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At least 1,261 records · Page 70Linked to original sources

PubMed2001

Rapid, local adaptation of zooplankton behavior to changes in predation pressure in the absence of neutral genetic changes.

Organisms producing resting stages provide unique opportunities for reconstructing the genetic history of natural populations. Diapausing seeds and eggs often are preserved in large numbers, representing entire populations captured in an evolutionary inert state for decades and even centuries. Starting from a natural resting egg bank of the waterflea Daphnia, we compare the evolutionary rates of change in an adaptive quantitative trait with those in selectively neutral DNA markers, thus effectively testing whether the observed genetic changes in the quantitative trait are driven by natural selection. The population studied experienced variable and well documented levels of fish predation over the past 30 years and shows correlated genetic changes in phototactic behavior, a predator-avoidance trait that is related to diel vertical migration. The changes mainly involve an increased plasticity response upon exposure to predator kairomone, the direction of the changes being in agreement with the hypothesis of adaptive evolution. Genetic differentiation through time was an order of magnitude higher for the studied behavioral trait than for neutral markers (DNA microsatellites), providing strong evidence that natural selection was the driving force behind the observed, rapid, evolutionary changes.

Adaptation, Physiological↗

PubMed2006

The role of target elevation in prey selection by tiger beetles (Carabidae: Cicindela spp.).

The elevation of objects in the visual field has long been recognized as a potential distance cue, but it has been demonstrated to a reasonable extent in only four species: humans, frogs, fiddler crabs and backswimmers. Many tiger beetles hunt in flat, sandy areas, and their eyes show "flat-world" adaptations, such as an extended visual streak of higher acuity that corresponds to the horizon. They are therefore possible candidates for the use of elevation as a cue for distance. We tested this empirically and with simulation. In a behavioral prey selection paradigm, in which starved beetles were presented moving prey-targets having different size, speed and elevation, the beetles showed a strong preference for large targets when these were low in the visual field and a weaker preference for small targets when these were near the horizon. Striking of targets above the horizon was reduced compared to sub-horizontal targets, and lacked the size-elevation interaction. We simulated these empirical results with a model that converted elevation to distance, and used distance to estimate the absolute size of the targets. Simulated strike probability was then determined by the similarity between this absolute size and an independently confirmed preferred prey size. The results of the simulation model matched the empirical data as well as the best statistical model of the behavioral results. While some aspects of the model, and the beetles' behavior, differ from the strict geometry of the "elevation hypothesis", our results nevertheless indicate that tiger beetles use elevation to estimate distance to prey, and that it is therefore one of the determinants of prey selection.

Altitude↗

PubMed2002

Homosexual tandem running as selfish herd in Reticulitermes speratus: novel antipredatory behavior in termites.

We investigated the predator avoidance mechanism of post-swarming alates of the lower subterranean termite, Reticulitermes speratus Kolbe. In some lower termites, homosexual tandem running is observed in addition to ordinary heterosexual tandem running. An experiment designed to compare the risk of predation by a termite-hunting ant, Brachyponera chinensis Emery, showed that homosexual tandem running reduced the predation risk until termites encounter the opposite sex. Since an individual ant cannot capture two dealates at once, one of the two dealates forming a tandem can escape while the ant captures its partner. Therefore, the "post-encounter risk" of individuals running in tandem was lower than that of single individuals. The "encounter risk" with predatory ants was also examined using a mathematical model considering the increased detectability of the predator due to enhanced size of the prey unit. It was suggested that tandem running reduces the predation risk of both participants, even when the enhanced encounter risk was taken into account. In males, competition for the back position was often observed, and consequently, the male at the back was always larger than the male in front. When a male-male tandem encountered a female, the back male won the female more often than the front male. This result suggested that male-male tandem running should result in selection pressure in favor of vigorous males. In conclusion, tandem running decreases the individual predation risk through the dilution effect, and it also plays a role as a mechanism of indirect sexual selection.

Animals↗

PubMed2026

A predator-derived odor specifically triggers avoidance in gregarious mated female Locusta migratoria.

