Lizard communication

Lizards are among the most diverse groups of reptiles and include more than 5,600 species.[1] They come in many shapes, sizes, and colors and vary widely in behavioral traits, such as their methods of reproduction and food foraging.[2] In addition to this diversity in physical and behavioral characteristics, lizards have evolved many different ways to communicate.[3]

Lizards have evolved to have different systems of communication depending on habitat, method of sexual selection, predator avoidance, and the communication needs of the species. These include visual, chemical, tactile, and vocal communication. Each method of communication utilizes various sensory systems, including visual, olfactory, and auditory systems.[4][5][6]

Methods of lizard communication

Communication refers to the transfer of information between individuals [7][8] (See Animal Communication for additional discussion). One individual (the signaler) sends information to another individual (the receiver), and the receiver modifies its behavior in response to the information it received.

Lizards communicate to gain information about the individuals around them by paying attention to various characteristics exhibited by those individuals and using various physical and behavioral traits to communicate. These traits differ based on the mode of communication being used.

Scenarios for lizard communication

Lizards are able to communicate in a variety of different scenarios. Lizards communicate with members of their own species (intraspecific communication) to find appropriate mates (courtship) and in competition for resources such as food or habitat. Lizards can use subtle variation in traits shared by members of the same species when choosing mates, which sometimes results in particular individuals mating more than others. (For more information see Sexual selection in lizards.)

Lizards communicate with members of different species (interspecific communication) as well. For example, some lizard species communicate with each other in competition for resources, and some lizards use interspecific communication during predator-prey interactions. The lizard Anolis cristatellus, for example, exhibits predator deterrence communication. Anolis cristatellus perform a behavior that communicates information about the lizard's physiological condition to potential predators.[9] Lizards that are in better condition (and may be more likely to outrun the predator) perform this behavior more frequently, and may communicate to the predator that they will be difficult to catch. Thus, the predator may choose to avoid lizards in good condition that are likely to outrun them and choose instead to pursue individuals that do not seem to be in good condition. In this case of interspecific communication, the lizard is communicating information about itself to the predator, and the predator modifies its behavior in response.

Modes of lizard communication

Lizards have evolved several modes of communication to accommodate their different communication needs, including visual, chemical, tactile, and vocal communication.[10][3] The chemical and visual communication modes are widespread among lizards, while the tactile and vibrational modes occur in just a handful of lizard species. Some species use a combination of several communication modes, while others seem to rely entirely on one. Visual communication is the most well-studied mode of lizard communication, but modern scientific techniques are making it easier to study the other modes, so lizards traditionally thought to rely on one mode of communication may also be using other modes.

Visual communication

Lizards that use visual communication gather information by observing other lizards' various physical and behavioral characteristics, somewhat like humans communicating using body language Lizards that use visual communication often have highly developed visual systems—most can see different colors, and some can see UV light.[11][12] Many different physical and behavioral traits are used by lizards in visual communication, most of which are designed to draw the visual attention of other lizards.

Lizards can have vibrant colors and patterns and flashy behaviors intended to communicate both inter- and intraspecifically. Vibrant colors and patterns may draw attention from predators or competition, so these colors may be located on a dewlap or a surface of the body like the belly that is not exposed unless the lizard intends to. A dewlap is a flap of skin on the throat that can be extended and retracted and is often colorful and/or patterned when extended and hidden when retracted. Many species of Anolis lizards have dewlaps[13] that they extend during behavioral interactions like attracting mates and dueling with competitors but are well camouflaged when the dewlap is retracted.[14] Sceloporous lizard species can also have hidden colors with some developing vibrant blue and black coloration on their bellies during the breeding season.[15] This color is not visible to other lizards unless the lizard engages in a behavior called dorsal ventral flattening, in which the lizard flattens its body to expose the colorful parts of its belly during behavioral interactions.[16]

Because lizards that use visual communication rely on being able to see other lizards, visual communication is common among species that live at relatively high population densities and frequently come into close contact. Visual communication is well suited for use in many different habitats and can be modified by lizards to accommodate changing habitat conditions [e.g.,[17]], so long as individuals come into contact frequently enough.

Chemical communication

Lizards that use chemical communication produce chemicals that they deposit in the environment, such as pheromones. [18]These chemicals elicit changes in the behavior, and sometimes in the physiology, of individuals that encounter them.[19] These chemicals contain unique combinations of chemical compounds and different combinations of these chemicals can provide information about the individual that produced them.[20] In many cases, chemical composition differs considerably between species, which allows lizards to tell whether a lizard that deposited the chemical was a member of the same or a different species.[18] In some lizard species (such as the Iberian rock-lizards, Lacerta monticola), their chemical secretions also differ based on the individual that produced them.[21] Lizards detecting the chemicals can determine whether the individual that produced the chemical is familiar or not,[21] much like a human knows whether they've met a person before based on unique facial characteristics.

