Antipredator Mechanisms Research Articles

Effect of salinity on the bioluminescence intensity of the heterotrophic dinoflagellates Noctiluca scintillans and Polykrikos kofoidii and the autotrophic dinoflagellate Alexandrium mediterraneum

Many dinoflagellate species are bioluminescent, which is one of the anti-predation mechanisms in these species. In addition, dinoflagellate species experience a wide range of salinities in the ocean. However, the effects of salinity on their bioluminescence intensity has only been investigated for one species. Here, we explored the effect of salinity on the bioluminescence intensity of the heterotrophic dinoflagellate Noctiluca scintillans NSDJ2010 feeding on the chlorophyte Dunaliella salina, the heterotrophic dinoflagellate Polykrikos kofoidii PKJH1607 feeding on the dinoflagellate Alexadrium minutum, and the autotrophic dinoflagellate Alexandrium mediterraneum AMYS1807. Moreover, to determine the cell volume and growth effects on bioluminescence intensity, the cell volume and growth rate of three bioluminescent dinoflagellates were simultaneously investigated. The mean 200-s-integrated bioluminescence intensity (BL) per cell, equivalent to the total bioluminescence, of N. scintillans, P. kofoidii, and A. mediterraneum was significantly affected by salinity and increased with increasing salinity from 10 to 40. The results of the present study suggest that the total bioluminescence of N. scintillans, P. kofoidii, and A. mediterraneum in offshore and oceanic waters is greater than that in estuarine waters.

Three sympatric host nestlings eavesdrop on cuckoo nestling distress calls.

In predator-prey interactions, the prey faces extreme challenges from predation, which drives the evolution of defense or anti-predator mechanisms. Compared with adult birds, nestlings are more vulnerable but not helpless. However, data on whether nestlings eavesdrop on the danger signals transmitted by other prey nestlings and the mechanisms of eavesdropping remain limited. In brood parasitism, common cuckoo (Cuculus canorus) nestlings, raised by host adults who are not closely related, offer an instructive system for studying the transmission and recognition of danger signals among nestlings of different species that share special relationships. We played back the distress calls of common cuckoo nestlings to nestlings of three sympatric host species (the oriental reed warbler Acrocephalus orientalis, which is a primary host of the common cuckoo, the reed parrotbill Paradoxornis heudei, an occasional host, and the vinous-throated parrotbill Sinosuthora webbiana, which is not parasitized in the study area) to investigate whether the host nestlings reduced their begging behavior. We also quantified the degree of inhibition toward begging behavior for these nestlings. The results revealed that, in response to the distress calls, the three sympatric host species markedly suppressed their begging behavior. This response can likely be attributed to the innate response of host nestlings caused by the general characteristics of distress calls, rather than the acoustic similarity and phylogenetic relationship between host nestlings and cuckoo nestlings. Furthermore, we observed that upon hearing the distress calls of cuckoo nestlings, the oriental reed warbler nestlings exhibited the greatest reduction in the total number of calls compared to the other two host species, potentially owing to stronger predation and parasitic pressures. This study suggests that host nestlings can detect danger signals emitted by parasitic nestlings; however, further investigation is needed to determine whether they can respond to distress calls from unfamiliar nestlings in different regions.

Global dynamics of an indirect prey-taxis system with an anti-predation mechanism

In this paper, we shall study the following model:{Nt=dNΔN+λN−N2−NP,x∈Ω,t>0,Pt=Δ(d(S)P)+μP−P2+γNP,x∈Ω,t>0,St=dSΔS+τN−ηS,x∈Ω,t>0,∂N∂ν=∂P∂ν=∂S∂ν=0,x∈∂Ω,(N,P,S)(x,0)=(N0,P0,S0)(x),x∈Ω, where Ω⊂Rn(n≥1) is a bounded domain with smooth boundary. Based on semigroup estimates and Moser iteration, we first establish the existence of the global classical solution with a uniform-in-time bound. Moreover, we build the global stabilization of constant steady states by constructing suitable Lyapunov functionals and give the decay rates of solutions. Furthermore, we find that the anti-predation mechanism will generate steady state bifurcation. We further prove the global existence of non-constant positive steady state solutions under certain conditions. Finally, we numerically demonstrate spatially inhomogeneous coexistence patterns (i.e., non-constant positive steady state solutions) for the predator, the prey and the signal.

