Predator avoidance,microhabitat shift,and risk-sensitive foraging in larval dragonflies

Summary Dragonfly larvae (Odonata: Anisoptera) are often abundant in shallow freshwater habitats and frequently co-occur with predatory fish, but there is evidence that they are underutilized as prey. This suggests that species which successfully coexist with fish may exhibit behaviors that minimize their risk of predation. I conducted field and laboratory experiments to determine whether: 1) dragonfly larvae actively avoid fish, 2) microhabitat use and foraging success of larvae are sensitive to predation risk, and 3) vulnerability of larvae is correlated with microhabitat use. I experimentally manipulated the presence of adult bluegills (Lepomis macrochirus) in defaunated patches of littoral substrate in a small pond to test whether colonizing dragonfly larvae would avoid patches containing fish. The two dominant anisopteran species, Tetragoneuria cynosura and Ladona deplanata (Odonata: Libellulidae), both strongly avoided colonizing patches where adult bluegills were present. Laboratory experiments examined the effects of diel period and bluegills on microhabitat use and foraging success, using Tetragoneuria, Ladona and confamilial Sympetrum semicictum, found in a nearby fishless pond. Tetragoneuria and Ladona generally occupied microhabitats offering cover, whereas Sympetrum usually occupied exposed locations. Bluegills induced increased use of cover in all three species, and use of cover also tended to be higher during the day than at night. Bluegills depressed foraging in Tetragoneuria and to a lesser extent in Ladona, but foraging in Sympetrum appeared unaffected. Other laboratory experiments indicated that Sympetrum were generally more vulnerable than Tetragoneuria or Ladona to bluegill predation, and that vulnerability was positively correlated with use of exposed microhabitats. Both fixed (generally low use of exposed microhabitats, diel microhabitat shifts) and reactive (predator avoidance, predator-sensitive microhabitat shifts) behavioral responses appear to reduce risk of predation in dragonfly larvae. Evidence indicates that vulnerability probably varies widely among species and even among instars within species, and suggests that spatial distributions of relatively vulnerable species may be limited by their inability to avoid predation.     

Learning-induced change in neural activity during acquisition and consolidation of a passive avoidance response in the rat

Time-dependent alterations in neural activity have been established during the acquisition and consolidation of a stepdown passive avoidance paradigm. Change in neural activity was established by administering a glucose analogue, [³H]2-deoxyglucose, 50min prior to sacrifice and estimating perchloric acid soluble counts in nine hand dissected brain regions. Change in [³H]2-deoxyglucose uptake was closely paralleled in both trained and yoked animals for up to 40min following task acquisition however the striatum was the only area to exhibit a task-specific increase in [³H]2-deoxyglucose uptake at 20–30min after training. Longterm changes in neural activity were also apparent as the amygdala and brainstem showed increased [³H]2-deoxyglucose uptake at the 24h time point. No further paradigm-specific changes were apparent at 48 h. These findings are concluded to suggest that the striatum is involved in the early events of acquiring a passive avoidance response and the amygdala and brainstem during the later events.     

恐惧记忆消散的神经生物学机制研究进展

恐惧消散被认为是一种通过形成新的抑制性学习来拮抗最初的恐惧记忆的复杂过程。目前,通过旨在促进恐惧消散的疗法治疗诸如焦虑症等神经精神疾病已在临床上取得了较好的疗效,因此,如何更有效持久地维持恐惧消散记忆具有重要的意义。围绕与恐惧记忆消散相关的脑区及恐惧记忆消散的分子机制进行阐述,有助于更深入地理解恐惧记忆消散相关的神经生物学机制,为后续研究提供新的方向。     

Learning to fear and cope with a natural stressor: individually and socially acquired corticosterone and avoidance responses to biting flies

Animals learn to recognize and respond to a variety of dangerous factors, with biting and blood-feeding flies being among the most prevalent of natural stressors. Here we describe the behavioral avoidance and hormonal (corticosterone) stress responses to biting fly exposure and the roles of individual and social learning in the acquisition of these fear-associated responses. Male mice exposed to a single 30-min session of attack by intact biting flies (stable fly, Stomoxys calcitrans L.) exhibited increased plasma corticosterone levels and active self-burying responses to avoid the flies. When exposed 24 h later to altered flies whose biting mouth parts were removed and were incapable of biting, the mice displayed conditioned increases in corticosterone and avoidance responses. This conditioned increase in corticosterone and self-burying was also acquired through social learning without direct individual experience with the intact biting flies. Fly naive "observer" mice that witnessed other "demonstrator" mice being attacked by biting flies, but were not exposed to intact flies themselves, displayed increases in corticosterone levels and self-burying to avoid flies when exposed 24 h later to altered flies. The social learning was not due to social facilitation or sensitization. Observers had to witness the self-burying avoidance responses of the demonstrator to the biting flies in order to subsequently recognize a potential threat to themselves and display the appropriate responses. These individually and socially acquired conditioned fear responses are likely part of the mechanisms that allow animals to defend themselves from biting and blood-feeding arthropods.     

