Anti-predator Strategies Research Articles

Background complexity and optimal background matching camouflage

Camouflage through background matching is a widespread antipredator strategy in which animals blend in with their background to avoid detection. To maximise survival in a variable natural environment, animals can have colourations that either match one of the backgrounds maximally (i.e. specialist strategy) or match multiple backgrounds partially (i.e. generalist strategy). Theoretical work indicates that the optimal strategy depends on the extent of visual difference between the backgrounds (i.e. heterogeneity) or how commonly the animal will encounter the background types. However, the role of another critical determinant of detection, the visual complexity of the background, on optimal camouflage strategy (specialist versus generalist) in the face of background heterogeneity, remains unknown. Here, we performed a virtual predation experiment employing humans as surrogate ‘predators’ and explored how background complexity influences camouflage in heterogeneous backgrounds. Under low heterogeneity, we found the latency to attack generalists was higher than that for specialists on a complex background, but there was no difference between specialists and generalists on a simple background. At intermediate heterogeneity, both specialist and generalist targets took a similar time to be attacked irrespective of complexity, suggesting that both the strategies may co-exist. In contrast, at high levels of heterogeneity, we found generalists were attacked sooner when compared to specialists irrespective of whether the background was simple or complex. Our results thus suggest that complex backgrounds favour the evolution of a generalist background matching strategy that maximises fitness in multiple backgrounds but only when the visual difference between the backgrounds is low. Overall, our study provides key insights highlighting the underappreciated role of background complexity on the optimization and evolution of camouflage colouration in a heterogeneous environment. Many animals often face the challenge of encountering multiple visually distinct backgrounds due to variation in their environment, i.e. background heterogeneity. How should animals optimise camouflage when there is background heterogeneity? Theoretical studies have proposed that animals may match one of the many backgrounds (specialise) or match multiple backgrounds partially (generalise) as an optimal solution. However, cognitive constraints from the predator’s perspective may also have a role to play in this optimization problem, but this has not been examined. Our experiments involving humans as ‘predators’ show that when background complexity renders the search task more difficult, generalist targets took a longer time to be attacked than specialist targets, but only in less heterogeneous backgrounds. However, irrespective of complexity, specialist targets are better than generalists at avoiding attack in highly heterogeneous backgrounds. Cognitive constraints of predators may, therefore, play a significant role in the optimization of camouflage colouration in heterogeneous environments.

Tonic Immobility Is Influenced by Starvation, Life Stage, and Body Mass in Ixodid Ticks.

The ability to escape predation modulates predator-prey interactions and represents a crucial aspect of organismal life history, influencing feeding, mating success, and survival. Thanatosis, also known as death feigning or tonic immobility (TI), is taxonomically widespread, but understudied in blood-feeding vectors. Hematophagous arthropods, such as ticks, are unique among animals as their predators (birds, mice, lizards, frogs, and other invertebrates) may also be their source of food. Therefore, the trade-off between predator avoidance and host-seeking may shift as the time since the last bloodmeal increases. Because ticks are slow-moving and unable to fly, or otherwise escape, we predicted that they may use TI to avoid predation, but that TI would be influenced by time since the last bloodmeal (starvation). We therefore aimed to quantify this relationship, examining the effect of starvation, body mass, and ontogeny on TI for two tick species: Dermacentor variabilis (Say) (Acari: Ixodidae) and Rhipicephalus sanguineus (Latreille) (Acari: Ixodidae). As we predicted, the duration and use of TI decreased with time since feeding and emergence across species and life stages. Therefore, ticks may become more aggressive in their search for a bloodmeal as they continue to starve, opting to treat potential predators as hosts, rather than avoiding predation by feigning death. Antipredator behaviors such as TI may influence the intensity and amount of time ticks spend searching for hosts, driving patterns of tick-borne pathogen transmission. This identification and quantification of a novel antipredation strategy add a new component to our understanding of tick life history.

