Two-headed parthenogenetic lizard embryo from southern Georgia (original) (raw)
Related papers
bioRxiv (Cold Spring Harbor Laboratory), 2024
Among vertebrates, obligate parthenogenesis occurs exclusively in squamate reptiles. Premeiotic endoreplication in a small subset of developing oocytes has been documented as the mechanism of production of unreduced eggs in minutely explored obligate parthenogenetic lineages, namely in teiids and geckos. The situation in the lacertid genus Darevskia has been discussed for decades. Certain observations suggested that ploidy level is restored during egg formation through a fusion of egg and polar body nuclei in D. unisexualis and D. armeniaca. In this study, we re-evaluated the fusion hypothesis by studying diplotene chromosomes in adult females of sexual species D. raddei nairensis and obligate parthenogens D. armeniaca, D. dahli and D. unisexualis. We revealed 19 bivalents in the sexual species and 38 bivalents in the diploid obligate parthenogens, which uncovers premeiotic endoreplication as the mechanism of the production of non-reduced eggs in parthenogenetic females. The earlier contradicting reports can be likely attributed to the difficulty in identifying mispairing of chromosomes in pachytene, and the fact that in parthenogenetic reptiles relying on premeiotic endoreplication only a small subset of developing oocytes undergo genome doubling and overcome the pachytene checkpoint. This study highlights co-option of premeiotic endoreplication for escape from sexual reproduction in all independent hybrid origins of obligate parthenogenesis in vertebrates studied to date.
Evolution of parthenogenetic reproduction in Caucasian rock lizards: a review
Current Zoology
Despite numerous works devoted to hybrid origin of parthenogenesis in reptiles, the causes of hybridization between different species, resulting in the origin of parthenogenetic forms, remain uncertain. Recent studies demonstrate that sexual species considered parental to parthenogenetic rock lizards (Darevskia spp.) avoid interspecific mating in the secondary overlap areas. A specific combination of environmental factors during last glaciation period was critical for ectotherms, which led to a change in their distribution and sex ratio. Biased population structure (e.g., male bias) and limited available distributional range favored the deviation of reproductive behavior when species switched to interspecific mates. To date, at least 7 diploid parthenogenetic species of rock lizards (Darevskia, Lacertidae) originated through interspecific hybridization in the past. The cytogenetic specifics of meiosis, in particular the weak checkpoints of prophase I, may have allowed the formation ...
Three probable cases of parthenogenesis in lizards (Agamidae, Chamaeleontidae, Gekkonidae)
Neither parthenogenesis nor triploidy has previously been reported in the infraorder Iguania, comprising the families Iguanidae, Agamidae, and Chamaeleontidae. During a study of agamid karyotypes certain butterfly lizards, Leiolepis belliana Gray, possibly from northern Malaysia, were found to be apparently triploid parthenogenones while others from Thailand were diploid and bisexual. Literature surveys revealed two other previously unsuspected cases of lizard parthenogenesis; one in the Chamaeleontidae and the other, which probably involves triploidy as well, in the Gekkonidae.
Biological Journal of The Linnean Society, 2006
The evolution of viviparity in squamates has been the focus of much scientific attention in previous years. In particular, the possibility of the transition from viviparity back to oviparity has been the subject of a vigorous debate. Some studies have suggested this reversal is more frequent than previously thought. However, none of them provide conclusive evidence. We investigated this problem by studying the phylogenetic relationships between oviparous and viviparous lineages of the reproductively bimodal lizard species Zootoca vivipara. Our results show that viviparous populations are not monophyletic, and that several evolutionary transitions in parity mode have occurred. The most parsimonious scenario involves a single origin of viviparity followed by a reversal back to oviparity. This is the first study with a strongly supported phylogenetic framework supporting a transition from viviparity to oviparity. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87, 1–11.
Tendency towards clonality: deviations of meiosis in parthenogenetic Caucasian rock lizards
Research Square (Research Square), 2024
Cytogenetic mechanisms of unisexuality in diploid parthenogenetic species of the genus Darevskia have remained debatable until recently. The mechanism that allows the unisexual form to maintain heterozygosity in a number of generations is important for its long-term existence in nature. In this work, for the rst time, for parthenogenetic species of the genus Darevskia, in addition to primary oocytes with the usual ploidy (18+ZW bivalents in meiotic prophase I), oocytes that underwent premeiotic genome endoduplication and carried a doubled number of bivalents (36+ZZ+WW) were found. Here, we present a detailed comparative analysis of the total preparation of synaptonemal complexes in oocyte nuclei without and with genome endoduplication and the behavior of sex Z and W chromosomes. We show the details of the assembly of bivalents in pachytene nuclei, where either homeologs or doubled identical copies of chromosomes compete for synapsis and form multivalents. For the rst time, the WW sex pseudobivalent has been visualized in parthenogenetic reptiles. We show the reverse side of meiotic deviations in obligate parthenogenesis-cases of nonviable embryos with speci c abnormalities.
PeerJ, 2021
Despite the long history of embryological studies of squamates, many groups of this huge clade have received only limited attention. One such understudied group is the anguimorphs, a clade comprising morphologically and ecologically very diverse lizards. We describe several stages of embryonic development of Anguis fragilis, a limbless, viviparous anguimorph. Interestingly, in several clutches we observe high morphological variation in characters traditionally important in classifying embryos into developmental stages. The causes of this variation remain unknown but environmental factors do not seem to be very important. Additionally, we describe the state of ossification in several perinatal specimens of A. fragilis. The cranial skeleton is relatively poorly ossified around the time of birth, with all of the bones constituting the braincase unfused. On the other hand, the vertebral column is well ossified, with the neurocentral sutures closed and the neural arches fused in all post...
Zoology, 2012
The evolutionary history of the lizard family Gymnophthalmidae is characterized by several independent events of morphological modifications to a snake-like body plan, such as limb reduction, body elongation, loss of external ear openings, and modifications in skull bones, as adaptive responses to a burrowing and fossorial lifestyle. The origins of such morphological modifications from an ancestral lizard-like condition can be traced back to evolutionary changes in the developmental processes that coordinate the building of the organism. Thus, the characterization of the embryonic development of gymnophthalmid lizards is an essential step because it lays the foundation for future studies aiming to understand the exact nature of these changes and the developmental mechanisms that could have been responsible for the evolution of a serpentiform (snake-like) from a lacertiform (lizard-like) body form. Here we describe the postovipositional embryonic development of the fossorial species Nothobachia ablephara and Calyptommatus sinebrachiatus, presenting a detailed staging system for each one, with special focus on the development of the reduced limbs, and comparing their development to that of other lizard species. The data provided by the staging series are essential for future experimental studies addressing the genetic basis of the evolutionary and developmental variation of the Gymnophthalmidae.