblers and red-backed shrikes respond differently to an avian predator, and (2) whether males and females differ in the intensity of nest defence. Decoys of a known nest predator and a non-predatory control species were used to examine the types and relative intensity of parental response. I measured behavioural responsiveness by recording aggressive behaviour toward each model during the nestling period. Barred warblers and red-backed shrikes showed considerable variation in their response. Warblers more vigorously defended their own territories than shrikes. No differences between the sexes in antipredator behaviour in red-backed shrike were found. By contrast, in barred warbler, male was more involved in nest defence. The experimental tests provide evidence that these two species are able to differentiate between a predator and non-predator species.

Experimental evidence for olfactory predator recognition in wild mouse lemurs

Although primates have remarkable olfactory capabilities, their ability for olfactory predator recognition is still understudied. We investigated this cognitive ability in wild gray and golden-brown mouse lemurs (Microcebus murinus and M. ravelobensis) that were confronted with four different olfactory stimuli, derived from two Malagasy predators (fossa and barn owl) and two local nonpredator species (brown lemur and sifaka). The predator response was tested (1) in a systematic cage setup and (2) in a two-way choice experiment with two Sherman traps on platforms in the forest (stimulus trap vs. nonstimulus trap). For part 1, the study animals were housed in cages during habituation and 5 days of experiments. One stimulus was tested per night and was presented underneath a drinking bottle. The changes in the time spent close to the stimulus and the drinking time at the bottle were used as indicators of predator recognition. A timidity score was established by classifying the strength of the antipredator response during the experiment. The study animals spent significantly less time drinking and less time in the stimulus area when confronted with fossa odor compared with the other stimuli. The timidity score was significantly higher during the fossa stimulus compared with the nonpredator and the control stimuli. The two-way choice experiments revealed a complete avoidance of the fossa odor, which was not found with the other stimuli. Thus, wild mouse lemurs showed clear signs of olfactory predator recognition in the case of the fossa in both experiments, but no signs of avoidance to the other presented stimuli. The lack of owl avoidance may be explained by less or no aversive metabolites in the owl stimulus or by lower significance for olfactory recognition of aerial predators. Furthermore, the results showed slight differences between the two mouse lemur species that may be linked to differences in their ecology.

Learning about non-predators and safe places: the forgotten elements of risk assessment

A fundamental prerequisite for prey to avoid being captured is the ability to distinguish dangerous stimuli such as predators and risky habitats from non-dangerous stimuli such as non-predators and safe locations. Most research to date has focused on mechanisms allowing prey to learn to recognize risky stimuli. The paradox of learned predator recognition is that its remarkable efficiency leaves room for potentially costly mistakes if prey inadvertently learn to recognize non-predatory species as dangerous. Here, we pre-exposed embryonic woodfrogs, Rana sylvatica, to the odour of a tiger salamander, Ambystoma tigrinum, without risk reinforcement, and later try to teach the tadpoles to recognize the salamander, a red-bellied newt Cynops pyrrhogaster—a closely related amphibian, or a goldfish, Carassius auratus, as a predator. Tadpoles were then tested for their responses to salamander, newt or fish odour. Pre-exposure to salamander did not affect the ability of tadpoles to learn to recognize goldfish as a predator. However, the embryonic pre-exposure to salamanders inhibited the subsequent learning of salamanders as a potential predator, through a mechanism known as latent inhibition. The embryonic pre-exposure also prevented the learned recognition of novel newts, indicating complete generalization of non-predator recognition. This pattern does not match that of generalization of predator recognition, whereby species learning to recognize a novel predator do respond, but not as strongly, to novel species closely related to the known predator. The current paper discusses the costs of making recognition mistakes within the context of generalization of predators and dangerous habitats versus generalization of non-predators and safe habitats and highlights the asymmetry in which amphibians incorporate information related to safe versus risky cues in their decision-making. Mechanisms such as latent inhibition allow a variety of prey species to collect information about non-threatening stimuli, as early as during their embryonic development, and to use this information later in life to infer the danger level associated with the stimuli.