Italian Wall Lizard

The Italian wall lizard or ruin lizard (''Podarcis siculus'', from the Greek meaning agile and feet) is a species of lizard in the family Lacertidae. ''P. siculus'' is native to Bosnia and Herzegovina, Croatia, France, Italy, Serbia, Montenegro, Slovenia, and Switzerland, but has also been introduced to Spain, Turkey, the United States, and Canada. It is the most abundant lizard species in southern Italy.

''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 their young in eggs, and they lay 3 or 4 clutches per year.

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.Dipineto L, Raia P, Varriale L, et al. (2018). "Bacteria and parasites in ''Podarcis sicula'' and ''P. sicula klemmerii'' ". ''BMC Veterinary Research'' 14 (1): 392. https://doi.org/10.1186/s12917-018-1708-5

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.Taverne M,  Fabre A-C,  King-Gillies N, et al.  (2019). "Diet variability among insular populations of ''Podarcis'' lizards reveals diverse strategies to face resource-limited environments". ''Ecology and Evolution''  9 (22): 12408–12420. https://doi.org/10.1002/ece3.5626

Range

''P. siculus'' is native to Italy and is one of the most common lizards found in the nation. Its range also includes Bosnia and Herzegovina, Croatia, France, Montenegro, Slovenia, and Switzerland. ''P. siculus'' has also been introduced to Spain, Turkey, and multiple sites in the United States.Crnobrnja-Isailovic J, Vogrin M, Corti C, Pérez Mellado V, Sá-Sousa P, Cheylan M, Pleguezuelos J, Sindaco R, Romano A, Avci A (2009). "''Podarcis siculus'' (errata version published in 2016)". ''The IUCN Red List of Threatened Species'' 2009: e.T61553A86151752. https://dx.doi.org/10.2305/IUCN.UK.2009.RLTS.T61553A12515189.en. Downloaded on 31 October 2021

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.Corti, Claudia; Biaggini, Marta; Berti, Roberto (2009). "Different habitats, different pressures? Analysis of escape behaviour and ectoparasite load in ''Podarcis sicula'' (Lacertidae) populations in different agricultural habitats". ''Amphibia-Reptilia'' 30 (4): 453-461. https://doi.org/10.1163/156853809789647068 Web. 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.Bonacci, Teresa; Capula, Massimo; Brandmayr, Tullia Zetto; Brandmayr, Pietro; Aloise, Gaetano (2008). "Testing the predatory behaviour of ''Podarcis sicula'' (Reptilia: Lacertidae) towards aposematic and non-aposematic preys". ''Amphibia-Reptilia'' 29: 449-453. https://doi.org/10.1163/156853808785111986 Web. 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.Rocha, Iolanda. "''Podarcis Sicula''". ''Invasive Species Compendium'', https://www.cabi.org/isc/datasheet/68192#tosummaryOfInvasiveness.

Reproduction

''P. siculus'' is oviparous. Females can lay 3 or 4 clutches of 4-7 eggs per year.Downes S, Bauwens D (2002). "Does reproductive state affect a lizard's behavior toward predator chemical cues?". ''Behavioral Ecology and Sociobiology'' ''52'' (6): 444–450. https://doi.org/10.1007/s00265-002-0538-3 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

Parasites 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.

Behavior

Feeding

''P. siculus'' has a strong preference for the consumption of non-conspicuous prey. Conspicuous coloration is a strong deterrent of consumption of carabid beetles. When consuming aposematic prey, ''P. siculus'' throws its head back and rubs its snout on the soil. Such behavior has been attributed to the unpalatability of aposematic prey. ''P. siculus'' is able to respond to chemical cues from some species of carabid beetles, evidence that the lizard has evolved to be able to detect the presence of dangerous chemicals in its prey.

Instances of extreme feeding behavior have been reported. One instance of cannibalism has been reported to have taken place between an adult male and a juvenile. The adult male captured the juvenile by biting down hard on his hips. An adult female has also been observed consuming a juvenile ''Hemidactylus turcicus'' in 2003, which is the first documented case of predation by ''P. siculus'' on a gecko. Additionally, an adult male has been observed feeding upon a dead adult '' Suncus etruscus'' in 2004. This is the first time ''P. siculus'' has been documented feeding upon the dead flesh of a small mammal.

