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Anolis aquaticus
Anolis aquaticus
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Anolis aquaticus
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Iguania
Family: Dactyloidae
Genus: Anolis
Species:
A. aquaticus
Binomial name
Anolis aquaticus
Taylor, 1956
A well-camouflaged aquarit anole
An aquatic anole in Corcovado National Park, Costa Rica

Anolis aquaticus, commonly known as the water anole, is a semi-aquatic species of anole, a lizard in the family Dactyloidae, native to southwestern Costa Rica and far southwestern Panama.[2] The species demonstrates adaptations that allows it to spend periods of time underwater up to approximately a quarter of an hour, forming an air bubble which clings to its head and serves to recycle the animal's air supply while it spends time beneath the surface.[3] Although highly unusual, similar adaptions and behavior are found in other species of semi-aquatic anoles.[4][5]

Taxonomy

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The order of the water anole is Squamata, which refers to scaled reptiles. Squamata is the largest order of reptiles, including species of lizards, snakes, and amphisbaenians. Members of this order are found on every continent other than Antarctica, and they live in a variety of habitats, while showcasing various different traits.[6]

Iguania is a suborder that includes species of chameleons, iguanas, and New World lizards such as the water anole. Most species in the Iguania suborder are arboreal, meaning they travel by tree, but many other notable species are described as being terrestrial. They typically have tongues that are non-prehensile and fleshy, with the exception of chameleons. There are fossil records of members of this suborder dating back to the Early Jurassic period, with the earliest known member being the Bharatagama which lived in modern day India around 190 million years ago.[6]

The water anole is categorized in the group Dactyloidae, which is a family under the suborder Iguania. Dactyloidae refer to lizards that are in locations ranging from Paraguay to the southeastern regions of the United States, and are commonly referred to as anoles.

Anolis refers to a genus of anoles that are native to North and South America. There are currently more than 425 species that are known, and they are under the suborder Iguania and family Dactyloidae. Anolis used to be included in the family Polychrotidae, but recently they have been categorized under the family Dactyloidae.[7]

Despite being under the same genus, different species under Anolis have exhibited many differences, mostly in the context of their habitat and location. They fill up different niches due to the isolation and separation of the species into significantly different habitats, which has led to morphological changes that better fit their habitats. Examples include a difference in limb length based on the diameter of the trees that different species walk on, with thinner trees leading to lizards with shorter limbs, and wider trees leading to lizards with longer limbs. The water anole, in contrast, is terrestrial, and spends most of its time on the ground or climbing rocks and large boulders.[7]

Physical description

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The order Squamata are notable for their jaw structure, which provides them flexible jaws and a powerful biting force. Members of this order have developed a movable hinge in their skull called the quadratojugal hinge, and along with increased jaw muscle development, have given these organisms a strong biting force. Squamata are divided into many different suborders, and the water anole is part of the suborder Iguania.[6]

In most species of Dactyloidae, males have a flap of skin that extends from their necks, which is often brightly colored and used for display. Despite being very distantly related, they show many similarities to geckos, such as their anatomy and the ability to break off their tail.[8]

Body coloration

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Being part of the group Dactyloidae, their bodies are most often a green or brown color, but like the water anole, many species are able to change colors. The water anole has the ability to change the color of the stripes that are throughout the length of their bodies. The colors display the level of stress that they are under. It has been determined through experimentation with the lizard species that brighter colored stripes signify that they are under more stress. When the lizard is exposed to a stressor, the stripes on the lizards' body transition from a brown color to a pale blue or green.[9]

These lizards also tend to use these brighter colored stripes when they are walking over surfaces that are dull colors, such as green and brown. This is called disruptive camouflage. With the use of contrasting colors and patterns, organisms are able to make the outlines of their body less visible to predators.[9]

The brighter body coloration is also used by individuals in the species to increase their mating success. By making their colors more noticeable and conspicuous, they are able to become more noticeable by potential mates. At the same time, however, the brighter colors also make them more susceptible to being attacked by predators. Water anoles with brighter body and dewlap coloration are attacked by predators at a higher rate than those with duller colors. Therefore, the trait of body coloration is one that is under the influence of two contradicting results: an increase in reproductive success and a decrease in survival rate.[10]

