Lizard Oviparity at High Elevations?The Case of the Bolivian Endemic Liolaemus variegatus

Abstract

Oviparity is the most widespread reproductive mode among reptiles. The South American genus Liolaemus contains both oviparous and viviparous species, the latter generally dominating at high latitudes and high elevations. We report for the first time evidence suggesting oviparity in Liolaemus variegatus, an Andean lizard endemic to Bolivia. We record its presence at elevations up to 4,200 m on the Cordillera de Tiraque, which is among the highest localities for oviparous lizards in the world. We characterize the content of oviductal and aborted eggs and the structure of the shell of aborted eggs. Eggshell is 66.7 µm thick and is composed of an outer calcareous layer, a thick fibrous mesh, and an inner boundary. The most abundant mineral crystals in the calcareous layer constitute a matrix of formless calcite depositions forming transversal grooves on the outer surface. In the bottom of those grooves are other pseudo-hexagonal prism crystals that could be aragonite and which contain some potassium. Computed tomographic reconstructions revealed a small region of higher density inside a flank of the yolk sac. Most of the oviductal and aborted eggs had non-distinguishable embryos even after opening them under an optic microscope, suggesting that the embryos were incipient. However, the oviductal eggs from two females were at embryonic stages 24–25. We document clutches of 4–8 eggs, which comprise up to 96% of female body mass without eggs. Future comparisons of egg morphology may shed some light on the physiological changes associated with the transition from oviparity to viviparity.