Defense Costs Research Articles

Targeted plant defense: silicon conserves hormonal defense signaling impacting chewing but not fluid-feeding herbivores.

Plants deploy an arsenal of chemical and physical defenses against arthropod herbivores, but it may be most cost efficient to produce these only when attacked. Herbivory activates complex signaling pathways involving several phytohormones, including jasmonic acid (JA), which regulate production of defensive compounds. The Poaceae also have the capacity to take up large amounts of silicon (Si), which accumulates in plant tissues. Si accumulation has antiherbivore properties, but it is poorly understood how Si defenses relate to defense hormone signaling. Here we show that Si enrichment causes the model grass Brachypodium distachyon to show lower levels of JA induction when attacked by chewing herbivores. Triggering this hormone even at lower concentrations, however, prompts Si uptake and physical defenses (e.g., leaf hairs), which negatively impact chewing herbivores. Removal of leaf hairs restored performance. Crucially, activation of such Si-based defense is herbivore-specific and occurred only in response to chewing and not fluid-feeding (aphid) herbivores. This aligned with our meta-analysis of 88 studies that showed Si defenses were more effective against chewing herbivores than fluid feeders. Our results suggest integration between herbivore defenses in a model Si-accumulating plant, which potentially allows it to avoid unnecessary activation of other costly defenses.

Variation in alarm calls during different breeding stages of the common kestrel (Falco tinnunculus).

ABSTRACTAcoustic signals play a key role in animal communication. Animals usually use alarm signals to warn mates or offspring of the presence of threats or to intimidate or distract predators. Birds commonly use acoustic signals as a means of communication. Alarm calls in passerines at different breeding stages can reflect their nest defense intensity. However, little is known about the characteristics, plasticity, and impact factors of alarm calls during the reproductive period in raptors. Here, from March to July in 2019, the alarm calls of eight pairs of common kestrels (Falco tinnunculus) during the breeding period were recorded using a portable recorder with a strongly directed microphone in the Zuojia Nature Reserve, Jilin province, China. The differences in acoustic parameters of parental alarm calls in different breeding stages were analyzed. The results showed that the alarm calls of common kestrels were composed of multi-harmonic arched frequency modulation with the maximum energy distribution in the second harmonic. The duration and rate of the alarm calls increased significantly as the breeding season progressed, showing that parents spent increasing amounts of time on nest defense. Additionally, the acoustic parameters of alarm calls in common kestrels were significantly different depending on offspring numbers, suggesting that offspring numbers influenced parental nest defense. These results showed that differences in alarm calls during different breeding stages may reflect a trade-off between defense costs and reproductive benefits.

