Unconventional signalling in tunicates

The zooids in colonial tunicates do not appear to be directly interconnected by nerves, but this has not prevented the evolution of coordinated behaviour in several groups. In Botryllus and other colonial styelid asci‐dians the endothelium lining the blood vessels is excitable and transmits action potentials from cell to cell via gap junctions. These signals mediate protective contractions of the zooids and synchronize contractions of the vascular ampullae. In didemnid ascidians such as Diplosoma a network of myocytes in the tunic serves to transmit excitation and to cause contractions of the cloacal apertures. Individual zooids of Pyrosoma protect themselves by closing their siphons and arresting their branchial cilia when stimulated. At the same time a flash of light is emitted. Neighbouring zooids sense the flash with their photoreceptors and respond in turn with protective responses and light emission. Protective responses thus spread by photic signalling and propagate from zooid to zooid through the colony in a saltatory manner. In chains of Salpafusifortnis, changes in the direction and/or speed of swimming are transmitted from zooid to zooid via adhesion plaques. When a zooid is stimulated, its body‐wall epithelium conducts action potentials to the plaque connecting it to the next zooid, exciting receptor neurons in that zooid. These receptors have sensory processes that bridge the gap between the two zooids. The sensory neurons so excited in the second zooid conduct impulses to the brain where they alter the motor output pattern, and at the same time generate epithelial action potentials that travel to the next zooid in line, where the same thing happens.

It is not clear why these unconventional signalling methods have evolved but the tunic may be an inhospitable environment for nerves, making conventional nervous links impossible.     

Beyond black and white: divergent behaviour and performance in three rapidly evolving lizard species at White Sands

Determining which traits enable organisms to colonize and persist in new environments is key to understanding adaptation and ecological speciation. New environments can present novel selective pressures on colonists' morphology, behaviour, and performance, collectively referred to as ecomorphology. To investigate ecomorphological change during adaptation and incipient ecological speciation, we measured differences in morphology (body shape and size), behaviour (startle response), and performance (sprint speed) in three New Mexican lizard species: Holbrookia maculata, Sceloporus undulatus, and Aspidoscelis inornata. Each species is represented by dark morphs, cryptic on the brown adobe soils of the Chihuahuan Desert, and white morphs, cryptic on the gypsum substrate of White Sands. For each species, we then determined the effects of morphology and startle response on sprint speed on matched and mismatched substrate. For two of the three species, white morphs had larger body size and longer limbs. However, we found no statistical evidence that these morphological differences affected sprint speed. Colour morphs also exhibited different escape responses on the two substrates: in all species, dark morphs were less likely to immediately sprint from a simulated predator on white sand. As a result, escape response had a significant effect on sprint speed for two of the three species. Not surprisingly, all lizards sprinted faster on dark soil, which was probably due to the lizards' more immediate escape response and the higher compaction of dark soil. The relationship between escape response and sprint performance across the dark soil and white sand habitats suggests that behavioural differences may be an important component of adaptation and speciation in new environments. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 169–182.     

Are fleeing ”noisy” lizards signalling to predators?

Many prey signal to predators with the intention of deterring further pursuits. In the lizard Psammodromus algirus, individuals sometimes escape with noisy long runs on dry leaves, whereas on many other occasions they escape quietly and with short flights. We hypothesised that the duration of this noisy display might be considered as an auditory signal of their alertness and ability to escape directed to predators. We examined in the field the escape behaviour of the lizard P. algirus in response to a human observer acting as a predator and tested a series of predictions to analyse this hypothesis. During a noisy escape response, lizards escaped sooner and ran further and for a longer time, while passing potential refuges before hiding. Production of noise was not entirely dependent on environmental factors, such as temperature or microhabitat, and was not directed to warn conspecifics because most individuals were solitary. Lizards still made noise when concealed and in response to successive approaches, which might be interpreted as a signal of alertness to the predator approach. In addition, condition of individuals with noisy responses could be assessed from their ability to run further and for a longer time, and because, in contrast to quiet responses, speed and distance were not positively correlated with environmental temperature. Thus, they might be in a better condition or internal state because they were able to run at high speed under unfavourable conditions. We suggest that lizards with noisy escape responses might be honestly signalling their alertness and ability to escape to avoid being chased. Received: 7 February 2000 / Received in revised form: 25 May 2000 / Accepted: 30 May 2000     

Experimental test of the influence of light availability on the evolution of eye size and behaviour in Daphnia

