Lacerta vivipara Lichtenstein, 1823
The viviparous lizard or common lizard, Zootoca vivipara (formerly Lacerta vivipara), is a Eurasian lizard. It lives farther north than any other reptile species, and most populations are viviparous (giving birth to live young), rather than laying eggs as most other lizards do. It is the only species in the monotypic genus Zootoca.
Zootoca vivipara can be seen in a variety of different colors. Female Zootoca vivipara undergo color polymorphism (biology) more commonly than males. A female lizard's display differs in ventral coloration, ranging from pale yellow to bright orange and a mixed coloration. There have been many hypothesis for the genetic cause of this polymorphic coloration. These hypothesis test for coloration due to thermoregulation, predator avoidance, and social cues, specifically sexual reproduction. Through an experiment conducted by Vercken et. al., color polymorphism in viviparous lizard is caused by social cues, rather than the other hypotheses. More specifically, the ventral coloration that is seen in female lizards is associated with patterns of sexual reproduction and sex allocation. 
The length of the body is less than 12 cm (5 in) (excluding the tail). The tail is up to twice as long as the body, although it is often partially or wholly lost. The limbs are short, and the head is rather round. Males have more slender bodies than females. The neck and the tail are thick. The collar and other scales seem jagged.
The colour and patterning of this species is variable. The main colour is typically medium brown, but it can be also grey, olive brown or black. Females may have dark stripes on their flanks and down the middle of their backs. Sometimes females also have light-coloured stripes, or dark and light spots along the sides of their backs. Most males and some females have dark spots in their undersides. Males have brightly coloured undersides – typically yellow or orange, but more rarely red. Females have paler, whitish underparts. The throat is white, sometimes blue.
The viviparous lizard is widely distributed throughout Europe and Asia. Its range extends to the north of the Arctic Circle. It ranges from Ireland to Hokkaidō and Sakhalin. It is absent from most of the Mediterranean area, although it occurs in northern Spain, northern Italy, Serbia, Republic of Macedonia and Bulgaria. It is also absent from the area surrounding the Black Sea.
In the southern parts of its distribution range, the species lives at high elevations, occurring as high as 3,000 metres (9,800 ft) above sea level in the Alps. In these areas, the viviparous lizard lives in damp locations, often near water, including meadows, swamps, rice fields, by brooks and in damp forests. In the northern part of the range, the species is also found in lowlands, where it occurs in drier environments, including open woodland, meadows, moorland, heathland, fens, dunes, rocks, roadsides, hedgerows and gardens. It lives mainly on the ground, although it may climb onto rocks, logs and low-growing vegetation.
The viviparous lizard feeds on invertebrates, mostly small insects. It shakes larger prey in its jaws before chewing it and swallowing it whole. In early spring, late autumn, and cool summer days, it basks in the sun to reach its optimum body temperature, which is about 30°C (86°F).
These lizards mate in April or May. Males take females in their jaws before mating – if the female is not interested, she will bite the male fiercely. The offspring develop inside the female for about three months.
The name of the species is derived from its ability to give birth to live young, an adaptation to a cool climate, but some southern populations are oviparous (egg-laying). The three to 10 young (or eggs) are usually produced in July. The blackish young measure about 3 cm (1.2 in), and when first born are surrounded by egg membrane, from which they break free after about a day. Males reach sexual maturity at two years old, females at three years old. Individuals from viviparous and oviparous populations may be hybridized, but with significant embryonic malformation. Viviparous Z. vivipara do develop placentae to facilitate pregnancy but there is no substantial transport of nutrients as seen in some other species of viviparous reptiles (e.g. Pseudemoia entrecasteauxii).
Due to the cool climate, in northern regions, viviparous lizards begin hibernation in September or October, underground or in log piles. Hibernation ends about mid-February. Further south, the species is active throughout the year.
|Wikimedia Commons has media related to Zootoca vivipara.|
The color polymorphism of Zootoca vivipara has not been thoroughly studied in past years, regardless of the extensive research done on the species itself. More specifically, the color morphs seen in females have been ignored. Although there is much to uncover, few researchers have detailed experiments describing the lizard's behavior in regards to its color variations.
