Lampropholis delicata, the delicate skink,A new genus and a new species of skink from Victoria dark-flecked garden sun skink,Lampropholis delicata , James Cook University garden skink, delicate garden skink, rainbow skink or plague skink, or the metallic skink is native to Australia and invasive in New Zealand and Hawaii where it is commonly found in gardens. The species is known for their color dimorphism between males and females; striped morphs and non-striped morphs exist in this species, however the stripe is less pronounced in males. This species' diet consists of a wide range of prey, such as spiders, bees, larvae, and termites. Mating occurs in the late summer and generally one clutch of 2 to 4 eggs are laid per year by each female.
Description and identification The delicate skink is more common in suburban gardens than in adjacent native bushland. It has a moderate body with a medium length, slender tail. Its scales are smooth. The back and sides are greyish-brown to rich brown, often with darker and paler flecks. A narrow yellowish-brown stripe is usually present on the outer edge of the back. The species can also have two distinct forms: a prominent white stripe and a less prominent white stripe. This dimorphism is not strictly distinguished by gender.
Lampropholis delicata were accidentally introduced into Lord Howe Island, a remote oceanic island between Australia and New Zealand, in the 1980s and subsequently introduced into the Hawaiian islands. Upon introduction, these lizards have rapidly spread themselves across the islands. On Lord Howe Island specifically, they reside in low-elevation vegetation communities. They are a diurnal species whose activity varies seasonally, in which activity peaks during the months of November and December. Sexual dimorphism is present in L. delicata, in which males have broader, longer heads and females have larger abdomen and body sizes. Female reproduction takes place in the spring season and more commonly in the late summer, ranging between the months of September and February. A positive correlation exists between the clutch size and body size of the female, and although it is common for clutch sizes to vary between 1 and 7 eggs, the average clutch size is between 2 and 4. Communal egg nests are also common, with anywhere between 11 and over 200 eggs. Tail loss and subsequent regeneration occurs frequently with these lizards but is observed most commonly in females and adults.
Physiology Autotomy and spinal cord regeneration Autotomy is the ability for organisms, such as L. delicata, to intentionally shed an appendage or limb, and this ability has independently evolved in many vertebrates such as other reptiles, fish, and amphibians. Caudal autotomy has developed as a last resort anti-predator behavior, when other anti-predator behaviors like fleeing and crypsis fail. By detaching their tails, lizards are able to flee from their predators quicker, while the thrashing of the detached tails post-autotomy serves to distract the predator and allow the lizard to successfully escape. These lizards are able to shed their tail at any point along the length of it, as most of their caudal vertebrae have fracture planes. Although the immediate survival benefits are evident, the subsequent lack of a tail hinders locomotion, interferes with habitat use and activity, and increases an individual's susceptibility to future encounters with predators. After losing their tails, L. delicata cannot utilize their caudal autotomy capabilities as a defense strategy again until their tail regrows to a sufficient length. Furthermore, the benefits of a long tail include increased stride lengths, which become significantly smaller with the loss of their tail, thus hindering locomotor performance and enhancing future predation risks. The tails also serve as fat reserves, so the length of the tail discarded correlates to the amount of energy storage lost due to autotomy. Additionally, because lizards become less active after autotomy, they increase the amount of time spent in shelters or microhabitats, which may decrease their vulnerability to predators in the short term, but impacts their foraging ability, thermoregulatory mannerisms, and tail regeneration efficiency.
Biological evidence suggests that tail regrowth is stimulated by a regenerating spinal cord. These lizards' spinal cords consist primarily of ependymal cells that group around a tubular central canal containing cerebrospinal fluid. Axons are interspersed between these ependymal cells and encased in collagenous leptomeninges, and although their exact origin is unknown, it is hypothesized that the axons come from differentiated cells in the regenerate or from neuronal somata in the tail stump. Within the spinal cords of regenerating tails, specialized types of cells known as cerebral spinal fluid contacting neurons (CSFCN) have been observed, and they grow in a pear-like shape and are about the size of or bigger than their neighboring ependymal cells. Some distinct biomolecular features of CSFCNs include the mitochondria with few tube-like invaginations and the network of microtubules. Fingerlike luminal protrusions, large amounts of cytoskeletal elements, and the contact between fingerlike projections of receptor cell dendrites and Reissner fibres allow for the regeneration of secretory, mechanical, and sensory functions of the tail respectively.
