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In cats with the distal paw shaved and the claws painted with nail varnish, claw movements were recorded during the approach to a morsel of food with a conventional video camera; supplementary results were obtained with a high frequency video system. The claws can be protruded in two directions, either ventrally or more dorsalwards. Measurements of the outer contour of the paw suggest that these two modes are not due to differences in angular movements in the proximal interphalangeal joints; it is suggested that they depend on some (so far unknown) function in the distal interphalangeal joints. Differential movements of the claws of the different digits suggest some degree of individual control of the digits.
The behavioral effects of the amino (N)-terminal fragment of substance P (SP(1-7)) on the marmoset (Callithrix penicillata) predator confrontation test of fear/anxiety were investigated. The test apparatus consisted of a figure-eight maze with three parallel arms interconnected at each extremity to a perpendicular arm. A taxidermized oncilla cat (Felis tigrina) was placed outside the maze facing one of its corners. Subjects were submitted to seven 30 min maze habituation trials (HTs), in the absence of the 'predator', and then to six 30 min treatment trials (TTs), in the presence of the 'predator', consisting of four doses of SP(1-7) (5, 50, 250 and 500 microg/kg; IP), saline and sham injection. SP(1-7) treatment reversed, in a dose-dependent way, the fear-induced avoidance behavior due to the predator's presence and increased the frequency of exploratory behaviors. Locomotor activity decreased during successive HTs, yet increased after all SP(1-7) treatments. These results indicate that systemic administration of SP(1-7) produces anxiolytic-like effects in marmosets tested in the predator confrontation model of fear/anxiety.
Argentine ants, Linepithema humile, were attacked by their nestmates following contact with a particular prey item, the brown-banded cockroach, Supella longipalpa. Contact with prey, as brief as 2 min, provoked nestmate aggression. Argentine ants contaminated with hydrocarbons extracted from S. longipalpa also released nestmate aggression behavior similar to that released by the whole prey item, confirming the involvement of hydrocarbons. In contrast to S. longipalpa, little or no nestmate aggression was induced by other ant prey from diverse taxa. A comparison of prey hydrocarbon profiles revealed that all hydrocarbons of S. longipalpa were very long chain components with 33 or more carbons, while other prey had either less, or none, of the very long chain hydrocarbons of 33 carbons or greater. We identified the hydrocarbons of S. longipalpa and some new groups of long chain hydrocarbons of L. humile. The majority of S. longipalpa hydrocarbons were 35 and 37 carbons in length with one to three methyl branches, and closely resembled two previously unidentified groups of compounds from L. humile of similar chain length. The hydrocarbons of S. longipalpa and L. humile were compared and their role in the Argentine ant nestmate recognition is discussed.
In most social ungulate species, males are larger than females and the sexes live in separate groups outside the breeding season. It is important for our understanding of the evolution of sociality to find out why sexual segregation is so widespread not only in ungulates but also in other mammals. Sexual body size dimorphism was proposed as a central factor in the evolution of sexual segregation in ungulates. We tested three hypotheses put forward to explain sexual segregation: the predation-risk, the forage-selection, and the activity budget hypothesis. We included in our analyses ungulate species ranging from non-dimorphic to extremely dimorphic in body size. We observed oryx, zebra, bighorn sheep and ibex in the field and relied on literature data for 31 additional species. The predation-risk hypothesis predicts that females will use relatively predator-safe habitats, while males are predicted to use habitats with higher predation risk but better food quality. Out of 24 studies on different species of ungulates, females and their offspring chose poorer quality but safer habitat in only eight cases. The forage-selection hypothesis predicts that females would select habitat based on food quality, while males should prefer high forage biomass. In fact, females selected higher quality food in only six out of 18 studies where males and females segregated, in eight studies there was no difference in forage quality and in four studies males were in better quality habitat. The activity budget hypothesis predicts that with increasing dimorphism in body size males and females will increasingly differ in the time spent in different activities. Differences in activity budgets would make it difficult for males and females to stay in mixed-sex groups due to increased costs of synchrony to maintain group cohesion. The predictions of the activity budget hypothesis were confirmed in most cases (22 out of 23 studies). The heavier males were compared to females, the more time females spent foraging compared to males. The bigger the dimorphism in body mass, the more males spent time walking compared to females. Lactating females spent more time foraging than did non-lactating females or males. Whether species were mainly bulk or intermediate feeders did not affect sexual differences in time spent foraging. We conclude that sexual differences in activity budgets are most likely driving sexual segregation and that sexual differences in predation risk or forage selection are additive factors.
2,3,4-Tribromopyrrole (1) and 2,3,5-tribromopyrrole (2) were each synthesized from pyrrole. Spectral data and antifeedant effects for synthetic 1 and the antipredatory chemical defense compound of the marine hemichordate Saccoglossus kowalevskii were in agreement, confirming the structure of the deterrent natural product as 1. Spectral data for 2 differed from synthetic and natural 1.