Perception of con- and heterospecific injury cues in tadpoles of dendrobatid, ranid and bufonid frogs (Anura)

Predator-prey interactions are vital for organismal survival. They shape anti-predator mechanisms and often depend on sensory abilities. Tadpoles use chemical cues, such as injury cues (alarm cues), to assess predation risks and modify their life-history, morphology, and behaviours accordingly. However, the prevalence of chemically mediated anti-predator responses in species with distinct ecological niches (e.g. within phytotelmata) remains unknown, hindering our understanding of the ecological significance and evolution of alarm substances. Therefore, our study aimed to investigate chemically mediated anti-predator responses in tadpoles of two Neotropical poison dart frogs, Ranitomeya sirensis and Epipedobates anthonyi (and compare their responses to two Palearctic model organisms, Rana temporaria and Bufo bufo, which are known to utilise alarm substances). Through behavioural bioassays, we exposed predator-naïve tadpoles to extracts of each species (i.e. con- and heterospecific cues), including water as a control (i.e. five treatments per species). We assessed changes in their activity before and after stimulus introduction. Our results show that E. anthonyi did not respond to any of the stimuli, whereas R. sirensis displayed increased activity levels exclusively in response to conspecific cues, but not to heterospecific cues. With this, our findings suggest a specialized recognition system in R. sirensis, potentially directed at conspecific competitors but likely unrelated to anti-predator mechanisms. In contrast, E. anthonyi may be insensitive to injury cues or utilize alternative sensory modalities to respond to acute predation events. This study sheds light on the chemical alarm response system of Neotropical poison dart frog tadpoles, providing foundational understanding of how dendrobatids react to injury cues. It prompts questions about the ecological significance and evolutionary implications of chemical communication in species facing extreme resource limitation during development and underscores the importance of comparative research for understanding chemical communication in diverse aquatic ecosystems.

Predation fear and its carry-over effect in a fractional order prey–predator model with prey refuge

This research article centers on the formulation and analysis of a novel prey–predator model that integrates the impacts of predation fear, prey refuge, and carry-over effects. The model is formulated and analyzed using fractional differential equations (FDEs). The model incorporates ecological concepts such as anti-predator behaviours and memory effects to maintain a better understanding of prey–predator interactions. The mathematical model is developed based on a basic prey–predator model with a Michelis–Menten functional response and includes fear-induced carry-over effects, prey refuge, and fractional order derivatives. The study investigates the well-posedness, stability, and Hopf bifurcation of the proposed model and conducts detailed numerical investigations. The integration of different anti-predatory mechanisms and the use of FDEs contribute to a comprehensive understanding of the dynamics of prey–predator interactions and provide useful insights into the complexities of ecological systems.

Fear effect exerted by carnivore in grassland ecosystem

A four-dimensional mathematical model is formulated to explore the fear effect exerted by large carnivore in the grassland ecosystem. The model depicts the interactions among herbage, domestic herbivore, wild herbivore and large carnivore, which incorporates both direct predation and anti-predator mechanisms. The dynamic properties of the model are analytically investigated, including the dissipativity of solutions, and the existence and stability of different equilibria. Some numerical simulations are also presented to exhibit rich dynamical behaviors, such as various types of bistabilities, periodic oscillation and chaotic oscillation. The study reveals that the appropriate level of fear factors can stabilize the system and increase the density of herbage and domestic herbivore. The fear effect plays an important role in maintaining the balance of the grassland ecosystem and promoting the economy of human society.

Artificial light at night causes conflicting behavioural and morphological defence responses in a marine isopod.