There exists extensive variation in eye size. Much work has provided a connection between light availability and differences in eye size across taxa. Experimental tests of the role of the light environment on the evolution of eye size are lacking. Here, we performed a selection experiment that examined the influence of light availability on shifts in eye size and the connection between eye size and phototactic (anti-predator) behaviour in Daphnia. We set-up replicate experimental populations of Daphnia, repeatedly evaluated phenotypic shifts in eye size during the ~50-day experiment, and performed a common garden experiment at the end of the experiment to test for evolutionary shifts in eye size and behaviour. Our phenotypic analyses showed that eye size rapidly diverged between the light treatments; relative eye size was consistently larger in the low versus high light treatments. Selection on eye size was also modified by variation in density as increases in Daphnia density favoured a larger eye. However, we did not observe differences in eye size between the light treatments following two generations of common garden rearing at the end of the experiment. We instead observed strong shifts in anti-predator behaviour. Daphnia from the low light treatment exhibited decreased phototactic responses to light. Our results show that decreased light relaxes selection on anti-predator behaviour. Such trends provide new insights into selection on eye size and behaviour.     

Responses to conspecific and heterospecific disturbance odours in the Australian crayfish Euastacus armatus and Cherax destructor

The responses of individuals of Cherax destructor and Euastacus armatus to water containing stressed or unstressed crayfish were tested in the laboratory. Individuals of E. armatus showed only an increase in locomotion when stressed crayfish water was introduced. Individuals of C. destructor showed a decrease in the time spent in a lowered posture, an increase in the time spent in the raised posture and in grooming behaviour when stressed crayfish water was introduced. Individuals of C. destructor responded more strongly to heterospecific animals (Cherax rotundus and E. armatus) than to conspecifics. The levels of responses to the two heterospecific species were similar.     

Epithelial conduction: recent findings,old questions,and where do we go from here?

Work on the roles of excitable epithelia in hydromedusan behaviour is reviewed from the historical point of view. Of special interest are cases where epithelial impulses excite or inhibit nerves. It is suggested that nerves running in the endoderm canals as described in several species with excitable endodermal epithelia may function to convey excitation to nerves in the ectoderm, but the precise pathways and mechanisms whereby epithelial depolarizations lead to the generation or suppression of neurally mediated processes are still poorly understood. Recent work on feeding in Aglantha digitaleshows a component (lip-flaring) that may be a version of the crumpling behaviour seen in other medusae. The pathways mediating feeding and crumpling behaviours are reviewed.     

Responses to Light in Epigean and Hypogean Populations of Gambusia Affinis (Cyprinodontiformes: Poeciliidae)

The responses to light among the fish Gambusia affinis, permanent residents of hypogean brackish water basins of the Spunnulate dolinas system of Torre Castiglione, in southeastern Italy, were studied at light intensities of 180 and 430 lux. These fish showed, on the average, a negative phototactic behaviour (scotophilia) with a low coefficient of variability. On the other hand, epigean, spring-dwelling individuals of G. affinis from the same region showed a positive phototactic behaviour with a greater variability in the responses when compared with cave-dwelling conspecifics. Possible causes for the detachment of hypogean from epigean forms are discussed.     

The effect of different chiral morphs on visitation rates and fruit set in the orchid Spiranthes spiralis

Background: The arrangement of flowers on inflorescences is important for determining the movement of pollinators within the inflorescence and, consequently, the overall mating success and fruit set of a plant.

Aims: Spiranthes spiralis is an orchid that has a spiralled inflorescence. The species has two chiral forms that show opposite coiling directions (clockwise and anti-clockwise). We tested if this arrangement of inflorescence influences pollinator attraction and behaviour.

Methods: We surveyed two natural populations, analysed the reproductive compatibility of the two morphs and estimated pollination success in natural and experimental populations.

Results: We found that the two morphs were not isolated by pre- or post-mating barriers, occurred with a similar proportion in natural populations and showed similar levels of pollination success both in natural and artificial populations. However, we found a different pattern of pollination success along the inflorescences. In the two morphs, lower flowers experienced a higher pollination rate and this rate decreased along the inflorescence faster in anti-clockwise than in clockwise individuals.

Conclusions: This finding suggests that pollinators visit the flowers sequentially from the lower part of the inflorescences and leave the anti-clockwise individuals more rapidly than the clockwise ones. However, this pollinator behaviour is not detrimental for the pollination success of either of the two morphs.     

