Sex-specific visual performance: female lizards outperform males in motion detection

In animal communication, complex displays usually have multiple functions and, male and female receivers often differ in their utilization and response to different aspects of these displays. The perceptual variability hypothesis suggests that different aspects of complex signals differ in their ability to be detected and processed by different receivers. Here, we tested whether receiver male and female Sceloporus graciosus lizards differ in visual motion detection by measuring the latency to the visual grasp response to a motion stimulus. We demonstrate that in lizards that largely exhibit complex motions as courtship signals, female lizards are faster than males at visually detecting motion. These results highlight that differential signal utilization by the sexes may be driven by variability in the capacity to detect different display properties.     

Motion perception and visual signal design in Anolis lizards

Anolis lizards communicate with displays consisting of motion of the head and body. Early portions of long-distance displays require movements that are effective at eliciting the attention of potential receivers. We studied signal-motion efficacy using a two-dimensional visual-motion detection (2DMD) model consisting of a grid of correlation-type elementary motion detectors. This 2DMD model has been shown to accurately predict Anolis lizard behavioural response. We tested different patterns of artificially generated motion and found that an abrupt 0.3° shift of position in less than 100 ms is optimal. We quantified motion in displays of 25 individuals from five species. Four species employ near-optimal movement patterns. We tested displays of these species using the 2DMD model on scenes with and without moderate wind. Display movements can easily be detected, even in the presence of windblown vegetation. The fifth species does not typically use the most effective display movements and display movements cannot be discerned by the 2DMD model in the presence of windblown vegetation. A number of Anolis species use abrupt up-and-down head movements approximately 10 mm in amplitude in displays, and these movements appear to be extremely effective for stimulating the receiver visual system.     

Lateralization of lateral displays in convict cichlids

We examine lateralization of lateral displays in convict cichlids, Amatitlania nigrofasciata, and show a population level preference for showing the right side. This enables contesting pairs of fish to align in a head-to-tail posture, facilitating other activities. We found individuals spent a shorter mean time in each left compared with each right lateral display. This lateralization could lead to contesting pairs using a convention to align in a predictable head-to-tail arrangement to facilitate the assessment of fighting ability. It has major implications for the common use of mirror images to study fish aggression, because the 'opponent' would never cooperate and would consistently show the incorrect side when the real fish shows the correct side. With the mirror, the 'normal' head-to-tail orientation cannot be achieved.     

Scared and less noisy: glucocorticoids are associated with alarm call entropy

The nonlinearity and arousal hypothesis predicts that highly aroused mammals will produce nonlinear, noisy vocalizations. We tested this prediction by measuring faecal glucocorticoid metabolites (GCMs) in adult yellow-bellied marmots (Marmota flaviventris), and asking if variation in GCMs was positively correlated with Wiener entropy-a measure of noise. Contrary to our prediction, we found a significant negative relationship: marmots with more faecal GCMs produced calls with less noise than those with lower levels of GCMs. A previous study suggested that glucocorticoids modulate the probability that a marmot will emit a call. This study suggests that, like some other species, calls emitted from highly aroused individuals are less noisy. Glucocorticoids thus play an important, yet underappreciated role, in alarm call production.     

Working against gravity: horizontal honeybee waggle runs have greater angular scatter than vertical waggle runs

The presence of noise in a communication system may be adaptive or may reflect unavoidable constraints. One communication system where these alternatives are debated is the honeybee (Apis mellifera) waggle dance. Successful foragers communicate resource locations to nest-mates by a dance comprising repeated units (waggle runs), which repetitively transmit the same distance and direction vector from the nest. Intra-dance waggle run variation occurs and has been hypothesized as a colony-level adaptation to direct recruits over an area rather than a single location. Alternatively, variation may simply be due to constraints on bees' abilities to orient waggle runs. Here, we ask whether the angle at which the bee dances on vertical comb influences waggle run variation. In particular, we determine whether horizontal dances, where gravity is not aligned with the waggle run orientation, are more variable in their directional component. We analysed 198 dances from foragers visiting natural resources and found support for our prediction. More horizontal dances have greater angular variation than dances performed close to vertical. However, there is no effect of waggle run angle on variation in the duration of waggle runs, which communicates distance. Our results weaken the hypothesis that variation is adaptive and provide novel support for the constraint hypothesis.     