Encroachment of artificial light at night (ALAN) into natural habitats is increasingly recognized as a major source of anthropogenic disturbance. Research focussed on variation in the intensity and spectrum of ALAN emissions has established physiological, behavioural and population-level effects across plants and animals. However, little attention has been paid to the structural aspect of this light, nor how combined morphological and behavioural anti-predator adaptations are affected. We investigated how lighting structure, background reflectance and the three-dimensional properties of the environment combined to affect anti-predator defences in the marine isopod Ligia oceanica. Experimental trials monitored behavioural responses including movement and background choice, and also colour change, a widespread morphological anti-predator mechanism little considered in relation to ALAN exposure. We found that behavioural responses of isopods to ALAN were consistent with classic risk-aversion strategies, being particularly exaggerated under diffuse lighting. However, this behaviour was disconnected from optimal morphological strategies, as diffuse light caused isopods to become lighter coloured while seeking out darker backgrounds. Our work highlights the potential for the structure of natural and artificial light to play a key role in behavioural and morphological processes likely to affect anti-predator adaptations, survival, and ultimately wider ecological effects.

Anti-predatory responses of two native gastropods to an invasive predator

As native prey species lack a co-evolutionary history with invasive predators, they often have limited capacity to identify and respond to the threat of predation. This phenomenon has led to the prey naivety hypothesis. Invasive predators can have devastating impacts on native prey populations. Thus, there is a need to better understand the ability of native species to respond to invasive predators. Here, laboratory behavioural experiments tested the anti-predatory responses of two gastropods, Cominella lineolata and Dicathais orbita, against an invasive predator, Asterias amurensis, and a native predator, Coscinasterias muricata. There was no chemical exudate released by any D. orbita to either species of seastar or a wax seastar control. Only a small percentage of D. orbita individuals fled from the invasive (12.5%) and native (17%) seastars. The overall separation distance between D. orbita and the two seastars was recorded for a further three minutes. While the measured distance between the invasive seastar and D. orbita was greater (61 ± 7 mm) than the distance between the native seastar (39 ± 10 mm), this was not statistically significant. In contrast, C. lineolata exhibited strong responses to the native seastar, but less strongly to the invasive seastar. Only 50% of snails fled and 15% released an exudate in response to A. amurensis, compared to 80% of snails fleeing and releasing an exudate to the native seastar. In contrast to expectations, C. lineolata collected from naïve populations tended to respond less frequently (25% of snails) by fleeing from the invasive seastar than snails collected from exposed (50% of snails), however this was not significant. This same trend was observed for C. muricata with 70% and 90% of snails fleeing from exposed and naïve populations, respectively. After recording the behavioural responses of both seastars and snails for three minutes, the release of exudate resulted in an increased separation distance between C. lineolata and C. muricata of 122 mm (± 31 mm) compared with just 28 mm (± 16 mm) when the snails failed to release the exudate, whereas the separation distances between C. lineolata and A. amurensis was 143 mm (± 31 mm) and 87 mm (± 10 mm) with and without exudate release, respectively. This latter result indicates that while the exudate appears to be an effective anti-predatory mechanism against the native seastar, it appears less effective against the invasive seastar.

Commentary: using prey naïveté to inform ecological management.

Commentary: using prey naïveté to inform ecological management.

The Effects of Artificial Night Lighting on Tail Regeneration and Prey Consumption in a Nocturnal Salamander (Plethodon cinereus) and on the Behavior of Fruit Fly Prey (Drosophila virilis).