Behavior

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Physiological

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The water anole is unusual in that it is able to stay underwater for long periods of time – a behavior that is described as "scuba diving". Experiments have confirmed that this species has the ability to remain underwater for up to 16 minutes. Since these lizards have relatively slow running speeds compared to their predators, it has been hypothesized that these lizards have adapted this "scuba diving" to enable them to avoid predators. By submerging themselves underwater for prolonged periods of time, the water anole is able to remain invisible to its predator. These lizards often endure extreme hypoxia before returning to the surface if they perceive a predator and compromise their ability for future escape ability.[4] It has also been confirmed that many of the insects found in the water anoles' stomachs live primarily underwater. The water anoles use this "scuba diving" ability to hunt prey that live underwater and would otherwise be inaccessible to the lizards. Therefore, the anoles can escape predators and forage for food with this unique "scuba diving" behavior.[11][12]

The reason that these lizards are able to remain submerged for long periods of time is their ability to create a bubble of air over heads while underwater. These anoles are semi-aquatic and when threatened or searching for prey they will jump from trees or rocks into water. When submerged, the lizards exhale and form an air bubble on the end of their snouts. Researchers have suggested that this species inhales and exhales the oxygen in the air bubble for a lengthy time period - a mechanism that ultimately permits their prolonged submersion. Researchers have also measured the oxygen saturation inside the air bubble over time and have found that it decreases with time underwater. This suggests the lizards are rebreathing through the air bubble.[12] In addition, it has been suggested that the lizard simultaneously uses the air bubble to remove carbon dioxide from its body. The inspiration of carbon dioxide shortens the duration of the dive and the air bubble can serve as a way to get rid of waste carbon dioxide. Carbon dioxide is highly soluble in water and because the partial pressure of carbon dioxide is much higher in the bubble than in the surrounding water, the carbon dioxide can easily be cleared from the bubble.[4] The formation of an air bubble in water anoles is likely facilitated by the highly hydrophobic character of their skin.[5] In 2024, the idea that these lizards use air bubbles for rebreathing was empirically tested by applying an emollient to their skin to prevent bubble formation. Lizards that could rebreathe normally were able to stay underwater an average 32% longer than those which could not. [13]

Social

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The water anole exhibits the behavior of residing in different locations based on age and gender. These locations are determined based on their distance from the river, and their height above the river. Members of the species prefer to be located as close to the river as they can. Those of higher social or demographic class reside on higher perches, and live closer to the river. These perches are occupied by adult males, who tend to live on the highest perches and live closest to the river. Juvenile lizards and male lizards tend to live in exposed areas beside the river, while adult female lizards tend to choose areas that have cover.[14]

Reproduction

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The reproductive season for this species is year round. On average, their clutch size is around one or two eggs per reproductive cycle. Female water anoles reach sexual maturity at an earlier age than their male counterparts, and also have a smaller snout-anus length than males do at their sexual maturity. Males have a larger growth rate than females, and they reach a greater body size than females when they are of the same age. Site selection has been determined to be carried out by the female, meaning that the male approaches the female in the mating process. Complete copulation takes from around 90 seconds to 105 seconds, and they do not exhibit any courtship behaviors after the copulation has concluded. The water anoles lay their eggs in cracks and openings in rocks and earth. The average incubation temperature is from 19° to 23 °C in natural conditions, and the average incubation time is from 75 to 82 days.[15]

Predators

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There are three species that have been documented to be preying on the Anolis aquaticus: one species of crab and two species of bird.[16] When threatened, the Anolis aquaticus partakes in a combination of surface swimming and "scuba diving". These anti-predatory behaviors allow this lizard to migrate between the banks and boulders of its habitat into nearby streams. These behaviors may also allow the water anole to swim a short distance with upstream current or with the downstream current to a different location. In both scenarios, the water anole's ability to remain underwater for a prolonged period enables them to engage in both of these effective anti-predatory strategies.[17]

Population

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There is some notable activity within the water anole species that can be seen by analyzing characteristics within the species' populations. The sex ratio in the population remains at around 1:1 between males and females. Females reach sexual maturity at around 4 to 6 months of age, and males reach sexual maturity at around 5 to 7 months of age. This means that on average, females reach sexual maturity earlier than males. Males in the species tend to keep one to three females in their territory, and these females do not allow other females from entering the territory. There is significant sexual dimorphism that can be seen by the size difference between males and females in the species, with males being larger than females. Although male adults grow to a larger size than female adults, their growth rates after they have reached adulthood is about the same. The growth rate of a juvenile male is therefore significantly greater than the growth rate of a juvenile female.[18]

