The Noronha Skink (Trachylepis atlantica) – A Unique Island Dweller

The Noronha skink (Trachylepis atlantica) is a fascinating reptile species endemic to the Fernando de Noronha archipelago off the northeastern coast of Brazil. This small lizard has adapted to its isolated island habitat over millions of years, developing unique characteristics that set it apart from its mainland relatives. In this article, we’ll explore the taxonomy, habitat, history, features, behavior, and life cycle of this intriguing creature.

Taxonomy

The Noronha skink, scientifically known as Trachylepis atlantica, belongs to the family Scincidae, which includes over 1,500 species of skinks worldwide. The genus Trachylepis comprises numerous skink species found primarily in Africa and surrounding islands, with the Noronha skink being a notable exception due to its location in the Atlantic Ocean.

Previously, this species was classified under the genus Mabuya, but recent genetic studies have led to its reclassification within the Trachylepis genus. This taxonomic change reflects our evolving understanding of skink phylogeny and highlights the unique evolutionary history of the Noronha skink.

Habitat and Distribution

The Noronha skink is found exclusively on the Fernando de Noronha archipelago, a group of 21 islands and islets located approximately 354 kilometers (220 miles) off the coast of Brazil. The main island, also called Fernando de Noronha, serves as the primary habitat for this species, although it can be found on some of the smaller surrounding islets as well.

The archipelago’s tropical climate, characterized by warm temperatures year-round and distinct wet and dry seasons, has shaped the Noronha skink’s habitat preferences and adaptations. These lizards can be found in various microhabitats across the islands, including:

1. Rocky outcrops and cliffs
2. Coastal vegetation
3. Forest edges
4. Human-modified areas such as gardens and buildings

The Noronha skink has demonstrated remarkable adaptability to different environments within its limited range. This flexibility has allowed the species to thrive despite the islands’ relatively small size and the introduction of non-native species.

Species History and Temporal Range

The exact timeline of when the Noronha skink first colonized the Fernando de Noronha archipelago remains a subject of scientific debate. However, it is believed that the species’ ancestors arrived on the islands millions of years ago, possibly through rafting on vegetation carried by ocean currents from the African continent.

Since its arrival, the Noronha skink has undergone significant evolutionary changes, adapting to its new island environment. This process of island evolution has resulted in the development of unique traits not found in its mainland relatives.

The species’ temporal range extends from its arrival on the islands to the present day. Despite facing challenges such as habitat alteration and the introduction of non-native predators, the Noronha skink has managed to persist and maintain a stable population on the archipelago.

Distinguishing Features and Description

The Noronha skink is a medium-sized lizard with several distinctive features that set it apart from other skink species. Here’s a detailed description of its physical characteristics:

Size and Weight:

• Length: Adults typically measure 20-30 centimeters (8-12 inches) from snout to tail tip.
• Weight: Average weight ranges from 30 to 50 grams (1-1.8 ounces).

Coloration and Patterns:

• The Noronha skink displays a striking coloration that aids in camouflage and thermoregulation.
• The dorsal (upper) surface is typically dark brown or black, often with a metallic sheen.
• A distinctive golden or yellowish stripe runs along each side of the body, from the snout to the base of the tail.
• The ventral (underside) surface is usually lighter in color, ranging from pale yellow to whitish.
• Some individuals may exhibit variations in pattern, such as speckles or mottling on the dorsal surface.

Anatomy and Locomotion:

• Body: The Noronha skink has a robust, elongated body typical of many skink species.
• Limbs: Four well-developed limbs with five digits on each foot, equipped with sharp claws for climbing and digging.
• Tail: The tail is long and can be shed (autotomy) as a defense mechanism against predators. If lost, the tail can regenerate, although the regrown portion may differ in color and texture from the original.
• Head: A triangular head with a slightly pointed snout and well-developed jaw muscles for capturing and crushing prey.
• Eyes: Large eyes with movable eyelids, unlike some gecko species.

Thermoregulation and Shedding:

Like all reptiles, the Noronha skink is ectothermic, relying on external sources for body heat. It regulates its body temperature by basking in the sun or retreating to shaded areas. The dark coloration of its dorsal surface helps absorb heat efficiently.

The species undergoes periodic shedding (ecdysis) to accommodate growth and replace worn scales. Unlike snakes that shed their skin in one piece, skinks typically shed their skin in patches over several days.