Female lizards exhibit three types of body coloration within a population: yellow, orange, and mixture of the two. These traits are inherited maternally and exist throughout the individual’s lifestyle. These traits are classified as discrete categories when seen by the human eye.
The frequency of colored female lizards can dependent on the phenotypic diversity and density of a population. In two types of populations, first population, termed “high quality zone”, refers to a population that carries high diversity and high lizard density while a second population, “low quality zone”, refers to low diversity and low lizard density. Among these two, color polymorphism is most notable in a low quality zone. Color polymorphisms are more obvious in low quality zones as opposed to high quality zones, where they could be easily hidden. Viviparous lizards thrive in environments where Intraspecific Competition is low. Increased competition among individuals results in lower survival rates of lizards. Additionally, female lizards choose their habitats and disperse based on the frequency of color types already present in the population. This could prove why the color polymorphism remains in the population; species gain advantages in environments where intraspecific competition is low, and the coloration of lizards allows for them to disperse according to the density and diversity of the population.  Female lizard’s reproductive abilities vary in reference to their coloration as well. A females' coloration directly responds to how many offspring they produce, and how successful these reproductive abilities are: yellow females produce the fewest offspring, while orange females produce more than yellow, but fewer than mixed females, which produce the most offspring. Moreover, the amount of offspring produced also varies in regards to color density of the population; for example, if more yellow females are in the population, clutch size for orange lizards is usually lower. Again, this could be due to competition between individuals; the increase in competition between female lizard’s results in fewer offspring being produced or a decreased success in survival of those offspring.
The differences in coloration correlate with specific social cues, such as variation in the clutch size of offspring, the ratio of females to males in the clutch, as well as the diversity in reproduction and behavior. The frequency of these colors within a population depends on the individual’s environment and its reproductive success; how frequent a lizard with a certain phenotype is in a population depends on its survival and reproduction in its environment. Since coloration remains stable throughout an individual’s lifetime, environmental influence on the plasticity of the color, cannot be a great influence for the color morph, or for the color itself appearing. Therefore, color variation must be influenced more by genetic factors and environmental interactions before birth. The heritability (h2) of color in common lizards raised in laboratory approaches 1. This indicates that more of the variation is due to heritability, or to genetics rather than its environment. 
- A. Agasyan; et al. (2010). "Zootoca vivipara". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved May 11, 2012.
- Josef Friedrich Schmidtler1 & Wolfgang Böhme (2011). "Synonymy and nomenclatural history of the Common or Viviparous Lizard, by this time: Zootoca vivipara (Lichtenstein, 1823)" (PDF). Bonn Zoological Bulletin 60 (2): 214–228.
- Harris, D. J. and M. A. Carretero. (2003). Comments on the taxonomic value of (sub)genera within the family Lacertidae (Reptilia). Amphibia-Reptilia 24 119-22.
- Vercken, E., Massot, M., Sinervo, B., Clobert, J.2006. Colour Variation and Alternative Reproductive Strategies in Females of the Common Lizard Lacerta vivipara. Journal of Evolutionary Biology 20(1): 221-232
- Heulin, B., Arrayago, M. J., and Bea, A. 1989. Expérience d'hybridation entre les souches ovipare et vivipare du lézard Lacerta vivipara. Comp. Rend. Acad. Sci. Series 3 308: 341-346 (cited by the Reptile Database).
- Svensson, E.I., Abbott, J., Gosden, T., Coreau, A. 2009. Female polymorphisms, sexual conflict, and limits to speciation processes in animals. Behavioral Evology 23(1) 93-108.
- Vercken, E., Sinervo, B., Colbert, J. 2008. Colour Variation in Female Common Lizards: why we should speak of morphs, a reply to Cote et al. Journal of Evolutionary Biology 21(4): 1160-1164.
- Vercken, E., Sinervo B., Clobert, J. 2012. The Importance of a good neighborhood: dispersal decisions in juvenile common lizards are based on social environment. Behavioral Ecology 23(5) 1059-1067
- Sinervo, B., Bleay, C. & Adamopoulou, C. 2001. Social causes of correlational selection and the resolution of a heritable throat color polymorphism in a lizard. Evolution 55: 2040–2052