The abundance of all members of a population, including males, females, and juveniles, fluctuates based on the season, with drier seasons yielding larger population sizes. The population sizes have been seen ranging from 86 individuals to 575 individuals, which would lead to different population densities based on the season. In populations of this species, there tends to be greater numbers of individuals that are mature and large in size compared to the relatively fewer individuals that are still considered juvenile. New members are introduced to a population and recruited at a rate of around 25% to 37% of the population size before recruitment. On average, more males are recruited than females, and males also tend to outlive and survive for a longer time than females.[16]

Evolution and adaptation

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Diving lizards, such as the Anolis aquaticus, are believed to have evolved to be able to respire while staying underwater by holding air between their cuticles and the water that they are surrounded with. This is a development that was necessary for the lizards, that were initially terrestrial creatures restricted only to breathing directly through the air, to be able to dive underwater, which aids them in concealing themselves from predators. It is through this mechanisms that these semi-aquatic anoles are able to stay underwater for such long periods of time. These lizards have developed a method known as "rebreathing", in which they are able to breathe in and out using a nasal air bubble, which is made possible by a layer of air between the water and hydrophobic skin of the lizard. This hydrophobic skin, however, is a trait that can be seen among terrestrial anole species as well, that may benefit them in their ability to effectively dive. This suggests that a shift in function, or exaptation, may have occurred over the course of the anoles' evolution.[4]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Anolis aquaticus

View on Grokipedia
from Grokipedia
Anolis aquaticus, commonly known as the water anole, is a semi-aquatic lizard species in the family , endemic to the lowland and premontane wet forests of southwestern and extreme western . Described by Edward H. Taylor in from specimens collected near Palmar, , , it belongs to the Norops auratus species group within the genus . Adults are medium-sized, with snout-vent lengths ranging from 52 to 77 mm, a slender body, long tail, and adhesive toe pads typical of anoles; the species exhibits rapid color change in its eye and lateral stripes from dark brown to pale green and blue, providing facultative against varied backgrounds. Males possess a colorful , varying from vibrant red-orange to dull brownish-red, used in visual signaling for territory defense and mate attraction. This species inhabits riparian zones along fast-flowing streams and rivers, where it perches on boulders, rocks, and low vegetation near the , often at elevations from to about 1,200 meters. A. aquaticus is oviparous, laying eggs in moist sites such as leaf litter or crevices, and exhibits with males typically larger and more colorful than females. Its diet consists primarily of small , including , captured via active on perches or during brief dives. The species is classified as Least Concern on the as of 2023. One of the most remarkable adaptations of Anolis aquaticus is its proficiency in underwater evasion, diving into to escape predators like birds and snakes, where it can remain submerged for up to 18 minutes or longer. This ability is facilitated by a specialized rebreathing mechanism, in which the lizard expires air from its nostrils to form a thin, hydrophobic air plastron trapped against its rugose skin, then reinspires the oxygen-depleted bubble to extract additional oxygen—effectively acting as a "physical ." Such , observed routinely in this semi-aquatic specialist, represents a among diving anoles and underscores its in dynamic, predator-rich environments.

Taxonomy and Distribution

Taxonomy

Anolis aquaticus belongs to the kingdom Animalia, phylum Chordata, class Reptilia, order , suborder Iguania, family , genus , and aquaticus. The was originally described by Edward H. Taylor in 1956 from specimens collected in . Initially classified within the family Polychrotidae, which encompassed all anole , the genus underwent significant taxonomic revision based on molecular phylogenetic studies. In , a comprehensive reclassification elevated to family status for anoles, separating them from other iguanian , with this framework reinforced by a 2016 multilocus phylogeny encompassing all known . Within the genus, A. aquaticus is assigned to the Norops auratus group, reflecting its placement among mainland Central American anoles. The specific aquaticus derives from the Latin term meaning "living in or near water," a reference to the lizard's distinctive semi-aquatic adaptations. As one of approximately 436 in the highly diverse Anolis, A. aquaticus stands out for its riparian preferences, differing from the predominantly arboreal of most congeners; it is native to southwestern and extreme western .

Geographic Distribution

Anolis aquaticus is endemic to the lowland and premontane wet forests of southwestern and extreme western . In , its range includes the and the Golfo Dulce region, with the type locality at Palmar in . The species occupies elevations from sea level to approximately 1,200 meters. This lizard is strictly associated with riparian zones near permanent streams and rivers within humid, evergreen tropical rainforests. Preferred microhabitats consist of rocky riverbanks, large boulders, and low-lying along these watercourses, where the species exploits semi-aquatic lifestyles. There are no records of introduced populations beyond its native distribution. The species inhabits a wet characterized by high humidity, annual rainfall exceeding 3,000 mm—often reaching 4,100 mm in areas like Golfito—and average temperatures between 24°C and 28°C.

