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At least 1,135 records · Page 63Linked to original sources
PubMed1998

Retinal location is the key to identifying predators in fiddler crabs (Uca pugilator).

Fiddler crabs (Uca pugilator Bosc; Crustacea, Decapoda) feed and court in open, flat spaces. Their visual system has several putative adaptations to their flat habitat, including the tendency to keep the vertical axis of their eyes perpendicular to the plane of the substratum. It is hypothesized that one of the functions of this behavior is to distinguish accurately predators from conspecifics by aligning the region of the eye sensitive to predators with the region in space in which predators occur. To test this hypothesis, a crab was placed in a glass dish, and a moving stimulus was presented between 20 degrees above and below eye level (horizontal). Stimuli below the crab's horizon hardly ever evoked escape responses, while identical stimuli above the horizon produced escape responses whose frequency varied with the angular size, not the absolute size, of the stimulus. Experiments with artificial horizons showed that it is the position of the stimulus relative to the eye that is important, rather than its position relative to external cues such as the visible horizon, the vertical light gradient or the gravitational horizon. It is concluded that a crab responds to stimuli according to their position relative to its retinal equator. This conclusion is discussed in light of the crabs' natural behavior with respect to supra-horizontal stimuli.

Animals↗
PubMed2000

Analysis of a bone assemblage made by chimpanzees at Gombe National Park, Tanzania.

Chimpanzee hunting provides information on prey characteristics and constraints acting on a large-bodied primate lacking a hunting technology, and has important implications for modeling hunting by fossil hominids. Analysis of the remains of five red colobus monkeys captured and consumed by Gombe chimpanzees in a single hunting bout provides one of the first opportunities to investigate the characteristics of prey bones surviving chimpanzee consumption. Four of the five individuals (an older infant, two juveniles and one subadult) were preserved in the bone assemblage; a neonate was entirely consumed. Cranial and mandibular fragments had the highest survivorships, followed by the scapulae and long bones. Post-cranial axial elements had the lowest survivorships. A high percentage (80%) of the long bones and ribs surviving consumption were damaged, most commonly through crenulation and step fracturing of bone ends. One of two partially reconstructed crania preserves a canine puncture through its left parietal. Proposed characteristics of faunal assemblages formed through chimpanzee-like hunting include small modal prey size, limited taxonomic diversity, a high proportion of immature individuals and a high frequency of skull bones. These characteristics would not uniquely identify hunting by fossil primates in the geological record, necessitating a contextual approach to diagnose hunting by hominids not forming an archeological record. Hominid utilization of vertebrate tissue is first unambiguously documented at 2.5 m.y.a. Rather than representing a strict "scavenging phase" in the evolution of hominid-prey interactions, Oldowan hominid carnivory may represent the overlay of large mammal scavenging on a tradition of small mammal hunting having a low archeological visibility.

Animals↗
PubMed1975

Chlordiazepoxide and diazepam induced mouse killing by rats.

Chlordiazepoxide HCl, at dose levels from 2.5 mg/kg to 80 mg/kg, significantly increased the low base rates of mouse killing (3-9%) observed in large samples (N = 100/dose) of Holtzman strain albino male rats. Maximal killing rates were obtained at doses from 7.5 mg/kg to 20 mg/kg. Diazepam was equally effective, and several times more potent than chlordiazepoxide. Pentobarbital did not increase killing. Killing induced by chlordiazepoxide was blocked by d-amphetamine SO4, but not by l-amphetamine, at dose levels similar to those that block undrugged killing in this strain (ED50 = 1.5 mg/kg). Unlike pilocarpine-induced killing, the effects of chlordiazepoxide were not increased or decreased significantly by either peripherally or centrally active anticholinergic drugs, over wide dose ranges of these agents; nor were the effects of chlordiazepoxide increased by repeated daily administration.

Aggression↗
PubMed1988

Stimulus-specific long-term habituation of visually guided orienting behavior toward prey in toads: a 14C-2DG study.

The regional distribution of cerebral glucose utilization, revealed by the 14C-2DG technique, was compared between (i) toads after stimulus-specific long-term habituation of the orienting response toward a repeatedly presented prey dummy ('habituation group') and (ii) non-habituated toads, readily orienting toward the repetitively presented prey stimulus ('naive group'). In the 'habituation group', the ventral medial pallium (vMP), a certain portion of the preoptic area (PO), and the dorsal hypothalamus (dHYP) showed a statistically significant increase in 14C-2DG-uptake; decrease was observed in the ventral layers of the optic tectum (vOT), a portion of the tegmental reticular formation (RET), the ventral cerebellum (vCB), and the striatum (STR). The results suggest that stimulus-specific long-term habituation of prey-catching affects both, components of the stimulus-response mediating circuit (e.g., involving OT), and structures extrinsic to it, (e.g., vMP, PO, dHYP), which may belong to a modulatory circuitry. Bilateral lesions to vMP strongly delay habituation. Our results are suggesting that damping of the adequate behavioral motor response during habituation involves active inhibitory processes of a modulatory system that develops in strength during stimulus repetition so as to suppress response output, which basically supports Sokolov's hypothesis (1975).