转录因子Egr-1参与长期性恐惧记忆和焦虑

锌指转录因子点Egr-1在将细胞外信号和胞内基因表达的变化相耦联过程中发挥重要的作用。海马和杏仁体是记忆形成和储存的两个主要的脑区。在海马和杏仁体中,Egr-1可被长时程增强（long-term potentiation,LTP）和学习过程上调。在Egr-1敲除小鼠上观察到晚时相声音恐惧记忆受损,而短时的痕迹和场景记忆却不受影响;另外,在Egr-1敲除小鼠上,用theta burst刺激杏仁体和听觉皮层所引起的突触增强被明显减弱或完全阻断。因此,我们的研究表明,转录因子Egr-1选择性地在晚时相听觉恐惧记忆中发挥作用。     

大鼠恐惧应激模型的建立及其视觉认知效果分析

目的构建不同程度恐惧应激大鼠模型,探究恐惧应激对LE大鼠视觉认知能力的影响。方法采用足底电击作为应激刺激,设计认知抉择实验,采集杏仁核脑区神经响应信号进行功能网络分析,评价大鼠视觉认知效果。首先,将实验大鼠分成强(S+)、弱(S)恐惧应激组与对照组(N),分别设定不同强度的足底电击刺激;然后对其进行单一图形"△"的视觉认知强化训练;最后,采用双图("△"和"十"图形)进行视觉抉择测试实验。另外结合复杂网络理论,构建恐惧应激大鼠杏仁核神经核团的视觉认知功能网络,通过平均路径长度和聚类系数表征脑功能网路的信息传递效率。结果完成视觉认知强化训练所需时间,S+组显著高于S、N组,强化训练前期S组显著高于N组,后期两组无显著性差异;认知抉择实验中,S组与N组均形成视觉认知联结,而S+组未形成视觉认知联结;脑功能网络分析中,S组与N组杏仁核神经元之间形成有效的视觉信息传递,而S+组未形成。结论恐惧应激对视觉认知造成消极影响,且随着恐惧程度的增强认知效果显著变差。     

A hippocampal insulin-growth factor 2 pathway regulates the extinction of fear memories

Extinction learning refers to the phenomenon that a previously learned response to an environmental stimulus, for example, the expression of an aversive behaviour upon exposure to a specific context, is reduced when the stimulus is repeatedly presented in the absence of a previously paired aversive event. Extinction of fear memories has been implicated with the treatment of anxiety disease but the molecular processes that underlie fear extinction are only beginning to emerge. Here, we show that fear extinction initiates upregulation of hippocampal insulin-growth factor 2 (Igf2) and downregulation of insulin-growth factor binding protein 7 (Igfbp7). In line with this observation, we demonstrate that IGF2 facilitates fear extinction, while IGFBP7 impairs fear extinction in an IGF2-dependent manner. Furthermore, we identify one cellular substrate of altered IGF2 signalling during fear extinction. To this end, we show that fear extinction-induced IGF2/IGFBP7 signalling promotes the survival of 17-19-day-old newborn hippocampal neurons. In conclusion, our data suggest that therapeutic strategies that enhance IGF2 signalling and adult neurogenesis might be suitable to treat disease linked to excessive fear memory.     

Non-random foraging in certain bird pests of field crops

Two systems of bird-crop interactions were studied to explain the between- and the within-field variation in the foraging pattern of bird pests in agro-ecosystems. Weaverbirds and munias select rice fields with greater vegetation complexity and not based on the resource status. Within a selected area the concentration of feeding birds was greater close to vegetation cover and decreased non-linearly with increase in distance. Certain structural features and earhead characters of rice plants predisposed particular varieties for intense grain predation by birds. In the parakeet-sunflower system the extent of damage among plants within a field was closely linked to the foraging pattern of parakeets. The extent of achene predation by parakeets was influenced by certain structural features of sunflower plants and not the resource load of each plant. Selective feeding on sunflower plants was governed by the predator vigilance pattern; parakeets prefer to feed on plants that offered better field of vision. The results suggest that the observed pattern of foraging by bird pests in agro-ecosystems is non-random and is dependent on factors favouring predator avoidance behaviour and not on resource maximization.     

Tubes and foraging behavior in larval Chironomidae: implications for predator avoidance

Summary In laboratory experiments, I studied differential susceptibility of four co-occurring species of chironomids to a predatory damselfly. The chironomids differed in foraging behavior and could be ranked according to the amount of time they spent outside of their tubes. In choice experiments, the predator consistently selected the prey which spent more time out of the tube, and time out of tube was a significant predictor of the predation rate coefficient. Electivity indices, calculated from field samples and diet analyses of the predator, supported the laboratory results. The data suggest that exposure to predators in a heterogeneous prey community is largely determined by tubedwelling behavior.     

Sex and age differences in the avoidance of reptile exhibits by zoo visitors

Visitors at two zoos were observed as they approached the reptile exhibits at the respective institutions. Both age and sex differences were discovered among several variables designed to measure avoidance behavior. At most ages, females more often refused to enter the exhibits than males. Females also spent less time within the exhibits than males. With respect to age differences, teen aged visitors refused to enter less often and spent more time in the exhibits than did individuals of other ages.     

