Lizard Development

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Introduction

Anolis carolinensis (green anole) mating.
Australian water skink embryo

Lizards and snakes represent scaled reptiles (squamata). Lizard development involves an amniotic egg, that evolutionary (~320 million years ago) freed the vertebrates from their aquatic (water) to a terrestrial (land) environment. The Galápagos Islands marine iguana was also made famous by Charles Darwin's historic evolution studies.

The genome of the lizard Anolis carolinensis (green anole) from southeastern United States has a karyotype of 18 chromosomes, comprising six pairs of large macrochromosomes and 12 pairs of small microchromosomes, and has recently been sequenced [1]. Interestingly, almost all reptilian genomes also contain "microchromosomes", very small chromosomes less than 20 Mb in sequence size. (More? Genome)

Some Recent Findings

  • Identifying the evolutionary building blocks of the cardiac conduction system[2] "The endothermic state of mammals and birds requires high heart rates to accommodate the high rates of oxygen consumption. These high heart rates are driven by very similar conduction systems consisting of an atrioventricular node that slows the electrical impulse and a His-Purkinje system that efficiently activates the ventricular chambers. While ectothermic vertebrates have similar contraction patterns, they do not possess anatomical evidence for a conduction system. ... Mammalian and avian ventricles uniquely develop thick compact walls and septum and, hence, form a discrete ventricular conduction system from the embryonic spongy ventricle. Our study uncovers the evolutionary building plan of heart and indicates that the building blocks of the conduction system of adult ectothermic vertebrates and embryos of endotherms are similar."
  • Tooth development in a model reptile: functional and null generation teeth in the gecko Paroedura picta[3] "This paper describes tooth development in a basal squamate, Paroedura picta. Due to its reproductive strategy, mode of development and position within the reptiles, this gecko represents an excellent model organism for the study of reptile development. ...We show evidence for a stratum intermedium layer in the enamel epithelium of functional teeth and show that the bicuspid shape of the teeth is created by asymmetrical deposition of enamel, and not by folding of the inner dental epithelium as observed in mammals."
  • Patterns of interspecific variation in the heart rates of embryonic reptiles[4] "New non-invasive technologies allow direct measurement of heart rates (and thus, developmental rates) of embryos. We applied these methods to a diverse array of oviparous reptiles (24 species of lizards, 18 snakes, 11 turtles, 1 crocodilian), to identify general influences on cardiac rates during embryogenesis. Heart rates increased with ambient temperature in all lineages, but (at the same temperature) were faster in lizards and turtles than in snakes and crocodilians. We analysed these data within a phylogenetic framework. Embryonic heart rates were faster in species with smaller adult sizes, smaller egg sizes, and shorter incubation periods."
  • Reptilian spermatogenesis: A histological and ultrastructural perspective[5] "Until recently, the histology and ultrastructural events of spermatogenesis in reptiles were relatively unknown. Most of the available morphological information focuses on specific stages of spermatogenesis, spermiogenesis, and/or of the mature spermatozoa. No study to date has provided complete ultrastructural information on the early events of spermatogenesis, proliferation and meiosis in class Reptilia. Furthermore, no comprehensive data set exists that describes the ultrastructure of the entire ontogenic progression of germ cells through the phases of reptilian spermatogenesis (mitosis, meiosis and spermiogenesis)."

Taxon

Iguana - historic drawing

root; cellular organisms; Eukaryota; Opisthokonta; Metazoa; Eumetazoa; Bilateria; Coelomata; Deuterostomia; Chordata; Craniata; Vertebrata; Gnathostomata; Teleostomi; Euteleostomi; Sarcopterygii; Tetrapoda; Amniota; Sauropsida; Sauria; Lepidosauria

Squamata (squamates) - snakes and lizards.

  • Iguania (iguanian lizards) - arboreal with primitively fleshy, non-prehensile tongues, highly modified in the chameleons.
    • Acrodonta
    • Iguanidae (iguanid lizards)
  • Scleroglossa
    • Amphisbaenia
    • Anguimorpha (anguimorph lizards)
    • Gekkota - all geckos and the limbless Pygopodidae.
    • Scincomorpha (scincomorph lizards)
    • Serpentes (snakes)
  • unclassified Squamata
Links: Taxonomy Browser Lizards

Development Overview

Australian Water Skink

Genome

Anolis carolinensis (green anole) mating.

Anolis carolinensis (green anole)

The genome of the lizard Anolis carolinensis (green anole) from southeastern United States has a karyotype of 18 chromosomes, comprising six pairs of large macrochromosomes and 12 pairs of small microchromosomes, and has recently been sequenced [1]. Interestingly, almost all reptilian genomes also contain "microchromosomes", very small chromosomes less than 20 Mb in sequence size.

It is a model organism for laboratory-based studies of organismal function and for field studies of ecology and evolution. This species was chosen for genome sequencing in part because of the ease and low expense of captive breeding, well studied brain, and sophisticated color vision. It is also well suited for studies involving the role of hormones in development and adult nervous system plasticity. (modified from Genome)

Search PubMed Genome: Lizard

Historic

Fig. 343. Head of a Lizard Embryo (Sphenodon punctatum Hatteria)

Schwalbe (1891) points out the significant fact that in reptiles that lack an external ear (lizard and turtle) there occur distinct hillocks in the embryo, resembling those in vertebrates that develop an auricle. These hillocks undergo degeneration and are reduced to the level of the surrounding skin. He finds in both birds and reptiles hillocks corresponding to the tragus and antitragus hillocks of His. These animals have one hillock (Auricularkegel), situated dorsal to the first cleft, which seems to represent a more primitive apparatus than is present in mammals, although it may be related to the helix system. In Salachians it possesses a spiracle.

(From Contributions to Embryology No.69)

References

  1. 1.0 1.1 <pubmed>21881562</pubmed>
  2. <pubmed>22984480</pubmed>
  3. <pubmed>22780101</pubmed>
  4. <pubmed>22174948</pubmed>| PMC3184186
  5. <pubmed>22319673</pubmed>

Reviews

<pubmed>21573966</pubmed> <pubmed>21513818</pubmed> <pubmed>20234154</pubmed> <pubmed></pubmed> <pubmed></pubmed> <pubmed></pubmed>

Articles

<pubmed>19645023</pubmed> <pubmed>19097047</pubmed> <pubmed>17872995</pubmed>| J Exp Biol. <pubmed>17415759</pubmed> <pubmed>15521466</pubmed> <pubmed>5437480</pubmed> <pubmed>6429113</pubmed>

Books

Search PubMed

Search PubMed: Lizard development | Anolis carolinensis

External Links

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Cite this page: Hill, M.A. (2021, June 20) Embryology Lizard Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Lizard_Development

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© Dr Mark Hill 2021, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G