Animals↗
PubMed1987

Distribution of motoneurons involved in the prey-catching behavior in the Japanese toad, Bufo japonicus.

Coordinated activities of several muscles in the head region underlie the prey-catching behavior of anuran amphibians. As a step in elucidating the neural mechanisms generating these activity patterns in the Japanese toad, we labelled the motoneurons innervating 8 behaviorally relevant muscles using intramuscular (i.m.) injection technique of horseradish peroxidase (HRP), and examined their localization within the motor nuclei whose boundaries were determined by HRP application to the nerve trunk. All the motoneurons innervating the two jaw closer muscles (m. masseter major, m. temporalis) and m. submentalis were localized within the rostral subdivision of the trigeminal motor nucleus. The motoneurons innervating the only mouth opener muscle (m. depressor mandibulae) were scattered throughout the facial motor nucleus. The motoneurons innervating tongue (m. hypoglossus, m. genioglossus) and hyoid muscles (m. sternohyoideus, m. geniohyoideus) appeared within the hypoglossal nucleus with distribution patterns characteristic of the target muscles. Thus, we have revealed the neuroanatomical organization of the motoneurons relevant to the prey-catching behavior.

Animals↗
PubMed1983

A stone's throw and its launch window: timing precision and its implications for language and hominid brains.

Did bigger brains for more precise throwing lead to language, much as feathers for insulation may have set the stage for bird flight? Throwing rocks even at stationary prey requires great precision in the timing of rock release from an overarm throw, with the "launch window" narrowing eight-fold when the throwing distance is doubled from a beginner's throw. Paralleled timing neurons can overcome the usual neural noise limitations via the law of large numbers, suggesting that enhanced throwing skill could have produced a strong selection pressure for any evolutionary trends that provided additional timing neurons. This enhanced timing circuitry may have developed secondary uses for language reception and production.

Animals↗
PubMed1991

Individual differences in temporal lobe sensory processing of threatening stimuli in the cat.

In Experiment I, neurosensory responses from three limbic areas in the cat brain were recorded when cats of differing defensive temperamental traits were exposed to species characteristic threat. The cats investigated were more or less defensive in response to rats and conspecific threat howls. The behavioral disposition of these cats was stable over retest periods of more than one year. It was found that during visual inspection of rats, more defensive cats displayed greater neural activity in the amygdala and the ventromedial hypothalamus than less defensive cats, who showed no change over baseline. Neurosensory response of the amygdala to conspecific threat howls was also found to be greater in more defensive cats. In contrast, there was no neural response to threat howls in the hypothalamus. Neurosensory response to mice was different from the response to rats and threat howls. Visual inspection of the mouse was associated with a decrease in activity in the amygdalas of more defensive cats. Finally, response of the ventral hippocampus was unspecific, appearing to signal only a change in the stimulus environment. The increase in hypothalamic neural activity in response to rats in more defensive cats appeared to be driven by a potentiated output from the amygdala, since the ratio of hypothalamic to amygdala neurosensory response to rats was greater than one in more defensive cats, but equal to one in less defensive cats. Output of the amygdala was directly investigated using evoked potential techniques in Experiment II. Potentials evoked in the hypothalamus by amygdala stimulation were larger in more defensive cats. Size of the hypothalamic potential was highly correlated with the ratio of hypothalamic to amygdala neurosensory response (ratio response) to rats. Removing the effects of size of the hypothalamic evoked potential from the ratio response by analysis of covariance eliminated the difference between more and less defensive cats in ratio response to rats. The significance of these findings for the physiological bases of defensive response to threat and of temperamental traits are discussed.

Aggression↗
PubMed2005

An alternative experimental procedure for studying predator-related defensive responses.

