Italian wall lizard
The Italian wall lizard or ruin lizard, is a species of lizard in the family Lacertidae. P. siculus is native to southern and southeastern Europe, but has also been introduced elsewhere in the continent, as well as North America, where it is a possible invasive species. P. siculus is a habitat generalist and can thrive in natural and human-modified environments. Similarly, P. siculus has a generalized diet as well, allowing it to have its large range.
P. siculus is notable for having many subspecies within its large range. Studies evidence how rapidly P. siculus subspecies can become distinguishable from larger populations given geographic isolation. A 2008 study detailed distinct morphological and behavioral changes in a P. siculus population indicative of "rapid evolution".
P. siculus is a sexually dimorphic lizard species whose physical description varies across its subspecies, but it generally has a green or brown back and white or green belly. It is also oviparous, meaning females lay eggs, and they lay 3 or 4 clutches per year.
Taxonomy
Subspecies and hybridization
P. siculus contains dozens of subspecies. Many different subspecies of P. siculus have been described, though some distinguished by very few morphological differences. Henle and Klaver described 52 subspecies of P. siculus. Podnar et al described 6 groupings of P. siculus in the species' native range. The first clade is the Sicula clade, which includes Southwestern Calabria, Sardinia, and Sicily. The Monesterace clade includes the Istrian coast. The Cantazaro clade includes central Calabria. The Tuscany clade spans across Western Italy. The Suzac clade includes islands in southern and central Dalmatia. The final clade is the Campestris-sicula clade, which spans Northern Italy and the Adriatic Islands inhabited by P. siculus.There have also been reports of hybridization between P. siculus and other species of the Podarcis genus, such as P. tiliguerta and P. raffonei.
"Island syndrome" and sources of phenotypic variation
Given the sheer number of subspecies of P. siculus and its vast geographic range, the evolutionary history of this species has been studied as case studies for certain evolutionary concepts. One such concept is "island effects," purported expansions of phenotypic range due to the availability of new niches. The evidence for island effects in reptiles, and lizards in particular, is not uniform or cohesive. A study evaluated the evidence of island effects among 30 island and 24 mainland populations of P. siculus for variation in head shape, size, and sexual dimorphism. Most of the disparities between sizes of individuals were explained by sexual dimorphism, though a low, but significant amount of centroid size variation could be attributed to being from a mainland versus an island population. Generally, individuals from island populations were smaller and had less sexually dimorphic body sizes. There was no connection between insularity and head shape sexual dimorphism, however insular head sizes were on average lower. These results complicate how P. siculus fits in with the island syndrome hypothesis, which posits that body and head sizes should be higher in insular populations. However, the island syndrome hypothesis also predicts a reduction in sexual dimorphism among insular populations, which was observed.Another study that sought to understand causes of phenotypic variation among populations of P. siculus analyzed variation in head size, cranial musculature, and bite force. Using 16 populations, 14 from Adriatic Islands and two from mainland populations, the researchers found significant links between the ecology of the habitat occupied, bite force, and cranial musculature. For example, the consumption of mechanically resistant foods on islands with fewer sources of food was associated with stronger bite forces and musculature, along with increased sexual dimorphism in head dimensions. This study demonstrated that cranial musculature responds in predictable ways given similar ecological conditions. Population-level ecological pressures can result in the macroevolutionary emergence of variation between populations in P. siculus.
Physical description
The snout–vent length of P. siculus is on average. P. siculus is characterized by a green or brown back with a white or green belly. There is variation in length and color diversity due to the many subspecies and populations of P. siculus. For example, some subspecies are melanic, meaning that parts of the back and belly have hints of blue. Such coloration is found on island populations of P. siculus rather than continental populations.Head size is a sexually dimorphic trait, with males having larger heads and stronger jaws than females. It is hypothesized that this size difference is due in part to prey consumption needs in males and male–male aggression.