Mobbing responses of great tits (Parus major) do not depend on the number of heterospecific callers

AbstractNumerical competence—the ability to estimate and process the number of objects and events—is important during antipredator strategies because it influences individual's survival chances. Animals can benefit from numerical competence during mobbing—when a prey moves toward and vocalizes at or harasses a predator. Mobbing responses of some species are related to the number of conspecific callers, and responses are stronger during playbacks simulating multiple callers. Here, we tested heterospecific individual vocal recognition (IVR) in combination with numerical competence in great tits (Parus major). Since previous work showed that great tits respond to mobbing calls of chaffinches (Fringilla coelebs), we predict that great tits showed a stronger response when two or four different individual chaffinches were played back versus only one individual by keeping the duty cycle (number of total calls/min) identical. Individuals were exposed to playbacks simulating calling by one, two or four heterospecific callers, or singing by one caller (control song). Great tits approached the speaker closer and produced more calls during the mobbing calls treatments than during the control treatment (song). However, in contrast to our prediction, great tits responded similarly to mobbing calls from several heterospecific callers as they did toward mobbing calls from one heterospecific caller. Maybe the great tits still are capable of determining the identity of the callers, but what might matter most for them in this very specific situation might be the mobbing intensity. We assume that the duty cycle itself has the stronger impact on the response.

PREDATION OF PALE-BREASTED THRUSH EGGS BY THE ARIEL TOUCAN IN BRAZIL: FAILURE OF THE ANTI-PREDATORY STRATEGY

The Channel-billed Toucan (Ramphastos vitellinus ariel) is an omnivorous bird that eventually is nest-robbers. Several birdsongs display anti-predatory strategies such as attacks and mobbing calls to face this kind of predators. This note reports a predatory event of one Channel-billed Toucan upon eggs of Pale-breasted Thrush (Turdus leucomelas), and describe the anti-predatory behavior, principally alert and mobbing calls of the thrush. Even though the Pale-breasted Thrush displayed the anti-predatory behaviors to harass the toucan, the egg predation was not avoided. Although the predation upon eggs by Ramphastos vitellinus has been reported several times, the majority of reports lacks of identity of the bird species affected, this being the first confirmed record in Turdus leucomelas.

A context analysis of bobbing and fin-flicking in a small marine benthic fish.

Most antipredator strategies increase survival of individuals by signaling to predators, by reducing the chances of being recognized as prey, or by bewildering a predator's perception. In fish, bobbing and fin‐flicking are commonly considered as pursuit‐deterrent behaviors that signal a predator that it has been detected and thus lost its surprise‐attack advantage. Yet, very few studies assessed whether such behavioral traits are restricted to the visual presence of a predator. In this study, we used the yellow black‐headed triplefin Tripterygion delaisi to investigate the association between these behaviors and the visual exposure to (a) a black scorpionfish predator (Scorpaena porcus), (b) a stone of a size similar to that of S. porcus, (c) a conspecific, and (d) a harmless heterospecific combtooth blenny (Parablennius sanguinolentus). We used a laboratory‐controlled experiment with freshly caught fish designed to test for differences in visual cues only. Distance kept by the focal fish to each stimulus and frequency of bobbing and fin‐flicking were recorded. Triplefins kept greater distance from the stimulus compartment when a scorpionfish predator was visible. Bobbing was more frequent in the visual presence of a scorpionfish, but also shown toward the other stimuli. However, fin flicks were equally abundant across all stimuli. Both behaviors decreased in frequency over time suggesting that triplefin become gradually comfortable in a nonchanging new environment. We discuss why bobbing and fin‐flicking are not exclusive pursuit‐deterrent behaviors in this species, and propose additional nonexclusive functions such as enhancing depth perception by parallax motion (bobbing) or signaling vigilance (fin‐flicking).

Different ontogenetic trajectories of body colour, pattern and crypsis in two sympatric intertidal crab species

AbstractAnimals frequently exhibit great variation in appearance, especially in heterogeneous habitats where individuals can be concealed differentially against backgrounds. Although background matching is a common anti-predator strategy, gaps exist in our understanding of within- and among-species variation. Specifically, the drivers of changes in appearance associated with habitat use and occurring through ontogeny are poorly understood. Using image analysis, we tested how individual appearance and camouflage in two intertidal crab species, the mud crab Panopeus americanus and the mottled crab Pachygrapsus transversus, relate to ontogeny and habitat use. We predicted that both species would change appearance with ontogeny, but that resident mud crabs would exhibit higher background similarity than generalist mottled crabs. Both species showed ontogenetic changes; the mud crabs became darker, whereas mottled crabs became more green. Small mud crabs were highly variable in colour and pattern, probably stemming from the use of camouflage in heterogeneous habitats during the most vulnerable life stage. Being habitat specialists, mud crabs were better concealed against all backgrounds than mottled crabs. Mottled crabs are motile and generalist, occupying macroalgae-covered rocks when adults, which explains why they are greener and why matches to specific habitats are less valuable. Differential habitat use in crabs can be associated with different coloration and camouflage strategies to avoid predation.

