Disturbance cues as a source of risk assessment information under natural conditions

1. Disturbance cues are released by stressed or disturbed prey prior to a predator attack and convey useful risk assessment information regarding local threats. While studies have shown that disturbance cues may be important early on within the predation sequence (prior to an attack), their role in predator–prey interactions remains relatively overlooked by ecologists. Critically, experimental studies examining disturbance cues, especially among prey fishes, have been conducted primarily under laboratory or semi-natural conditions.
2. Here, we tested the prediction that disturbance cues function as sources of risk assessment information in situ. We exposed Trinidadian guppies, in two natural populations differing in predation risk, to a model predator paired with stream water or the disturbance cue collected from guppies from either a high- or low-predation risk population.
3. We found that the predator inspection response of guppies to disturbance cues depends on the level of risk of both the focal and the cue source population. Guppies from both populations exhibited increased latencies to inspect, lower inspection rates and reduced inspecting group sizes towards the model paired with conspecific disturbance cues versus a stream water control. Interestingly, guppies of both populations showed evidence of higher perceived predation risk towards the disturbance cues collected from high-predation risk donors compared to low-predation risk donors.
4. Our results support the hypothesis that disturbance cues function as a source of information used by prey fish in the assessment of predation risk and provide the first evidence of disturbance cue function under fully natural conditions.

     

Onset of morning activity in bumblebee foragers under natural low light conditions

Foraging on flowers in low light at dusk and dawn comes at an additional cost for insect pollinators with diurnal vision. Nevertheless, some species are known to be frequently active at these times. To explore how early and under which light levels colonies of bumblebees, Bombus terrestris, initiate their foraging activity, we tracked foragers of different body sizes using RFID over 5 consecutive days during warm periods of the flowering season. Bees that left the colony at lower light levels and earlier in the day were larger in size. This result extends the evidence for alloethism in bumblebees and shows that foragers differ in their task specialization depending on body size. By leaving the colony earlier to find and exploit flowers in low light, larger‐sized foragers are aided by their more sensitive eyes and can effectively increase their contributions to the colony''s food influx. The decision to leave the colony early seems to be further facilitated by knowledge about profitable food resources in specific locations. We observed that experience accrued over many foraging flights determined whether a bee started foraging under lower light levels and earlier in the morning. Larger‐sized bees were not more experienced than smaller‐sized bees, confirming earlier observations of wide size ranges among active foragers. Overall, we found that most foragers left at higher light levels when they could see well and fly faster. Nevertheless, a small proportion of foragers left the colony shortly after the onset of dawn when light levels were below 10 lux. Our observations suggest that bumblebee colonies have the potential to balance the benefits of deploying large‐sized or experienced foragers during dawn against the risks and costs of foraging under low light by regulating the onset of their activity at different stages of the colony''s life cycle and in changing environmental conditions.     

Cannibalism and intraguild predation in Typhlodromus exhilaratus and T. phialatus (Acari: Phytoseiidae) under laboratory conditions

Two species of Phytoseiidae are found in the same agroecosystem: Typhlodromus exhilaratus prevails in vine plots, while T. phialatus prevails in uncultivated surrounding areas. The objective of the present paper was to investigate whether the poor settlement of T. phialatus in vine plots can be explained by intraguild predation of these two species and/or cannibalism. Predatory abilities of the females on larvae and protonymphs were studied under laboratory conditions. A first experiment was conducted with only conspecific or heterospecific phytoseiid prey, in a second experiment Tetranychus urticae eggs were added to the phytoseiid prey. Oviposition, prey consumption, and escape rates of females were recorded. Oviposition and intraguild predation rates were higher for T. exhilaratus than for T. phialatus. Typhlodromus exhilaratus consumed fewer conspecifics than heterospecific phytoseiids, and oviposited when feeding on both diets. Typhlodromus phialatus consumed equal amounts of con- and heterospecifics. Although these two generalist predators belong to the type III defined by McMurtry and Croft (Annual Review of Entomology 42:291–321, 1997), our results suggest that they have different predation behaviour. However, because these results were obtained in experiments where no choice was given between the two phytoseiid species, they are difficult to link to previous studies conducted on the intraguild predation of the Phytoseiidae. The greater voracity and prolificacy of T. exhilaratus could partially explain the poor settlement of T. phialatus in vineyards and the predominance of T. exhilaratus. However, a full understanding of this phenomenon will require the study of other factors, such as susceptibility to pesticides and micro-climatic conditions, as well as the ability to cope with different food sources and host plants.     