Social learning of fear and safety is determined by the demonstrator's racial group

Social learning offers an efficient route through which humans and other animals learn about potential dangers in the environment. Such learning inherently relies on the transmission of social information and should imply selectivity in what to learn from whom. Here, we conducted two observational learning experiments to assess how humans learn about danger and safety from members (‘demonstrators'') of an other social group than their own. We show that both fear and safety learning from a racial in-group demonstrator was more potent than learning from a racial out-group demonstrator.     

Learning in the nectar foraging behaviour of Helicoverpa armigera

Abstract .1. Learning may enable insects to obtain nectar from flowers more efficiently. Learning in nectar foraging has been shown primarily in studies of bees and butterflies. Here, learning is demonstrated in the nectar foraging behaviour of a noctuid moth, Helicoverpa armigera .
2. The present studies show that: (1) previous experience with a flowering host species increases the probability of that species being selected for nectar foraging, and (2) previous experience of a particular flower type (food source at bottom or top of the corolla tube) increases the likelihood of the food source being found when that flower type is being searched.
3. The implications of these findings for understanding the pattern of oviposition observed in wild populations of this important pest species are discussed.     

Infection avoidance behavior: Viral exposure reduces the motivation to forage in female Drosophila melanogaster

Infection avoidance behaviors are the first line of defense against pathogenic encounters. Behavioral plasticity in response to internal or external cues of infection can therefore generate potentially significant heterogeneity in infection. We tested whether Drosophila melanogaster exhibits infection avoidance behavior, and whether this behavior is modified by prior exposure to Drosophila C Virus (DCV) and by the risk of DCV encounter. We examined 2 measures of infection avoidance: (1) the motivation to seek out food sources in the presence of an infection risk and (2) the preference to land on a clean food source over a potentially infectious source. While we found no evidence for preference of clean food sources over potentially infectious ones, previously exposed female flies showed lower motivation to pick a food source when presented with a risk of encountering DCV. We discuss the relevance of behavioral plasticity during foraging for host fitness and pathogen spread.     

Social foraging: individual learning and cultural transmission of innovations

We present two stochastic models of individual and social learningthat count the number of individuals exhibiting a learned, resource-producingtrait in a group of social foragers. The novelty of our modelingresults from incorporating the empirically based assumptionthat rates of both individual and social learning should dependon the frequency of the learned trait within the group. Whenresources occur as clumps shared by group members, a naive individual'sacquisition of the skill required for clump discovery/productionshould involve opposing processes of frequency dependence. Theopportunity to learn via cultural transmission should increasewith the trait's frequency, but the opportunity for learningindividually should decrease as the trait's frequency increases.The results of the model suggest that the evolution of the capacityfor cultural transmission may be promoted in environments wherescrounging at resource clumps inhibits rates of individual learning.     

Structure-guided foraging in long-tailed macaques

The aim of this study was to identify some of the cues that macaques follow when they search for new food sites. A social group of 37 long-tailed macaques was confined to a holding cage while an experimenter concealed food in an outdoor enclosure according to one of the following rules: (1) along the edge of a visible environmental border, (2) within structures of the same general type, or (3) along an ecologically irrelevant, invisible straight line. To provide the animals with a cue for detecting the rule, three piles of visible food were also presented according to the rule. Each of the 60 trials involved a different location in the 880 m² enclosure. The animals showed clear evidence of utilizing the first two rules from the outset of testing and the third rule about five trials. The animals found concealed food along environmental borders and within matching objects more quickly than along invisible lines. They also showed a rapid improvement in food finding on the invisible line. The results suggest that long-tailed macaques extend their search for food to a given class of environmental structure rather than exclusively by pure spatial gradients. © 1996 Wiley-Liss, Inc.     

Inheritance of optimal foraging behaviour in Columbian ground squirrels

Summary I examined the potential inheritance of the ability of Columbian ground squirrels (Spermophilus columbianus) to select an optimal diet. I calculated the diet that would maximize daily energy intake for each of 21 adult females and their litters, using a linear programming optimization model for each individual. The absolute value of the difference between an individual's predicted optimal diet and observed diet (deviation from an optimal diet) was used as a measure of an individual's foraging ability. The foraging ability of individuals was consistent over time and in different foraging environments, so I considered foraging ability to be a potentially heritable trait.Inheritance was determined from correlations of mother and offspring foraging ability. I experimentally removed some mothers just as they weaned their offspring so that offspring could not be influenced by their mother while learning to forage, while leaving the other mothers to raise their litters normally. In both cases, offspring strongly resembled their mother in foraging ability. However, offspring with mothers absent exhibited significantly larger deviations from their optimal diet. Offspring with mothers absent appeared to imitate their mother's diet during lactation, and this tendency partially explained their greater deviation. Consequently, offspring appear to inherit the ability to forage optimally from their mother, perhaps through observational learning or imitation. There may also be a genetic basis to foraging ability, but uncontrolled maternal effects in the experiment prevent a proper test for it.