Simple SummaryAmphibians, including salamanders, are declining worldwide at an alarming rate due to a variety of factors that include habitat decline and destruction and environmental pollutants. Artificial light at night (ALAN) due to human activities is a nearly ubiquitous pollutant and can have serious consequences for amphibians. We examined the impact of ecologically-relevant levels of ALAN on tail regeneration in the eastern red-backed salamander, prey consumption by these salamanders and behavior of their fruit fly prey. We found that ALAN reduced the rate of salamander tail regeneration at some light levels above the naturally dark nocturnal illumination and increased the activity of their prey but not always in a simple, linear fashion. Thus, ALAN, even at very low levels, can influence the physiology and regeneration of a nocturnal salamander.As human development continues to encroach into natural habitats, artificial light at night (ALAN) has increasingly become a concern for wildlife. Nocturnal animals are especially vulnerable to ALAN, as the physiology and behavior of nocturnal species have evolved under conditions associated with predictably dark environments. Studies exposing amphibians to constant bright light provide evidence for changes to normal metabolism, growth, and behavior, but few of these studies have used treatments of dim ALAN comparable to that found in affected habitats. Eastern red-backed salamanders, Plethodon cinereus, use their tails for fat storage and communication, are capable of tail autotomy as an antipredator mechanism, and can regenerate the tail in its entirety. We examined the effect of different, ecologically-relevant intensities of ALAN on the rate of tail regeneration in adult P. cinereus. We hypothesized that ALAN would increase tail regeneration rates such that salamanders exposed to higher levels of light at night would regenerate tails faster than those exposed to lower light levels. In a controlled laboratory setting, we exposed salamanders (N = 76) in test chambers to nocturnal illuminations of 0.0001 lx (no ALAN, natural nocturnal illumination dark control), 0.01 lx (weak ALAN), 1 lx (moderate ALAN), or 100 lx (bright ALAN, equal to dim daytime and our day lighting treatment) for a period of 90 d immediately following tail autotomy. In addition, because these salamanders eat mostly live, moving prey, we investigated the impact of ALAN on the behavior of prey (Drosophila virilis) fed to the salamanders in our laboratory trials, which could alter feeding and regeneration rates in salamanders. We predicted that prey consumption would not be affected by ALAN and measured both prey consumption and prey behavior (activity) to examine the potential influence on regeneration. For tail regeneration, we found a non-monotonic response to ALAN, with salamanders exposed to nocturnal illuminations 0.1 lx and 100 lx regenerating tails significantly slower than salamanders in the 0.0001 lx or 1 lx treatments. Prey consumption did not differ among light treatments; however, fruit fly activity increased with increasing ALAN. These results suggest that ALAN influences regeneration rates, but the rate of regeneration is not dose-dependent and is not explained easily by prey consumption or movement of prey. We suggest that tail regeneration in these salamanders may involve a complex mechanism of altered gene expression and/or modulation of hormonal activity (corticosterone, melatonin, serotonin, and/or prolactin) at different intensities of nocturnal lighting.

On the stream-dwelling Crossodactylus timbuhy (Anura, Hylodidae): taxonomy, natural history, and geographic distribution.

The genus Crossodactylus has taxonomic problems due to the difficulty in properly identifying some populations to the species level. The deficient species diagnosis rises mostly due to high intraspecific variation and lack of information on topotypes. Crossodactylus timbuhy was described based only on external morphology of preserved adult specimens. Based on topotypic specimens, we provide further information on C. timbuhy regarding color in life (both adult and larvae), tadpole external morphology, vocal repertoire, natural history, and geographic distribution. The species identification was confirmed through comparison to the type series, 16S rRNA analysis, and bioacoustics. Crossodactylus timbuhy vocalizes during daylight along shallow slow-flowing streams. The advertisement call has ascendant amplitude modulation, duration of 2.18.4 s, 2375 pulsed notes, and peak frequency of 3.64.8 kHz. Our report on male unilateral sac inflation is the first within Crossodactylus. Although overall tadpole external morphology and coloration resemble other species of hylodids, we report ventral depression and golden iridophores also for the first time within Crossodactylus. Adult males display five antipredator mechanisms (interrupt calling, escape, aggression, posture, and aposematism). Finally, we restrict its geographic distribution to the Municipality of Santa Teresa, State of Esprito Santo, Southeastern Brazil.

Endoplasmin regulates differentiation of tonsil-derived mesenchymal stem cells into chondrocytes through ERK signaling

It is well-known that some species of lizard have an exceptional ability known as caudal autotomy (voluntary self-amputation of the tail) as an anti-predation mechanism. After amputation occurs, they can regenerate their new tails in a few days. The new tail section is generally shorter than the original one and is composed of cartilage rather than vertebrae bone. In addition, the skin of the regenerated tail distinctly differs from its original appearance. We performed a proteomics analysis for extracts derived from regenerating lizard tail tissues after amputation and found that endoplasmin (ENPL) was the main factor among proteins up-regulated in expression during regeneration. Thus, we performed further experiments to determine whether ENPL could induce chondrogenesis of tonsil-derived mesenchymal stem cells (T-MSCs). In this study, we found that chondrogenic differentiation was associated with an increase of ENPL expression by ER stress. We also found that ENPL was involved in chondrogenic differentiation of T-MSCs by suppressing extracellular signal-regulated kinase (ERK) phosphorylation.