Description

Morphology

Anolis aquaticus is a medium-sized with adults typically exhibiting a snout-vent length (SVL) of 52–77 mm. The body is slender yet robust, featuring a taller and wider build compared to some other semi-aquatic anoles, which supports both terrestrial and aquatic locomotion. The tail is long, providing balance and propulsion during . Limbs are strong and adapted for versatility, with relatively long forelimbs and shorter hindlimbs relative to body size, facilitating on vegetation and rocks near water as well as efficient swimming strokes. The head is moderately sized with flexible jaws that enable a strong bite force, significantly higher than that of closely related semi-aquatic species, aiding in capturing prey and defense. Toe pads are equipped with adhesive lamellae, enhanced for gripping wet and slippery surfaces such as rocks and stream banks. The skin features hydrophobic scales with microscopic hair-like spines and spinules (approximately 1 μm long), creating a hierarchical microstructure that increases surface hydrophobicity, evidenced by higher water contact angles (substantially greater than those of terrestrial anoles, with semi-aquatic species reaching up to 120° compared to 59°). Males possess a prominent , a colorful throat fan measuring up to approximately 5 cm in extent with an area of about 580 mm², used for visual signaling. Females lack a fully developed or have it greatly reduced. Sexual dimorphism is pronounced, with males averaging larger body sizes (SVL up to 117% of female size), more robust builds, and enhanced display structures like the , while females are smaller and less ornate overall.

Coloration

Anolis aquaticus exhibits a base coloration that varies across its body surfaces, with the dorsal side typically featuring tones interspersed with lighter stripes and spots, while the ventral surface is pale or . The flanks and eye regions bear prominent stripes that serve as key visual elements, ranging from dark in resting states to blue or green during active phases. These patterns contribute to the lizard's overall cryptic appearance in its riparian habitats. Sexual dimorphism is evident in coloration, particularly during reproductive periods. Males display more vivid flank stripes and possess a dewlap—a extensible throat fan—that is orange-red with yellow accents, used prominently in displays to signal fitness. In contrast, females show subtler variations, with lateral stripes becoming bluer and less green when in optimal body condition, potentially indicating and to conspecifics; however, no significant sex-based differences in overall brightness or stripe intensity occur outside of reproductive contexts. Color changes in A. aquaticus are rapid and physiologically driven by chromatophores, including melanophores, xanthophores, and iridophores, which expand or contract to alter pigmentation. These shifts, from dark brown to lighter stripes on the flanks and a paler dorsum, occur within minutes and are primarily triggered by stress, such as handling or restraint, rather than or light levels; social contexts, like proximity to conspecifics, elicit similar responses but do not intensify them beyond isolation effects. Unlike , these changes are not extreme and do not involve full-body transformations. Adaptively, these color dynamics balance and signaling. Darker, cryptic patterns enhance and reduce detectability by avian predators like and through background matching or edge disruption in varied microhabitats. Brighter phases, including vivid dewlaps and healthier stripes, signal reproductive fitness during but increase visibility, highlighting a where enhanced communication risks predation; males achieve more consistent across phases than females, who may appear more conspicuous when lightened.

Habitat and Behavior

Habitat Preferences

Anolis aquaticus exhibits a strong preference for streamside microhabitats in lowland and premontane wet forests, where individuals at heights typically ranging from 0 to 2 meters above the ground, with mean perch heights around 0.6 to 1 meter. These perches are often selected near the 's edge, particularly at higher elevations (approximately 1100 m), where position themselves farther from streams (horizontal distance of 86-104 cm) compared to lower elevations (, 38-44 cm). Unlike more arboreal congeners, A. aquaticus avoids dense canopies, favoring open or semi-open riparian zones that allow quick access to . Substrate use in these microhabitats is highly selective, with a strong bias toward rocky and woody elements available along streams. Boulders and rocks constitute the primary substrates, especially at higher elevations, while ground substrates are used more frequently there than at low elevations but still selectively avoided in favor of rocky elements. At higher elevations, usage shifts toward ground-level rocks near stream eddies, whereas lower-elevation populations exploit a broader array of substrates including trees and vines. This selectivity reflects adaptations to the structural features of rocky stream environments, differing from the leafy or woody preferences of related species like A. oxylophus. Environmental tolerances align with the humid, shaded conditions of tropical wet forests, where body temperatures average 25.0–25.4 °C (SD 0.5–0.8 °C) at low elevations and 20.4–21.0 °C (SD 1.0–1.1 °C) at high elevations. show limited heat tolerance, often displaying stress at handling temperatures, and prefer shaded perches to regulate . Variations by age and sex are evident: perch height increases with snout-vent length (SVL), so larger adult males (SVL 65–68 mm) occupy higher and more exposed positions than smaller females (SVL 59–62 mm) or juveniles, which use lower, more concealed spots in or . Territorial adult males defend linear riverbank areas, maintaining dominance over females within their ranges. These choices support behaviors like diving into streams for escape.

