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Animal signals must be detected by the receiver sensory system and overcome various local ecological factors that may affect their transmission and reception. Habitat structure, competition, avoidance of accidental receivers and changing environmental conditions, have been shown to affect the way animals signal, environmental noise is also important, and animals change their behavior in response to environmental noise.
Animals that produce movement-based visual signals must fight windblown plants that produce movement noise and may affect detection of significant movement. The lizard Amphibolurus muricatus uses a tail flick at the beginning of the display to attract attention.
Assuming that tail movement is well suited for this function, we compared the visual amplitude produced by tail movement to push-ups, which are a key component of the rest of the display.
The amplitude of tail movement varies greatly during the display, but is always greater than the amplitude produced by push-ups and is not limited by the viewing position. These features, combined with the fact that the tail is a lightweight structure that does not affect other activities, provide an ideal introductory component for attracting attention in the ecological environment in which they are produced.
Animals exchange signals to influence the behavior of the recipient. Effective signaling is most important about capturing attention, so sensory and brain properties of the receiver mediate whether the signal is detected and subsequently processed, and theories suggest that one way the signal evolves is to exploit biases in the receiver's sensory abilities for other functional tasks.
Even for signals that evolve by other pathways, the signal structure must match the sensory capabilities of the receiver. However, changes in structure within and between taxa influence other factors on signal structure and signal behavior. In addition to the inherent variations in signalman identity, motivation and background, there are various ecological factors that are major contributors to signal diversity.
The ecological impact on the signal structure is diverse. They include habitat structure, competition from other signaling species, unexpected receivers, and the direction of the signal relative to the sun. Another key ecological factor that influences signal structure and signal behavior is environmental noise, which represents a stimulus in the same sensory channel as the signal.
Importantly, the noisy environment is not static, and many species experience changes in the noisy environment, which requires them to adjust the signal accordingly. The masking effect of noise and the resulting adjustment of the signaller have received considerable attention in acoustic signal species, which have been reported in different taxa, including primates, mammals, birds, reptiles, and insects.
Less well known is the masking effect of noise on electrical and chemical signals. Visual signals can also be affected by noise, interfering with reliable detection and processing, including increasing recognition of the role of unrelated plant movements in detecting motion-based visual displays and adjustments made by signalmen to overcome ambient motion noise.
Many lizard species utilize dynamic visual signals in social interaction and must deal with the limitations imposed by their signaling environment. Windblown plants are defined by the movement of the signal as the main source of noise and inhibit the receiver on the detection of the signal Lizards adjust their signaling strategies to counteract the masking effect of plant movement in a species-specific manner.
Anolis cristatellus increased display speed, A gundlachi inserted faster and faster movements in adverse signal conditions, and Amphibolurus muricatus extended the duration of introductory tail swings, before other sport modes were produced in rapid succession.
Amphibolurus muricatus is an Australian Agamid lizard and one of several lizards that have tail movements in their signal repertoire. However, few of these species perform tail movements as reliably as Amuricatus.
Amuricatus' tail flick has an alarm function that draws the receiver's attention to other movement modes. However, it is not clear why this species relies more on tail movement than other species in this family, and we speculate that it is related to the interaction of sensory systems and ecology.
The habitat used by Amuricatus for most of its geographic distribution is dense vegetation, usually located near these plants. They are a semi-arboreal species that bask in sunny places, either near the ground or a few meters above the ground. When opponents enter their field of vision, they react from a position in the sun.
Therefore, their orientation relative to the intruder varies greatly. We think the tail is great for sustained movement because it's a lightweight structure that doesn't affect the lizard's ability to respond to other events, and another non-mutually exclusive hypothesis is that Amuricatus' tail movement provides a more optimized attention-grabbing signal than other movements in its repertoire.
The signaller is surrounded by plants, usually in close proximity, and the position of the annunciator relative to the receiver will be highly variable and span three dimensions of space.
The purpose of this study was to compare the visual amplitude of movement at tail flicking to the visual amplitude of the substitution movement in its repertoire, and the main feature of the second half of the display is push-ups. This pattern of movement is relatively common in the Australian Agamid lizard, as well as species around the world, and is characterized by lifting the head and upper part of the body by the movement of the front legs.
Taking into account the tendency to observe the movement from above, below, and both sides of the annunciator, we compared the amplitudes of the two movements from the perspective of a receiver located anywhere around the lizard. Our general approach, introduced by New and Peters, and using archival footage of wild, free-roaming lizards, we predicted that tail movements would result in greater amplitude than push-ups.
Data acquisition
We used wild Amuricatus signal lenses obtained from previous studies. The study compared two Amuricatus populations from different habitat types: Croajingolong National Park off coast Victoria and Avisford Nature Reserve, which has a lower density of vegetation in New South Wales.
Full details about the differences between these populations and display shots can be found in the original paper. Briefly, two cameras were used to film a display of wild, unlabeled male lizards in response to tethered intruders, followed by a calibrated object with 20 points of varying depths and heights.
The calibration coefficients that can be used for 3D reconstruction of motion can then be calculated. We selected eight sequences for further analysis, including four sequences from each of the two populations.
