Embedding information flows within ecological networks

Natural communities form networks of species linked by interactions. Understanding the structure and dynamics of these ecological networks is pivotal to predicting species extinction risks, community stability and ecosystem functioning under global change. Traditionally, ecological network research has focused on interactions involving the flow of matter and energy, such as feeding or pollination. In nature, however, species also interact by intentionally or unintentionally exchanging information signals and cues that influence their behaviour and movement. Here we argue that this exchange of information between species constitutes an information network of nature-a crucial but largely neglected aspect of community organization. We propose to integrate information with matter flow interactions in multilayer networks. This integration reveals a novel classification of information links based on how the senders and receivers of information are embedded in food web motifs. We show that synthesizing information and matter flow interactions in multilayer networks can lead to shorter pathways connecting species and a denser aggregation of species in fewer modules. Ultimately, this tighter interconnectedness of species increases the risk of perturbation spread in natural communities, which undermines their stability. Understanding the information network of nature is thus crucial for predicting community dynamics in the era of global change.

Antlion larvae localize long distant preys by a mechanism based on time difference

Pit building antlions Euroleon nostras have been submitted to artificial cues in order to delineate their faculty to localize a prey. Series of propagating pulses in sand have been created from an extended source made of 10 piezoelectric transducers equally spaced on a line and located at a large distance from the pit. The envelope of each pulse encompasses six oscillations at a carrier frequency of 1250 Hz and up to eight oscillations at 1666 Hz. In one set of experiments, the first wave front is followed by similar wave fronts and the antlions respond to the cue by throwing sand in the opposite direction of the wave front propagation direction. In another set of experiments, the first wave front is randomly spatially structured while the propagation of the wave fronts inside the envelope of the pulse are not. In that case, the antlions respond less to the cue by throwing sand, and when they do, their sand throwing is more randomly distributed in direction. The finding shows that the localization of vibration signal by antlions are based on the equivalent for hearing animals of interaural time difference in which the onset has more significance than the interaural phase difference.

Acacia Ants Respond to Plant-Borne Vibrations Caused by Mammalian Browsers

Living in the African savanna is dangerous, especially for plants. Many plants therefore engage in mutualism with ants, in which plants provide food and shelter in exchange for protection against herbivores. Ants become alarmed when the plant takes on some sort of damage. They immediately emerge from their plant shelter and aggressively defend the plant. Mammalian herbivores can have devastating effects on trees by browsing, breaking tree branches, stripping bark, and pushing over entire trees. However, mutualistic ants substantially reduce the amount of damage. To efficiently protect the tree, ants need to rapidly react together when the tree is under attack. Here, we show that the acacia ant Crematogaster mimosae defends its host tree by exploiting plant-borne vibrations caused by browsers feeding on the tree. Experiments with controlled vibrations show that ants discriminate browser-induced vibrations from those induced by wind, become alarmed, and patrol on the branches. Browser-induced vibrations serve as a long-distance alarm cue. The vibrations propagate through the whole acacia tree and trigger ants' defensive behavior, even on the other side of the tree. Furthermore, the ants make use of tropotactic directional vibration sensing to orient to the attacked part of the tree and fight back the attacker.

Adult-larval vibrational communication in paper wasps: the role of abdominal wagging in Polistes dominula

Communication through vibrational signals is widespread among social insects and regulates crucial social activities. Females of the social wasp Polistes dominula produce substrate-borne vibrations on the combs by performing a conspicuous abdominal oscillatory behavior, known as abdominal wagging. Several studies have reported correlative evidence in support of its signaling role, but direct evidence is still lacking. Because abdominal wagging is strictly associated with the presence of larvae in the nest and with cell inspection, it has been suggested that it could be involved in adult-larvae communication. According to this hypothesis, abdominal wagging vibrations would have short-term effects related to food and trophallactic exchanges between adults and larvae by modulating salivary secretion (decreasing its amount, to prepare larvae to receive food, or stimulating the release of larval saliva to adults). Here, by using an electro-magnetic shaker, we assessed, for the first time, the short-term effects of abdominal wagging on larval behavior by recording larval responses and by measuring the amount of saliva released immediately after abdominal wagging playback. Our results show that larvae are able to perceive the substrate-borne vibrations produced by abdominal wagging and react by increasing the movement of their body, possibly in order to attract the attention of adult females during feeding nest inspection. Yet, we found that vibrations neither increase nor decrease the release of larval saliva. Our results support the hypothesis of the alleged role of vibrations in adult-larvae communications; however, they do not support the long-lasting hypothesis of salivary release modulation.