Formicidal activity of indole derivatives on Atta opaciceps (Borgmeier): Lethal,behavioural and locomotive effects

The leaf‐cutting ants of the genus Atta are of extreme importance for agriculture and forestry. Few active products can be employed to control these pests and, therefore, the discovery of new insecticidal products represents a fundamental strategy for its management. In this study, we evaluated the mortality, behaviour and locomotion of workers of Atta opaciceps (Borgmeier) exposed to synthesized indole derivatives. The most active compound was 4d [1‐(1H‐indol‐3‐yl)pentan‐1‐one] (LD₅₀ = 0.018 μg/mg), while the 4e [1‐(1H‐indol‐3‐yl)hexan‐1‐one] (LD₅₀ = 3.82 μg/mg) was the least active compound. These two derivatives reduced the survival of A. opaciceps over time and altered the behaviour and locomotion of these ants. This study demonstrates the potential of indole derivatives to produce new formicidal products, since, in addition to being effective, it also affects the ant's behaviour and locomotion.     

Locomotion and shell-righting behaviour in adult and juvenile Aporrhais occidentalis (Gastropoda: Strombacea)

Differences in behaviour between adult and juvenile Aporrhais occidentalis are related to age-dependent changes in shell morphology and habitat. Juvenile snails right their shells by pulling with the propodium, and do not ‘kick’ at the substratum until the expanded outer lip of the adult shell has formed. Locomotion of juveniles is by arhythmical crawling, with ‘leaping’ taking place only during escape from predators. Adult snails leap during both normal and escape locomotion. Data are presented that demonstrate the importance of the outer lip in stabilizing the shell during leaping locomotion. Escape reactions of A. occidentalis are similar to, but slower than, those reported in the literature for species of strombids. Most of the basic locomotory and shell-righting behaviour patterns seen in the highly specialized Strombidae are observable in the more primitive A. occidentalis. However, the use of the operculum in locomotion and shell righting, although characteristic of the Strombidae, is not found in A. occidentalis. The behaviour of Aporrhais is discussed in relation to evolution within the superfamily Strombacea.     

Relative Cost/Benefit Trade‐Off Between Cover‐Seeking and Escape Behaviour in an Ancestral Fish: The Importance of Structural Habitat Heterogeneity

Fleeing from predators and moving into protective habitats are two common antipredator behaviours in the animal kingdom. Surprisingly, the relative cost/benefit trade‐off of each behavioural option has rarely been examined empirically. Here, we investigate the interplay between decisions surrounding escape behaviour and rocky microhabitat occupancy in lake sturgeon, Acipenser fulvescens. In high‐risk clear‐water environments, sturgeon responded to danger by evoking an escape response and by seeking cover in rocky microhabitats. However, in low‐risk turbid environments, we found that sturgeon responded to danger by seeking cover in rocky microhabitats, but not fleeing to a significant degree. Cover‐seeking behaviour may therefore be a relatively low‐cost/high‐benefit antipredator strategy. These findings highlight the importance of structural habitat heterogeneity for prey animals in predator‐dominated landscapes.     

Agonistic behaviour in final-instar larvae of Austrolestes colensonis (Odonata: Lestidae)

Abstract

The agonistic displays of Austrolestes colensonis larvae are described. A terminology is developed to classify larval agonistic displays in the family Lestidae.     

Competitive Exclusion,Harem Behaviour and Host Specificity of the Water Mite Unionicola ypsilophora (Hydrachnellae,Acari) Inhabiting Anodonta cygnea (Unionidae)

The co-occurring freshwater mussels Anodonta cygnea and A. anatina serve as hosts for the water mites Unionicola ypsilophora and U. intermedia, respectively. Male U. ypsilophora display a territorial behaviour. They fight with other males, and as a result, there is usually only one male per host. As a consequence, this intrasexual aggression results in female-defence polygyny, or a harem mating system. In contrast, U. intermedia shows no antagonistic behaviour between males. A. cygnea can serve as a host for U. intermedia, but this mite species apparently is excluded from the mussel by U. ypsilophora. In this way, U. intermedia is restricted by competitive exclusion to the mussel A. anatina.     

