The Italian wall lizard or ruin lizard (Podarcis siculus, from the Greek meaning foot and agile), 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 (1986) described 52 subspecies of P. siculus. Podnar et al. (2005) 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 150–250 mm (5.9–9.8 in) 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.
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