Multiple selection pressures influence Trinidadian guppy (Poecilia reticulata) antipredator behavior

Animals alter their behavior to avoid a variety of differenttypes of predators. Trinidadian guppies (Poecilia reticulata)have been an important system for examining the evolution ofantipredator behavior because geographically isolated populationsexperience different amounts of aquatic predation. Althoughthe influence of aquatic predators has been well documented,selective pressures from other types of predators are less wellunderstood. We examined the response of wild-caught individualsfrom upstream and downstream populations to an aquatic predatorand a simulated aerial predator. As previously documented, fishfrom the downstream population responded more strongly to theaquatic predator than did fish from the upstream population,inspecting for longer periods of time. Guppies also exhibiteda strong behavioral response to the potential aerial predator.Although both populations displayed a similar magnitude of response,they differed in the specific behaviors used. Upstream fishtended to freeze on the tank bottom, whereas downstream fishtended to hide under shelter. Field observations suggest thatthese strategies are related to habitat features specific toeach site. The behaviors used against aerial predators differedsubstantially from the behaviors used against aquatic predators,suggesting that different types of predators exert conflictingselection pressures. This research demonstrates the importanceof considering multiple selection pressures acting on an organismwhen trying to understand the evolutionary history of behavioraland morphological traits.     

Can snakes hide in plain view? Chromatic and achromatic crypsis of two colour forms of the Western Terrestrial Garter Snake (Thamnophis elegans)

Colours influence numerous aspects of an animal's ecology. One possibility is that colour helps make an animal cryptic against the background on which it is resting. We test this hypothesis for two different, geographically separated colour forms (dark forms and light forms) of the Western Terrestrial Garter Snake, Thamnophis elegans. We quantified crypsis of snakes, in terms of colour (chromatic crypsis) and brightness (achromatic crypsis), by using objective measures of spectral reflectance of snakes and the surrounding habitat. These data were visually modelled from the perspective of potential snake predators and human researchers. Overall, snakes of both colour forms selected basking sites that increased chromatic crypsis over that which would have been achievable on random backgrounds. Both colour forms of T. elegans appear to exhibit similar achromatic and chromatic crypsis when viewed by potential predators, such as mammals and birds. From the perspective of the human visual model, dark T. elegans were generally more chromatically cryptic than light T. elegans, contrary to our a priori subjective impression. The main contribution of the present study is that we provide one of the first objective comparisons of snakes and their backgrounds as a measure of crypsis. Although we found some evidence for crypsis as a factor in choice of basking sites for snakes, other factors (e.g. thermoregulatory opportunities) undoubtedly play important roles as well. We also have not addressed whether snakes involved in other activities are cryptic or whether there are differences between the sexes or between reproductive and nonreproductive females. The adaptive significance of colour variation has been studied in diverse taxonomic groups. Although the mechanisms are not straightforward, the opportunities to carry out further work in this area are enhanced by the availability of objective approaches. © 2013 The Linnean Society of London,     

Impact of predation on early stages of the armoured catfish Hoplosternum thoracatum (Siluriformes-Callichthyidae) and implications for the syntopic occurrence with other related catfishes in a neotropical multi-predator swamp

This study investigated the role of predators in preventing competitive exclusion among three closely related armoured catfishes (Callichthys callichthys, Hoplosternum littorale and H. thoracatum) that occur synthopically in multi-predator freshwater swamps of Suriname, South America. The potential impact of predation on armoured catfish was determined by combining laboratory measurements of predation rates on five early developmental stages of the armoured catfish H. thoracatum for 24 aquatic predators with field studies of the density of the predators in the swamps. The contribution of a particular predator to the total predation pressure on its prey was determined to a large extent by the density of the predator in the swamp. Seemingly innocuous predators with low or moderate predation rates in the laboratory may be extremely important in the swamps due to their high abundance. Small-sized omnivorous fishes and aquatic invertebrates were major predators of early developmental stages of armoured catfish. Both qualitative and quantitative ontogenetic changes in the predation pressure on armoured catfish were observed. Major predation on eggs, larvae and juveniles of H. thoracatum resulted from a different set of predators in each developmental stage of the prey. In all developmental stages of H. thoracatum the predation pressure involved several predator species and not a single, dominant predator. The potential predation pressure of the 24 predators taken together and the number of predators that were able to prey on H. thoracatum decreased sharply with increasing age (size) of the prey. Even if egg (nest) predation is prevented by the guarding male, the potential impact of the 24 predators on the populations of armoured catfish is large. Predation may account for the high mortality of H. thoracatum observed in the swamps. The high predation pressure on callichthyid catfishes may help to explain the coexistence of three closely related and morphologically quite similar armoured catfishes in Surinamese swamps.     

