The Common side-blotched lizard (Uta stansburiana) is a small lizard in the family Phrynosomatidae. It is notable for having a unique form of polymorphism wherein each of the three different male morphs utilizes a different strategy in acquiring mates. The three morphs compete against each other following a pattern of rock paper scissors, where one morph has advantages over another but is outcompeted by the third.
The degree of pigmentation in Common side-blotched lizards varies with sex and population. Some males can have blue flecks spread over their backs and tails, and their sides may be yellow or orange, while others may be unpatterned. Females may have stripes along their backs/sides, or again may be relatively drab. Both sexes have a prominent blotch on their sides, just behind their front limbs. Coloration is especially important in Common side-blotched lizards, as it is closely related to the mating behavior of both males and females. The different throat morphologies that the side-blotched lizard adopts also affect their sprinting speed. Across all three morphs, sprinting speed is positively correlated with the blue hue, the brightness of the yellow throat, and the level of saturation of the orange throat. While aspects of throat coloration are positively related to sprinting speed and mass of the lizard, they do not affect the lizard’s snout-vent and hind limb length. Researchers from Utah State University have suggested that this relationship between physical capabilities and coloration plays a role in competition amongst male side-blotched lizards during the breeding season. The speed of these male lizards during the end of their reproductive seasons is dependent on their body temperature. The maximum sprinting speed is achieved when their body temperature is between 35-38 degrees Celsius.
Common side-blotched lizards are found in dry regions of the western United States and northern Mexico. They occur in areas with scrubby vegetation, bushes, rocky canyons, desert, and chaparral.
These lizards are diurnal and typically spend their time on the ground, under shrubs, or other vegetation where they can stay unnoticed by predators. During the heat of the day and bad weather, they will find shelter underground or under rocks and woody debris. Common side-blotched lizards are also good climbers and can hop between stones. They are gregarious and often interact with one another. Side-blotched lizards come in three different morphs; the orange and blue morphs are known to be territorial while the yellow morphs are known to be non-territorial. Dominant males are aggressive in the defense of their territories. Upon spotting another conspecific within their territories, resident individuals enter a state of heightened alertness. They perform one or more “pushups” (vertical bobbing motions), arch their backs, and extend their limbs before approaching the intruder. If the intruder is another male, the resident follows up by rushing, butting, or nipping at the intruder, which will then usually proceed to run away. Tail length is important in the determination of dominance hierarchies. Like many other lizard species, side-blotched lizards use tail autotomy as an escape mechanism; their ability to survive without a tail allows them to escape predation after being caught. For these lizards, the loss of a tail is also accompanied by a loss of social status amongst their peers. This can contribute to them having a hard time acquiring and maintaining a superior home range.
Common side-blotched lizards are carnivores (insectivores) and eat a wide variety of insects and other arthropods. Their diet also includes spiders, scorpions, and mites.
Male side-blotched lizards exhibit distinct polymorphism in their throat colors and can be divided into three different categories. Each of these three different morphs varies in how it competes for mates. Orange-throated males are "ultradominant." They are the largest and most aggressive morph, defending relatively large territories and keeping harems of females with which they mate. Blue-throated males are "dominant". They are intermediate in size and guard smaller territories containing only a single female. As they only have one mate to defend, they are better at catching yellow-throated sneaks but are also susceptible to having their mates stolen by the larger, more aggressive orange-throated males. Yellow-throated males are “sneakers”. Their coloration is similar to that of reproductively mature females, and they typically mimic female “rejection” displays when they encounter dominant orange- or blue-throated males. Unlike the other morphs, yellow-throated males do not hold territories but have wide-reaching home ranges that may overlap with several other lizards’ territories. They rely on their mimicry to sneak matings with unattended females. Female side-blotched lizards have also been shown to exhibit behaviorally correlated differences in throat coloration. Orange-throated females are considered r-strategists. They typically produce large clutches consisting of many small eggs. In contrast, yellow-throated females are K-strategists that lay fewer, larger eggs. Females lay clutches with an average of 5 eggs and a maximum of 9 eggs in a single clutch. The breeding season usually lasts from March until August. Young side-blotched lizards show displays and aggression shortly after hatching, and even minute differences in size can lead to increased social dominance and capacity to outcompete the smaller hatchlings.
There are no major threats to this species at present.
According to IUCN Red List, the adult population size of the Common side-blotched lizard snake is unknown but exceeds 1,000,000 individuals. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.