BACKGROUND: Insects possess a highly specialized olfactory system. The migratory locust (Locusta migratoria), a major agricultural pest, is thought to emit odors that serve as aposematic signals to protect gregarious individuals from predation. However, whether locusts can detect the odors of their natural enemies to preemptively avoid predation remains unclear. RESULTS: Here, we show that gregarious mated female locusts exhibit strong avoidance behavior toward the odors of two avian predators, Numida meleagris and Anas platyrhynchos. Through volatile compound profiling, we identified 1-octen-3-ol, a key predator-released odor, which elicited significant aversive responses specifically in gregarious mated females; notably, virgin females showed no behavioral response to this odor. Through screening 82 olfactory receptors in L. migratoria, we identified two receptors, LmOR1 and LmOR17, that detect 1-octen-3-ol. A temporal expression study of LmOR1 and LmOR17 across different developmental stages of two locust phases using quantitative real-time polymerase chain reaction (qRT-PCR) showed that both genes are significantly more highly expressed in the gregarious mated females. Genome editing of these receptors revealed that knockout of LmOR1 significantly reduced both the electrophysiological response and the behavioral avoidance of 1-octen-3-ol, whereas knockout of LmOR17 had no effect. In our results we thus uncover a striking mating-state dependence of an innate avoidance behavior to a predator-derived odor, and further we identify LmOR1 as the major receptor mediating this olfactory-driven defense. CONCLUSION: Our findings provide crucial insights into the behavioral and olfactory mechanisms underlying insect-predator interactions, as well as the role of mating status in modulating defensive responses, offering potential olfactory targets for locust management. © 2026 Society of Chemical Industry.

Animals↗

PubMed2006

Tie them up tight: wrapping by Philoponella vicina spiders breaks, compresses and sometimes kills their prey.

We show that uloborid spiders, which lack the poison glands typical of nearly all other spiders, employ thousands of wrapping movements with their hind legs and up to hundreds of meters of silk line to make a shroud that applies substantial compressive force to their prey. Shrouds sometimes break the prey's legs, buckle its compound eyes inward, or kill it outright. The compressive force apparently results from the summation of small tensions on sticky lines as they are applied to the prey package. Behavioral details indicate that wrapping is designed to compact prey; in turn, compaction probably functions to facilitate these spiders' unusual method of feeding. This is the first demonstration that prey wrapping by spiders compacts and physically damages their prey, rather than simply restraining them.

Animals↗

PubMed2003

Regime changes in ecological systems: an information theory approach.

We present our efforts at developing an ecological system index using information theory. Specifically, we derive an expression for Fisher Information based on sampling of the system trajectory as it evolves in the space defined by the state variables of the system, i.e. its state space. The Fisher Information index, as we have derived it, is a measure of system order, and captures the characteristic variation in speed and acceleration along the system's periodic steady-state trajectories. When calculated repeatedly over the system period, this index tracks steady states and transient behavior. We believe that such an index could be useful in detecting system 'flips' associated with a regime change, i.e. determining when systems are in a transient between one steady state and another. We illustrate the concepts using model ecosystems.

Animals↗

PubMed2006

Tactile guidance of prey capture in Etruscan shrews.

Whereas visuomotor behaviors and visual object recognition have been studied in detail, we know relatively little about tactile object representations. We investigate a new model system for the tactile guidance of behavior, namely prey (cricket) capture by one of the smallest mammals, the Etruscan shrew, Suncus etruscus. Because of their high metabolic rate and nocturnal lifestyle, Etruscan shrews are forced to detect, overwhelm, and kill prey in large numbers in darkness. Crickets are exquisitely mechanosensitive, fast-moving prey, almost as big as the shrew itself. Shrews succeed in hunting by lateralized, precise, and fast attacks. Removal experiments demonstrate that both macrovibrissae and microvibrissae are required for prey capture, with the macrovibrissae being involved in attack targeting. Experiments with artificial prey replica show that tactile shape cues are both necessary and sufficient for evoking attacks. Prey representations are motion- and size-invariant. Shrews distinguish and memorize prey features. Corrective maneuvers and cricket shape manipulation experiments indicate that shrew behavior is guided by Gestalt-like prey descriptions. Thus, tactile object recognition in Etruscan shrews shares characteristics of human visual object recognition, but it proceeds faster and occurs in a 20,000-times-smaller brain.

Animals↗

PubMed2004

Reproductive character displacement of male stickleback mate preference: reinforcement or direct selection?