Using Extrinsic Evidence to Excuse a Liability Insurer's Duty to Defend

Most Americans and American businesses purchase liability insurance to protect against financial loss should they ever be sued. In furnishing this protection, liability insurers contractually promise policyholders that they will defend them against lawsuits seeking covered damages and indemnify them for such damages up to the policy limits. As important as the insurer’s promise of indemnification is to an insured, the insurer’s agreement to defend the insured in litigation is an equally essential aspect of the liability insurance bargain. An insurer must decide whether it has a duty to defend its insured at the outset of a case. There are two approaches to determining an insurer’s duty to defend. First, there is the eight corners rule, under which the factual allegations in the plaintiff’s complaint or petition are compared with the policy, and the insurer owes a defense only if those allegations potentially implicate the insurer’s duty to indemnify the insured. Second, there is the extrinsic evidence approach. Courts employing an extrinsic evidence approach hold that an insurer must look beyond the pleadings and consider any facts brought to its attention or any facts that it reasonably could discover at the time suit was filed in deciding whether it has a duty to defend. Liability insurance policies typically provide that the insurer will pay the cost of the insured’s defense in addition to the policy’s liability limits. This is a potentially significant expense for the insurer because defense costs may, and often do, exceed any settlement or judgment ultimately paid. Given the expense associated with providing a defense, it is not surprising that an insurer may want to disclaim its duty to defend based on extrinsic evidence that establishes that it will have no duty to indemnify the insured. Of course, an insurer generally cannot decline to defend its insured if, in making that determination, it is limited to the facts alleged in the plaintiff’s petition or complaint; after all, even in extrinsic evidence states, it usually is the allegations in that pleading that triggered the insurer’s duty to defend in the first place. Thus, insurers frequently test their ability to rely on extrinsic evidence to disclaim their duty to defend when the plaintiff’s complaint or petition alleges facts that trigger the duty. In other words, if an insurer must, in many states, consider extrinsic evidence in accepting its duty to defend, can it also rely on extrinsic evidence to deny or exit a defense? The answer generally is no; the use of extrinsic evidence is rarely a two-way street. Although the general rule holds that an insurer may not rely on extrinsic evidence to refuse to defend an insured, some courts that adhere to the general rule occasionally recognize exceptions. Plus, there is a contrary minority rule. It is therefore fair to ask whether an insurer should be allowed to rely on extrinsic evidence to disclaim or extinguish its duty to defend when the plaintiff’s complaint or petition alleges facts that implicate coverage, and, if so, under what circumstances? This question is timely first because of two 2020 Texas Supreme Court decisions addressing it and offering different answers based on the facts presented: Richards v. State Farm Lloyds and Loya Insurance Co. v. Avalos. Second, as Richards and Loya demonstrate, insurers’ use of extrinsic evidence to excuse their defense obligations is an ongoing litigation strategy. That is not to say that the strategy is good or bad, but it is to say that the extrinsic evidence issue will continue to surface in key cases in various jurisdictions. Third, while insurers’ use of extrinsic evidence to defeat the duty to defend is hotly contested by policyholders, courts that have considered the issue over the years have rarely discussed it in meaningful fashion in their opinions. The resulting lack of guidance hampers courts either confronting the issue for the first time or entertaining reconsideration of prior holdings. This Article provides that guidance.

The effect of testosterone suppression on health and parasite burden in male eastern grey kangaroos (

Testosterone has a dualistic effect in males by promoting sexual ornamentation at the cost of immune defence. This trade-off has been demonstrated in several taxa, such that males often host a greater parasite burden compared with female conspecifics. We suppressed testosterone in wild male eastern grey kangaroos (Macropus giganteus) for 10 weeks using a novel gonadotropin-releasing hormone (GnRH) vaccine, Bopriva. We evaluated the impact of testosterone suppression on testes width, parameters of health, tick and worm burden in kangaroos using a before-after-control-impact (BACI) experimental design. Given the potential impact of animal movement on parasite burden, core area use of a subset of males was also determined. Bopriva significantly reduced testosterone in male kangaroos as well as reducing the combined size of testes by 9.6% (P = 0.01). There was no detectable effect of testosterone suppression on parasite burden and core area use in Treated kangaroos compared to Control (placebo) and Before treatment animals. Our results suggest that a duration of suppression longer than 10 weeks may be required to observe changes in parasite burden. Overall, this study provides a suitable framework for future studies to test whether reproductive hormones influence energy allocation, parasitism, and reproductive strategies in marsupials.

Optimal Strategy for Cyberspace Mimic Defense Based on Game Theory

Traditional defensive techniques are usually static and passive, and appear weak to confront highly adaptive and stealthy attacks. As a novel security theory, Cyberspace Mimic Defense (CMD) creates asymmetric uncertainty that favors the defender. CMD constructs multiple executors which are diverse functional equivalent variants for the protected target and arbitral mechanism. In this way, CMD senses the results of current running executors and changes the attack surface. Although CMD enhances the security of systems, there are still some critical gaps with respect to design a defensive strategy under costs and security. In this paper, we propose a dual model to dynamically select the number of executors being reconfigured according to the states of the executors. First, we establish a Markov anti-attack model to compare the effects of CMD under different types of attack. Then, we use a dynamic game of incomplete information to determine the optimal strategy, which achieves the balance of the number of reconfiguration and security. Finally, experimental results show that our dual model reduces defensive costs while guarantees security.

