The common side-blotched lizard (Uta stansburiana) is a species of side-blotched lizard in the family Phrynosomatidae. The species is native to dry regions of the western United States and northern Mexico. 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.
Etymology The specific epithet, stansburiana, is in honor of Captain Howard Stansbury of the US Corps of Topographical Engineers, who collected the first specimens while leading the 1849-1851 expedition to explore and survey the Great Salt Lake of Utah.Moll, Edward (2005). "Uta stansburiana Baird and Girard, 1852 - Common Side-blotched Lizard". Sonoran Herpetologist.Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). The Eponym Dictionary of Reptiles. Baltimore: Johns Hopkins University Press. xiii + 296 pp. . (Uta stansburiana, p. 251).
Taxonomy
The systematics and taxonomy of the widespread and variable lizards of the genus Uta is much disputed. Countless forms and morphs have been described as subspecies or even distinct species. The forms which occur in most of Mexico (except Baja California) have been recognized as a very distinct species, the eastern side-blotched lizard, Uta stejnegeri. Populations from San Benito and Cedros Islands were separated as distinct species Uta stellata and U. concinna, but are now included in U. stansburiana. Those of Isla Santa Catalina and Isla Salsipuedes, U. squamata and U. antiqua are sometimes included in this species, too, but this is certainly not correct in the latter case, and probably in the former also. Based on the same data that would give U. squamata species rank, the southern Baja California populations could arguably be split off (as Uta elegans), too. The proposed subspecies martinensis and taylori are probably not valid. The populations on Isla Ángel de la Guarda, Isla Mejia and Isla Rasa almost certainly constitute a separate species closer to Uta palmeri, and that of San Esteban Island may so too, being close to squamata. The status of the Isla Encantada group populations named as Uta encantadae, U. lowei and U. tumidarostra is not completely resolved; these distinct populations are of comparatively recent origin and are sometimes included in this species, but their unique adaptations to living in intertidal habitat suggest they should be considered distinct; whether as one or as three species remains unresolved.Murphy, Robert W. & Aguirre-León, Gustavo (2002): The Nonavian Reptiles: Origins and Evolution. In: Case, Ted & Cody, Martin (eds.): A New Island Biogeography of the Sea of Cortés: 181-220. Oxford University Press. PDF fulltext Appendices 2-4
Physical description The common side-blotched lizard displays a moderate degree of sexual dimorphism. Males can grow up to 60mm (2.4 inches) from snout to vent, while females are typically a little smaller. Females may have stripes along their backs/sides, or may be relatively drab. Both sexes have a dark blotch on the lateral aspect (side) of the thorax, just behind the front limbs. This dark blotch is generally less prominent in females than in males. The degree of pigmentation varies with both 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. Males are usually more brightly colored than females, and often have blue spots on the dorsum, especially near the base of the tail. Also, males display a hemipenal bulge at the base of the tail.
Males of the species exhibit three distinct color polymorphisms in their throat colors. The skin of the throat may be orange, blue, or yellow. Coloration of the throat is critical, as it is closely related to the mating behavior of both males and females. The different throat morphologies displayed by the male side-blotched lizard is also correlated with their sprinting speed. Across all three morphs, sprinting speed is positively correlated with blue hue, the brightness of the yellow throat, and the level of saturation of the orange throats. The relationship between physical capabilities and coloration may play a role in sexual competition amongst male side-blotched lizards.
The speed of these male lizards during the end of their reproductive seasons is dependent on their body temperature. The maximum sprinting speed of these lizards is achieved when the body temperature is between 35-38 degrees Celsius.
Physiology When comparing populations within wind farms and in neighbouring control sites, no differences in oxidative stress are seen in the side-blotched lizard. In females oxidative stress also increases with the number of yolk follicles produced.