In and out: an analysis of epibiotic vs periplasmic bacterial predators

Bdellovibrio and like organisms (BALO) are obligate predators of Gram-negative bacteria, belonging to the α- and δ-proteobacteria. BALO prey using either a periplasmic or an epibiotic predatory strategy, but the genetic background underlying these phenotypes is not known. Here we compare the epibiotic Bdellovibrio exovorus and Micavibrio aeruginosavorus to the periplasmic B. bacteriovorus and Bacteriovorax marinus. Electron microscopy showed that M. aeruginosavorus, but not B. exovorus, can attach to prey cells in a non-polar manner through its longitudinal side. Both these predators were resistant to a surprisingly high number of antibiotic compounds, possibly via 26 and 19 antibiotic-resistance genes, respectively, most of them encoding efflux pumps. Comparative genomic analysis of all the BALOs revealed that epibiotic predators have a much smaller genome (ca. 2.5 Mbp) than the periplasmic predators (ca. 3.5 Mbp). Additionally, periplasmic predators have, on average, 888 more proteins, at least 60% more peptidases, and one more rRNA operon. Fifteen and 219 protein families were specific to the epibiotic and the periplasmic predators, respectively, the latter clearly forming the core of the periplasmic ‘predatome'', which is upregulated during the growth phase. Metabolic deficiencies of epibiotic genomes include the synthesis of inosine, riboflavin, vitamin B6 and the siderophore aerobactin. The phylogeny of the epibiotic predators suggests that they evolved by convergent evolution, with M. aeruginosavorus originating from a non-predatory ancestor while B. exovorus evolved from periplasmic predators by gene loss.     

Invertebrate zooplankton predator composition and diversity in tropical lentic waters

Invertebrate zooplankton predators are generally less diverse in average species numbers in tropical than in temperate lakes and reservoirs. Predatory Copepoda which comprise the majority of limnetic predators are particularly low in species numbers in the tropics. Predatory Cladocera are confined to the North Temperate zone. Chaoborus appears to be cosmopolitan. Among Rotifera, only the cosmopolitan predator Asplanchna occurs in tropical waters while the other common limnetic carnivorous genus Ploesoma is restricted to higher latitudes. Hydracarina, and insects besides Chaoborus, are generally restricted to the littoral and appear to be more diverse in the tropics. Lakes Awasa and Zwai, Ethiopia, are almost devoid of predators in the limnetic, which is invaded by a littoral chydorid Alona diaphana. Low diversity of lake types and low production of tropical zooplankton could restrict predator diversity too. Very low diversity of invertebrate predators in the limnetic and higher diversity in the littoral may characterize tropical lakes in contrast to temperate lakes, which have more invertebrate predators in the limnetic and perhaps relatively less in the littoral. Tropical zooplankton in freshwaters, appears to be a very immature community. Hence opportunistic species can readily invade the limnetic and even dominate in isolated situations as has been shown for Alona davidi, Hydracarina and some other unconventional forms.     

Major claws make male fiddler crabs more conspicuous to visual predators: a test using human observers

One of the possible costs of the male fiddler crabs enlarged claw can be conspicuousness to predators. This hypothesis was tested using human observers as a model of visual predators. In the European fiddler crab, Uca tangeri Eydoux, the males' major claw is white contrasting with the orange-brownish colour of the carapace and of the feeding claw, and the mudflat background. The following morphotypes were created from close-up photographs taken in nature using an image processing software: male, male without claw, female, female with enlarged claw, male with enlarged claw of the same colour of the feeding claw, male with 75% sized claw, male with 50% sized claw. These morphotypes were then presented in a randomised order to students, using a psychology test software, which allows the measurement of response time in msec. The subjects were allowed to look at the images for an unlimited amount of time, until they detected the individual or until they decided to pass on to another image. Backgrounds (i.e. mudflat picture) without individuals were also presented as a control. Male crabs were detected significantly sooner than females. When we compared males with the claw removed with females with an enlarged claw added, the pattern is reversed and the latter are detected significantly faster. Thus, the enlarged claw seems to be the key feature that makes the individuals more conspicuous. Size and colour seem to be the main aspects of the claw's conspicuousness. The data of these experiments support the initial prediction of males being more conspicuous than females because of their enlarged claw. The possible costs and benefits of this trait, related to predation, are discussed.     