Locomotion and Physiological Adaptations

Anolis aquaticus exhibits versatile locomotion adapted to its , functioning as an agile climber on and rocks near . On land, it employs quadrupedal typical of anoles, facilitating quick movements across uneven surfaces. When threatened, individuals jump from perches into , demonstrating effective leaping capabilities to initiate escape dives. In aquatic environments, A. aquaticus is a proficient swimmer, utilizing an undulating body motion combined with a flattened, rudder-like for and steering during submersion. This behavior supports both evasion and occasional , though the species primarily relies on terrestrial predation. A key adaptation is the lizard's ability to dive underwater for extended periods, up to 16 minutes, primarily to escape predators. During dives, A. aquaticus exhales to form a narial air bubble that clings to its head, enabling rebreathing of exhaled air. This rebreathing mechanism, confirmed through experiments where bubble formation was disrupted, extends dive duration by an average of 32% compared to controls without bubbles. Physiologically, the species' hydrophobic plays a crucial role by trapping the air bubble against the nostrils, preventing water ingress and facilitating . Additionally, individuals perform gular ( to renew oxygen within the bubble, maintaining respiration without surfacing. Underwater, A. aquaticus occasionally pursues , leveraging its diving prowess for opportunistic foraging while predominantly ambushing terrestrial prey from perches.

Social Interactions

Adult males of Anolis aquaticus exhibit territorial behavior by defending streamside territories along rivers and creeks, where they space themselves out to minimize with other males. These linear territories are oriented parallel to water edges, allowing males to perch on rocks or low while monitoring and responding to intruders. Aggressive displays used in territorial defense include head-bobbing, movements, and extension of the colorful to signal dominance, with such behaviors intensifying when rivals approach closely. Physical combat, involving biting and grappling, can occur if visual displays fail to deter intruders. Communication among A. aquaticus individuals is primarily visual, relying on extensions and body color changes to convey information during social encounters. The , a fan that varies in size relative to body condition, serves as an honest signal of quality, including and potential competitive , with larger dewlaps associated with reduced vigilance and greater willingness to engage in risky behaviors. Color shifts, often rapid brightening or darkening of stripes, may enhance visibility during displays but are more commonly linked to ; however, they can play a role in signaling during close-range interactions. Acoustic signals are rare, though tail whips may be employed in escalated conflicts to assert dominance or ward off threats. The social structure of A. aquaticus populations features small home ranges with substantial overlap among individuals of all sexes and ages, suggesting a generally tolerant dynamic rather than strict exclusivity. Males may form small harems around their territories during the breeding season, but females and juveniles show high tolerance for conspecifics, often co-occurring in dense groups on outcrops near . Female-female interactions are less aggressive than male-male encounters, with occasional displays but minimal combat; females may show aggression toward intruding males outside breeding periods. Juveniles tend to disperse rapidly from natal areas, integrating into peripheral overlaps without eliciting strong territorial responses. These patterns peak in activity during the , aligning with heightened mating displays.

Reproduction

Mating and Courtship

Males of Anolis aquaticus are polygynous, defending territories along stream banks where they court multiple females using visual displays. rituals primarily involve head-bobbing and extension of the male's orange-red , a sexually selected signal that advertises male quality to potential mates. Larger size correlates with male boldness, characterized by reduced vigilance behaviors such as head scanning, which may enhance success by signaling competitive ability and condition to females. Females exhibit , preferring males with brighter, more conspicuous dewlaps over those with muted coloration, as these signals indicate superior or resource-holding potential in the riparian . This preference likely contributes to , though conspicuous displays also increase predation risk from visually hunting predators. Male-male for territories and mates is common, with bolder individuals potentially gaining advantage in agonistic encounters and access to receptive females. The reproductive season for this species is year-round. Copulation follows successful and is relatively brief, though specific durations have not been quantified in detail for this species.