Приоритеты госфинансирования и перспективы развития отрасли искусственного интеллекта в США

The US Government has initiated a large-scale activity on artificial intelligence (AI) development and implementation. Numerous departments and agencies including the Pentagon, intelligence community and citizen agencies take part in these efforts. Some of them are responsible for technology, materials and standards development. Others are customers of AI. State AI efforts receive significant budget funding. Moreover, Department of Defense costs on AI are comparable with the whole non-defense funding. American world-leading IT companies support state departments and agencies in organizing AI technologies development and implementation. The USA's highest military and political leadership supports such efforts. Congress provides significant requested funding. However leading specialists criticize the state's approach to creating and implementing AI. Firstly, they consider authorized assignments as not sufficient. Secondly, even this funding is used ineffectively. Therefore Congress created National Security Commission on Artificial Intelligence (NSCAI) in 2018 for identifying problems in the AI area and developing solutions. This article looks at the stakeholders and participants of the state AI efforts, the budget funding authorization, the major existing problems and the NSCAI conclusions regarding the necessary AI funding in FYs 2021-2032.

Обсуждение проблемы участия США в Первой мировой войне на заседаниях 65-го американского Конгресса

The article is devoted to the problem of discussing the participation of the United States in the First World War at the meetings of the 65th Congress. The importance of the topic lies in the fact that the materials of the sessions of the Congress, being important historical sources, make it possible, by interpolation, to introduce into scientific circulation new data on the entry and participation of the United States in the war, as well as to determine the attitude of American congressmen to this issue. The research is based on the materials of the American Congress, containing resolutions, draft laws and laws, verbatim records. The main ones are: Resolution on the Declaration of War on the German Empire by the United States; "A law allowing the issuance of bonds to cover the cost of national security and defense, as well as the provision of assistance to foreign governments in the conduct of war through the provision of loans"; discussion and amendment of the "Law on the Allocation of Appropriations for the Naval Service for the Fiscal Year Ending June 30, 1917", etc. The author paid special attention to the analysis of the message of the American President to the US Congress dated April 2, 1917. The materials of the meetings of the 65th Congress are located on the official website of the US Library of Congress and contain information about the entry and participation of the United States in the First World War.

Climate influences the value of a plant structural defence against browsing

Abstract The circumstances that select for plant anti‐herbivore defences are not well understood. In New Zealand, the ‘divaricate’ cage‐like architecture of many woody plants may have arisen as a defence against avian browsing; it also has some ability to deter browsing by introduced deer. Its prominence on alluvial soils in frosty and droughty areas led us to hypothesize that structural defences are of most value where fertile soils coincide with climatic constraints that prevent plants from quickly growing out of the browse zone. We tested this hypothesis by growing seedlings of three divaricate species and their broadleaved congeners on fenced and unfenced plots beneath tree‐fall gaps at three humid frost‐free sites in the North Island of New Zealand, and at three colder and drier sites in the South Island. Soil total phosphorus levels were moderate to high at all sites (344–961 ppm), and pellet counts indicated similar average deer densities at North and South Island sites, enabling us to attribute variation in seedling growth and survival primarily to climatic differences between our sites. On fenced plots, average relative height growth rates in the North Island exceeded those on the southern sites by 64%, and growth of broadleaved species averaged 132% and 99% greater than that of divaricate congeners at North and South Island sites, respectively. On the northern sites, broadleaved species also held a large (137%) net height growth advantage over divaricates even on unfenced plots. In contrast, exposure to browsing on the coldest sites resulted in complete loss of the broadleaved net height growth advantage. Synthesis. Even in the presence of deer, divaricate plants were overgrown on humid frost‐free sites, but not on colder and drier sites, where browsing neutralized the superior growth potential of broadleaved species. The cost of structural defences therefore paid off only on sites where climatic adversity reduces the ability of plants lacking such defences to grow quickly out of the browse zone, in agreement with our hypothesis.

Great Himalayan Leaf-Nosed Bats Produce Different Territorial Calls to Respond to Sympatric Species and Non-Living Objects.