Chemical defense of toad tadpoles under risk by four predator species

Many organisms use inducible defenses as protection against predators. In animals, inducible defenses may manifest as changes in behavior, morphology, physiology, or life history, and prey species can adjust their defensive responses based on the dangerousness of predators. Analogously, prey may also change the composition and quantity of defensive chemicals when they coexist with different predators, but such predator‐induced plasticity in chemical defenses remains elusive in vertebrates. In this study, we investigated whether tadpoles of the common toad (Bufo bufo) adjust their chemical defenses to predation risk in general and specifically to the presence of different predator species; furthermore, we assessed the adaptive value of the induced defense. We reared tadpoles in the presence or absence of one of four caged predator species in a mesocosm experiment, analyzed the composition and quantity of their bufadienolide toxins, and exposed them to free‐ranging predators. We found that toad tadpoles did not respond to predation risk by upregulating their bufadienolide synthesis. Fishes and newts consumed only a small percentage of toad tadpoles, suggesting that bufadienolides provided protection against vertebrate predators, irrespective of the rearing environment. Backswimmers consumed toad tadpoles regardless of treatment. Dragonfly larvae were the most voracious predators and consumed more predator‐naïve toad tadpoles than tadpoles raised in the presence of dragonfly cues. These results suggest that tadpoles in our experiment had high enough toxin levels for an effective defense against vertebrate predators even in the absence of predator cues. The lack of predator‐induced phenotypic plasticity in bufadienolide synthesis may be due to local adaptation for constantly high chemical defense against fishes in the study population and/or due to the high density of conspecifics.     

No evidence of modulation of indirect plant resistance of Brassica rapa plants by volatiles from soil-borne fungi

1. Upon herbivory, plants emit specific herbivore-induced plant volatiles (HIPVs) that can attract natural enemies of the herbivore thus serving as indirect plant resistance. Not only insect herbivores, but microorganisms may also affect HIPV emission before or after plant colonisation, which in turn can affect behaviour of natural enemies of the herbivore. Yet, it remains elusive whether volatiles from microorganisms influence HIPV emission and indirect plant resistance.
2. In this study, we investigated whether exposure of Brassica rapa roots to volatiles from soil-borne fungi influence HIPV emission and the recruitment of natural enemies of Pieris brassicae larvae.
3. Using a two-compartment pot system, we performed greenhouse and common-garden experiments, and we profiled plant HIPV emission.
4. We found that exposure of plant roots to fungal volatiles did not affect the number of P. brassicae larvae recollected from the plants, suggesting a neutral effect of the fungal volatiles on natural predation. Likewise, in a greenhouse, similar numbers of larvae were parasitised by Cotesia glomerata wasps on control plants as on fungal volatile-exposed plants. Additionally, chemical analysis of HIPV profiles revealed no qualitative and quantitative differences between control plants and fungal volatile-exposed plants that were both infested with P. brassicae larvae.
5. Together, our data indicate that root exposure to fungal volatiles did not affect indirect plant resistance to an insect herbivore. These findings provide new insight into the influence of indirect plant resistance by fungal volatiles that are discussed together with the effects of fungal volatiles on direct plant resistance.

     

The predator guild associated withAceria litchii (Acari: Eriophyidae) in Australia and China

Lychees were surveyed in Queensland, Australia and in Guangdong Province and Hainan Island China, for natural enemies of the lychee erinose mite,Aceria litchii (Keifer), one of the most serious pests of lychee in Australia. A guild of seventeen predators, including ten species of phytoseiid mites, was associated with lychee erinose in Queensland. Six other predaceous mite species and a cecidomyiid larva,Arthrocnodax sp. were also part of the complex. Despite the apparent predation of most of the seventeen species recorded in Queensland onA. litchii, the pest continues to cause major problems. In China, whereA. litchii is a relatively minor pest, nine phytoseiid species were collected in lychee orchards. The value of introducing additional predators to Australia, especially from China, is discussed.     

The aggregative numerical response of polyphagous predators to aphids in cereal fields: attraction to what?