The paradise fish, a small insectivore, coinhabits marshes of Southeast Asia with several predator fish species. Its ability to recognize and avoid harmful fish may depend upon both genetic factors and experience. Here we demonstrate genetic variability between the 20-day-old larvae of two inbred strains of paradise fish (P and S) in predator exploration and avoidance, using predator models. We show that, in comparison to S larvae, P larvae exhibited an elevated frequency of leaping and backing and an increased approach latency when faced with a predator model with eyespots. Analysis of a classical cross system between the two strains revealed significant departure from an additive-dominance genetic model and suggested the involvement of both epistatic effects of several genes and paternal effects. The effect of the paternal influence during the 5-day postspawning period was found to be strain dependent: later predator avoidance behaviors were influenced by the presence of the father in P larvae but not in S larvae. On the basis of these and previous results, we speculate that the 5 postspawning days may represent a developmentally sensitive period during which specific environmental stimulation, e.g., stimuli associated with the father, is critical for later development of appropriate antipredatory responses. We conclude that developmental aspects of antipredatory behavior in paradise fish are influenced by a complex interplay between genetic and environmental factors.
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Apostatic selection occurs when predators concentrate disproportionately on the common varieties of non-mimetic polymorphic prey species. This has been tested in 14 experiments by presenting populations of green and brown lard-and-flour "baits" to inexperienced wild passerine birds in their normal surroundings. In seven experiments a 9 green : 1 brown population was presented for a number of days, followed by a 1 green : 9 brown population for a similar period. in the remaining seven experiments the populations were presented in the reverse order. The birds often had strong "natural" colour preferences (for example, blackbirds and songthrushes preferred browns) which were not caused by the relative conspicuousness of the two colours. The data within most of the experiments were very heterogeneous, but in every experiment there was good evidence that the birds tended to concentrate on the common colour. The consistency of the replicated experiements gives strong reason to believe that apostatic selection is a widespread phenomenon among avian predators, and provides an explanation for many of the non-mimetic colour and pattern polymorphisms found among their prey.
Haematophagous female blackflies (Diptera: Simuliidae) are serious biting pests and obligate vectors of vertebrate pathogens, namely filarial Dirofilaria, Mansonella, Onchocerca and protozoal Leucocytozoon. Immature stages of Simuliidae inhabit lotic waterways, the sessile larvae filter-feeding and often forming a large proportion of the benthic biomass, usually aggregated in well-oxygenated sections of streams, rivers, waterfalls and spillways. Simuliid control practices depend on larvicidal chemicals, biological products (bacteria, nematodes) and environmental modification. The potential use of predators for biological control of Simuliidae has not been exploited. Predators of Simuliidae include examples of at least 12 families of Diptera and other predaceous arthropods (Crustacea and insects: Coleoptera, Odonata, Plecoptera, Trichoptera), invertebrates (notably Turbellaria), as well as browsing fish. Diptera impacting upon simuliid populations comprise mainly Chironomidae, Empididae and Muscidae, although several other families (Asilidae, Dolichopodidae, Phoridae, Drosophilidae, Scathophagidae) play a significant role as predators. Details of predator and prey species and life stages are presented, by zoogeographical region, including the prevalence of cannibalism among Simuliidae.
Catastrophic population collapses such as observed in many exploited fish populations have been argued to result from depensatory growth mechanisms (i.e., reduced reproductive success at low population densities, also known as Allee effect). Empirical support for depensation from population-level data is, however, hard to obtain and inconclusive. Using a size-structured, individual-based model we show that catastrophic population collapses may nonetheless be an intrinsic property of many communities, because of two general aspects of individual life history: size- and food-dependent individual growth and individual mortality decreasing with body size. Positive density dependence, characteristic for depensatory growth mechanisms and catastrophic behavior, results as a direct and robust consequence of the interplay between these individual life-history traits, which are commonly found in many species.
Some islands in the Gulf of California support very high densities of spiders. Spider density is negatively correlated with island size; many small islands support 50-200 spiders per m3 of cactus. Energy for these spiders comes primarily from the ocean and not from in situ productivity by land plants. We explicitly connect the marine and terrestrial systems to show that insular food webs represent one endpoint of the marine web. We describe two conduits for marine energy entering these islands: shore drift and seabird colonies. Both conduits are related to island area, having a much stronger effect on smaller islands. This asymmetric effect helps to explain the exceptionally high spider densities on small islands. Although productivity sets the maximal potential densities, predation (by scorpions) limits realized spider abundance. Thus, prey availability and predation act in concert to set insular spider abundance.