Habitat and distribution Lampropholis delicata is a skink of the subfamily Lygosominae, originally from Eastern Australia. Accidentally introduced and invasive in New Zealand, Hawaii, and Lord Howe Island.
Phylogeographic divergence in eastern Australia As a result of topographic and dry habitat barriers, Lampropholis delicata have evolved to demonstrate a complex mosaic of non-overlapping, geographically oriented clades and subclades. Since the accidental introduction of L. delicata into eastern Australian habitats, many biogeographic barriers and climatic oscillations have contributed to the evolutionary history of these lizards. They reside over a vast array of moist habitats, including woodland and heaths, sclerophyll forests, and rainforests, while also making appearances in suburban gardens near the eastern coast. L. delicata can be classified into nine main clades, which diverged during the late Miocene through Pliocene epochs. This divergence correlates to a period of a drying climate in the rainforest habitats, which restricted the rainforests to a series of disjunct remnants. L. delicata, which resides on the fringes of the rainforest, thus probably also encountered similar fragmentation and reduction. Dry habitat corridors suggest that drier vegetation served as effective barriers to enable these mesic-adapted lizards to disperse, and high elevation areas—which are patchy remnants of the moist rainforests—located more inland have also created such geographic isolation, as they offer a wetter and cooler refuge for these lizards. Additionally, the phylogeographic breaks demonstrated by L. delicata along with many other lizard species is believed to be caused by cycles of marine inundation experienced by the area since the Miocene epoch.
Behavior
Diet and foraging behavior Lampropholis delicata can be classified as diurnal, terrestrial, arthropod feeders, and they consume a wide range of prey. An in depth analysis of L. delicata gut samples—taken from their foregut, hindgut, and stomach—reveals the wide variety of prey taxa and size classes incorporated into their diets. These gut samples are taken from L. delicata that reside in the Mumbulla State Forest, a region with a vast history of fires and logging. As a result of intense fires, several canopies and ground vegetation have ceased to sustain the lizard population, resulting in a primarily carnivorous diet. L. delicata primarily consumes spiders, insects, snails, and crustaceans. Gut analysis after a major fire in 1980 reveals that these lizards ate limited amounts of invertebrates, and they had a preference for bees, wasps, and springtails over beetles, termites, and ants relative to their related species L. guichenoti, which also reside in the Mumbulla State Forest.
L. delicata are characterized as general feeders, and their prey can be described as aerial and arboreal (i.e. bugs, beetles), slow-moving (i.e. larvae), concentrated (i.e. termites, ants), concealed (i.e. crickets, cockroaches), and active (i.e. spiders). These lizards demonstrate foraging behavior and employ "active foraging" and "sit-and-wait" strategies to capture their prey. Because their environment is prone to fires and droughts, L. delicata have adapted flexibility into their foraging ecology. They practice opportunistic foraging in that they consume a wide variety of prey and adapt to whatever food becomes available, rather than following a foraging pattern and consuming similar prey. As a result of droughts, arthropods become less abundant; however, L. delicata are not dependent on resident invertebrates, like those that reside in litters, and instead forage after a broader range of insects spanning both aerial-arboreal invertebrates and ground-dwelling invertebrates.
Microhabitat selection With selecting a habitat, animals must consider the cost and benefit trade-offs of acquiring shelter and food while evading competitors and predators. Because lizards are ectothermic, thermal conditions and subsequent impacts on physiological performance must also be taken into consideration for habitat selection. Thus deciding the degree of exposure or insulation, canopy or ground cover, structure of litter layer, or amount of grasses, forbs, rocks, and woody debris within the shelter remain prevalent considerations for lizard habitats. For small lizards like L. delicata, the structure of the leaf litter layer influences thermoregulation, feeding, and refuge seeking, making it an influential factor in microhabitat selection.
Experimental evidence suggests that L. delicata prefer leaf litters to bare substrate, with more nuanced preferences for different types of leaves, as they adjust the structure, depth, and distribution of their litter layer accordingly. Generally, these lizards select more open structures. Such open structure makes thermoregulation more effective, as lizard individuals can move into different positions within their habitat to avoid overheating or raise their temperature to more optimal levels. Achieving optimum temperature levels influences their efficiency in avoiding predators and capturing prey, thus making open habitats conducive to many other behavioral characteristics. Furthermore, open litters allow for more effective foraging movements and also provide lizards with more access points and space to move, which is necessary when accessing refuge for predator avoidance. The abundance of L. delicata in an area may also be influenced by habitat modifications that vary the structure of their litter layers.
Reproduction and life cycle