Range
True to its name, P. siculus is native to Italy and is one of the most common lizards there. Its range also includes Bosnia and Herzegovina, Croatia, France, Montenegro, Serbia, Slovenia, and Switzerland, but it has also been introduced to Spain, Turkey, the United States, and Canada.As an introduced species
Populations of P. siculus in North America have been documented from Topeka, Kansas; Long Island, New York; Greenwich, Connecticut; Levittown, Pennsylvania; Joplin, Missouri; and the Cincinnati area of Ohio, Indiana and Kentucky where P. siculus and P. muralis can both be found in very high concentrations and have become so well established that the Ohio Department of Natural Resources now classifies them as a resident species rather than an invasive species because they are so successful and have been present for so long. Although illegal, it is not uncommon for people in the Cincinnati area to "trade" P. muralis lizards with people who live in areas with high population of P. siculus and then releasing significant numbers of the lizards in their own yards and rock walls.The species seems to be extending its range from an initial colonization event in western Long Island, presumably by using railroad tracks as dispersal corridors along the middle East Coast. Wall lizards seem to have colonized along the southwest Connecticut coast near Greenwich, as well as around Burlington County, New Jersey. There are some reports that these lizards descended from a group of lizards released in Mount Laurel in 1984. In 2020, a large number of P. s. campestris entered Great Britain as stowaways among shipments of grapes, before being intercepted.
P. siculus has also entered the Iberian Peninsula as an invasive species where it competes with the native Podarcis virescens species. Competition between the two lizard species has led to displacement of P. virescens lizards as they are outcompeted by P. siculus lizards.
Habitat and ecology
P. siculus is a habitat generalist and thrives in many natural and human-modified environments. Habitats of P. siculus include forests, grasslands, shrublands, rocky areas, and farmland. It is able to live in such open habitats due to biological characteristics, such as high thermophily, which is the ability to thrive in high temperatures.Diet
P. siculus is a generalist predator. Its diet consists of a wide variety of invertebrates, mainly arthropods. P. siculus predates on small vertebrates as well. Plant matter comprises a much greater percentage of the diet of P. siculus than other related lizards. There is also a disparity in diet diversity between the sexes, with males having a more diverse diet than females. Contrary to common ecological thought, there is little relationship between habitat area and diet diversity for P. siculus. Different levels of taxonomic prey diversity does not seem to affect the diversity of diets in different P. siculus populations, but insular populations of P. siculus do consume a greater percentage of plant matter as a part of their diet.Predation
Predators of P. siculus include snakes, birds, and feral cats.Reproduction
P. siculus is oviparous. Females can lay 3 or 4 clutches of 4-7 eggs per year. The number of eggs laid per clutch does vary by population. For example, populations on small islands of Croatia lay fewer eggs that hatch into larger offspring. The reproductive season of P. siculus begins in May and ends in July. Gravidity does not impose major physical burden upon females. Gravid females engage in more basking behavior than their non-gravid counterparts.The activity of P450 in the brain of male P. siculus differs based on the reproductive stage of the individual. Importantly, P450 localizes to parts of the brain involved in reproductive and behavioral regulation. Thus, P450 is implied in the regulation of sexual behavior in P. siculus.
Disease
and bacteria are common among P. siculus and its various subspecies. Common bacterial species include Pantoea, Citrobacter, Morganella morganii, Pseudomonas aeruginosa, Coagulase-Negative Staphylococci, Enterobacter, E. coli, Schewanella, and Providencia. When tested, one out of ten isolated strains of Citrobacter were multidrug-resistant. Other isolated strains were antibiotic resistant as well.Parasite species include pinworms, Ophionyssus natricus, coccidia, and Dicrocoelidae.
Some of the bacteria and parasites specific to continental populations of P. siculus have been identified to be zoonotic. Insular populations of P. siculus have similar levels of bacterial diversity to mainland populations.
Tick infestation of P. siculus can be common in man-made habitats. Tick infestation is generally more pronounced in large males, which may be a result of their increased home ranges. Tick load varies based on the type of environment that P. siculus inhabits. For example, females inhabiting traditionally-managed olive plantations have significantly higher tick loads than those residing in intensively-managed olive plantations.