Lionfish predators use flared fin displays to initiate cooperative hunting

Despite considerable study, mystery surrounds the use of signals that initiate cooperative hunting in animals. Using a labyrinth test chamber, we examined whether a lionfish, Dendrochirus zebra, would initiate cooperative hunts with piscine partners. We found that D. zebra uses a stereotyped flared fin display to alert conspecific and heterospecific lionfish species Pterois antennata to the presence of prey. Per capita success rate was significantly higher for cooperative hunters when compared with solitary ones, with hunt responders assisting hunt initiators in cornering the prey using their large extended pectoral fins. The initiators would most often take the first strike at the group of prey, but both hunters would then alternate striking at the remaining prey. Results suggest that the cooperative communication signal may be characteristic to the lionfish family, as interspecific hunters were equally coordinated and successful as intraspecific hunters. Our findings emphasize the complexity of collaborative foraging behaviours in lionfish; the turn-taking in strikes suggests that individuals do not solely try to maximize their own hunting success: instead they equally share the resources between themselves. Communicative group hunting has enabled Pteroine fish to function as highly efficient predators.     

Keeping up appearances: male fiddler crabs wave faster in a crowd

Courtship displays are often energetically and temporally costly as well as highly conspicuous to predators. Selection should therefore favour signalling tactics that minimize courtship costs while maintaining or increasing signal attractiveness. In fiddler crabs, males court females by waving their one greatly enlarged claw in a highly conspicuous and costly display. Here, we investigate whether courting males adjust their wave rate, and therefore the cost of courtship, to the current level of competition. We show that display rate increases as competition increases and that when competition is removed, males reduce their display rate by 30 per cent. These results suggest that male fiddler crabs actively reduce the cost of courtship by adjusting their wave rate in response to the immediate level of competition.     

Nestling colouration is adjusted to parent visual performance in altricial birds

Hitherto, most of the investigation on the perceptual efficacy of begging signals has dwelled on how patterns of nestling colouration adjust to predominant nest luminosity. However, visual sensitivity of birds varies across species, which raises the question of whether colouration of traits involved in begging displays is adjusted to parent visual capacities. Here, by comparing nestling colouration and visual sensitivity across 22 altricial bird species, we provide a first test of this hypothesis. Firstly, we assessed differences in performance of typical UV‐tuned and violet‐tuned bird eyes when looking at the nestling traits under the light regimes prevailing at their nests. Secondly, while controlling for common ancestry in a comparative approach, we explored variation in colouration of nestlings in relation to parent visual system. The colour discrimination model indicated a general higher performance of the ultraviolet over the violet eye at detecting gape and body skin traits in either open‐ or hole‐nest light conditions. Gape colouration was associated with parental visual system as the nestlings of UVS species displayed more yellow and less pure ultraviolet mouths than the nestlings of VS species. Thus, our results agree with an adaptive parent–offspring communication scenario where the nestlings’ colours tuned the perception capacities of their parents.     

Individual contributions to territory defence in a cooperative breeder: weighing up the benefits and costs

While investment in territory defence is expected to be influenced by its benefits, the additional role that costs may play is rarely considered. Here, we quantify both benefits and costs of repelling prospecting males in cooperative meerkats, and demonstrate that both are required to explain the substantial variation in individual contributions to the defence observed. Males benefit more from repelling prospectors than females, as males may lose dominance and be expelled during intrusions. Accordingly, males invest the most in repelling prospectors. We also show that males experience an associated cost in the form of reduced weight gain and, as such, heavier males contribute more to chasing prospectors. Finally, we show evidence of a cost not restricted to individuals engaged in chasing: both males and females reduce their contributions to feeding dependent pups when prospectors are present, resulting in a reduction in pup weight gain in this context. Males appear to adjust their contributions to chasing in light of this cost, chasing at lower rates when their group contains dependent young. Our findings support the view that investment in cooperative behaviours can be attributed to benefits and costs, and highlight the additional importance of considering trade-offs in investment between cooperative behaviours.     