In the present study, we introduce an experimental procedure to study, in rats, a wide range of natural defensive reactions. Animals were tested in an experimental apparatus that consisted of a home cage (25 x 25 x 25 cm) connected to another chamber (25 x 25 x 25 cm-the food compartment) by a hallway (12.5 cm wide and 100 cm long, with 25-cm high walls). During 10 days before the testing procedures, each animal was isolated in the home cage, and, at the beginning of the dark phase, allowed to explore the rest of the apparatus and obtain food pellets stored in the food compartment. The testing consisted of three phases: exploring a familiar and safe environment (phase 1, on the 10th day), cat exposure (phase 2, on the 11th day), and, on the following day, exposure to the environment where the predator had been previously encountered (phase 3). These three conditions thus provided a low-defense baseline; a high level of freezing during cat exposure; and a high level of risk assessment to the hostile environment condition. An important feature of the present experimental procedure was that the behavioral responses were very stable among the animals tested within each individual phase of the testing schedule. In each phase of the testing schedule, we have also examined the Fos immunoreactivity in pontine periventricular sites related to controlling behavioral activation (i.e. the nucleus incertus) or attentional status (i.e. the locus coeruleus). Animals actively exploring a safe and familiar environment presented an increased activation of the nucleus incertus; the locus coeruleus, in turn, was particularly activated during cat exposure, and also, to lesser degree, during exposure to the hostile environment. These results give further support to the view that the animals present quite distinct behavioral states during each one of the testing situations. Taken together, the evidence suggests the present experimental procedure as particularly suitable for analyzing the neural basis of a number of specific defensive responses.

Aggression↗
PubMed2003

Sex differences in cell proliferation, cell death and defensive behavior following acute predator odor stress in adult rats.

Males show suppressed cell proliferation in the hippocampus in response to acute stress but no studies to date have examined cell proliferation in response to acute stress in females. In the current study, we examined the effects of acute exposure to a predator odor stressor [trimethyl thiazoline (TMT); the main component of fox feces] or a control odor on cell proliferation and cell death in the dentate gyrus and on behavior in adult male and female [intact, ovariectomized (OVX) or OVX+estradiol benzoate (EB)] rats. Further, we examined whether TMT-induced changes in behavior were related to cellular changes. During TMT exposure, rats were injected with the cell synthesis marker bromodeoxyuridine and perfused 24 h later. Acute TMT exposure suppressed both cell proliferation and death in males but not in any group of females. Interestingly, in the OVX females we observed an increase in cell death that was eliminated by EB treatment. Consistent with prior studies, estradiol treatment increased cell proliferation regardless of odor condition. Regardless of sex or hormone treatment, TMT increased defensive behavior, suggesting that the behavioral response to TMT is dissociated from this cellular response. This is the first demonstration of a sex difference in cell proliferation and death in the adult dentate gyrus in response to stress.

Aggression↗
PubMed2005

Complex interactions among mammalian carnivores in Australia, and their implications for wildlife management.

Mammalian carnivore populations are often intensively managed, either because the carnivore in question is endangered, or because it is viewed as a pest and is subjected to control measures, or both. Most management programmes treat carnivore species in isolation. However, there is a large and emerging body of evidence to demonstrate that populations of different carnivores interact with each other in a variety of complex ways. Thus, the removal or introduction of predators to or from a system can often affect other species in ways that are difficult to predict. Wildlife managers must consider such interactions when planning predator control programmes. Integrated predator control will require a greater understanding of the complex relationships between species. In many parts of the world, sympatric species of carnivores have coexisted over an evolutionary time scale so that niche differentiation has occurred, and competition is difficult to observe. Australia has experienced numerous introductions during the past 200 years, including those of the red fox (Vulpes vulpes) and the feral cat (Felis catus). These species now exist in sympatry with native mammalian predators, providing ecologists with the opportunity to study their interactions without the confounding effects of coevolution. Despite an increasing body of observational evidence for complex interactions among native and introduced predators in Australia, few studies have attempted to clarify these relationships experimentally, and the interactions remain largely unacknowledged. A greater understanding of these interactions would provide ecologists and wildlife managers world-wide with the ability to construct robust predictive models of carnivore communities, and to identify their broader effects on ecosystem functioning. We suggest that future research should focus on controlled and replicated predator removal or addition experiments. The dingo (Canis lupus dingo), as a likely keystone species, should be a particular focus of attention.

Animals↗
PubMed2002

On the dynamics of discrete food chains: low- and high-frequency behavior and optimality of chaos.

In this paper we derive and analyze a discrete version of Rosenzweig's (Am. Nat. 1973) food-chain model. We provide substantial analytical and numerical evidence for the general dynamical patterns of food chains predicted by De Feo and Rinaldi (Am. Nat. 1997) remaining largely unaffected by this discretization. Our theoretical analysis gives rise to a classification of the parameter space into various regions describing distinct governing dynamical behaviors. Predator abundance has a local optimum at the edge of chaos.

Animals↗
PubMed2003

Differential modulation of feline defensive rage behavior in the medial hypothalamus by 5-HT1A and 5-HT2 receptors.