Behavioural strategies of cormorants (Phalacrocoracidae) foraging under challenging light conditions

Diving is indicative of foraging in cormorants (Phalacrocoracidae). We have investigated a range of parameters associated with diving in Great Cormorants Phalacrocorax carbo to provide insight into the bases of cormorant predatory strategies. We hypothesize that if vision is important in cormorant foraging behaviour, and if they are not constrained by the position of their prey in the water column, then diving behaviour will be modulated primarily in response to the diel variation in ambient light levels. Specifically, we propose that cormorants forage at shallower depths when light levels are low, and more deeply when light levels are high. We provide evidence that this is the case. We recorded the occurrence of cormorant diving behaviour using implanted data loggers and recorded ambient light levels and water temperature using leg-mounted loggers in a sample of free-living Great Cormorants in Greenland. Our results show that dives are shallower at the beginning and end of each day when light levels are lower. We suggest that these data support the hypothesis that cormorant foraging is visually-guided even though recent evidence has shown that their underwater visual acuity is poor.     

Stimulus discrimination by horses under scotopic conditions

Scotopic vision in horses (Equus caballus) was investigated using behavioral measurements for the first time. Four horses were tested for the ability to make simple visual discriminations of geometric figures (circles and triangles) under various brightness levels within an enclosed building. Measurements of brightness ranging from 10.37 to 24.12 magnitudes per square arcsecond (mag/arcsec²; in candelas per square meter—7.70 to 2.43E-05 cd/m²) were taken using a Sky Quality Meter. These values approximated outdoor conditions ranging from twilight in open country to a dark moonless night in dense forest. The horses were able to solve the discrimination problems in all brightness settings up to 23.77 mag/arcsec² (3.35E-05 cd/m²). Moreover, they easily navigated their way around obstacles located within the testing area in extremely dim light (>23.50 mag/arcsec²; 4.30E-05 cd/m²), which were in conditions too dark for the human experimenters to see. These findings support physiological data that reveal a rod-dominated visual system as well as observations of equine activity at night.     

Beyond the response—High throughput behavioral analyses to link genome to phenome in Caenorhabditis elegans

The development and application of methods for automated behavioral analysis have revolutionized behavioral genetics across model organisms. In this review we summarize the history of automated behavioral analysis in the nematode Caenorhabditis elegans. We highlight recent studies of learning and memory to exemplify just how complex the genetic and neural circuit mechanisms underlying a seemingly simple single behavioral response can be. We finish by looking forward at the exciting prospects of combing genomic technologies with connectomic and phenomic level measurements.     

High cleavage specificity of a subtilisin-like protease from a hyperthermophilic archaeon under extreme conditions

The cleavage specificity of Pernisine, a subtilisin-like protease from the hyperthermophilic archaeon Aeropyrum pernix, was established by mass spectrometry, analysing the peptides generated by digestion of oxidised bovine insulin B chain. The specificity was explored by changing several factors such as substrate/enzyme ratio, temperature and reaction media. Using a S/E ratio of 1000 (w/w) and a temperature of 60 °C, five primary cleavage sites in the insulin B chain were detected suggesting a broad specificity of Pernisine, which is different from that found for other bacterial subtilisin-like proteases. When the S/E ratio and/or temperature were increased, a higher selectivity of Pernisine was observed with a unique cleavage site occurring between Leu15 and Tyr16. In addition, the influence on the enzymatic hydrolysis of different organic solvent concentrations was investigated. The results demonstrated that Pernisine could specifically digest the peptide substrate even in the presence of 80% acetonitrile solution or 30% dimethyl sulfoxyde. Thereby the cleavage specificity of Pernisine can be opportunely modulated by controlling the in vitro digestion conditions, suggesting that this enzyme could be an attractive candidate to use in a variety of biotechnological applications.     

