Lizards are a group of squamate reptiles, found in all continents except Antarctica, and on most oceanic islands. Approximately 7,000 species have been identified. The diversity of lizards is immense. Learn about this incredible animal and its habitats. The most interesting fact about lizards: they are the only reptiles that reproduce sexually.
Viviparity is a widespread reproductive pattern that occurs in most mammals. However, in squamate reptiles, it occurs only in about one fifth of species. The evolutionary history of viviparity has been largely unclear, but phylogenetic analysis suggests that it has occurred over 100 times within the lizard family. However, there is still considerable controversy https://www.autouko.net/the-health-benefits-of-cooked-meals/regarding the antiquity of the trait, as the only direct fossil evidence was in the Late Cretaceous mosasauroids. A more recent example is the Early Cretaceous lizard Yabeinosaurus, which is thought to have hatched more than 15 young.
The reproductive investment of viviparous lizards is associated with their large body size, according to research conducted by Horvathova and colleagues (2013). The findings are supported by genetic analysis of closely related geographical lineages and do not show any phylogenetic bias.
During evolution, viviparous females have exhibited dramatic changes in morphology, physiology, ecology, and behavior. While viviparous lizards exhibit a number of fitness benefits, such as protection of the embryo against predation, higher reproductive output, and larger offspring, viviparity is not without its disadvantages.
Viviparity is the most common mode of reproduction in lizards. Although the transition to viviparity is relatively recent, there is still much to learn about the trade-offs between the two reproductive modes. It is also possible that viviparous lizards evolved earlier than oviparous lizards. Viviparous lizards are more suited for cold climates.
While Lambert’s mollic-clock calculations look authoritative, they are based on unverifiable assumptions about the past. Furthermore, seasonal temperature variability was the most important factor in the first split of the classification tree. A lower temperature variation was associated with viviparity during the reproductive period and oviparity throughout the year.
While oviparous lizards have larger clutches, the size of the clutch is not significantly larger. This may be due to the larger weight of viviparous females. But most viviparous species do not differ significantly in clutch size. This suggests that females are less efficient at reproduction.
Researchers have studied sensory regression in viviparous lizards. In viviparous lizards, the outer segments of rudimentary photoreceptors (as found in the pineal gland) decrease after birth. This is a common phenomenon among lizards.
Viviparity occurs in some lizard species
Viviparity is an evolutionary feature of some lizard species that allows them to persist in different environments. The evolution of viviparity in reptiles increased morphological and lineage diversification, while the rate of evolution was lower in oviparous species. Nevertheless, the evolution of viviparity has been associated with changes in the timing of reproductive events.
Some lizard species exhibit a bimodal reproductive mode, and studies of these bimodal reproductive forms can provide valuable insights into the evolution of viviparity. For example, lizard species with extended retention of eggs inside the uterus, such as L. bougainvillii, may be considered to be bimodal. These transitional forms are best studied by applying molecular tools to clarify the mechanisms that underlie their reproductive modes. Population genetic approaches are recommended for understanding these transitional forms.
The evolution of viviparity is also a complicated process that involves multiple genes. Specifically, genes that affect multiple physiological processes may be tightly linked. This could lead to decreased interspecific variation and fewer evolutionary options. Other factors, such as non-selective factors and higher mutation rates, may also play a role in the evolution of viviparity.
Viviparity is also found in some lizard species that exhibit both oviparous and viviparous modes. The evolutionary history of these lizard species is not clear. The most plausible explanation is that both types of reproductive modes were divergent from each other. During the Pleistocene, some species remained confined to refugia in warm regions, and the viviparous ones dispersed to cooler climates. In addition, there was secondary contact between oviparous and viviparously occurring populations.
Using population genetic methods, viviparity modes can be studied by examining genomic evidence for introgression and sexual dimorphism. This enables researchers to determine which regions of the genome are under selection in viviparous and oviparous populations.
In some species, the female reproductive tract is ovoviviparous, and eggs are deposited in the uterus at a late stage. Most species that are oviparous, however, will not lay eggs after stage 35, the end of the limb-bud stages. By the time the embryos reach stage 35, their metabolic rates, water and oxygen demands, and limb-bud development have accelerated. These changes can lead to an intermediate phenotype known as ‘late oviposition’.
Although facultative changes in parity modes are rare in vertebrates, they can provide fascinating opportunities to study parity mode evolution. An example is the bimodal skink Saiphos equalis. Its eggs exhibit shell characteristics of both oviparous and viviparous species. Hence, it may have evolved a reproductive lability that confers a selective advantage over oviparous individuals.
Some lizard species are viviparous, and these species produce their young using unfertilized eggs. These species are mainly found in tropical areas and do not face the same environmental challenges as other species. Most of these species are evenly divided in population between male and female.
This reproductive mode is heritable. In fact, the morphology of eggs and their thickness are remarkably similar in different lizard species. However, their eggshells and embryos undergo different incubation periods depending on their parity. This suggests that the incubation period of the embryos in the post-oviposition stage of Saiphos equalis is different from those of viviparous individuals.
Some lizard species are diurnal, and can use the sun to raise their body temperature. In hotter areas, lizards can raise their body temperature up to 35 degrees Celsius. The desert night lizard has a specialized microhabitat that keeps it cool in a hot environment.