Reproductive isolation can evolve between species as a byproduct of adaptation to different niches, through reinforcement, and by direct selection on mating preferences. We investigated the potential role of direct selection in the reproductive isolation between sympatric species of threespine sticklebacks. Each sympatric pair consists of a small-bodied limnetic species and large-bodied benthic species. We compared the mate preferences and courtship behavior of males from one sympatric limnetic population and two allopatric populations. We used limnetic-like allopatric populations to control for the effects of ecological character displacement and adaptation to different niches on mate preferences. The sympatric limnetic males preferred the small limnetic females, whereas the allopatric limnetic-like males preferred the large benthic females, suggesting that adaptation to the limnetic niche does not automatically confer a preference for small limnetic females. This reproductive character displacement of male preference is consistent with the predictions of both reinforcement and direct selection on mate preferences. To test for direct selection, we assessed a prediction of one proposed mechanism: predation by benthic females on eggs guarded by limnetic males. The allopatric males come from populations in which there is no egg predation. Sympatric limnetic males were more aggressive toward benthic females than toward limnetic females, whereas the allopatric limnetic-like males did not treat the two types of females differently. The contrast in male behavior suggests that egg predation has shaped male preferences. Direct selection is potentially more effective than indirect selection via reinforcement, and it is likely that it has been important in building up reproductive isolation between limnetic and benthic sticklebacks.

Adaptation, Physiological↗

PubMed2003

Sequential megafaunal collapse in the North Pacific Ocean: an ongoing legacy of industrial whaling?

Populations of seals, sea lions, and sea otters have sequentially collapsed over large areas of the northern North Pacific Ocean and southern Bering Sea during the last several decades. A bottom-up nutritional limitation mechanism induced by physical oceanographic change or competition with fisheries was long thought to be largely responsible for these declines. The current weight of evidence is more consistent with top-down forcing. Increased predation by killer whales probably drove the sea otter collapse and may have been responsible for the earlier pinniped declines as well. We propose that decimation of the great whales by post-World War II industrial whaling caused the great whales' foremost natural predators, killer whales, to begin feeding more intensively on the smaller marine mammals, thus "fishing-down" this element of the marine food web. The timing of these events, information on the abundance, diet, and foraging behavior of both predators and prey, and feasibility analyses based on demographic and energetic modeling are all consistent with this hypothesis.

Animals↗

PubMed1998

The effects of telencephalic lesions on visually mediated prey orienting behavior in the leopard frog (Rana pipiens). I. The effects of complete removal of one telencephalic lobe, with a comparison to the effects of unilateral tectal lobe lesions.

In this paper, we report studies aimed at characterizing the relationship between forebrain and midbrain systems involved in the control of prey orienting behavior in the leopard frog. In frogs, unilateral forebrain lesions, like unilateral tectal lobe lesions, have their most prominent effects in the contralateral monocular visual field. Such lesions produce partial reductions in response frequency in the binocular visual field as well. Similar sequelae follow unilateral tectal lobe removal. These findings suggest that the effects of unilateral forebrain removal can be largely attributed to removal of a facilitating influence on the tectal lobe on the same side of the brain. In the case of both forebrain and midbrain lesions, behavior was assayed not only in terms of the frequency with which animals responded to stimuli at various locations in the visual field (as is usually done) but also in terms of the latency of whatever responses were observed. A striking inverse relationship between response frequency and response latency was found, both in lesioned and in normal frogs. This relationship has not previously been noticed, doesn't appear to be an obvious consequence of any existing models of the neuronal circuitry underlying anuran orienting behavior, and is difficult to account for in terms of the time scales associated with axonal conduction times and synaptic delays. It may be easier to account for in terms of the responses to perturbation of large interacting systems of neurons, and this possibility seems worthy of further exploration.

Animals↗

PubMed2004

Strikes and startles of northern pike (Esox lucius): a comparison of muscle activity and kinematics between S-start behaviors.