The high diversity and phylogenetic signal of antipredator mechanisms of the horned frog species of Proceratophrys Miranda-Ribeiro, 1920 (Amphibia: Anura: Odontophrynidae)

Phylogenetic signals indicate the phenotypic similarity of antipredator mechanisms among related species. Herein, we assessed the antipredator mechanisms of the horned frog Proceratophrys laticeps, compiled a database including closely phylogenetically-related species, and evaluated their phylogenetic signals. Our dataset comprises 80 records for 13 species of Proceratophrys, totalizing 11 antipredator mechanisms and 15 variations of these mechanisms. Six antipredator mechanisms show high similarity in the trees’ roots within Proceratophrys (e.g., aggression, aposematism, camouflage, distress call, immobility, and interrupt calling). Our observations show the first records of antipredator mechanisms for P. laticeps, and the first report of interrupt calling for Proceratophrys genus, contributing to the knowledge on the behavioural ecology of Proceratophrys species, addressing new insights for ecological trait evolution by multiple ancestral states of amphibians.

Cantharidin downregulates PSD1 expression and inhibits autophagic flux in yeast cells.

Cantharidin is a terpenoid compound of insect origin, naturally produced by male blister beetles as an antipredatory mechanism. Cantharidin has anticancer properties, which are attributed to its ability to induce cell cycle arrest, DNA damage, MAPK signaling pathway, and apoptosis. Cantharidin has been reported to induce apoptosis in triple‐negative breast cancer cells by suppressing autophagy via downregulation of Beclin 1 expression and autophagosome formation. However, it remains unclear which stage of the autophagic pathway is targeted by cantharidin. Herein, we report that yeast cells are sensitive to cantharidin, and external supplementation of ethanolamine (ETA) ameliorates the cytotoxicity. In addition, cantharidin downregulates phosphatidylserine decarboxylase 1 (PSD1) expression. We also report that cantharidin inhibits autophagic flux, and external administration of ETA could rescue this inhibition. Additionally, cotreatment with chloroquine sensitized the autophagy inhibitory effects of cantharidin. We conclude that yeast cells are sensitive to cantharidin due to inhibition of autophagic flux.

A new species of Ischnocnema (Anura: Brachycephalidae) from the mountainous region of Atlantic Forest, southeastern Brazil, with a new phylogeny and diagnose for Ischnocnema parva series.

We describe a new species of Rain Frog from Brazils Atlantic Forest, which harbors high richness, endemism and threatened species of anurans. Ischnocnema crassa sp. nov. is a leaf litter breeder from the montane rainforest of Santa Teresa, state of Esprito Santo, southeastern Brazil. Remarkably, the new species is so far unique amongst Ischnocnema for having moderate hand webbing between fingers. Ischnocnema crassa sp. nov. is the third species belonging to I. parva series and we present a new phylogeny based on molecular data and propose a new diagnosis for the series. We provide field and laboratory observations regarding amplexus, antipredator mechanisms, microhabitat preferences and conservation remarks. Although Santa Teresa is one of the most sampled areas in Brazil, new species are often discovered. Santa Teresa is a priority for amphibian conservation because it harbors 109 species of anurans (9% of Brazils species).

Echidnas of the Sea: The Defensive Behavior of Juvenile and Adult Crown-of-Thorns Sea Stars.