We tested in a field experiment two hypotheses for why polyphagous predators aggregate at concentrations of aphids: 1) because they are attracted directly to aphids as prey, or 2) because they are attracted to alternative prey that aggregate around the honeydew produced by aphids. Small plots were established in the field with two experimental treatments, aphid addition and honey spraying, and a watersprayed control, each replicated 10 times. Arthropods were recorded by pitfall traps and sticky traps in each plot. Diptera were significantly more abundant in the honey plots. Of the predators, Agonum dorsale, “All carabids” and Philonthus sp. were most abundant in the honey plots; Tachyporus spp. and carabid and staphylinid larvae were most abundant in the aphid addition plots. It is suggested that these results reflect differences among the predators in their ability to tolerate and utilise aphids as food.     

Insect predation on pike fry

Laboratory tests evaluated the predatory impact of the macroinvertebrates Erythromma najas larvae (Odonata, Zygoptera: Coenagrionidae), Notonecta glauca (Heteroptera: Notonectidae), Ilyocoris cimicoides (Heteroptera: Naucoridae), Libellula depressa larvae (Odonata, Anisoptera: Libellulidae), Dytiscus marginalis larvae (Coleoptera: Dytiscidae) and Anax imperator larvae (Odonata, Anisoptera: Aeshnidae) on 3-, 12-, 21- and 30-day-old pike fry Esox lucius . All these insect predators captured and ate pike fry during the test, although the numbers killed varied among species. Dytiscus marginalis, Anax imperator and Notonecta glauca were the most Voracious predators.     

Notes on the distribution and abundance of the caecilian Boulengerula uluguruensis (Amphibia: Gymnophiona: Caeciliidae) in the Uluguru Mountains, Tanzania

Boulengerula uluguruensis is a terrestrial caeciliid caecilian described from the Uluguru Mountains of Tanzania. We investigated the relative abundance of B. uluguruensis in agricultural and forested habitats at the beginning of the rainy season. This caecilian was found over a wide altitudinal range (450–1175 m a.s.l.), and in many land cover types (including natural forest, plantation forest and small scale agriculture), and different soil textures (including very compact soil). Based on quantitative and semi‐quantitative surveys, B. uluguruensis is more abundant than any other subterranean lower vertebrate in this area, with densities up to 0.4 individuals m^?2 in some agricultural plots. The hypothesis proposed, that B. uluguruensis is more abundant in agriculture than their native forest, could not be conclusively tested during this brief visit, although the data that were collected do not indicate to the contrary. Likewise, the size of animals from forest and agricultural populations could not be objectively compared.     

具有天敌捕食的鼠害综合防治模型研究

鼠害综合防治是以生态学为基础综合考察各种措施的有机结合与协调 ,综合运用生态学、经济学、环境保护学、系统工程学的观点 ,充分利用自然因素控制鼠害 ,以取得较好的经济效益、生态效益和社会效益。害鼠种群动态、天敌类群动态以及植物群体生长动态是综合防治的基本理论问题 ,确定经济阈值是实现害鼠种群数量科学控制的重要前提[1] 。在综合防治过程中 ,如何最大限度地发挥天敌的作用 ,并将这种作用与其他自然限制因素以及人为防治措施相互协调 ,共同作用 ,是鼠害防治实践中最重要的课题之一 [2 ]。本文先简要综述天敌控制鼠害的研究成果 …     

Chemosensory responses of Aporcelaimellus nivalis (Nematoda: Dorylaimida) towards kairomones emitted by prey nematodes belonging to different trophic groups

Abstract

Observations were made on the attraction of Aporcelaimellus nivalis towards kairomones/attractants emitted by prey nematodes belonging to different trophic categories, viz., saprophagous, epidermal, migratory semi-endodermal, predatory nematodes, virus vectors and cortical feeders. Aporcelaimellus nivalis responded positively and significantly to prey kairomones, but showed variation in their individual behaviour. Predators are most attracted towards epidermal feeders and least attracted to virus vectors. The differential responses of A. nivalis towards different prey were attributed to the inert behaviour of predators, their preference for a particular species of prey, chemical composition, concentration, quality, quantity of prey attractant, formation of minimum perceptible attraction gradient of prey and minimum response threshold of predators. Various factors such as prey density, period of prey incubation, starvation of predators, temperature, agar concentration, agar thickness and distance of predators from the source of attraction (prey) govern chemosensory responses of predator. Aporcelaimellus nivalis maximum response was towards Hirschmanniella oryzae, when tested as 10 day starved predators in agar plates containing 2 mm thick layer of 1% water-agar with 200 prey individuals previously incubated for 16 h at 30°C. Prey kairomones were most attractive when A. nivalis were tested from a distance of 2 and 3 cm.     