Vampires in the oceans: predatory cercozoan amoebae in marine habitats

Vampire amoebae (vampyrellids) are predators of algae, fungi, protozoa and small metazoans known primarily from soils and in freshwater habitats. They are among the very few heterotrophic naked, filose and reticulose protists that have received some attention from a morphological and ecological point of view over the last few decades, because of the peculiar mode of feeding of known species. Yet, the true extent of their biodiversity remains largely unknown. Here we use a complementary approach of culturing and sequence database mining to address this issue, focusing our efforts on marine environments, where vampyrellids are very poorly known. We present 10 new vampyrellid isolates, 8 from marine or brackish sediments, and 2 from soil or freshwater sediment. Two of the former correspond to the genera Thalassomyxa Grell and Penardia Cash for which sequence data were previously unavailable. Small-subunit ribosomal DNA analysis confirms they are all related to previously sequenced vampyrellids. An exhaustive screening of the NCBI GenBank database and of 454 sequence data generated by the European BioMarKs consortium revealed hundreds of distinct environmental vampyrellid sequences. We show that vampyrellids are much more diverse than previously thought, especially in marine habitats. Our new isolates, which cover almost the full phylogenetic range of vampyrellid sequences revealed in this study, offer a rare opportunity to integrate data from environmental DNA surveys with phenotypic information. However, the very large genetic diversity we highlight within vampyrellids (especially in marine sediments and soils) contrasts with the paradoxically low morphological distinctiveness we observed across our isolates.     

Ground squirrel tail-flag displays alter both predatory strike and ambush site selection behaviours of rattlesnakes

Many species approach, inspect and signal towards their predators. These behaviours are often interpreted as predator-deterrent signals-honest signals that indicate to a predator that continued hunting is likely to be futile. However, many of these putative predator-deterrent signals are given when no predator is present, and it remains unclear if and why such signals deter predators. We examined the effects of one such signal, the tail-flag display of California ground squirrels, which is frequently given both during and outside direct encounters with northern Pacific rattlesnakes. We video-recorded and quantified the ambush foraging responses of rattlesnakes to tail-flagging displays from ground squirrels. We found that tail-flagging deterred snakes from striking squirrels, most likely by advertising squirrel vigilance (i.e. readiness to dodge a snake strike). We also found that tail-flagging by adult squirrels increased the likelihood that snakes would leave their ambush site, apparently by elevating the vigilance of nearby squirrels which reduces the profitability of the ambush site. Our results provide some of the first empirical evidence of the mechanisms by which a prey display, although frequently given in the absence of a predator, may still deter predators during encounters.     

Behavioural flexibility and problem-solving in a tropical lizard

The role of behavioural flexibility in responding to new or changing environmental challenges is a central theme in cognitive ecology. Studies of behavioural flexibility have focused mostly on mammals and birds because theory predicts that behavioural flexibility is favoured in species or clades that exploit a diversity of habitats or food sources and/or have complex social structure, attributes not associated with ectothermic vertebrates. Here, we present the results of a series of experiments designed to test cognitive abilities across multiple cognitive modules in a tropical arboreal lizard: Anolis evermanni. This lizard shows behavioural flexibility across multiple cognitive tasks, including solving a novel motor task using multiple strategies and reversal learning, as well as rapid associative learning. This flexibility was unexpected because lizards are commonly believed to have limited cognitive abilities and highly stereotyped behaviour. Our findings indicate that the cognitive abilities of A. evermanni are comparable with those of some endothermic species that are recognized to be highly flexible, and strongly suggest a re-thinking of our understanding of the cognitive abilities of ectothermic tetrapods and of the factors favouring the evolution of behavioural flexibility.     

Convergent exaptation and adaptation in solitary island lizards

Independent evolutionary lineages often display similar characteristics in comparable environments. Three kinds of historical hypotheses could explain this convergence. The first is adaptive and evolutionary: nonrandom patterns may result from analogous evolutionary responses to shared conditions. The second explanation is exaptive and ecological: species may be filtered by their suitability for a particular type of environment. The third potential explanation is a null hypothesis of random colonization from a historically nonrandom source pool. Here we demonstrate that both exaptation and adaptation have produced convergent similarity in different size-related characters of solitary island lizards. Large sexual size dimorphism results from adaptive response to solitary existence; uniform, intermediate size results from ecological filtering of potential colonizers. These results demonstrate the existence of deterministic exaptive convergence and suggest that convergent phenomena may require historical explanations that are ecological as well as evolutionary.     