Conspicuous blue tails,dorsal pattern morphs and escape behaviour in hatchling Iberian wall lizards (Podarcis hispanicus)

Predation has profound effects on the phenotypes of animal prey and, in lizards, the relationship between coloration and antipredatory behaviour has been studied in depth. However, studies that address the relationships between dorsal patterns and tail coloration with escape behaviour in polymorphic lizards are absent in the literature. We describe dorsal morphs and measured tail coloration and escape behaviour in hatchling Iberian wall lizards, Podarcis hispanicus, a species with a previously undescribed female‐restricted dorsal polymorphism (reticulated‐blotched males, and either striped or reticulated‐blotched females) and juvenile tails with conspicuous blue coloration, which is probably used to divert predator attacks towards the autotomizable tail. Overall we provide evidence for the existence of sexual dimorphism in tail ultraviolet reflectance between reticulated females and males, with striped females being intermediate. We identified sex/dorsal morph, body size and tail brightness as predictors of different aspects of escape behaviour and suggest the existence of two alternative escape strategies between striped and reticulated‐blotched females that may be dependent on dorsal morph differences, independently of sex. Reticulated‐blotched females, and also males (all reticulated‐blotched), ran faster and spent less time paused than striped females, which might reflect an escape behaviour strategy based on endurance in striped females. In addition, lowland males displayed tail waving as a ‘last resort’ antipredator strategy that may be related to fatigue. We concluded that hatchling antipredatory behaviour is influenced by both dorsal pattern and tail conspicuousness. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 1094–1106.     

Distribution of Nerve Elements Showing FMRFamide-like Immunoreactivity in Hydromedusae

Immunofluorescence tests with antisera to various peptides reveal the presence of a FMRFamide-like peptide in neurons of hydromedusae belonging to three orders. An avian pancreatic polypeptide-like peptide may also be present in certain neurons. Distribution of FMRFamide-like immunoreactivity (Fa-IR) has been studied in Proboscidactyla (O. Limnomedusae), Phialidium and Aequorea (O. Leptomedusae) and Aglantha (O. Trachymedusae). These findings are compared with results obtained with Polyorchis (O. Anthomedusae) by Grimmelikhuijzen and Spencer [J. comp. Neurol. 230 , 361 (1984)]. All species show Fa-IR neurons in the tentacles linked by interconnecting neurites running in the outer marginal nerve ring. A Fa-IR plexus is present in the manubrium and, except in Aglantha, this system merges with a plexus associated with the subumbrellar radial muscles. As in Polyorchis, the swimming motor neurons are unstained. In contrast to this species, only a small percentage of the neurites composing the nerve rings are stained. The giant axons of Aglantha show no Fa-IR. The cnidothylaces of Proboscidactyla contain neurons reacting with antisera to FMRFamide and APP. Present evidence suggests that in hydromedusae Fa-IR is confined to distinct subsets of neurons. These appear to be either sensory units or units supplying smooth muscles, but they are not involved in the innervation of striated muscles.     

Danger detection and escape behaviour in wood crickets

The wind-sensitive cercal system of Orthopteroid insects that mediates the detection of the approach of a predator is a very sensitive sensory system. It has been intensively analysed from a behavioural and neurobiological point of view, and constitutes a classical model system in neuroethology. The escape behaviour is triggered in orthopteroids by the detection of air-currents produced by approaching objects, allowing these insects to keep away from potential dangers. Nevertheless, escape behaviour has not been studied in terms of success. Moreover, an attacking predator is more than “air movement”, it is also a visible moving entity. The sensory basis of predator detection is thus probably more complex than the perception of air movement by the cerci. We have used a piston mimicking an attacking running predator for a quantitative evaluation of the escape behaviour of wood crickets Nemobius sylvestris. The movement of the piston not only generates air movement, but it can be seen by the insect and can touch it as a natural predator. This procedure allowed us to study the escape behaviour in terms of detection and also in terms of success. Our results showed that 5-52% of crickets that detected the piston thrust were indeed touched. Crickets escaped to stimulation from behind better than to a stimulation from the front, even though they detected the approaching object similarly in both cases. After cerci ablation, 48% crickets were still able to detect a piston approaching from behind (compared with 79% of detection in intact insects) and 24% crickets escaped successfully (compared with 62% in the case of intact insects). So, cerci play a major role in the detection of an approaching object but other mechanoreceptors or sensory modalities are implicated in this detection. It is not possible to assure that other sensory modalities participate (in the case of intact animals) in the behaviour; rather, than in the absence of cerci other sensory modalities can partially mediate the behaviour. Nevertheless, neither antennae nor eyes seem to be used for detecting approaching objects, as their inactivation did not reduce their detection and escape abilities in the presence of cerci.     