Genetic determination of throat-color polymorphism Analysis of DNA nuclear microsatellites has provided genetic evidence for the rock-paper-scissors behavior pattern of male side-blotched lizard competition. In populations where all three morphs are present, shared paternity between yellow- and blue-throated individuals occurs at a rate significantly below random chance, while shared paternity between yellow- and orange-throated males occurs at a rate significantly above chance. In addition, blue-throated males often shared paternity with orange-throated males, despite having mostly yellow-throated neighbors.
Blood plasma testosterone levels play an important role in the creation of the three male morphs both during and after development. Orange-throated males have 46-48% higher plasma testosterone levels compared to their yellow- or blue-throated counterparts. Experimental elevation of plasma testosterone levels in the other two male morphs led to increases in endurance, aggressiveness, and territory size to the degree expressed by normal orange-throated males. In addition, the transformation of yellow-throated males to blue-throated males is accompanied by an increase in their plasma testosterone levels.
Throat color in side-blotched lizards is genetically determined, and has high heritability. It is determined by a single Mendelian factor with three alleles. In males, the o allele is the dominant allele, and the b allele is recessive to the y allele. Therefore, phenotypically orange-throated males have genotypes of either oo, ob, or oy. Yellow-throated males have genotypes of either yy or yb, and blue-throated males are exclusively bb. In females, all individuals with the dominant o allele are orange-throated, while those lacking an o allele develop yellow throats.
Tails For the side-blotched lizard, limbs serve as an anti-predatory defense – their ability to survive without a tail allows them to escape predation after being caught. While this defense mechanism can be advantageous, the loss of a tail can also negatively impacts a lizard’s survival and reproduction. For the Uta stranburiana, the loss of a tail is 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. The influence of tail loss on survivorship, however, is only significant during conditions of low mortality – when the overall mortality rate of side-blotched lizards is 30-40% higher than average, the condition of the tail does not impact the survival of adults and juveniles. This is because the tails of side-blotched lizards are not energetic lipids stores. As mentioned earlier, lizards that lose their tails are at a greater risk of predation than lizards with their tails intact. Since social status is an important survival mechanism amongst side-blotched lizards, researchers have suggested that the loss of a tail, which contributes to a decrease in social status, forces tailless side-blotched lizards to inhabit more inferior home ranges. Therefore, in addition to losing a physiological defense mechanism when losing their tails, side-blotched lizards are also inclined to inhabit inferior living conditions which bolsters their risk of predation.
Mating Rock–paper–scissors mechanism 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, and variation within a breeding population is maintained by a rock paper scissors mechanism of frequency-dependent sexual selection. A cycle is created where the least common morph of one breeding season often has the largest number of mature living offspring in the next year. This is because one morph does particularly well against another, but poorly in comparison to the third.
Orange-throated males are "ultradominant". They are the largest and most aggressive morph, defending relatively large (about 100 m2 or 120 yd2) territories and keeping harems of females with which they mate. They are adept at stealing mates from blue-throated individuals, but are vulnerable to cuckoldry by the yellow-throated female mimics. Orange-throated males also have significantly reduced yearly survival rates compared to the other two morphs. 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 sexually 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. Instead, they have wide-reaching home ranges that may overlap with several other lizards’ territories. They rely on their mimicry to sneak matings with unattended females. This is more easily achieved among the harems kept by orange-throated males than by the single, closely guarded mate of the blue-throated males. Though orange-throated males have the highest mortality rates, yellow-throated males have higher relative rates of posthumous fertilization (posthumous birth), indicating an increased reliance on sperm competition as part of their reproductive strategy. Yellow-throated males can in specific instances transform into blue-throated males over the course of the breeding season. This transformation is usually triggered by the death of a nearby dominant male, and the blue patches the yellow-throated males develop is qualitatively distinct from the blue patches of genetically blue-throated males. Not all yellow-throated males transform, but when they do, they give up their female mimicry and adopt the "dominant" morph's behavior pattern. No transformations in the other direction, in which dominant males gain yellow-throat coloration, have been observed.