Senses

The Noronha skink possesses well-developed senses that help it navigate its environment, locate prey, and avoid predators:

1. Vision: Excellent color vision and the ability to detect movement, crucial for hunting insects and avoiding threats.
2. Hearing: While not as acute as some other reptiles, the Noronha skink can detect low-frequency sounds and vibrations through the ground.
3. Smell: A highly developed sense of smell, aided by a forked tongue that collects chemical particles from the air and transfers them to the Jacobson’s organ in the roof of the mouth for analysis.
4. Touch: Sensitive skin that can detect changes in temperature and texture, useful for thermoregulation and navigation.

The Noronha skink is not known for producing distinct vocalizations, unlike some gecko species. However, they may emit soft hissing sounds when threatened or handled.

Behavior

The Noronha skink exhibits a range of interesting behaviors adapted to its island lifestyle:

Activity Patterns:

• Primarily diurnal (active during the day), with peak activity during morning and late afternoon hours.
• May become crepuscular (active at dawn and dusk) during extremely hot weather.

Territoriality:

• Males establish and defend territories, especially during the breeding season.
• Territorial disputes may involve displays of body posturing, head bobbing, and, in some cases, physical confrontations.

Communication:

• Visual signals play a crucial role in communication, including head bobs, push-ups, and tail movements.
• Chemical cues, deposited through scent glands, are used to mark territories and signal reproductive status.

Predator Avoidance:

• When threatened, the Noronha skink can shed its tail (caudal autotomy) to distract predators and escape.
• Utilizes its excellent climbing abilities to retreat to crevices and high perches when danger is perceived.

Foraging:

• Actively forages for food throughout its territory.
• Opportunistic feeder, consuming a variety of insects, spiders, and occasionally small fruits or nectar.

Reproduction

The reproductive biology of the Noronha skink is an essential aspect of its life history:

Mating and Breeding:

• Breeding typically occurs during the wet season (February to July) when food resources are most abundant.
• Males engage in courtship displays, including head bobbing and body arching, to attract females.
• Mating involves the male grasping the female with his jaws, a common behavior among skinks.

Egg-Laying and Incubation:

• Unlike some skink species that give birth to live young, the Noronha skink is oviparous (egg-laying).
• Females typically lay clutches of 2-5 eggs in hidden, moist locations such as under rocks or in leaf litter.
• Incubation period lasts approximately 60-80 days, depending on temperature and humidity conditions.

Hatchlings:

• Newborn skinks emerge from their eggs fully developed, measuring about 5-7 centimeters (2-3 inches) in total length.
• Hatchlings are independent from birth and must fend for themselves.
• Juvenile coloration may be more vibrant than adults, possibly serving as camouflage against predators.

Life Cycle and Growth

The life cycle of the Noronha skink can be divided into several stages:

1. Birth: Hatchlings emerge from their eggs after 60-80 days of incubation.
2. Juvenile Stage: Rapid growth occurs during the first year of life, with individuals reaching about half their adult size.
3. Subadult Stage: Continued growth and development of secondary sexual characteristics.
4. Adult Stage: Sexual maturity is typically reached at 2-3 years of age.
5. Reproductive Years: Adults can reproduce annually for several years.
6. Aging: As skinks age, growth slows, and reproductive output may decrease.

Growth Timeline:

• 0-6 months: Rapid growth phase, focusing on survival and avoiding predation.
• 6-18 months: Continued growth and development of adult coloration patterns.
• 18-36 months: Attainment of sexual maturity and full adult size.

Aging Changes:

• Older individuals may exhibit faded coloration and increased scarring.
• Regenerated tails in older skinks may be less coordinated and shorter than original tails.

The lifespan of the Noronha skink in the wild is estimated to be 5-7 years, although some individuals may live longer under favorable conditions.

Conclusion

The Noronha skink (Trachylepis atlantica) is a remarkable example of island evolution, having adapted to its unique habitat on the Fernando de Noronha archipelago over millions of years. Its distinctive features, behaviors, and life history strategies reflect the challenges and opportunities presented by its isolated environment.

As an endemic species, the Noronha skink plays a crucial role in the archipelago’s ecosystem, serving as both predator and prey. Its ability to thrive in various habitats, including human-modified areas, demonstrates the species’ adaptability. However, this adaptability should not be taken for granted, as the skink still faces threats from habitat alteration and introduced predators.

Continued research and conservation efforts are essential to ensure the long-term survival of this unique island dweller. By studying and protecting the Noronha skink, we not only preserve a fascinating species but also gain valuable insights into the processes of evolution and adaptation on oceanic islands.