Trade-off Investment between Tonic Immobility and Mate Search in the Sweetpotato Weevil, Cylas formicarius (Coleoptera: Brentidae).

Simple SummaryTonic immobility (TI) is considered as an important anti-predator strategy. In order to know the relationship between TI and mating behavior, we investigated the cost–benefit between TI and mate search in the sweetpotato weevil (SPW), Cylas formicarius. In this study, we used Y-tube olfactometer and determined that male mate searching increase after 3 h at night. Then, we confirmed that TI was affected by mate search in the males. Because the duration of TI of the male during mate search was significantly shorter duration than the males from the control. However, TI does not affect mate search in the females. Finally, the Y-tube olfactometer was used to compare the duration of mate search and the proportion of orientation towards the females in two artificial selection groups of the male SPWs. In this experiment, we found that mate search was affected by TI. Our study results provided a clear evidence that there is a trade-off between mate search and TI behavior in males of the SPW. Further, we quantified investment of anti-predator behavior and mating behavior by measuring the duration of TI and mate search in the SPW. We believe, these methods can be useful to determine the cost–benefit between anti-predator behaviors in the prey(s) and predator(s) in other species too.Tonic immobility (TI) is a well-known anti-predator strategy adopted by diverse preys. Numerous studies on the cost–benefit involve in TI have been reported. Although, some studies have reported the effect of mating behavior on TI, few studies highlight the phases of mate search. In the present study, we investigated the relationship between mate search and TI behavior in the sweetpotato weevil (SPW), Cylas formicarius (Coleoptera: Brentidae). First, we found the most active mate search period of male SPW within 24 h. Then, we measured whether the duration of TI of virgin male and female were affected during the mate search. In the end, the Y-tube olfactometer was used to compare the duration of mate search and the proportion of orientation towards the females in two artificial selection groups of the male SPW with longer and shorter duration of TI. Our study confirmed that male mate searching increase after 3 h at night, and up to 73% at midnight, TI was affected by mate search in male, because the duration of TI of the male during mate search (Mean ± SE = 214.53 ± 22.74 s) was significantly shorter duration than the control (679.64 ± 69.77 s). However, mate search did not affect the strength of TI in the females tested. This study determined that mate search was affected by TI due to males from the group with shorter duration of TI who had 28% higher proportion of orientation towards the females than the males with longer duration of TI. Investment trade-off between TI and mate search was confirmed in the males of the SPW.

Arousal from death feigning by vibrational stimuli: comparison of Tribolium species

Death feigning (or tonic immobility) is an effective antipredator strategy. However, prolonged immobility on the ground increases the risk of being parasitized or eaten by predators, and thus, insects must rouse themselves when appropriate stimulation is provided. Very few studies on the effect of stimulus intensity on arousal from death feigning have been conducted. A previous study using Tribolium castaneum showed an existing threshold for the intensity of the stimulus that causes arousal from death feigning. Whether there are differences between species in the threshold for arousal is an interesting question. In the present study, we, therefore, compared the effect of stimulus strength on arousal from death feigning in two closely related species, namely, T. confusum and T. freemani, which are established strains that have been artificially selected for longer duration of death feigning. Also, part of the study was to determine whether there was a positive association between intensity of stimulus needed to rouse and the duration of death feigning. We discuss why there is a difference in the strength of the stimulus needed for arousal from death feigning among Tribolium species, for which we included the data for T. castaneum from a previous study.