Simple SummaryMany animals produce keep-out signals to keep intruders from entering their territories. Studies have shown that bats produce territorial calls to defend the conspecifics intrusion. However, it remains unknown whether bats can adjust their territorial calls in response to different types of intruders, such as heterospecifics or non-living objects. We simulated the process of territory defense in male great Himalayan leaf-nosed bats toward two sympatric species and four non-living objects to investigate their acoustic responses. Bats displayed different acoustic responses for different types of intruders, suggesting that territorial calls of male great Himalayan leaf-nosed bats may convey emotional state information when the bats respond to invasion by sympatric species or non-living objects. Our results are valuable for understanding animal cognition and interactions among bat species from an acoustic perspective.Territorial signals are important for reducing the cost of territory defense. Normally, male animals will produce keep-out signals to repel intruders from entering their territory. However, there is currently no evidence that bats can adjust their territorial calls to respond differently to sympatric species or non-living objects. In this study, we simulated the process of territory defense in male Great Himalayan leaf-nosed bats (Hipposideros armiger) toward two sympatric species (Hipposideros pratti and Rhinolophus sinicus) and four different non-living objects (a fur specimen of H. armiger, a bat model, a speaker, and a speaker with playback of H. armiger echolocation calls) to investigate their acoustic responses. There were significant differences in the territorial call complexity, syllable rate, and syllable ratio produced by H. armiger under the different experimental conditions. Our results confirmed that bats can adjust their territorial calls to respond to different sympatric species and non-living objects. The results will further our understanding of animal cognition and interactions among bat species from an acoustic perspective.

The influence of social-grouping on territorial defense behavior in the black-crested titmouse (Baeolophus atricristatus)

Status signals have evolved for individuals to avoid energetic and physical costs of resource defense. These signals reflect an individual’s competitive ability and therefore influence competitors’ decisions on how to invest in a fight. We hypothesized that the response of receivers to status signals will depend on the social context. During territorial defense, group members may provide support to a territory owner by participating in defense. We investigated whether the presence of juveniles—who group together with territorial males—alters the territorial male’s attack decisions and level of aggression in the black-crested titmouse (Baeolophus atricristatus). Crest-length in this species functions as status signal. We simultaneously presented two taxidermic male models in a territory: one with an unmanipulated crest and one with a modified shortened crest. Models were presented to males that had resident juveniles cohabiting on their territory, and to males without juveniles. During intrusions, juveniles actively defended against the simulated intruders by approaching and sometimes attacking. The presence of juveniles affected how territorial males responded to the status signals of the intruders: when juveniles were present, males were more likely to first attack the model with the unmanipulated crest (i.e., longer, and more threatening), compared to males residing without juveniles. This suggests that juvenile support alters the risk-taking decision of the territorial male. To our knowledge, this is the first indication that behavioral responses to a status signal depends on the presence of supportive group members.Significance statementStatus signals can indicate relative quality of animals and can therefore be used to evaluate a competitor when deciding whether or not to fight over resources. The black-crested titmouse has been shown to use its crest length as a status signal during fights over food. In our study, we assessed if this status signal is also used in territorial defense, by conducting an experiment where we presented two taxidermic male models with different crest sizes to a territorial male. We also investigated whether juvenile presence influenced which model was attacked. In trials where juveniles were present, territorial males attacked the longer crested model significantly more often than in trials where territorial males were alone. This suggests that the presence of juveniles, which help the male defend the territory, allows the male to attack the more aggressive-appearing intruder.

A Learning-Based Solution for an Adversarial Repeated Game in Cyber-Physical Power Systems.