S-starts are a major class of fast-start behaviors that serve diverse locomotor functions in fishes, playing roles in both feeding strike and escape startle events. While movement patterns are similar during strike and startle, their motor control mechanisms have not been compared. To investigate heterogeneity in S-start responses and to test the hypothesis that S-starts are generated by the same patterns of muscle activity regardless of the behavioral context in which they function, we examined kinematic and muscle activity patterns of northern pike (Esox lucius) performing feeding and escape S-starts. Movements were recorded with high-speed video (250 Hz). Muscle activity was recorded from seven electrodes, one in the left adductor mandibulae and bilaterally in the anterior, midbody and posterior epaxial white muscle. Although S-shaped movements are produced in both feeding and escape, kinematics and electromyogram (EMG) patterns differ. Stage 1 (pre-propulsive movement) is significantly slower and more variable during feeding strikes and involves caudal bending with less rostral movement than recorded for startle behaviors. Correspondingly, there is strong caudal muscle activity prior to rostral activity during strikes, whereas in startles caudal muscle activity had near simultaneous onset with contralateral rostral activity. Onset of jaw muscle activity occurred significantly after the onset of axial muscle activity during feeding strikes. By contrast, during startles, jaw activity onset was nearly simultaneous with the onset of axial muscle activity. Stage 2 kinematics generally did not differ between the strike and startle; however, EMGs indicate that stage 2 movements are generated by different patterns of muscle activity for the two behaviors. Although strikes and startles are similar in their propulsive performance, they appear to be initiated and driven by fundamentally different motor control mechanisms. We suggest that S-start startle behavior is mediated by a simple system of descending reticulospinal input to spinal neurons while the S-start strike involves a more complex neural circuit, allowing greater modulation of stage 1 movements while maintaining high stage 2 performance.

Analysis of Variance↗

PubMed1995

Behavior on approach to surface prey by larvae of Toxorhynchites amboinensis and T. brevipalpis (Diptera: Culicidae).

Behavior of Toxorhynchites amboinensis (Doleschall) and Toxorhynchites brevipalpis (Theobald) larvae (starved 48 h) as they approach and capture surface prey is described quantitatively from videotaped records. Of 106 T. amboinensis and 82 T. brevipalpis larvae observed, 84.9 and 97.6%, respectively, responded to the presence of surface prey within 2 min (most < 20 s). Once they detected prey, larvae executed initial backward swims if prey was rearwardly positioned, then approached it in a series of undulatory forward swims with progressive adjustments of body angle so that the final movements were directly toward the prey. Swims consisted of an active phase, during which propulsive bodily flexions were made and a passive one of continued inertial drift after active motion had ceased. Quantitative changes in the nature of the swims in terms of interval separating active phases and also distances, times, and speeds throughout the approach sequence were analyzed from the video tapes. T. brevipalpis responded to the presence of prey more rapidly, captured prey in less time, and approached prey more rapidly, with shorter rest periods between active swim phases than T. amboinensis. The behavior indicated that Toxorhynchites larvae are able to assess both the angle to surface prey and its distance and that they interpolate this information to optimize the approach path. The degree of refinement in this behavior indicates that it is well adapted to take advantage of the important surface food source in nature. In this phase of their feeding, Toxorhynchites larvae are active hunters and are not entirely the passive ambush predators they have seemed to be from many studies that have used other mosquito larvae as (subsurface) prey.

Animals↗

PubMed2001

A computational sensorimotor model of bat echolocation.

A computational sensorimotor model of target capture behavior by the echolocating bat, Eptesicus fuscus, was developed to understand the detection, localization, tracking, and interception of insect prey in a biological sonar system. This model incorporated acoustics, target localization processes, flight aerodynamics, and target capture planning to produce model trajectories replicating those observed in behavioral insect capture trials. Estimates of target range were based on echo delay, azimuth on the relative intensity of the echo at the two ears, and elevation on the spectral pattern of the sonar return in a match/mismatch process. Flapping flight aerodynamics was used to produce realistic model trajectories. Localization in all three spatial dimensions proved necessary to control target tracking and interception for an adequate model of insect capture behavior by echolocating bats. Target capture using maneuvering flight was generally successful when the model's path was controlled by a planning process that made use of an anticipatory internal simulation, while simple homing was successful only for targets directly ahead of the model bat.

Animals↗

PubMed2006

Microgeographic evolution of snail shell shape and predator behavior.

Genetic divergence in geographically isolated populations is a prerequisite for allopatric speciation, one of the most common modes of speciation. In ecologically equivalent populations existing within a small, environmentally homogeneous area, an important role for environmentally neutral divergence is often found or inferred. We studied a species complex of conspicuously shaped Opisthostoma land snails on scattered limestone outcrops within a small area of lowland rainforest in Borneo. We used shell morphometrics, mitochondrial and nuclear DNA sequences, and marks of predation to study the factors involved in allopatric divergence. We found that a striking geographic divergence exists in shell morphology, which is partly associated with neutral genetic divergence. We also found geographic differentiation in the behavior of the snails' invertebrate predator and evidence of an evolutionary interaction between aspects of shell shape and predator behavior. Our study shows that adaptation to biotic aspects of the environment may play a more important role in allopatric speciation than previously suspected, even on a geographically very small scale.