3D Geometric Morphometrics Reveals Convergent Character Displacement in the Central European Contact Zone between Two Species of Hedgehogs (Genus Erinaceus)

Simple SummaryHedgehogs, being insectivores with slow metabolisms, are quite sensitive to temperature and food availability. As a consequence, their ranges have oscillated in relation to past climate changes. Species that have evolved in different regions, but their ranges have shifted and overlapped subsequently, often represent intense competitors as a result of ecological similarities. The present study focuses on this phenomenon in the contact zone in central Europe and adjacent regions, using genetic determination of species and description of size and shape of skull, the morphological structure mirroring many selection pressures related to ecology. While animals living outside of the contact zone show marked differences between the two species, individuals within the contact zone are more alike with a smaller skull size and a convergent jawbone shape. Changes in skull size can be related to inter-species competition and also facilitated by selection pressure, mediated by overpopulated medium-sized predators such as foxes or badgers. Since the function of the lower jaw is mainly connected to feeding, we hypothesize that this pattern is due to the selection to size and shape related to competition for food resources. The present study helps to describe general patterns related to species formation, as well as species responses to anthropogenic environmental changes.Hedgehogs, as medium-sized plantigrade insectivores with low basal metabolic rates and related defensive anti-predator strategies, are quite sensitive to temperature and ecosystem productivity. Their ranges therefore changed dramatically due to Pleistocene climate oscillations, resulting in allopatric speciation and the subsequent formation of secondary contact zones. Such interactions between closely related species are known to generate strong evolutionary forces responsible for niche differentiation. In this connection, here, we detail the results of research on the phenotypic evolution in the two species of hedgehog present in central Europe, as based on genetics and geometric morphometrics in samples along a longitudinal transect that includes the contact zone between the species. While in allopatry, Erinaceus europaeus is found to have a larger skull than E. roumanicus and distinct cranial and mandibular shapes; the members of the two species in sympatry are smaller and more similar to each other, with a convergent shape of the mandible. The relevant data fail to reveal any major role for either hybridisation or clinal variation. We, therefore, hypothesise that competitive pressure exerted on the studied species does not generate divergent selection sufficient for divergent character displacement to evolve, instead giving rise to convergent selection in the face of resource limitation in the direction of smaller skull size. Considering the multi-factorial constraints present in the relevant adaptive landscape, reduction in size could also be facilitated by predator pressure in ecosystems characterised by mesopredator release and other anthropogenic factors. As the function of the animals’ lower jaw is mainly connected with feeding (in contrast to the cranium whose functions are obviously more complex), we interpret the similarity in shape as reflecting local adaptations to overlapping dietary resources in the two species and hence as convergent character displacement.

What size of Neotropical frogs do spiders prey on?

Interactions between vertebrates and invertebrates at similar trophic levels can shape community diversity and interactions, being frogs acting as prey and predators. Although spiders are a common dietary item for anurans, reports of frog predation by spiders are increasingly common in the literature. Anurans are preyed by several arthropod taxa, and spiders are, by far, the most important invertebrate predator for the group. Herein we report six new predation events by spiders on frogs and, based on a literature review, we analyzed the relationship between frog and spider sizes, and on prey niche overlap between frog and spider families for the Neotropics. Records of predation increased substantially in the last decades, especially after 2005. We recovered a relationship between frog and spider sizes, with the spider predator similar-sized or smaller than frogs. Most anuran prey ranged from 15 to 25 mm in body size, while most spiders were about 53% smaller than the frogs. Spiders were not specialized in any anuran family. Large cursorial spiders were involved in most of the reports, especially Ctenidae spiders, and Hylidae was the most frequently predated frog family. Since this prey-predator relationship is often determined by size, spiders may avoid larger frogs, explaining the pattern of our recovered reports of predation on smaller frogs. Although common, we suggest that future reports on spider-frog predation events should include more information, such as prey/predator sizes and identification, antipredator strategies, time for capture and ingestion, anuran stage, and habitat characteristics.