Due to the rapidly expanding complexity of the cyber-physical power systems, the probability of a system malfunctioning and failing is increasing. Most of the existing works combining smart grid (SG) security and game theory fail to replicate the adversarial events in the simulated environment close to the real-life events. In this article, a repeated game is formulated to mimic the real-life interactions between the adversaries of the modern electric power system. The optimal action strategies for different environment settings are analyzed. The advantage of the repeated game is that the players can generate actions independent of the previous actions' history. The solution of the game is designed based on the reinforcement learning algorithm, which ensures the desired outcome in favor of the players. The outcome in favor of a player means achieving higher mixed strategy payoff compared to the other player. Different from the existing game-theoretic approaches, both the attacker and the defender participate actively in the game and learn the sequence of actions applying to the power transmission lines. In this game, we consider several factors (e.g., attack and defense costs, allocated budgets, and the players' strengths) that could affect the outcome of the game. These considerations make the game close to real-life events. To evaluate the game outcome, both players' utilities are compared, and they reflect how much power is lost due to the attacks and how much power is saved due to the defenses. The players' favorable outcome is achieved for different attack and defense strengths (probabilities). The IEEE 39 bus system is used here as the test benchmark. Learned attack and defense strategies are applied in a simulated power system environment (PowerWorld) to illustrate the postattack effects on the system.

Optimal leaf life strategies determine Vc,max dynamic during ontogeny.

Leaf photosynthetic properties, for example the maximum carboxylation velocity or Vc,max , change with leaf age due to ontogenetic processes. This study introduces an optimal dynamic allocation scheme to model changes in leaf-level photosynthetic capacity as a function of leaf biochemical constraints (costs of synthesis and defence), nitrogen availability and other environmental factors (e.g. light). The model consists of a system of equations describing RuBisCO synthesis and degradation within chloroplasts, defence and ageing at leaf levels, nitrogen transfer and carbon budget at plant levels. Model results show that optimal allocation principles explained RuBisCO dynamics with leaf age. An approximated analytical solution can reproduce the basic pattern of RuBisCO and Vc,max in rice and in two tropical tree species. The model also reveals leaf life complementarities that remained unexplained in previous approaches, as the interplay between Vc,max at maturation, life span and the decline in photosynthetic capacity with age. Furthermore, it explores the role of defence, which is not implemented in current models. This framework covers some of the existing gaps in integrating multiple processes across plant organs (chloroplast, leaf and whole plant) and is a first-step towards representing mechanistically leaf ontogenetic processes into physiological and ecosystem models.

Attack and Defense Strategies in Cyber War Involving Production and Stockpiling of Zero-Day Cyber Exploits

Two players strike balances between allocating resources for defense and production of zero-day exploits. Production is further allocated into cyberattack or stockpiling. Applying the Cobb Douglas expected utility function for equivalent players, an analytical solution is determined where each player’s expected utility is inverse U shaped in each player’s unit defense cost. More generally, simulations illustrate the impact of varying nine parameter values relative to a benchmark. Increasing a player’s unit costs of defense or development of zero-days benefits the opposing player. Increasing the contest intensities over the two players’ assets causes the players to increase their efforts until their resources are fully exploited and they receive zero expected utility. Decreasing the Cobb Douglas output elasticity for a player’s stockpiling of zero-days causes its attack to increase and its expected utility to eventually reach a maximum, while the opposing player’s expected utility reaches a minimum. Altering the Cobb Douglas output elasticities for a player’s attack or defense contests towards their maxima or minima causes maximum expected utility for both players.

Optimal Decision Making Approach for Cyber Security Defense Using Evolutionary Game

At present, there are many techniques for cyber security defense such as firewall, intrusion detection and cryptography. Despite decades of studies and experiences on this issue, there still exists a problem that we always pay great attention to technology while overlooking strategy. In the traditional warfare, the level of decision-making and the formulation of optimal strategies have a great effect on the warfare result. Similarly, the timeliness and quality of decision-making in cyber attack-defense also make great significance. Since the attackers and defenders are oppositional, the selection of optimal defense strategy with the maximum payoff is difficult. To solve this problem, the stochastic evolutionary game model is utilized to simulate the dynamic adversary of cyber attack-defense. We add the parameter $\lambda $ to the Logit Quantal Response Dynamics (LQRD) equation to quantify the cognitive differences of real-world players. By calculating the evolutionary stable equilibrium, the best decision-making approach is proposed, which makes a balance between defense cost and benefit. Cases studies on ransomware indicate that the proposed approach can help the defender predict possible attack action, select the related optimal defense strategy over time, and gain the maximum defense payoff.