Egg Laying and Development

Anolis aquaticus females typically lay clutches consisting of 1–2 , which are deposited in concealed sites such as moist soil cracks or under rocks adjacent to watercourses. These oviposition sites are influenced by local levels, ensuring adequate hydration for development. Eggs incubate for 75–82 days under temperatures ranging from 19–23°C, conditions common in the shaded, riparian environments of their range. Upon , juveniles measure approximately 25 mm (2.5 cm) in snout-vent length (SVL) and exhibit immediate independence, with no evidence of . Sexual is attained by females at 4–6 months of age and by males at 5–7 months, enabling relatively rapid into breeding populations. In the wild, individuals have a lifespan of 1–2 years due to predation and environmental pressures.

Ecology

Diet and Foraging

Anolis aquaticus primarily consumes non-aquatic , which make up approximately 75% of its diet, alongside a smaller proportion of aquatic prey such as insect larvae and potentially small crustaceans. Observed prey items include (Formicidae), beetles (Coleoptera: Limnichidae, Elmidae), flies (Diptera: , Heleidae), hemipterans (Saldidae), spiders (Araneae), eruciform larvae (), and adult odonates such as dragonflies () and damselflies. This composition reflects opportunistic feeding near riparian habitats, where terrestrial and semi-aquatic arthropods are abundant. The species employs a sit-and-wait strategy, typically perching on streamside boulders with its head positioned above the to scan for prey. It preferentially targets non-moving or dead , an adaptation to the visual challenges posed by flowing , and captures them using a projectile that extends up to nearly twice the distance of its head length. Boulders are used in over 56% of observations, facilitating access to both terrestrial and emerging during . A stronger bite force in A. aquaticus compared to closely related semi-aquatic suggests the inclusion of harder prey, such as crustaceans or small , which may require greater crushing ability. Juveniles tend to consume smaller prey items relative to their body size, while adults shift toward larger insects, consistent with ontogenetic growth in jaw size and strength across anoles. Occasionally, individuals engage in underwater foraging, using an exhaled air bubble for rebreathing to pursue submerged prey.

Predators and Defenses

Anolis aquaticus faces predation from a variety of animals in its riparian , including birds such as and , aquatic snakes, and . Juveniles are particularly vulnerable to smaller predators like spiders. These threats drive the evolution of specialized antipredator behaviors in the species. The primary defense mechanism of A. aquaticus is achieved through rapid body color changes that match surrounding microhabitats, reducing detectability to avian predators in heterogeneous environments. Additionally, the species employs tail , voluntarily shedding its tail to escape grasping predators, with autotomized individuals showing correlations to higher predation risk exposure. When fails, individuals rely on diving into nearby streams as an escape response; this behavior is highly effective against aerial predators, allowing prolonged submersion. To extend dive duration beyond simple breath-holding, A. aquaticus forms an air bubble over its nostrils by exhaling, which it re-breathes to recycle oxygen, enabling submersion times of up to 16 minutes—significantly longer than without the bubble. This , observed consistently during threat simulations, enhances evasion from pursuing predators like birds and snakes by outlasting their search time at the water surface. Diving physiology further supports this strategy. Human activities pose minimal direct predation risk but indirectly increase vulnerability through habitat degradation along .

Population and Conservation

Population Dynamics

The sex ratio of Anolis aquaticus is 1:1 at birth and remains consistent across juveniles and adults based on a mark-recapture study, with male survival probability at 51.6% compared to 40.1% for females. In a study at de Puriscal Canyon conducted from 1991 to 1993, a total of 292 unique individuals (including males, females, and juveniles) were recorded over an 8000 m² riparian area, yielding an estimated of approximately 36,500 individuals per km² when accounting for linear streamside distribution. Data from this period indicate no seasonal variations were quantified, and more recent population estimates are lacking. Recruitment rates show juvenile of 25–37%, with no significant sex-based differences (χ² = 3.48, df = 1, P > 0.05), though males demonstrate slightly higher rates at 37% compared to 25.4% for females. Maximum observed lifespan in mark-recapture studies reached 17 months. Capture-recapture censuses from the 1991-1993 study at key riparian habitats, involving body measurements and maturity assessments via dissections, provide data on fluctuations tied to reproductive outputs; however, no long-term monitoring data beyond 1993 is available, highlighting a gap in understanding current population trends up to 2025. Continued tracking is recommended to assess responses to climatic variability and other factors.

