Exceptional parallelisms characterize the evolutionary transition to live birth in phrynosomatid lizards.

Viviparity, an innovation enhancing maternal control over developing embryos, has evolved >150 times in vertebrates, and has been proposed as an adaptation to inhabit cold habitats. Yet, the behavioral, physiological, morphological, and life history features associated with live-bearing remain unclear. Here, we capitalize on repeated origins of viviparity in phrynosomatid lizards to tease apart the phenotypic patterns associated with this innovation. Using data from 125 species and phylogenetic approaches, we find that viviparous phrynosomatids repeatedly evolved a more cool-adjusted thermal physiology than their oviparous relatives. Through precise thermoregulatory behavior viviparous phrynosomatids are cool-adjusted even in warm environments, and oviparous phrynosomatids warm-adjusted even in cool environments. Convergent behavioral shifts in viviparous species reduce energetic demand during activity, which may help offset the costs of protracted gestation. Whereas dam and offspring body size are similar among both parity modes, annual fecundity repeatedly decreases in viviparous lineages. Thus, viviparity is associated with a lower energetic allocation into production. Together, our results indicate that oviparity and viviparity are on opposing ends of the fast-slow life history continuum in both warm and cool environments. In this sense, the 'cold climate hypothesis' fits into a broader range of energetic/life history trade-offs that influence transitions to viviparity.

Thermoregulatory strategies of three reclusive lizards (genus Xantusia) from the Baja California peninsula, Mexico, under current and future microenvironmental temperatures.

The thermal quality of the habitat is key for the regulation of body temperature in terrestrial ectotherms and, therefore, permits them to carry out their fundamental biological activities. In thermally heterogeneous environments, ectotherms might follow different behavioral or physiological strategies to maintain their body temperature within biologically adequate boundaries, for which they depend on microhabitat selection. These aspects are, thus, relevant in the context of habitat degradation and land-use change. In this study, we characterized the thermal ecology of three lizard species (genus Xantusia) that differ in microhabitat use along the Baja California peninsula, Mexico. We made three predictions: (1) the three species will follow different thermoregulatory strategies according to habitat thermal quality; (2) the thermal requirements and tolerances of these species will match the environmental or microenvironmental thermal conditions; and (3) due to their habitat and range restriction, the species studied will be highly vulnerable to climate change. Our results indicate the existence of thermoregulatory mechanisms in Xantusia to face thermal heterogeneity, including behavioral thermoregulation by choosing different microhabitats, shifts in activity periods, and adaptation to particular high thermal quality microhabitats. Furthermore, despite their association to specific microhabitats and specialized physiology, the studied species will not be adversely affected by climate change, as the increased microenvironmental temperatures will lead to a higher habitat thermal quality and lower costs of thermoregulation. However, we do not discard other indirect adverse effects of climate change not considered in this study.

A new species of Lepidophyma (Squamata: Xantusiidae) from San Luis Potosí, México, with notes on its physiological ecology.

In recent years, there has been an increase in the descriptions of members of the lizard genus Lepidophyma. Herein, we describe a new species of Lepidophyma from the Huasteca Potosina region of Mexico, previously confused with L. gaigeae, from which it differs in lacking parietal spot, among other characteristics. We inferred its phylogenetic position and provide information on its thermal and hydric physiology, as well as on some other aspects of natural history. Molecular and morphological data supported the independent taxonomic status of the new species, indicating its placement as the sister taxon of L. gaigeae and a wide morphological separation between these species. Lepidophyma lusca sp. nov. has a diurnal-crepuscular activity period and occurs at lower elevations than L. gaigeae. Also, the new species differ from its sister taxon in its physiology, as reflected by its tendency toward higher thermal parameters and water loss rates. With the description of L. lusca sp. nov., the number of species in the genus Lepidophyma rises to 21.