Lizards that use chemical communication have highly developed olfactory systems, which essentially give these lizards a very well-developed sense of "smell" and enable them to detect chemicals in the environment.[22] Lizards that produce these chemicals often have femoral glands or femoral pores on their back legs.[23] Chemicals are produced inside the lizard and are then released via these pores. Lizards that use chemical communication are often observed to drag their back legs or lower half of their body against a surface they are walking across to spread their chemical secretions across an area. Another behavior common among lizards that use chemical communication is tongue flicking in order to "taste" the chemicals present in the air and on various surfaces, such as rocks or logs that another lizard might have been sitting on. These chemicals can also be deposited in feces[24]—lizards have been observed to defecate systematically throughout the area that they live in, suggesting that they may be placing chemicals in particular areas, such as marking the boundaries of a territory.[24]

One unique aspect of chemical communication that differentiates it from other modes is that lizards do not need to come into direct contact in order to communicate using chemicals.[25] Once a chemical has been released onto a surface, it can be used in communication until it is washed away or otherwise removed. Lizards may come into contact with chemicals that were placed there by a lizard hours or days earlier, depending on how long the chemical lasts in the environment. Thus, lizards that live at relatively low population densities or do not come into close contact can use chemical communication. Chemical communication is usually better suited for use in dry environments as water from water sources or precipitation can wash away the chemicals.

Recent advances in our ability to detect and measure the compounds present in these chemicals have dramatically increased our understanding of lizard chemical communication.[26][27][28] As the composition of these chemicals is analyzed and researched further, more information about the individual that produced them and how they communicate in different contexts is known.[29][30][31]

In Podarcis hispaniscus

Podarcis hispanicus secrete chemicals that are generally more volatile and have higher chemical stability than other similar species. In courtship, chemosensory allows for male lizards to identify females during breeding season and identify the female’s special identity. Chemosensory recognition is greater among males as they are greatly utilized in intra-sexual aggression. This also allows males to recognize their known neighbors and will not engage in anti-predatory behaviors. In male lizards, the chemical stimuli is released from the femoral glands.[32]

Tactile communication

Lizards that use tactile communication either use direct or indirect touch as a form of communication.[10] Some species come into direct contact with one another, such as nudging, licking, biting, or bumping another lizard. This type of direct contact may be associated with courtship (i.e., attracting a mate), or with aggression—in many lizards, fights can escalate to direct physical contact, such as biting and bumping into one another. Species that engage in these physical conflicts often rely on other forms of communication (such as visual or chemical), and resort only to physical contact when other methods of deterring potential rivals have failed. In the case of courtship, some lizards such as the male Komodo dragon, Varanus komodoensis, lick females to determine whether they are sexually receptive.[33] While this is direct touch, it also incorporates chemical communication, as the male is detecting different chemicals present in the female's body in addition to directly touching her.

There are also forms of tactile communication that do not involve direct touch, including vibrational communication.[34] Some chameleon species communicate with one another by vibrating the substrate that they are standing on, such as a tree branch or leaf.[35] Animals that use vibrational communication exhibit unique morphological adaptations that enable them to detect vibration and use it in communication. These include unique adaptations in ear and jaw morphology that give the animal direct contact with the surface they are standing on and enable them to detect subtle vibrations.[36] Lizards that live on substrates that can be easily moved (such as thin tree branches or leaves) are more likely to use vibrational communication than lizards that live on substrates that do not transmit vibrations as easily, such as the ground or thick tree trunks.

Vocal communication
Lizard on a wall
Tokay gecko is known for its vocalizations

This mode of communication is primarily limited to nocturnal geckos, many of which produce vocalizations during behavioral interactions such as male competition[3][37][38] or predator avoidance.[39] Another lizard, Liolaemus chiliensis, emits distress calls in the wild. Other lizards can produce vocalizations, but most have not been observed to do so in the wild. For instance, some lizards vocalize when handled,[3] but have not been heard doing so undisturbed in the wild. It is possible that these vocalizations are used for communication, but observations of this behavior in natural populations would be needed to make this assertion.

Lizards that use vocal communication need to produce vocalizations and need an appropriate auditory system to process the sounds. Vocal communication is well suited for lizards that live in habitats that make it hard to see other individuals or are active at night because it can be used to communicate without the need to come into contact with other lizards or being able to see them.

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