Conservation Status

Anolis aquaticus is classified as Least Concern on the , with the assessment originally conducted in 2007 and no updates indicating a change in status as of 2025. This designation reflects its relatively wide distribution across riparian habitats in southwestern and extreme western , although populations tend to be localized and dependent on streamside environments. The species faces moderate threats from caused by and agricultural activities, which can isolate stream habitats and reduce available riparian vegetation essential for its survival. poses a potential through alterations in flow regimes and increased , which could impact its semi-aquatic foraging and escape behaviors, though of severe effects remains limited. does not represent a significant concern for A. aquaticus. Populations of A. aquaticus benefit from occurrence in protected areas, including in , where habitat preservation supports stable local abundances. Given its Least Concern status and broad tolerance for varied stream conditions, no targeted species-specific conservation plans are deemed necessary at present. Key research gaps include the need for long-term monitoring to assess cumulative climate change impacts on population viability and suitability, as well as updated studies post-1993. Recent studies from 2024 underscore the species' adaptive resilience, particularly through physiological mechanisms like rebreathed air bubbles that enhance underwater endurance and thermal regulation.

Evolution and Adaptations

Evolutionary History

Anolis aquaticus belongs to the subgenus Norops within the genus Anolis, part of the diverse mainland radiation of anoles in Central and South America. Phylogenetic analyses place it within the Draconura clade, a group of primarily Central American species. Molecular phylogenies indicate that the Draconura clade, which includes A. aquaticus and closely related semi-aquatic species such as A. oxylophus, A. robinsoni, and A. riparius, diversified during the Miocene, approximately 10–15 million years ago, coinciding with the broader diversification of mainland anoles in Central America; a 2023 analysis based on mitochondrial COI sequences places A. aquaticus basal to a clade containing A. robinsoni, A. riparius, and A. woodi, suggesting more recent evolution within this semi-aquatic subgroup. The fossil record for Anolis aquaticus specifically is absent, but the genus Anolis exhibits a sparse history primarily from Miocene amber deposits in the Caribbean, which preserve early representatives of various ecomorphs and suggest an ancient radiation beginning in the Eocene but accelerating in the . Inferences from these s and molecular clocks indicate that mainland lineages, including those ancestral to A. aquaticus, likely originated and diversified in northern before dispersing northward into during the . Genetic studies using , such as the COI , reveal low sequence divergence between A. aquaticus and its terrestrial ancestors within Norops, supporting a relatively recent colonization of semi-aquatic habitats despite the deep phylogenetic history of the . These molecular data also highlight patterns of ecomorph convergence, where aquatic adaptations have evolved independently multiple times across anole lineages, including in Central American .

Key Adaptations

One of the most remarkable adaptations in Anolis aquaticus is its ability to rebreathe exhaled air underwater through a bubble formed over its nostrils, enabling extended submersion times. This trait relies on the lizard's hydrophobic , which traps air exhaled from the nostrils, creating a stable bubble that clings to the head due to specialized microstructural spines on the scales. A 2024 study experimentally confirmed that oxygen is extracted from this bubble, with rebreathing extending average durations by 32% compared to conditions where bubble formation was impaired, allowing up to several minutes in duration. This rebreathing mechanism represents an from the lizard's pre-existing hydrophobic skin properties, which originally facilitated terrestrial functions such as collection or rapid water shedding, but were co-opted for aquatic respiration without major morphological overhaul. In addition to rebreathing, A. aquaticus exhibits limb morphology suited for on boulders and perching in low riparian , with relatively long fore- and hindlimbs inherited from ancestors in the lineage, aiding in movement across rocky stream edges and during brief underwater escapes. Complementing these physical traits is the species' capacity for rapid whole-body color change, shifting from dark brown to light tan stripes, which enhances against aquatic and riparian substrates to evade visual predators. These adaptations collectively facilitate predator evasion by allowing prolonged underwater refuge, a not feasible for more arboreal congeners, thereby enabling niche partitioning along stream edges where A. aquaticus exploits semi-aquatic habitats distinct from the canopy-dwelling niches of other species. This specialization may also represent an for opportunistic foraging in shallow waters, though primarily serving antipredator functions. Such traits have evolved convergently in other semi-aquatic anoles, including Anolis vermiculatus in , where similar hydrophobic skin microstructures support bubble retention and extended dives, highlighting repeated adaptive solutions to aquatic lifestyles within the genus.