On the spot: utilization of directional cues in vibrational communication of a stink bug

Although vibrational signalling is among the most ancient and common forms of communication, many fundamental aspects of this communication channel are still poorly understood. Here, we studied mechanisms underlying orientation towards the source of vibrational signals in the stink bug Nezara viridula (Hemiptera, Pentatomidae), where female vibrational song enables male to locate her on the bean plant. At the junction between the main stem and the leaf stalks, male placed his legs on different sides of the branching and orientation at the branching point was not random. Analyses of signal transmission revealed that only a time delay between the arrival of vibrational wave to receptors located in the legs stretched across the branching was a reliable directional cue underlying orientation, since, unexpectedly, the signal amplitude at the branching point was often higher on the stalk away from the female. The plant and the position of the vibrational source on the plant were the most important factors influencing the unpredictability of the amplitude cue. Determined time delays as short as 0.5 ms resulted in marked changes in interneuron activity and the decision model suggests that the behavioural threshold is in the range between 0.3 and 0.5 ms.

Vibration-guided mate searching in treehoppers: directional accuracy and sampling strategies in a complex sensory environment

Animal movement decisions involve an action-perception cycle in which sensory flow influences motor output. Key aspects of the action-perception cycle involved in movement decisions can be identified by integrating path information with measurement of environmental cues. We studied mate searching in insects for which the primary sensory cues are mechanical vibrations traveling through the tissues of living plants. We mapped search paths of male thornbug treehoppers locating stationary females through an exchange of vibrational signals. At each of the males' sampling locations, we used two-dimensional laser vibrometry to measure stem motion produced by female vibrational signals. We related properties of the vibrational signals to the males' movement direction, inter-sample distance and accuracy. Males experienced gradients in signal amplitude and in the whirling motion of the plant stem, and these gradients were influenced to varying degrees by source distance and local stem properties. Males changed their sampling behavior during the search, making longer inter-sample movements farther from the source, where uncertainty is higher. The primary directional cue used by searching males was the direction of wave propagation, and males made more accurate decisions when signal amplitude was higher, when time delays were longer between the front and back legs, and when female responses were short in duration. The whirling motion of plant stems, including both the eccentricity and the major axes of motion, is a fundamental feature of vibrational environments on living plants, and we show for the first time that it has important influences on the decisions of vibrationally homing insects.

Directional vibration sensing in the leafcutter ant Atta sexdens

Leafcutter ants communicate with the substrate-borne component of the vibratory emission produced by stridulation. Stridulatory signals in the genus Atta have been described in different behavioural contexts, such as foraging, alarm signalling and collective nest building. Stridulatory vibrations are employed to recruit nestmates, which can localize the source of vibration, but there is little information about the underlying mechanisms. Our experiments reveal that time-of-arrival delays of the vibrational signals are used for tropotactic orientation in Atta sexdens. The detected time delays are in the same range as the time delays detected by termites. Chemical communication is also of great importance in foraging organization, and signals of different modalities may be combined in promoting the organization of collective foraging. Here we show that the tropotactic orientation to vibrational signals interacts with chemical communication signals.

Summary: Leafcutter ants communicate via substrate vibrations. Here we show that time delays between legs are used for orientation in a foraging context and that alarm pheromones interfere by changing the social context.

Escapes in copepods: comparison between myelinate and amyelinate species

Rapid conduction in myelinated nerves keeps distant parts of large organisms in timely communication. It is thus surprising to find myelination in some very small organisms. Calanoid copepods, while sharing similar body plans, are evenly divided between myelinate and amyelinate taxa. In seeking the selective advantage of myelin in these small animals, representatives from both taxa were subjected to a brief hydrodynamic stimulus that elicited an escape response. The copepods differed significantly in their ability to localize the stimulus: amyelinate copepods escaped in the general direction of their original swim orientation, often ending up closer to the stimulus. However, myelinate species turned away from the stimulus and distanced themselves from it, irrespective of their original orientation. We suggest that faster impulse conduction of myelinated axons leads to better precision in the timing and processing of sensory information, thus allowing myelinate copepods to better localize stimuli and respond appropriately.