Uta stansburiana

Uta stansburiana: The Common Side-Blotched Lizard

The common side-blotched lizard, scientifically known as Uta stansburiana, is a small reptile native to the dry and arid regions of the western United States and northern Mexico. This species is particularly notable for its complex social structure and mating system, which revolves around a unique form of polymorphism in males.

Physical Characteristics and Habitat

Uta stansburiana exhibits moderate sexual dimorphism, with males typically growing slightly larger than females, reaching up to approximately 60mm in snout-to-vent length. Both sexes share a characteristic dark blotch on the side of their thorax. Coloration can vary, with males often displaying brighter hues, including blue flecks and yellow or orange sides, while females may be more drab or possess stripes. A key distinguishing feature in males is the polymorphism of their throat coloration, which can be orange, blue, or yellow. These lizards inhabit rocky, arid environments, utilizing their speed and agility to navigate their environment and escape predators.

The "Rock-Paper-Scissors" Mating System

The most striking aspect of the common side-blotched lizard is the "rock-paper-scissors" mating strategy employed by males. This system involves three distinct male morphs, each with a different throat color and reproductive strategy:

• Orange-throated males: These are the "ultradominant" individuals. They are the largest and most aggressive, defending extensive territories and maintaining harems of females. They excel at stealing mates from blue-throated males but are vulnerable to being cuckolded by yellow-throated males.
• Blue-throated males: These are "dominant" males, intermediate in size. They guard smaller territories, typically containing only a single female. They are effective at catching "sneaky" yellow-throated males but are susceptible to losing their mates to the more aggressive orange-throated males.
• Yellow-throated males: These are "sneaker" morphs. Their coloration often mimics that of sexually mature females, allowing them to mimic female rejection displays and sneak matings with unattended females, particularly those within the harems of orange-throated males. They do not hold territories and instead rely on wide-ranging home ranges.

This cyclical dominance pattern, where each morph has advantages over one other but disadvantages against a third, is genetically determined and plays a crucial role in maintaining the species' genetic diversity over millions of years. This polymorphism is also influenced by testosterone levels, with higher levels in orange-throated males correlating with increased aggression and territoriality.

Reproduction and Behavior

Female side-blotched lizards lay clutches averaging around 5.1 eggs, with a maximum of up to nine. Their reproductive strategies also differ based on throat coloration, with orange-throated females acting as r-strategists (producing many small eggs) and yellow-throated females as K-strategists (producing fewer, larger eggs). Factors such as female age, environmental conditions, and rainfall can influence fecundity. The presence and length of a tail are important for social status and mating success in both sexes, as tailless individuals face increased predation risk and reduced mating opportunities. While tail loss can be a defense mechanism, it also leads to a decrease in social standing, forcing lizards into less favorable habitats.