Learning

Multiple experiments confirm the ability of ''P. siculus'' to learn a variety of different tasks. ''P. siculus'' can be trained to remove colored caps from food-containing pods.Damas-Moreira I, Oliveira D, Santos JL, Riley JL, Harris DJ, Whiting MJ (2018) "Learning from others: an invasive lizard uses social information from both conspecifics and heterospecifics". ''Biology Letters'' 14: 20180532. http://dx.doi.org/10.1098/rsbl.2018.0532 However, there is controversy over the ability of ''P. siculus'' to perform quantitative discrimination tasks.Miletto Petrazzini, Maria Elena, et al. (2018). "Quantity Discrimination in Trained Lizards (''Podarcis sicula'')". ''Frontiers in Psychology'' 9: 274. https://doi.org/10.3389/fpsyg.2018.00274.Miletto Petrazzini ME, Fraccaroli I, Gariboldi F, Agrillo C, Bisazza A, Bertolucci C, Foà A (2017). "Quantitative abilities in a reptile (''Podarcis sicula'')". ''Biology Letters'' 13: 20160899. http://dx.doi.org/10.1098/rsbl.2016.0899 One experiment found that while 60% of subjects were able to distinguish between 1 and 4 items, very few were able to distinguish between 2 and 4 items, and none were able to distinguish between single objects with different surface areas. However, a previous study found that ''P. siculus'' was able to effectively discriminate between stimuli with different surface areas. This experiment did find that ''P. siculus'' was unable to discriminate between groups of food items of various quantities (1 food item, 2 food items, etc). The ability of ''P. siculus'' to perform different quantitative discrimination tasks may be dependent on the type of stimuli, biological versus non-biological.

''P. siculus'' has also been demonstrated to engage in social learning. An experiment that had ''P. siculus'' individuals observe others remove colored caps from a food containing pod demonstrated that those who observed others before attempting the task were more successful than those in the control group. It took longer for ''P. siculus'' observer to learn from demonstrators of a different species. That being said, ''P. siculus'' was still able to learn from a heterospecific demonstrator.

Aggression

The incidence of missing toes is extremely high in some populations of ''P. siculus'', indicating a potentially high level of intraspecies competition. A 2009 study found that in one population of ''P. siculus'' on Croatian island Pod Mrčaru had significantly high rates of missing toes (55.48%). In this population, males were significantly more likely to have a missing toe than females. Additionally, members of the subpopulation facing higher levels of toe loss had significantly stronger bite forces than other populations of ''P. siculus.'' However, this study did not find significantly higher levels of predation between ''P. siculus'' on Pod Mrčaru and its counterparts elsewhere. The higher rates of toe loss among males combined with the higher population density of ''P. siculus'' on Pod Mrčaru suggests that intraspecific aggression may explain this disparity.

Additionally, a study has found that the more aggressive individual in a dyad spends more time basking than its less aggressive opponent. This relationship is prolonged: the individual that is more aggressive in a dyadic encounter can make continued use of a thermally favorable environment over a long period of time. These more aggressive individuals grow faster than their less aggressive counterparts. In lizard dyads with low levels of aggression, there were smaller disparities between time spent basking. In such pairs, the two individuals may spend significant periods of time basking together. Regardless of aggression level in an initial encounter, this type of relationship was maintained between the dyad over a long period of time, demonstrating that social behavior is established quickly. However, basking behavior in isolation seemed to be replicated in the aftermath of these social encounters as well, suggesting that the relationship between sociality and basking depends on a more nuanced basis than behavior during an initial encounter.