Previous studies have established that the expression of defensive rage behavior in the cat is mediated over reciprocal pathways that link the medial hypothalamus and the dorsolateral quadrant of the midbrain periaqueductal gray matter (PAG). The present study was designed to determine the roles played by 5-HT(1A) and 5-HT(2C) receptors in the medial hypothalamus on the expression of defensive rage behavior elicited from electrical stimulation of the PAG. Monopolar stimulating electrodes were placed in the midbrain PAG from which defensive rage behavior could be elicited by electrical stimulation. During the course of this study, defensive rage was determined by measuring the latency of the "hissing" component of this behavior. Cannula-electrodes were implanted into sites within the medial hypothalamus from which defensive rage behavior could also be elicited by electrical stimulation in order that serotonergic compounds could be microinjected into behaviorally identifiable regions of the hypothalamus at a later time. Microinjections of the 5-HT(1A) receptor agonist 8-OHDPAT (0.1, 1.0 and 3.0 nmol) into the medial hypothalamus suppressed PAG-elicited hissing in a dose-dependent manner. Administration of the 5-HT(1A) antagonist p-MPPI (3.0 nmol) blocked the suppressive effects of 8-OHDPAT upon hissing. The suppressive effects of 8-OHDPAT were specific to defensive rage behavior because this drug (3 nmol) facilitated quiet biting attack. Microinjections of the 5-HT(2C) receptor agonist (+/-)-DOI hydrochloride into the medial hypothalamus (0.5, 1.0, and 3.0 nmol) facilitated the occurrence of PAG-elicited hissing in a dose-dependent manner. In turn, these facilitating effects were blocked by pretreatment with the selective 5-HT(2) antagonist, LY-53,857, which was microinjected into the same medial hypothalamic site. The findings of this study provide evidence that activation of 5-HT(1A) and 5-HT(2) receptors within the medial hypothalamus exert differential modulatory effects upon defensive rage behavior elicited from the midbrain PAG of the cat.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2004

Extinction dynamics of Lotka-Volterra ecosystems on evolving networks.

We study a model of a multispecies ecosystem described by Lotka-Volterra-like equations. Interactions among species form a network whose evolution is determined by the dynamics of the model. Numerical simulations show power-law distribution of intervals between extinctions, but only for ecosystems with sufficient variability of species and with networks of connectivity above certain threshold that is very close to the percolation threshold of the network. The effect of slow environmental changes on extinction dynamics, degree distribution of the network of interspecies interactions, and some emergent properties of our model are also examined.

Adaptation, Physiological↗
PubMed2006

Long-range interactions and evolutionary stability in a predator-prey system.

Evolving ecosystems often are dominated by spatially local dynamics, but many also include long-range transport that mixes spatially separated groups. The existence of such mixing may be of critical importance since research shows spatial separation may be responsible for long-term stability of predator-prey systems. Complete mixing results in rapid global extinction, while spatial systems achive long term stability due to an inhomogeneous spatial pattern of local extinctions. We consider the robustness of a generic evolving predator-prey or host-pathogen model to long-range mixing and find a transition to global extinction at nontrivial values implying that even if significant mixing already exists, a small amount of additional mixing may cause extinction. Our results are relevant to the global mixing of species due to human intervention and to global transport of infectious disease.

Animals↗
PubMed1985

A natural toxic defense system: cardenolides in butterflies versus birds.

We have verified that wild birds can become conditioned to reject naturally toxic insects either visually (experiment 1) or by taste (experiment 2). We have also verified, however, that unconditioned taste rejection of noxious chemicals by wild birds also occurs (experiment 3). Such unconditioned responses to the aposematic visual and taste cues of many insects, in fact, often appear to be as important as, or more important than, conditioned responses. In a large number of laboratory feeding experiments with wild birds as predators of aposematic insects, initial and/or long-term rejection occurs without prior laboratory conditioning experience. Although in some experiments the birds may have previously been exposed to (and therefore perhaps conditioned by) the aposematic prey in the wild, other experiments have used naive birds or insects whose ranges do not overlap those of the birds. Wiklund and Jarvi, for example, tested the response of 47 naive hand-raised birds of four species to five aposematic insect species, and found that 69/136 (51%) insects were rejected visually without even tasting, while 63 were tasted and then rejected. Only four of the insects were actually ingested. Similarly, in Bowers' study of the response of Massachusetts blue jays to aposematic western U.S. Euphydryas butterflies, several blue jays consistently rejected the butterflies visually or by taste without having eaten any. While these studies were not designed to separate neophobic effects from innate visual and/or taste aversions, they do differentiate between conditioned and unconditioned responses. Since both conditioned and unconditioned rejections can be demonstrated in the lab by insectivorous birds, and our available field evidence does not yet let us distinguish the mechanisms behind the observed patterns, our initial question, of the relative importance of conditioned versus unconditioned rejection mechanisms in different natural situations, is not yet answerable. The most important requirement of a food-rejection strategy is that it prevents both poisoning and starvation. We have shown, however, that rejection of a noxious insect by a bird can take place at four distinct levels (visual, non-destructive taste sampling, destructive taste sampling, or post-ingestional physiological rejection), the first three of which may be either unconditioned or conditioned by a physiological reaction to ingestion.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