Adaptation, Physiological↗

PubMed1977

Rearrangements of the retinotectal projection in Rana pipiens after unilateral caudal half-tectum ablation.

When the caudal half-tectum is ablated and the optic nerve is cut in adult Rana pipiens, recordings from optic nerve terminals show that the entire visual field comes to be represented in retinotopic order on the remaining rostral half-tectum (compression). In contrast, if the caudal half-tectum is ablated but the optic nerve is left intact, no compression of the retinotectal projection results. Instead, the terminals displaced from the ablated tissue form a permanently disorganized projection to the rostral half-tectum superimposed on the unaltered representation of those parts of the retina which normally project there. The receptive field locations of tectal neurons in both groups of animals show that the altered retinotectal projections make functional synapses. This conclusion is further supported by behavioral data, which show that the accuracy of prey-catching movements is altered in both groups of frogs. The anomalous retinotectal maps can be interpreted by means of a model which includes polarity cues derived from the tectum and ordering cues derived from repelling interactions among fiber terminals.

Animals↗

PubMed1994

Increases of excitatory receptive fields of retinal ganglion cells in common toads under apomorphine are not associated with size preference in prey-snapping.

After systemic administration of the dopamine agonist apomorphine (APO) in common toads Bufo bufo spinosus, the excitatory receptive fields of retinal R2 and R3 ganglion cells doubled their size and the response activities of these neurons to moving visual stimuli were generally increased. Comparable investigations of the stimulus-response relationships in the snapping behavior of toads pre- and post-APO showed a general increase in the snapping responses, but no shift in the preferred prey size. This is consistent with the current concept, suggesting that size evaluation in amphibians does not rely on retinal ganglion cell output but on interacting networks beyond the retina.

Animals↗

PubMed1987

Neuronal organization underlying visually elicited prey orienting in the frog--III. Evidence for the existence of an uncrossed descending tectofugal pathway.

A complete transverse hemisection of the neuraxis just caudal to the optic tectum in the frog, Rana pipiens, results in a failure to orient toward stimuli in one visual hemifield [Kostyk and Grobstein (1986) Neuroscience 21, 41-55]. This finding indicates that each tectal lobe gives rise to a crossed descending pathway adequate to cause turns in a direction contralateral to that tectal lobe, and suggests that each may also give rise to an uncrossed descending pathway adequate to cause turns in the ipsilateral direction. To determine whether there is in fact such an uncrossed pathway, we have studied the orienting behavior of frogs after lesions which interrupt crossed pathways. Two groups of animals were studied. In one group we made midline lesions of the ansulate commissure, through which run the major crossed descending projections from both tectal lobes. In the other group, we combined a complete transverse hemisection with removal of the tectal lobe on the same side of the brain, leaving intact only an uncrossed pathway from one tectal lobe. A persistence of orienting turns was observed in both groups of animals. In both, the direction of the turns was that expected on the assumption that an uncrossed pathway would cause ipsilateral turns. We conclude that such a pathway exists. While both groups of animals turned in the expected directions, they did so for stimuli at unexpected locations. Increasingly eccentric stimulus locations to one side of the mid-sagittal plane were associated with increasing amplitude turns to the other. The observation suggests that tectal regions mapping areas of visual space to one side of the mid-sagittal plane are capable of triggering turns not only in that direction but in the opposite direction as well. In the case of ansulate commissure section, mirrored orienting responses were observed for tactile stimuli as well. These and other behavioral anomalies described in the preceding papers [Kostyk and Grobstein (1986) Neuroscience 21, 41-55 and 57-82] suggest that between the topographic retinotectal projection and the premotor circuitry for orienting there may exist an intermediate processing step, one in which stimulus location is represented in a generalized spatial coordinate frame.

Animals↗

PubMed1998

On the stabilizing role of stage structure in piscene consumer-resource interactions.

A stage-structured consumer-resource model is investigated using plausible biological parameter estimates. The model, developed from patterns in energy allocation across fish life-history strategies, explicitly considers the effects of delays in maturation on juvenile growth and mortality. It is found that stage structure in the consumer fish population tends to locally stabilize consumer-resource dynamics for realistic parameters. Additionally, it is shown that stage structure bounds nonequilibrium behavior relative to the case without stage structure. Finally, it is shown that the increased stability and bounding of solutions has the seemingly paradoxical consequence of promoting nonequilibrium dynamics when even small amounts of noise are added to the system.

Age Factors↗