Anti-predatory

''P. siculus'' is able to detect chemical cues of common predators and modify its behaviors appropriately. ''P. siculus'' is also able to distinguish between scents of dangerous snakes and non-dangerous snakes. Studies have shown that ''P. siculus'' increase tongue-flicking behavior, commonly associated with stress, when exposed to predator scents. Similarly, experiments show that running behavior, tail-vibrating behavior, starting behavior, and stationary behavior all increase when ''P. siculus'' is exposed to predator scents than in control trials.Van Damme, Raoul; Quick, Kathleen (2001). "Use of Predator Chemical Cues by Three Species of Lacertid Lizards (''Lacerta bedriagae, Podarcis tiliguerta'', and ''Podarcis sicula'')". ''Journal of Herpetology'' 35 (1): 27–36. https://doi.org/10.2307/1566019. Sudden, unpredictable starts may be more difficult to detect. Tail-waving may deflect attention of predators from the body of ''P. siculus'' to its tail.

Anti-predator behavior is mediated by the reproductive state of ''P. siculus.'' Gravid females display fewer tongue-flicks than their non-gravid counterparts when exposed to predator scents. Non-gravid females also spend significantly more time moving slowly when exposed to predator scents than their gravid counterparts. Gravid females also spend less time basking and spent more time being stationary when exposed to predator scents. Non-gravid females, on the other hand, increased the number of stand-ups and starts when exposed to predator scents. These results suggest that ''P. siculus'' balance the threat of predation while basking with the thermoregulatory needs of embryo development during gravidity. Increases in slow locomotion and stationary behavior may be ways of avoiding detection by predators.

Anti-predator behavior may also be different among the various subpopulations of ''P. siculus.'' Lizards from sub-populations facing greater threats of predation achieve higher maximal running speeds. These lizards also flee faster and further when presented with a predator threat than their counterparts that face lower levels of predation in their habitat. These behavioral and associated phenotypic changes in these two subpopulations arose rather quickly, highlighting the ability of ''P. siculus'' for rapid adaptation. Anti-predator behavior may also differ based on the lived environment of ''P. siculus.'' A 2009 study compared anti-predator behavior in ''P. siculus'' juveniles collected from olive tree plantations and vineyards. Juveniles from the olive tree plantations responded to a simulated predator threat by escaping towards an olive tree instead of running and stopping in a temporary refuge, despite the increase in distance traversed. Juveniles from vineyards instead ran short distances, stopped in a temporary refuge, then ran again.

Light polarization

Animals can use the polarization of light to determine their orientation. The polarization of light affects orientation behavior in a variety of species, and has been demonstrated to be the mode of orientation for ''P. siculus''. ''P. siculus'' can learn a training direction when operating under white polarized light with the direction of the electric field parallel to the training axis. Under blue and cyan light, ''P. siculus'' is able to correctly orient itself under polarization axes both parallel and perpendicular to the training axis. Red light polarization completely disoriented ''P. siculus'' under experimental conditions. Additionally, there is evidence that ''P. siculus'' has a time-compensated celestial compass. The time-compensated mechanism does not seem to be affected by whether or not the sun is in view.

Effect of habitat on behavior

A 2005 study compared seasonal and diel behaviors of an introduced population of ''P. siculus'' to its Italian counterparts. The activity period of ''P. siculus campestris'' was reduced compared to ''P. siculus'' in Rome, where lizards are active year-round. Colder mean temperatures in the New York habitat of ''P. siculus campestris'' may explain why this population’s activity is limited to the months of April through October. ''P. siculus campestris'' was also active for fewer hours during the day compared to its Roman counterparts. The photoperiod of Long Island, New York, the home of ''P. siculus campestris'', is similar to that of Rome. This similarity strengthens the argument for temperature explaining the discrepancy in activity levels.

Taxonomy and Variation

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. tilguerta'' 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 disparities between sizes of individuals was 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.Avramo, Vasco; Senczuk, Gabriele; Corti, Claudia; Böhme, Wolfgang; Capula, Massimo; Castiglia, Riccardo; Colangelo, Paolo (2021). "Evaluating the island effect on phenotypic evolution in the Italian wall lizard, ''Podarcis siculus'' (Reptilia: Lacertidae)". ''Biological Journal of the Linnean Society'' 132 (3): 655–665. https://doi.org/10.1093/biolinnean/blaa190 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 2 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 were 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''.