Drosophila rely on learning while foraging under semi‐natural conditions

Learning is predicted to affect manifold ecological and evolutionary processes, but the extent to which animals rely on learning in nature remains poorly known, especially for short‐lived non‐social invertebrates. This is in particular the case for Drosophila, a favourite laboratory system to study molecular mechanisms of learning. Here we tested whether Drosophila melanogaster use learned information to choose food while free‐flying in a large greenhouse emulating the natural environment. In a series of experiments flies were first given an opportunity to learn which of two food odours was associated with good versus unpalatable taste; subsequently, their preference for the two odours was assessed with olfactory traps set up in the greenhouse. Flies that had experienced palatable apple‐flavoured food and unpalatable orange‐flavoured food were more likely to be attracted to the odour of apple than flies with the opposite experience. This was true both when the flies first learned in the laboratory and were then released and recaptured in the greenhouse, and when the learning occurred under free‐flying conditions in the greenhouse. Furthermore, flies retained the memory of their experience while exploring the greenhouse overnight in the absence of focal odours, pointing to the involvement of consolidated memory. These results support the notion that even small, short lived insects which are not central‐place foragers make use of learned cues in their natural environments.     

MIZ1-regulated hydrotropism functions in the growth and survival of Arabidopsis thaliana under natural conditions

Background and Aims

Root hydrotropism is a response to water-potential gradients that makes roots bend towards areas of higher water potential. The gene MIZU-KUSSEI1 (MIZ1) that is essential for hydrotropism in Arabidopsis roots has previously been identified. However, the role of root hydrotropism in plant growth and survival under natural conditions has not yet been proven. This study assessed how hydrotropic response contributes to drought avoidance in nature.

Methods

An experimental system was established for the study of Arabidopsis hydrotropism in soil. Characteristics of hydrotropism were analysed by comparing the responses of the miz1 mutant, transgenic plants overexpressing MIZ1 (MIZ1OE) and wild-type plants.

Key Results

Wild-type plants developed root systems in regions with higher water potential, whereas the roots of miz1 mutant plants did not show a similar response. This pattern of root distribution induced by hydrotropism was more pronounced in MIZ1OE plants than in wild-type plants. In addition, shoot biomass and the number of plants that survived under drought conditions were much greater in MIZ1OE plants.

Conclusions

These results show that hydrotropism plays an important role in root system development in soil and contributes to drought avoidance, which results in a greater yield and plant survival under water-limited conditions. The results also show that MIZ1 overexpression can be used for improving plant productivity in arid areas.     

Plant choice,herbivory and weight gain of wood crickets under the risk of predation

Predators can indirectly reduce herbivory by killing herbivores. In addition, predation risk can influence the feeding rate and feeding location of herbivores. Herbivores are expected to avoid plants currently occupied by a predator. Consequently, less herbivory is expected on plants bearing fresh predator cues. We examined whether wood crickets, Nemobius sylvestris Bosc (Orthoptera: Gryllidae), avoided plants bearing the chemical cues of nursery web spiders, Pisaura mirabilis Clerck (Araneae: Pisauridae), or red wood ants, Formica rufa L. (Hymenoptera: Formicidae). We conducted a series of behavioural experiments, in which crickets had the choice between a plant with spider or ant cues vs. a control plant, a plant with spider cues vs. a plant with ant cues, or two control plants. For all plants, we quantified leaf damage and the position and weight change in the crickets. Crickets avoided plants with spider cues. In contrast, ant cues did not significantly deter crickets. The herbivory pattern among the plants reflected the plant choice of the crickets. However, net herbivory was not affected by the presence of predator cues. Thus, our results suggest that spider cues affect feeding location rather than the total amount of herbivory.