Efficient Defense Decision-Making Approach for Multistep Attacks Based on the Attack Graph and Game Theory

In the multistep attack scenario, each rational attack-defense player tries to maximize his payoff, but the uncertainty about his adversary prevents him from taking the favorable actions. How to select the best strategy from the candidate strategies to maximize the defense payoff becomes the core issue. For this purpose, the paper innovatively designs a game theory model from the point of network survivability in combination with the attribute attack graph. The attack graph is created based on the network connectivity and known vulnerabilities using the MulVAL toolkit, which gives the full view of all the known vulnerabilities and their interdependence. Then, we use the attack graph to extract attack-defense actions, candidate attack-defense strategies, attack-defense payoffs, and network states, as well as other game modeling elements. Afterwards, the payoffs of attack-defense strategies are quantified by integrating attack-defense strength and network survivability. In addition, we input the above elements into the game model. Through repeated learning, deduction, and improvement, we can optimize the layout of defense strategies. Finally, the efficient strategy selection approach is designed on the tradeoff between defense cost and benefit. The simulation of attack-defense confrontation in small-scale LAN shows that the proposed approach is reliable and effective.

A Minimum Defense Cost Calculation Method for Attack Defense Trees

The cyberphysical system (CPS) is becoming the infrastructure of society. Unfortunately, the CPS is vulnerable to cyberattacks, which may cause environmental pollution, property losses, and even casualties. Furthermore, in contrast to the conventional Internet, the devices in CPSs are more specific, and the device systems may not be upgraded or installed with new programs during their life spans. The selection of the best defense nodes for defeating cyberattacks is quite challenging in CPSs. To overcome this issue, several attack-defense modeled methods have been proposed. However, few existing studies have considered the defense cost, which is usually a determinant in practice. In this paper, we propose a method for choosing optimal defense nodes that (1) can defeat specific attacks and (2) are inexpensive. First, the atom attack defense tree (A2DTree) is proposed by adding constraints to the conventional attack defense tree (ADTree). Second, the algebraic method is used to efficiently calculate the minimum defense cost. On this basis, a minimum defense cost calculation tool is designed and implemented. Finally, the effectiveness of the proposed method is verified with two typical case studies, and a comparative experiment of related work is carried out. The results show that the method can correctly and efficiently identify the optimal defense nodes and calculate the minimum defense cost of a CPS.

Diatom defence: Grazer induction and cost of shell‐thickening

Abstract Diatoms account for 40% of the ocean primary production and play a key role in the oceans’ ability to sequester carbon. The evolutionary success of diatoms and their role in ocean biogeochemistry are related to the siliceous shell that provide partial protection against grazing. The structure and function of phytoplankton communities are governed by environmental constraints and organismal trade‐offs. Defence mechanisms may help explain the high diversity of phytoplankton (incl. diatoms) in the ocean, but only if the defence comes at a cost. Defence costs have been notoriously difficult to demonstrate and quantify in marine phytoplankton. Here, we demonstrate for seven species of planktonic diatoms that their shell thickens and their growth rate declines when cells are exposed to chemical cues from copepods, important predators of diatoms. The responses are proportional to the concentration of grazer cues, but are also highly variable, both between and within species. At our standard experimental condition, the typical decline in growth rate is 10%, and the typical increase in cellular biogenic silica is 16%. The latter value corresponds to a decline in grazing mortality due to small copepods of 11%. Thus, silification in response to grazers is exactly warranted. The similar magnitude of the costs and benefits of silification suggests a flat fitness landscape along the competition‐defence axis. This may help explain the high diversity of coexisting diatoms in the ocean. The significant but variable contribution of diatoms to the downward flux of organic carbon in the ocean depends to a large extent on the silica content of the cells. This is due less to the ballasting effect of silica, but mainly to the different life histories of more or less defended cells that are governed by evolutionary adaptations and—as demonstrated here—plastic responses to grazers. A free Plain Language Summary can be found within the Supporting Information of this article.

Modern Maize Hybrids Have Lost Volatile Bottom-Up and Top-Down Control of Dalbulus maidis, a Specialist Herbivore.