Rapid adaptation

In 1971, 10 adult specimens (five breeding pairs) of ''P. siculus'' were transported from the Croatian island of Pod Kopište to the island Pod Mrčaru (about 3.5 km to the east). Both islands lie in the Adriatic Sea near Lastovo), where the lizards founded a new bottlenecked population. The two islands have similar size, elevation, microclimate, and a general absence of terrestrial predators and ''P. siculus'' expanded for decades without human interference, even outcompeting the (now locally extinct) '' Podarcis melisellensis'' population.

In the 1990s, scientists returned to Pod Mrčaru and found that the lizards currently occupying Mrčaru differ greatly from those on Kopište. While mitochondrial DNA analyses have verified that ''P. siculus'' specimens currently on Mrčaru are genetically very similar to the Kopište source population, the new Mrčaru population of ''P. siculus'' was described as having a larger average size, shorter hind limbs, lower maximal sprint speed, and altered response to simulated predatory attacks compared to the original Kopište population. These population changes in morphology and behavior were attributed to "relaxed predation intensity" and greater protection from vegetation on Mrčaru.

In 2008, further analysis revealed that the Mrčaru population of ''P. siculus'' has significantly different head morphology (longer, wider, and taller heads) and increased bite force compared to the original Kopište population. This change in head shape corresponded with a shift in diet: Kopište ''P. siculus'' are primarily insectivorous, but those on Mrčaru eat substantially more plant matter. The changes in foraging style may have contributed to a greater population density and decreased territorial behavior of the Mrčaru population.

Another difference found between the two populations was the discovery, in the Mrčaru lizards, of cecal valves, which slow down food passage and provide fermenting chambers, allowing commensal microorganisms to convert cellulose to nutrients digestible by the lizards. Additionally, nematodes were common in the guts of Mrčaru lizards, but absent from Kopište ''P. siculus'', which do not have cecal valves. The cecal valves, which occur in less than 1% of all known species of scaled reptiles, have been described as an "adaptive novelty, a brand new feature not present in the ancestral population and newly evolved in these lizards".

As an introduced species

Populations of ''P. siculus'' in North America have been documented from Topeka, Kansas, Long Island, New York, Greenwich, Connecticut, and Levittown, Pennsylvania. 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. In 2020, a large number of ''P. s. campestris'' entered Great Britain as stowaways among shipments of grapes, before being intercerpted.

''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.

Conservation status

The Italian wall lizard is listed as being of least concern by the International Union for Conservation of Nature (IUCN) on the IUCN Red List. Its current population numbers are increasing.

Pesticide exposure

Because ''P. siculus'' is commonly found in agricultural areas, there is a concern about the effects of pesticide exposure on their health and reproductive capabilities. A 2021 study assessing biomarkers in ''P. siculus'' on conventional and organic farms found that those on conventional farms (and therefore likely exposed to pesticides) had higher levels of oxidative stress, indicating that ''P. siculus'' can quickly activate antioxidant systems to counteract reactive oxygen species (ROS) formation. Free radical damage was much higher in pesticide-exposed individuals than control and organic lizards.Simbula, G., Moltedo, G., Catalano, B., et al. (2021). "Biological responses in pesticide exposed lizards (''Podarcis siculus'')". ''Ecotoxicology'' 30: 1017–1028. https://doi.org/10.1007/s10646-021-02440-3 Gravid females exposed to pesticides also lay larger, worst-quality eggs than control gravid females. Hatchling locomotion ability does not seem to be affected by maternal pesticide exposure.Simbula, Giulia, et al. (2021). "Effects of Pesticides on Eggs and Hatchlings of the Italian Wall Lizard (''Podarcis siculus'') Exposed via Maternal Route". ''Zoologischer Anzeiger'' 293: 149–155. https://doi.org/10.1016/j.jcz.2021.06.001. Also, it was found that some commonly used agricultural pesticides are either not neurotoxic to ''P. siculus'' or that the organism is capable of resisting the studied chemical’s neurotoxicity, and that the ''P. siculus'' immune system was not significantly affected by the studied pesticides.

See also

* List of reptiles of Italy

References

External links

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Reptiles described in 1810
Taxa named by Constantine Samuel Rafinesque
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