AbstractCrown-of-thorns sea stars are one of the most ecologically important tropical marine invertebrates, with boom-bust population dynamics that influence the community structure of coral reefs. Although predation is likely to influence the development of population outbreaks, little is known about the defensive behavior of crown-of-thorns sea stars. Righting behavior after being overturned, a key defensive response in echinoderms, was investigated for the newly settled herbivorous juvenile, the corallivorous juvenile, and adult stages of crown-of-thorns sea stars. The average righting time of the newly settled juveniles (0.3-1.0-mm diameter) was 2.74 minutes. For the coral-eating juveniles (15-55-mm diameter), the righting time (mean = 6.24 min) was faster in larger juveniles, and the mean righting time of the adults was 6.28 minutes. During righting and in response to being lifted off of the substrate, the juveniles and adults exhibited an arm curling response, during which their arms closed over their oral side, often forming a spine ball, a feature not known for other asteroids. The righting and curling responses of the corallivorous juveniles were influenced by the presence of a natural enemy, a coral guard crab, which caused the juveniles to spend more time with their arms curled. These behaviors indicate that crown-of-thorns sea stars use their spines to protect the soft tissue of their oral side. The highly defended morphology and behavioral adaptations of crown-of-thorns sea stars are likely to have evolved as antipredator mechanisms. This points to the potential importance of predators in regulating their populations, which may have decreased in recent times due to fishing, a factor that may contribute to outbreaks.

Loss of the Acetate Switch in Vibrio vulnificus Enhances Predation Defense against Tetrahymena pyriformis.

ABSTRACTVibrio vulnificus is an opportunistic human pathogen and autochthonous inhabitant of coastal marine environments, where the bacterium is under constant predation by heterotrophic protists or protozoans. As a result of this selection pressure, genetic variants with antipredation mechanisms are selected for and persist in the environment. Such natural variants may also be pathogenic to animal or human hosts, making it important to understand these defense mechanisms. To identify antipredator strategies, 13 V. vulnificus strains of different genotypes isolated from diverse environments were exposed to predation by the ciliated protozoan Tetrahymena pyriformis, and only strain ENV1 was resistant to predation. Further investigation of the cell-free supernatant showed that ENV1 acidifies the environment by the excretion of organic acids, which are toxic to T. pyriformis. As this predation resistance was dependent on the availability of iron, transcriptomes of V. vulnificus in iron-replete and iron-deplete conditions were compared. This analysis revealed that ENV1 ferments pyruvate and the resultant acetyl-CoA leads to acetate synthesis under aerobic conditions, a hallmark of overflow metabolism. The anaerobic respiration global regulator arcA was upregulated when iron was available. An ΔarcA deletion mutant of ENV1 accumulated less acetate and, importantly, was sensitive to grazing by T. pyriformis. Based on the transcriptome response and quantification of metabolites, we conclude that ENV1 has adapted to overflow metabolism and has lost a control switch that shifts metabolism from acetate excretion to acetate assimilation, enabling it to excrete acetate continuously. We show that overflow metabolism and the acetate switch contribute to prey-predator interactions.IMPORTANCE Bacteria in the environment, including Vibrio spp., interact with protozoan predators. To defend against predation, bacteria evolve antipredator mechanisms ranging from changing morphology, biofilm formation, and secretion of toxins or virulence factors. Some of these adaptations may result in strains that are pathogenic to humans. Therefore, it is important to study predator defense strategies of environmental bacteria. V. vulnificus thrives in coastal waters and infects humans. Very little is known about the defense mechanisms V. vulnificus expresses against predation. Here, we show that a V. vulnificus strain (ENV1) has rewired the central carbon metabolism, enabling the production of excess organic acid that is toxic to the protozoan predator T. pyriformis. This is a previously unknown mechanism of predation defense that protects against protozoan predators.

Parallel morphological evolution and habitat-dependent sexual dimorphism in cave- vs. surface populations of the Asellus aquaticus (Crustacea: Isopoda: Asellidae) species complex.