References

  1. https://reptile-database.reptarium.cz/species?genus=anolis&species=aquaticus
  2. https://www.researchgate.net/publication/395907247_Differences_in_Habitat_Use_Thermal_Ecology_and_Behavior_of_the_Semiaquatic_Lizard_Anolis_aquaticus_at_a_High-_and_Low-Elevation_Site
  3. https://www.journals.uchicago.edu/doi/10.1086/717678
  4. https://www.binghamton.edu/news/story/2766/research-flashy-lizards-are-more-attractive-to-mates-and-to-predators
  5. https://par.nsf.gov/servlets/purl/10354029
  6. https://www.researchgate.net/publication/377978658_Anolis_aquaticus_Norops_aquaticus_Water_Anole_Diet
  7. https://www.sciencedirect.com/science/article/pii/S0960982221005753
  8. https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=323567
  9. https://www.mapress.com/zootaxa/2012/f/zt03477p108.pdf
  10. https://academic.oup.com/sysbio/article/66/5/663/3056323
  11. https://pmc.ncbi.nlm.nih.gov/articles/PMC6430965/
  12. https://www.mdpi.com/1424-2818/17/10/673
  13. https://www.climatestotravel.com/climate/costa-rica
  14. https://royalsocietypublishing.org/doi/10.1098/rsbl.2024.0371
  15. http://www.marthamunoz.com/uploads/2/3/4/5/23454312/munoz_2015_jnathist.pdf
  16. https://pmc.ncbi.nlm.nih.gov/articles/PMC8541734/
  17. http://www.bio.utexas.edu/faculty/antisense/papers/Copeia1984Anolis.pdf
  18. https://www.anoleannals.org/2016/10/02/super-honest-dewlaps-and-trait-scaling-relationships-in-semi-aquatic-anoles/
  19. https://cdnsciencepub.com/doi/10.1139/cjz-2016-0200
  20. https://academic.oup.com/biolinnean/article/doi/10.1093/biolinnean/blaf075/8268837
  21. https://link.springer.com/article/10.1007/s00265-024-03493-0
  22. https://www.anoleannals.org/2017/05/24/what-drives-substrate-use-patterns-in-semiaquatic-anoles/
  23. https://www.researchgate.net/publication/353608811_Anolis_aquaticus_Norops_aquaticus_Water_Anole_Underwater_breathing
  24. https://www.researchgate.net/publication/232674807_Use_of_Habitat_by_the_Semiaquatic_Lizard_Norops_aquaticus
  25. https://www.anoleannals.org/2017/01/14/24289/
  26. https://doi.org/10.1098/rsbl.2024.0371
  27. http://www.anthonyherrel.fr/publications/Mahler%20et%20al%202010%20Anolis%20newsletter%206.pdf
  28. https://onlinelibrary.wiley.com/doi/10.1111/1749-4877.12238
  29. https://eprints.whiterose.ac.uk/id/eprint/168862/1/GEB-2019-0253.R4_final.pdf
  30. https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2022.821115/full
  31. http://www.scielo.org.pe/scielo.php?script=sci_arttext&pid=S1726-22162005000100009
  32. http://bio-nica.info/biblioteca/leal2002anolis.pdf
  33. https://blog.willyvanstrien.nl/2021/06/03/bubble-on-the-head/
  34. https://academic.oup.com/cz/article/68/1/129/6332003
  35. https://www.binghamton.edu/news/story/1722/scuba-diving-lizard-can-stay-underwater-for-16-minutes
  36. https://www.binghamton.edu/news/story/4779/research-explores-the-cooling-effects-of-scuba-diving-in-lizards
  37. http://www.scielo.org.pe/pdf/ecol/v4n1-2/a09v4n1-2.pdf
  38. https://www.iucnredlist.org/species/203077/2759916
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  40. https://pubmed.ncbi.nlm.nih.gov/35948691/
  41. https://www.inaturalist.org/taxa/116393-Anolis-aquaticus
  42. https://www.researchgate.net/publication/372621159_Two_new_species_of_semiaquatic_Anolis_Squamata_Dactyloidae_from_Costa_Rica
  43. https://www.biotaxa.org/Zootaxa/article/view/zootaxa.5319.2.6
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  47. https://journals.biologists.com/jeb/article/224/19/jeb242939/272432/Convergent-evolution-of-skin-surface
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