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.

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.^[9]

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.^[10]

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.^[11]

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.^[7]

L. delicata in Hawaii

Lampropholis delicata was accidentally imported to the Hawaiian islands from Australia around the 1900s via shipments of plant materials and lumber. It was noted as an unreported specimen taken on the Oahu island and identified as a Lipinia noctua at that time, then later reclassified as Lygosomoa metallicum (the metallic skink) because of its physical appearance. L. Metallicum does not occur in Hawaii, however, and is instead a misidentification of L. delicata.^[15] L. delicata are most common on the Oahu island but are also present on other islands in Hawaii, including the main island and Kauai. These lizards bear great importance in Hawaiian zoogeography because they have established high-altitude records amidst all the Hawaiian reptiles at 1220 meters on the Kauai island and 1130 meters on the main island. In fact, these lizards prefer and thrive at much higher and wetter altitudes in Hawaii and other species of lizards. Because these lizards are semi-mountainous and found in dry to wet sclerophyll forests, they are distributed throughout the dry lowland and wet upland.^[15]

The three populations of L. delicata found on the main island, Oahu, and Kauai differ with respect to their average body length and in the numbers of eggs they produce. Female lizards at a sexually mature age are larger on the big island and Kauai relative to those on Oahu. The Oahu females average about 38.6 millimeters in body length while those from the main island and Kauai average a length of 41.2 millimeters and 41.8 millimeters respectively. It is theorized that Oahu females grow to a relatively smaller body size because of their higher population densities, thus creating competition amongst individuals for food and space availability.  Competition against other species might also be a possibility, and the inter and intraspecific competition experienced by Oahu females may also serve to explain the reduced egg production, as generally body size correlates to clutch size (smaller individuals with less internal body capacity lay fewer eggs than larger individuals). As such, Oahu females have a lower average number of eggs per clutch relative to the sexually mature female lizards on the main island and Kauai. Female lizards from Oahu have an average of 2.9 eggs, while the main island females average 4.7 eggs per clutch and Kauai females average 4.1 eggs per clutch.^[15]