We test the predictive value of the main energetic currencies used in foraging theory using starlings that choose between two foraging modes (walking versus flying). Walking is low-cost, low-yield, whereas flying is the opposite. We fixed experimentally, at 11 different values, the amount of flight required to get one food reward, and for each flight cost value, we titrated the amount of walking until the birds showed indifference between foraging modes. We then compared the indifference points to those predicted by gross rate of gain over time, net rate of gain over time, and the ratio of gain to expenditure (efficiency). The results for the choice between modes show strong qualitative and quantitative support for net rate of gain over time over the alternatives. However, the birds foraged for only a fraction of the available time, indicating that the choice between foraging and resting could not be explained by any of these currencies. We suggest that this discrepancy could be accounted for functionally because nonenergetic factors such as predation risk may differ between resting and foraging in any mode but may not differ much between foraging modes, hence releasing the choice between foraging modes from the influence of such factors. Alternatively, the discrepancy may be attributable to the use of predictable (rather than stochastic) ratios of effort per prey in our experiment, and it may thus be better understood with mechanistic rather than functional arguments.
The food intake rate of foragers may be reduced as a result of interference, which may be asymmetric among individuals and occur as a result of intimidation, direct aggression or filtering. It is important to distinguish among these types of interference, because each can have different consequences for individuals, foraging groups and populations. We demonstrate the application of the functional response as a tool for distinguishing between types of interference. We apply the approach to juvenile Atlantic salmon and show that stepwise elimination of interference types is possible from regression analyses of functional responses, identifying filtering as the only effective type of interference in the study environment.
We are becoming increasingly aware of animal communication outside the range of human sensitivity. Web decorations are silk structures used by orb-web spiders to deceive prey and predators. However, despite the level of interest in these structures, their visibility to prey and predators has never, to our knowledge, been objectively assessed. Here, we use spectrophotometric analyses to show that the decorations of all five tested spider species are visible to honey bees and birds over short and long distances. Furthermore, the discoid decorations of one species may provide some protection against arthropod predators. However, these decorations are inefficient at camouflaging the spider against birds, despite the overlap between the spider's body and web decoration.
Imprinting provides precocial offspring with an efficient means to optimize their subsequent behaviours. We discovered food imprinting using a sophisticated invertebrate model: the cuttlefish. We showed that early juveniles preferred the prey to which they have been visually familiarized, when the amount of information was sufficient and only if such familiarization occurred during a short sensitive period. We also demonstrated that the effects of visual food imprinting overcame those of the first food ingested. Our study shows that visual imprinting is a critical process in animals, surpassing more direct reward experiences that occur outside the critical exposure period.
The evolution of warning coloration (aposematism) has been difficult to explain because rare conspicuous mutants should suffer a higher cost of discovery by predators relative to the cryptic majority, while at frequencies too low to facilitate predator aversion learning. Traditional models for the evolution of aposematism have assumed conspicuous prey phenotypes to be genetically determined and constitutive. By contrast, we have recently come to understand that warning coloration can be environmentally determined and mediated by local prey density, thereby reducing the initial costs of conspicuousness. The expression of density-dependent colour polyphenism is widespread among the insects and may provide an alternative pathway for the evolution of constitutive aposematic phenotypes in unpalatable prey by providing a protected intermediate stage. If density-dependent aposematism can function as an adaptive intermediate stage for the evolution of constitutive aposematic phenotypes, differential reaction norm evolution is predicted among related palatable and unpalatable prey populations. Here, I present empirical evidence that indicates that (i) the expression of density-dependent colour polyphenism has differentially evolved between palatable and unpalatable populations of the grasshopper Schistocerca emarginata (= lineata) (Orthoptera: Acrididae), and (ii) variation in plasticity between these populations is commensurate with the expected costs of conspicuousness.
Cannibalism of small numbers of offspring by a parent has been proposed as an adaptive parental strategy, by providing energy to support parental care. However, there are few empirical studies to support this hypothesis. We conducted field and laboratory experiments to investigate partial filial cannibalism in Stegastes leucostictus, a coral reef fish with paternal care. Partial cannibalism was shown to be common, and males were found to remove developing embryos from throughout a clutch in a random pattern, rather than in the more aggregated pattern seen during embryo predation. Males that received a diet supplement grew faster than control males, but did not engage in less cannibalism. Also, males did not concentrate cannibalism on early embryonic stages with the highest energetic value. Experimental reduction of embryo densities was found to significantly increase embryo development rate and survival from egg deposition to hatching, and experimental reduction of oxygen levels significantly increased rates of partial filial cannibalism by males. Artificial spawning sites with low oxygen levels were avoided by spawning females, and cannibalism rates by males were higher. We propose that partial filial cannibalism serves as an adaptive parental strategy to low oxygen levels in S. leucostictus by increasing the hatching success of embryos.