Presence of Cuckoo reliably indicates high bird diversity: A case study in a farmland area

Here we studied the occurrence of Cuckoo Cuculus canorus and top predators as indicators of biodiversity in agro ecosystems of Western Poland, to identify local hotspots. Bird species richness and land-use diversity were used as measures of biodiversity. The relationship between the presence of Cuckoos and four avian top predators with biodiversity measures were examined using Generalized Linear Mixed Models.Cuckoos were mainly distributed on sites with greater species richness, but were absent from the low species richness sites, while the top predators were distributed uniformly. The performance of the best models using the presence of Cuckoo was 27% higher than the best models using top predators. Our results highlight the predictive capacity of Cuckoos as an indicator of bird species richness than top predators and the usefulness of this species in biodiversity studies. The cookoo is charismatic, widespread across the main types of landscapes, and is easy to detect from its song. Importantly, our findings propose that cookoo can be used as effective and cheap tool to monitor the high bird diversity in different European countries.     

Contributions of Robert (Bob) J. O’Neil to the field of predaceous Heteroptera

Predaceous Heteroptera are important components of natural and managed habitats. The extent of predatory habits among taxa ranges from those that are totally (or nearly totally) predaceous to those that are nearly totally phytophagous, but occasionally feed on arthropod prey. Because of that variability in predatory habit, the contributions of heteropteran taxa to management of pest species will vary greatly. The late Robert (Bob) J. O’Neil (1955–2008) added significantly to understanding the roles of and benefits from facultatively predaceous Heteroptera. His focus on behavioral and physiological attributes that permitted facultatively predaceous species to persist in agricultural habitats demonstrated that facultative predators could help prevent pest outbreaks, but were less effective at reducing numbers of species already considered above economic thresholds.     

Quantifying the effects of predators on aphid populations

Four methods of analysis based on a simple population model and applicable to aphid and predator field density data are described. Two of the analyses determine the extent to which predators accounted for an observed change in aphid densities, and the other two estimate by how much the aphid population would have increased if the predators had not been present. The methods are illustrated with examples taken from cereal aphid research, and their advantages and limitations are discussed.

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Résumé Quatre méthodes d'analyse, basées sur un modèle de population simple, applicables aux données concernant les densités de pucerons et de prédateurs dans la nature, sont décrites. Deux des analyses déterminent l'importance de l'intervention des prédateurs lorsque l'on observe une modification de la densité de pucerons; les deux autres estiment de combien la population de pucerons aurait dû s'accroître en l'absence de prédateurs. Ces méthodes sont illustrées d'exemples tirés des recherches sur les pucerons des céréales. Possibilités et limites de ces méthodes sont discutées.

     

Attraction of Allodorylaimus americanus (Nematoda: Dorylaimida) towards different prey nematodes and factors influencing this attraction

Abstract

The attraction of Allodorylaimus americaus towards excised (cut into two pieces) and non-excised (live) individuals of plant parasitic nematodes viz., Tylenchorhynchus mashhoodi, Hoplolaimus indicus, Helicotylenchus indicus, Hirschmanniella oryzae, Xiphinema americanum and Hemicriconemoides mangiferae used as prey were tested in a Petri dish. A. americanus responded positively and significantly to prey kairomones but showed variation in their individual behaviour. A. americanus was most attracted towards excised individuals of T. mashhoodi. The differential responses of A. americanus towards different prey were attributed to the inert behaviour of the predator, their preference for a particular species of prey, chemical composition, concentration, quality, quantity of prey attractant, formation of minimum perceptible attraction gradient of prey and minimum response threshold of predators. Different factors such as temperature, period of prey incubation, prey density, starvation of predators, agar concentration, and agar thickness governed the attraction responses of the predator. A. americanus responded maximally towards T. mashhoodi, when tested as 5-day starved predators in agar plates containing a 2 mm thick layer of 1% water-agar with 200 prey individuals previously incubated for 16 h at 30°C.