Determining Stingray Movement Patterns in a Wave-Swept Coastal Zone Using a Blimp for Continuous Aerial Video Surveillance

Stingrays play a key role in the regulation of nearshore ecosystems. However, their movement ecology in high-energy surf areas remains largely unknown due to the notorious difficulties in conducting research in these environments. Using a blimp as an aerial platform for video surveillance, we overcame some of the limitations of other tracking methods, such as the use of tags and drones. This novel technology offered near-continuous coverage to characterise the fine-scale movements of stingrays in a surf area in Kiama, Australia, without any invasive procedures. A total of 98 stingray tracks were recorded, providing 6 h 27 min of movement paths. The tracking data suggest that stingrays may use a depth gradient located in the sandflat area of the bay for orientating their movements and transiting between locations within their home range. Our research also indicates that stingray behaviour was influenced by diel periods and tidal states. We observed a higher stingray occurrence during the afternoon, potentially related to foraging and anti-predatory strategies. We also saw a reduced route fidelity during low tide, when the bathymetric reference was less accessible due to stranding risk. Considering the increasing threat of anthropogenic development to nearshore coastal environments, the identification of these patterns can better inform the management and mitigation of threats.

Factors influencing riverine utilization patterns in two sympatric macaques

Many species of terrestrial animals, including primates, live in varied association with the aquatic (e.g., riverine or coastal) environment. However, the benefits that each species receive from the aquatic environment are thought to vary depending on their social and ecological characteristics, and thus, elucidating those benefits to each species is important for understanding the principles of wild animal behaviour. In the present study, to gain a more complete picture of aquatic environment use, including social and ecological factors in primates, factors affecting riverine habitat utilization of two macaque species (Macaca nemestrina and M. fascicularis) were identified and qualitative comparisons were made with sympatric proboscis monkeys (Nasalis larvatus), which have different social and ecological characteristics. Temporal variation in sighting frequency of macaques at the riverbanks was positively related to the fruit availability of a dominant riparian plant species and negatively related to the river water level which affects the extent of predation pressure. Riverine utilization of macaques was greatly influenced by distribution and abundance of food (especially fruit) resources, possibly in association with predation pressure. Additionally, qualitative ecological comparisons with sympatric proboscis monkeys suggest that the drivers of riverine utilization depend on the feeding niches of the species, and different anti-predator strategies resulting from their differing social structures.

Effect of nest age and habitat variables on nest survival in Marsh Harrier (Circus aeruginosus) in a fishpond habitat.

BackgroundOne important anti‐predator strategy adopted by birds involves nest site selection and timing of breeding. Nest-site selection by marsh-nesting birds often involves nest concealment and water depth as key features influencing nest survival. Marsh Harrier (Circus aeruginosus) is an obligate ground nester, which sets it apart from other raptors. The aim of the present study was to identify for the first time possible temporal and habitat factors affecting nest survival in Marsh Harrier. Understanding features which affect nest survival are essential for assessing relevant conservation strategies.MethodsTo understand the relative contributions of different temporal and habitat variables to brood losses, it is useful to determine the daily survival rate (DSR). We examined 82 Marsh Harrier nests located on fishponds in eastern Poland, where predation is the main cause of nest loss. Six habitat variables were measured for each active nest. DSR was calculated using known-fate models with the RMark package.ResultsThe best-supported model predicted that DSR decreased with nest age and was positively affected by the water depth and the diameter of reed stems, but not by the height or density of vegetation at the nest site. The distances of nests to the fishpond dyke and to open water received no support in the models. The chances of nest survival were lower if a neighbouring nest had been depredated. This result suggests that the Marsh Harrier is more susceptible to mammalian than avian predation and confirms the high level of predator pressure in fishpond habitats.

Anti-predator behavior of Coimbra-Filho’s titi monkeys (<i>Callicebus coimbrai</i>)


 
 
 Predation pressure has an important role in shaping the behavioral, ecological and social patterns of primates. In this study, we describe two types of anti-predator behavior performed by Coimbra-Filho’s titi monkeys (Callicebus coimbrai), and compare our reports with the anti-predator strategies adopted by other Neotropical primates. The reports were performed on a small and isolated Atlantic forest fragment (14 ha) located in a highly-fragmented landscape in north-eastern Brazil. Although the titi monkey group was systematically monitored (July/2009 - August/2012: 1,513 hours) over the years, the events were recorded ab libitum method. Four events of anti-predator behavior were reported: three were in response to a medium-sized arboreal primate, the yellow-breasted capuchin monkey (Sapajus xanthosternos), and one in response to a large bird, the turkey vulture (Cathartes aura). When in the presence of S. xanthosternos, the titi monkeys emitted a quiet alert vocalization and descended to the dense undergrowth in order to avoid predation. On the other hand, when the titi monkeys were exploiting fleshy fruit on a tree, they verified the presence of an individual of C. aura and jumped to the ground. Both types of anti-predator behavior had been previously described for Neotropical primates. The anti-predator behaviors performed by the titi monkeys can contribute to the understanding of the adaptive processes of these poorly studied primates in fragmented habitats. Moreover, the passive behavior and the habitat characteristics may be an important aspect in the choice of strategy to be used, since the habitat pro- vided adequate refuges and allowed the titi monkeys to seek an alternative escape route.
 