Following damage by herbivores, many plants release volatiles that dissuade future conspecifics from feeding. In many crop plants however, induced volatiles mediating this kind of interactions among plants, herbivores and also their natural enemies have been altered through the process of domestication. The selection of crops for increased yield may have gone at a cost of defense, possibly including defense-related volatiles. Dalbulus maidis (Hemiptera: Cicadellidae), a specialist leafhopper that only feeds on Zea spp., is a vector of Corn Stunt Spiroplasma, a serious maize disease. Here, we compared the volatiles released following D. maidis attack by a maize landrace and two maize hybrids of temperate and tropical background. Also, we performed behavioral assays with the leafhopper contrasting healthy non-attacked maize seedlings versus attacked seedlings. The maize landrace produced more than 6-fold larger quantities of induced volatiles compared to the maize hybrids after herbivory. Corn leafhopper females were able to detect and significantly preferred the odors of healthy seedlings over the attacked ones only in the landrace. They did not discriminate between the attacked and non-attacked hybrids. Additionally, we found that the attraction of the parasitoid wasp Anagrus virlai (Hymenoptera: Mymaridae) to its host was diminished in the tested hybrids. The parasitoid was able to detect the odors of the attacked landrace, however it was unable to discriminate between healthy and attacked maize hybrid plants. These results suggest that those more domesticated germplasms may have lost the ability not only to release volatiles that avoid colonization of future herbivores, but also to attract their natural enemies in a tritrophic system.

The arbuscular mycorrhizal mycelium from barley differentially influences various defense parameters in the non-host sugar beet under co-cultivation.

The interactions between arbuscular mycorrhizal fungi (AMF) and non-host species are poorly studied. Particularly scarce is information on members of the Amaranthaceae/Chenopodiaceae family. Sugar beet (Beta vulgaris) plants were co-cultivated with a host species (Hordeum vulgare) in the presence (+AMF) or absence of Rhizophagus intraradices to explore the hypothesis that the presence of an active, pre-established AMF mycelium induces defense responses in the non-host species. Biomass of sugar beet did not respond to the +AMF treatment, while its root exudation of organic acids and phenolic acids was drastically decreased upon co-cultivation with +AMF barley. The most conspicuous effect was observed on a wide range of potential defense parameters being differentially influenced by the +AMF treatment in this non-host species. Antioxidant defense enzymes were activated and the level of endogenous jasmonic acid was elevated accompanied by nitric oxide accumulation and lignin deposition in the roots after long-term +AMF treatment. In contrast, significant reductions in the levels of endogenous salicylic acid and tissue concentration and exudation of phenolic acids indicated that AM fungus hyphae in the substrate did not induce a hypersensitive-type response in the sugar beet roots and downregulated certain chemical defenses. Our results imply that the fitness of this non-host species is not reduced when grown in the presence of an AMF mycelium because of balanced defense costs. Further studies should address the question of whether or not such modulation of defense pattern influences the pest resistance of sugar beet plants under field conditions.

Solitary breeding barn swallows pay a higher nest defense cost

Successful reproduction depends on the ability of parents to defend from nest predators. Breeding birds often put their life at risk to defend their offspring from predators. Communal nest defense has been proposed as an individual benefit of group living. We tested this by experimentally exposing a short-lived avian species to a potential risk of predation. We presented decoys of both a diurnal and a nocturnal predator to barn swallows Hirundo rustica breeding solitarily and in large colonies in South-western Spain. We found clear benefits of group living compared to solitary pairs in relation to investment in individual nest defense and the capacity to deter a challenging predator. Although we did not find differences in the time needed to detect the predator, we found that the number of individuals recruited to participate in nest defense was greater for colonial breeding pairs, leading to fewer attacks per individual in comparison to solitary breeding pairs. We also found that barn swallows defended their nests more vigorously against a nocturnal predator than against a diurnal predator. Therefore, barn swallows living in groups obtained clear benefits in communal nest defense by reducing the risk, energy and time dedicated to nest defense. Colonial breeding is thus a more effective strategy for decreasing nest predation rates.