Orchestrating the score: complex multimodal courtship in the Habronattus coecatus group of Habronattus jumping spiders (Araneae: Salticidae)

Jumping spiders in the genus Habronattus use complex multimodal signals during courtship displays. In the present study, we describe multimodal displays from the Habronattus coecatus clade, comprising a diverse group of 23 described species. Habronattus coecatus group displays are made up of sex‐specific ornamentation and temporally coordinated combinations of motion displays and vibratory songs. Vibratory songs are complex, consisting of up to 20 elements organized in functional groupings (motifs) that change as courtship progresses. This temporal structuring of displays is analogous to a musical composition. Vibratory elements are associated with movement displays involving coloured and patterned ornaments on the male body. We describe general patterns of multimodal displays for 11 species including one, Habronattus borealis, which appears to have lost complex display behaviour. Habronattus coecatus group courtship is one of the most complex communication systems yet described in arthropods and this group may reveal important factors driving the evolution of complex signals. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 522–547.     

Locomotion and Escape Modes in Rodents of the Monte Desert (Argentina)

Modes of locomotion and escape tactics are attributes that affect the structure of animal communities, promoting exploitation of different microhabitats and the coexistence of different species. Bipedal locomotion is considered to be more effective than a quadrupedal gait in escaping attacks by predators because it allows for higher speed, a faster response to attack, sudden changes of direction and better detection of aerial raptors. The aim of this study was to determine the type of locomotion used at the moment of escape by three rodent species of the Monte desert –Eligmodontia typus, Akodon molinae and Graomys griseoflavus. The study was carried out in three plant communities of the Ñacuñán Reserve (Mendoza). All three species showed differences in both mode of escape and locomotory pattern. Graomys griseoflavus exhibited the highest proportion of escapes using quadrupedal saltation. The mode of locomotion employed by E. typus varied according to the type of plant communities it inhabited. Those occurring at open sites (Medanal community) exhibited a greater propensity to jump during escapes than those from more sheltered habitats (Algarrobal community). Akodon molinae relied primarily on a quadrupedal gait when fleeing from predators, which would explain its greater dependence on plant cover. Therefore, the morphological and behavioural characteristics of these species are related to their mode of locomotion and the strategies they employ to diminish the risk of predation.     

Are antipredator behaviours of hatchery Salmo salar juveniles similar to wild juveniles?

This study explores how antipredator behaviour of juvenile Atlantic salmon Salmo salar developed during conventional hatchery rearing of eggs from wild brood stock, compared with the behaviour of wild‐caught juveniles from the same population. Juveniles aged 1+ years were tested in two unfamiliar environments; in one S. salar were presented with simulated predator attacks and in the other they were given the opportunity to explore an open‐field arena. No difference was found in their spontaneous escape responses or ventilation rate (reflex responses) after simulated predator attacks. Hatchery‐reared juveniles were more risk‐prone in their behaviours than wild‐caught individuals. Hatchery juveniles stayed less time in association with shelter. In the open‐field arena, hatchery juveniles were more active than wild juveniles. Hatchery juveniles were also immobile for less time and spent a shorter amount of time than wild juveniles in the fringe of the open‐field arena. Salmo salar size had no effect on the observed behaviour. Overall, this study provides empirical evidence that one generation of hatchery rearing does not change reflex responses associated with threats, whereas antipredator behaviour, typically associated with prior experience, was less developed in hatchery‐reared than in wild individuals.     

A review of shark agonistic displays: comparison of display features and implications for shark–human interactions

Agonistic displays in 23 species of sharks of six families are described and illustrated. These displays are reviewed in terms of ethological concepts and shark hydrodynamic models. Shark agonistic displays feature many common elements rendering them readily distinguishable from normal swimming and pseudodisplays caused by sharksucker irritation. Shark agonistic displays are most readily elicited by rapid, direct diver approach when food is absent and potential escape routes restricted. Such displays appear to be motivated by defence of self or the immediately surrounding space rather than defence of territory or resources. Costs and benefits of display versus attack in shark–shark and shark–diver contests are evaluated using payoff matrices and optimal strategies are identified. Shark–human interactions are modelled in terms of a system of nested critical approach distances. For divers faced with a displaying shark, responses which may decrease the likelihood of defensive attack are suggested. Recommendations for future work on shark agonistic behaviour are offered.