 

<p class="Body"><strong>Under pressure: predation risk defining mating investment in matured spider mite <em>Tetranychus urticae</em></strong></p>

The emergence of anti-predatory strategies for prey survival are ruled by the minimization of the encounters/interactions with potential predators, but at the same time by maximizing the access to limiting resources such as food or mating partners. Cues indicating predatory activity influence decision-making activities in the two-spotted spider mite Tetranychus urticae, such as dispersion, foraging activities, and reproductive effort. However, anti-predatory strategies studied in spider mites generally considers mainly the female perspective (e.g. oviposition), leaving a gap in how T. urticae couples deal with predatory risk. Here, through laboratory experiments, we observed that matured spider mite couples were only affected by predation risk during the pre-copulatory stages of the mating process, especially when deciding to proceed in a mating opportunity. The mating performance of individuals was independent of their exposure to predation risk, suggesting that couples would adopt full investment behavior after opting to proceed in a mating attempt. Though our working hypothesis predicted predation risk interference throughout the entire mating process, we conclude that decision-making activities by spider mite during pre-copulatory stages act independently from copulatory stages associated to insemination.

Immune challenge does not impair short-distance escape speed in a newt

Animals may face trade-offs when several simultaneous functions or processes compete for limiting resources. In that context, allocation of resources to the most fitness-enhancing competing function can be prioritized. Immune response and locomotor performance are relevant fitness components, mainly due to their important roles as defence against pathogens and predators, respectively. However, both promote oxidative stress and consume energy and metabolites. Consistently, trade-offs between immune response and locomotion have been reported in some taxa. In this work, we examine whether an immune challenge hinders short-distance swimming speed of adult Iberian ribbed newts, Pleurodeles waltl. To that end, we inoculated Escherichia coli cell wall lipopolysaccharide (LPS), an innocuous antigen that triggers an immune response, in the sole pads of experimental newts, and phosphate buffer saline, with no physiological effect, in those of control newts. We estimated immune response as sole pad swelling and calculated swimming speed from videos of newts swimming towards a refuge nearby, 24 h and 7 days after inoculation. Sole pad swelling was greater in LPS-inoculated newts, but short-distance swimming speed was not affected by the immune challenge. These results could indicate priority allocation of resources to locomotion, which might be a consequence of compensatory mechanisms capable of avoiding locomotion impairment due to immune challenge. In any case, these findings could highlight the importance of short-distance escape as an antipredator strategy.

Nests built on power lines: Nest-site selection by long-tailed broadbills (Psarisomus dalhousiae) in Nonggang of Guangxi, China

The quality of breeding habitat may directly affect the survival and development of progeny. Therefore, the selection of a suitable nest-site is an important factor affecting the reproductive success of birds. The most important reason for a bird’s reproductive failure is nest predation. Predation may cause birds to change their nest-sites and even nest morphology. Here we investigated the nest-site characteristics by long-tailed broadbills ( Psarisomus dalhousiae) in Nonggang, Guangxi, southwestern China. Our results showed that long-tailed broadbills in Nonggang mainly build their nests on power lines (88.5%) and nest-site selection was mainly affected by predation pressure and food resources. At the same time, nest-site concealment was trade-off against predator avoidance. This anti-predator strategy effectively utilizes human infrastructure.

Sand lizards Lacerta agilis with higher digit ratios are more likely to autotomy.