Signal analysis, to characterize the motion of the display, we use Matlab to track multiple parts of the lizard in successive frames. We tracked the position of the eyes to characterize the push-up assembly, as well as multiple sections of the tail in each frame. We use the bottom and tip of the tail and select three intermediate points to divide the tail into segments of equal size, limiting the selected points to clear and recognizable marks on the tail for easy tracking in all frames.
Therefore, the relative position of the track points varies slightly between individuals. Following Hedrick's program, each point is positioned frame by frame from two camera views. The position data from the camera view and calibration coefficients are then combined using a direct linear transformation to represent the motion as xyz coordinates in 3D.
For each point on the tail, we calculated the distance traveled between successive frames and then added them over time to get the total distance moved. The tail component shown by Amuricatus occurs mainly in the distal part of the tail, spanning five points unevenly.
The distal part of the tail shows steady incremental movement over time and, to a lesser extent, the midpoint. In contrast, the tail bottom and second point in most displays do not show noticeable movement until later in the sequence. Based on this analysis, we selected the tip of the tail for subsequent analysis.
Compare signal amplitudes
The goal is to compare and contrast the amplitude of push-ups and flick tail components, following the general method introduced by New and Peters, which involves calculating the angle of the reference point of a position data pair.
We hypothesize that an intruder can be placed anywhere around the annunciator and use the sphere function in Matlab to generate equally spaced observation positions around the lizard at an observation distance of 1 m from the bottom of the tail.
We used the default settings, created 20 × 20 faces around the lizard, and used their vertices as our position data, for a total of 441 potential receiver locations. The two components differ greatly in duration.
Push-ups are quick and complete in about 1 second, while tail flicks vary widely. We chose to divide the tail flick into 1-second non-overlapping segments, and for each push-up sequence and 1-second tail swing segment, we used the formula to calculate the viewing angle of all pairwise position data combinations in a given viewing position within a specified time window.
where v1 and v2 are separate lines connecting the viewing location and each of the two location data points, tan2 calculates the four-quadrant arctangent, and the cross and point are cross-product and dot product functions. Convert radian values to degrees and in each case choose the maximum angle to represent the angular displacement of motion from that observation position.
Repeat this for all observation positions, resulting in 1 angular displacement measurement for each push-up or 441-second tail swing segment. To make it easier to examine this data, the 3D data is presented in a flat format. We studied the dynamic characteristics of tail flicking and compared and compared the maximum angular displacement achieved by push-ups and tail flicking movements of 4 display sequences.
The analysis showed that tail movements consistently produced amplitudes greater than push-ups over comparable time windows. In addition, from all the observation positions around the signaler, the relative advantage of tail movement in this regard is obvious. Simplify the motion signals of two display components by characterizing the motion of a single point.
The complexity of the signal structure is ignored and the standard practice of quantifying lizard display is followed. While we are looking for alternative analytical methods, the results show that the use of tail flicking at the beginning of the display reflects the ecology of the Amuricatus signal, which provides the receiver with high relative amplitude movement from any angle and coincides with playback studies.
These studies show robustness to detecting directional differences. Tail movement can also be effective over a wider range of distances based on the amplitude of motion and is a good choice for dealing with motion noise in the environment. We outline our reasoning below.
Motion amplitude is a key parameter for lizards based on motion signals. Based on the function of the sensory system, Fleishman and Pallus predicted that the amplitude of motion would affect the distance at which motion could be detected. The amplitude of motion was subsequently shown to be a parameter of the head swing display modulated by Anolis gundlachi in response to different receiver distances, as well as by A. Gundlachi. Sagrei adjusts parameters in response to changes in predation pressure.
These adjustments help to alter the active space of the signal and have been shown to differ in motion-based displays of other taxa. However, Peters and Allen demonstrated that Amuricatus does not adjust the tail display in this way in response to receiver distance, and amplitude variability is a feature of each tail flick sequence, but in this study, the amplitude was always greater than the push-up.
This may help allow Amuricatus signals over a wider range. Our analysis keeps the signalman-receiver distance constant of 1 m, and we study the variation of amplitude with viewing distance to show the spatial advantage of activity with different amplitudes of motion.
conclusion
Different microhabitats produce different image movement environments. Although particularly challenging for motion-based visual signals, recent work has begun to quantify signal performance in different habitats, not allowing species to be transferred between habitats, so Bian et al. used complex 3D animations to simulate different microhabitats and signal species.
The sheltering potential of the densely vegetated environment was found to be greater than other habitat types used by the Australian Agamid lizard. We're just starting this kind of work, but it seems that Amuricatus has developed a signaling strategy that is a product of the signal context, including the environment in which they are typically found.
The ecological challenges faced by Australian Agamid lizards are uncommon and could explain the differences between species. Understanding of this group, and this signaling pattern, is limited by a lack of basic knowledge of natural history, but we see no reason to think that the interactions between ecology and sensory system function are irrelevant. The bird's song and the spectral characteristics of the lizard dew directly reflect ecological conditions, as do the movement-based lizard displays.
bibliography
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