Eavesdropping and signal matching in visual courtship displays of spiders

Eavesdropping on communication is widespread among animals, e.g. bystanders observing male-male contests, female mate choice copying and predator detection of prey cues. Some animals also exhibit signal matching, e.g. overlapping of competitors' acoustic signals in aggressive interactions. Fewer studies have examined male eavesdropping on conspecific courtship, although males could increase mating success by attending to others' behaviour and displaying whenever courtship is detected. In this study, we show that field-experienced male Schizocosa ocreata wolf spiders exhibit eavesdropping and signal matching when exposed to video playback of courting male conspecifics. Male spiders had longer bouts of interaction with a courting male stimulus, and more bouts of courtship signalling during and after the presence of a male on the video screen. Rates of courtship (leg tapping) displayed by individual focal males were correlated with the rates of the video exemplar to which they were exposed. These findings suggest male wolf spiders might gain information by eavesdropping on conspecific courtship and adjust performance to match that of rivals. This represents a novel finding, as these behaviours have previously been seen primarily among vertebrates.     

Evolutionary stasis and lability in thermal physiology in a group of tropical lizards

Understanding how quickly physiological traits evolve is a topic of great interest, particularly in the context of how organisms can adapt in response to climate warming. Adjustment to novel thermal habitats may occur either through behavioural adjustments, physiological adaptation or both. Here, we test whether rates of evolution differ among physiological traits in the cybotoids, a clade of tropical Anolis lizards distributed in markedly different thermal environments on the Caribbean island of Hispaniola. We find that cold tolerance evolves considerably faster than heat tolerance, a difference that results because behavioural thermoregulation more effectively shields these organisms from selection on upper than lower temperature tolerances. Specifically, because lizards in very different environments behaviourally thermoregulate during the day to similar body temperatures, divergent selection on body temperature and heat tolerance is precluded, whereas night-time temperatures can only be partially buffered by behaviour, thereby exposing organisms to selection on cold tolerance. We discuss how exposure to selection on physiology influences divergence among tropical organisms and its implications for adaptive evolutionary response to climate warming.     

Duetting in space: a radio-telemetry study of the black-bellied wren

In many birds, individuals 'answer' the songs of their pair-mates to produce vocal 'duets'. One hypothesized function of song answering is that it prevents extra-pair birds from intruding into the duetting pair's territory to obtain copulations or usurp one of the pair-mates. In this capacity, answering may signal that the pair-mates are close together, and so are prepared to defend against such an intrusion. Another functional hypothesis states that answering helps pair-mates maintain contact, and so predicts that a bird is more likely to approach its mate after a duet than after a solo song. I used radio-telemetry to monitor the distance between mated black-bellied wrens (Pheugopedius fasciatoventris). I found that birds of both sexes were more likely to answer their mate's song when the mate was close, and that maximum duet length was negatively related to the distance between pair-mates. Furthermore, song answering positively affected the likelihood of one pair-mate approaching the other after a song. In a significant majority of the approaches after duet songs, the answering bird approached the initiator. I conclude that in the black-bellied wren, (i) the occurrence and duration of vocal duets covary with physical closeness and (ii) contact maintenance is a secondary function of duet participation.     

Perception of edges and visual texture in the camouflage of the common cuttlefish, Sepia officinalis

The cuttlefish, Sepia officinalis, provides a fascinating opportunity to investigate the mechanisms of camouflage as it rapidly changes its body patterns in response to the visual environment. We investigated how edge information determines camouflage responses through the use of spatially high-pass filtered 'objects' and of isolated edges. We then investigated how the body pattern responds to objects defined by texture (second-order information) compared with those defined by luminance. We found that (i) edge information alone is sufficient to elicit the body pattern known as Disruptive, which is the camouflage response given when a whole object is present, and furthermore, isolated edges cause the same response; and (ii) cuttlefish can distinguish and respond to objects of the same mean luminance as the background. These observations emphasize the importance of discrete objects (bounded by edges) in the cuttlefish's choice of camouflage, and more generally imply that figure-ground segregation by cuttlefish is similar to that in vertebrates, as might be predicted by their need to produce effective camouflage against vertebrate predators.