Digit ratio is a morphological feature regarded as a biomarker of the balance of sex hormones during early development. The exposure of embryos to a set of sex hormones and the mutual relations between those hormones cause the emergence of individual morphological and/or behavioural characteristics as well as differences between sexes. We have thus hypothesised that differences in one of these morphological traits-digit ratio-may be a proxy representing a tendency towards tail autotomy. The aim of this study is to investigate the digit ratio (2D:3D, 2D:4D, 3D:4D) of the sand lizard, Lacerta agilis, Lacertidae, a species characterised by well-developed sexual dimorphism, whereby females are larger than males. We also tested associations between patterns in digit ratio and caudal autotomy, a common defensive mechanism among lizards. To our knowledge, the relationship between a tendency towards autotomy and digit ratio pattern has never been researched. To date, studies on autotomy have mainly focused on the consequences, costs or evolutionary background of tail loss. Hence, researchers examined mostly the frequency of autotomy in the context of predatory pressure or habitat conditions, omitting an individual's behavioural tendency to shed its tail. However, behavioural traits can affect an individual's exposure to predator attack and consequently the need to use an anti-predator strategy. Thus, following this logic, dropping the tail may be the result of the lizard's intraspecific personality characteristics, resulting from the effect of hormones on behaviour or innate traits. Therefore, we suggest that the inclusion of autotomy as a factor explaining observed digit ratio patterns and their variability between taxa has great potential. We used computerised measurements of photographed limbs to determine the length of digits. We found that the digit ratios for all four limbs were significantly lower in females than in males, excluding the 3D:4D ratio for the right hindlimbs. Therefore, the results confirmed the pattern already observed for most lizards. The novel element in our study is the detection of the relationship between a tendency towards caudal autotomy and digit ratio. Individuals with a tendency towards autotomy have a higher 2D:4D ratio in the right forelimbs and a lower 2D:3D ratio in the right hindlimbs. Obtained results suggest that these morphological characteristics are most likely related to intraspecific differences (between bold and shy individuals) which consequently may determine an individual's reaction or susceptibility to be a prey and escape behaviour. Thus, our results are probably the first attempt to link digit ratio to the susceptibility of lizards to tail autotomy.

Daily and seasonal movements of Cape Cod gray seals vary with predation risk

White sharks Carcharodon carcharias and gray seals Halichoerus grypus are re-establishing their ecological roles within the Northwestern Atlantic Ocean, presenting an opportunity to understand gray seal movement and at-sea behavior under predation risk. As with other shark-seal hotspots, movements to and from terrestrial haul outs can be risky for gray seals, thereby eliciting antipredator strategies. We investigated the movement and coastal behavior of gray seals on Cape Cod (USA) in relation to seasonal and diel changes in white shark activity. Analyzing 412 trips to sea by 8 seals and more than 25000 acoustic detections from 23 individual white sharks, we observed seasonally homogeneous movements in seal behavior during months with greater shark presence. During riskier months, seal behavior manifested in near-exclusive nocturnal foraging, reduced offshore ranging, and limited at-sea activity. On these nocturnal trips to sea, seals returning to haul outs tended to avoid daybreak and traversed during diel minima in shark activity. However, seals tended to depart haul outs at dusk when shark presence was maximal. As conservation efforts succeed in rebuilding depleted populations of coastal predators, studying re-emerging predator-prey interactions can enhance our understanding about the drivers of movement and behavior.

No link between nymph and adult coloration in shield bugs: weak selection by predators.

Many organisms use different antipredator strategies throughout their life, but little is known about the reasons or implications of such changes. For years, it has been suggested that selection by predators should favour uniformity in local warning signals. If this is the case, we would expect high resemblance in colour across life stages in aposematic animals where young and adults share similar morphology and habitat. In this study, we used shield bugs (Hemiptera: Pentatomoidea) to test whether colour and colour diversity evolve similarly at different life stages. Since many of these bugs are considered to be aposematic, we also combined multi-species analyses with predation experiments on the cotton harlequin bug to test whether there is evidence of selection for uniformity in colour across life stages. Overall, we show that the diversity of colours used by both life stages is comparable, but adults are more cryptic than nymphs. We also demonstrate that nymphs and adults of the same species do not tend to look alike. Experiments on our model system suggest that predators can generalise among life stages that look different, and exhibit strong neophobia. Altogether, our results show no evidence of selection favouring colour similarity between adults and nymphs in this speciose clade.