Studying parallel evolution (repeated, independent evolution of similar phenotypes in similar environments) is a powerful tool to understand environment‐dependent selective forces. Surface‐dwelling species that repeatedly and independently colonized caves provide unique models for such studies. The primarily surface‐dwelling Asellus aquaticus species complex is a good candidate to carry out such research, because it colonized several caves in Europe. By comparing 17 functional morphological traits between six cave and nine surface populations of the A. aquaticus species complex, we investigated population divergence in morphology and sexual dimorphism. We found habitat‐dependent population divergence in 10 out of 17 traits, likely reflecting habitat‐driven changes in selection acting on sensory systems, feeding, grooming, and antipredator mechanisms. Sexual dimorphism was present in 15 traits, explained by sexual selection acting on male traits important in male–male agonistic behavior or mate guarding and fecundity selection acting on female traits affecting offspring number and nursing. In eight traits, the degree of sexual dimorphism was habitat dependent. We conclude that cave‐related morphological changes are highly trait‐ and function‐specific and that the strength of sexual/fecundity selection strongly differs between cave and surface habitats. The considerable population variation within habitat type warrants further studies to reveal cave‐specific adaptations besides the parallel patterns.

The behavioural ecology behind anti-predator mechanisms: diversity, ontogenetic changes and sexual differences in anuran defence behaviours

Anti-predator mechanisms play a key role in the survival of any animal in nature. Anurans exhibit a great diversity of defensive behaviours and interact with the widest range of predators of any vertebrates. However, there are few systematic and experimental studies of anuran defensive behaviours, which are generally opportunistic. Here, we deploy a range of methods to investigate various facets of anuran defensive behaviour using the cane toad Rhinella marina as a model organism. This originally Amazonian anuran is now widely distributed across the globe and has caused several predators to decline at introduction sites where this species is not native, a direct result of its anti-predation defenses. First, we compiled previously published data on anuran predation events to assess the relationship between predator/anuran size and predator size and type. We then performed a systematic experiment to test the hypothesis that there is an ontogenetic variation in cane toad behavioural defense displays, as well as a variation in these displays between males and females. In total, we tested 173 individuals including juveniles, adult males and adult females. We show that the size and type of the predator is related to the size of the anuran as prey and that this, in turn, has led to the adoption of different predation-avoiding behavioural defensive strategies during ontogeny. Our results also indicate that both the sex and the size of anurans influence the adoption of defensive strategies.

Disruptive effects of chlorpyrifos on predator-prey interactions of Ceratophrys ornata tadpoles: Consequences at the population level using computational modeling

Large-scale ecotoxicological studies have technical and ethical limitations, both related to the need to expose large numbers of individuals to potentially harmful compounds. The computational modeling is a complementary useful and predictive tool that overcomes these limitations. Considering the increasing interest in the effects of pesticides on behavioral traits, the aim of this study was to evaluate the effects of chlorpyrifos (CPF) on intra- and inter-specific interactions of anuran tadpoles, complementing traditional ecotoxicological tools with a theoretical analysis verified by computational simulations. Experiments were developed under two consecutive phases: a first phase of exposure (treated and control group), and a second phase of interactions. The second phase consisted of evaluating the effects of CPF on intra- and inter-specific interactions of exposed C. ornata (Co) tadpoles acting as predators and unexposed Rhinella fernandezae (Rf) tadpoles acting as prey (Experiment I), under different predator-prey proportions (0/10 = 0Co–10Rf, 2/8, 4/6, 6/4, 8/2, 10/0). Also, intraspecific interactions of three Co tadpoles under different conditions of exposure were evaluated (Experiment II: 3 exposed Co, 2 exposed Co/1 non-exposed, 1 exposed Co/2 non-exposed). During the exposure phase, chlorpyrifos induced significant mortality from 48 h (48 h: p < 0.05, 72 h–96 h: p < 0.001), irregular swimming, tail flexure, and the presence of subcutaneous air. Also, it induced effects on the sounds emitted after 96 h of exposure, registering a smaller number of pulses and higher dominant frequencies, and altered intra- and inter-specific interactions. During the interaction phase, the larvae continued to show sound effects, however, the antipredator mechanism continued to be operating and efficient. Finally, it was possible to model the behavior of the larvae under the effects of chlorpyrifos. We conclude that experimental data and computational modeling matched. Therefore, computational simulation is a valuable ecotoxicological tool that provides new information and allows prediction of natural processes.