Natural parthenogenesis in the gekkonid lizardLepidodactylus lugubris

Single-cell analysis of lizard blastema fibroblasts reveals phagocyte-dependent activation of Hedgehog-responsive chondrogenesis

Lizards cannot naturally regenerate limbs but are the closest known relatives of mammals capable of epimorphic tail regrowth. However, the mechanisms regulating lizard blastema formation and chondrogenesis remain unclear. Here, single-cell RNA sequencing analysis of regenerating lizard tails identifies fibroblast and phagocyte populations linked to cartilage formation. Pseudotime trajectory analyses suggest spp1+-activated fibroblasts as blastema cell sources, with subsets exhibiting sulf1 expression and chondrogenic potential. Tail blastema, but not limb, fibroblasts express sulf1 and form cartilage under Hedgehog signaling regulation. Depletion of phagocytes inhibits blastema formation, but treatment with pericytic phagocyte-conditioned media rescues blastema chondrogenesis and cartilage formation in amputated limbs. The results indicate a hierarchy of phagocyte-induced fibroblast gene activations during lizard blastema formation, culminating in sulf1+ pro-chondrogenic populations singularly responsive to Hedgehog signaling. These properties distinguish lizard blastema cells from homeostatic and injury-stimulated fibroblasts and indicate potential actionable targets for inducing regeneration in other species, including humans.

Genome Evolution and the Future of Phylogenomics of Non-Avian Reptiles

Non-avian reptiles comprise a large proportion of amniote vertebrate diversity, with squamate reptiles-lizards and snakes-recently overtaking birds as the most species-rich tetrapod radiation. Despite displaying an extraordinary diversity of phenotypic and genomic traits, genomic resources in non-avian reptiles have accumulated more slowly than they have in mammals and birds, the remaining amniotes. Here we review the remarkable natural history of non-avian reptiles, with a focus on the physical traits, genomic characteristics, and sequence compositional patterns that comprise key axes of variation across amniotes. We argue that the high evolutionary diversity of non-avian reptiles can fuel a new generation of whole-genome phylogenomic analyses. A survey of phylogenetic investigations in non-avian reptiles shows that sequence capture-based approaches are the most commonly used, with studies of markers known as ultraconserved elements (UCEs) especially well represented. However, many other types of markers exist and are increasingly being mined from genome assemblies in silico, including some with greater information potential than UCEs for certain investigations. We discuss the importance of high-quality genomic resources and methods for bioinformatically extracting a range of marker sets from genome assemblies. Finally, we encourage herpetologists working in genomics, genetics, evolutionary biology, and other fields to work collectively towards building genomic resources for non-avian reptiles, especially squamates, that rival those already in place for mammals and birds. Overall, the development of this cross-amniote phylogenomic tree of life will contribute to illuminate interesting dimensions of biodiversity across non-avian reptiles and broader amniotes.

First record of Lepidodactylus lugubris (Duméril & Bibron, 1836) (Squamata, Gekkonidae) from Hainan Island, China

Lepidodactylus lugubris is known from tropical Asia, Oceania, and Latin America, but in China it was previously known only from Taiwan Island. In this paper, we report a new herpetofaunal record based on one specimen collected from Wanning, Hainan, China, which conforms to L. lugubris on both morphological and molecular data. Our finding brings the total species of the family Gekkonidae in Hainan to six.

Evolution of parthenogenetic reproduction in Caucasian rock lizards: A review

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 favoured the deviation of reproductive behaviour when species switched to interspecific mates. To date, at least seven 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 of hybrid karyotypes in rock lizards. Hybridization and polyploidization are two important evolutionary forces in the genus Darevskia. At present, throughout backcrossing between parthenogenetic and parental species, the triploid and tetraploid hybrid individuals appear annually, but no triploid species found among Darevskia spp on current stage of evolution. The speciation by hybridization with the long-term stage of diploid parthenogenetic species, non-distorted meiosis, together with the high ecological plasticity of Caucasian rock lizards provide us with a new model for considering the pathways and persistence of the evolution of parthenogenesis in vertebrates.

Introducing dorsoventral patterning in adult regenerating lizard tails with gene-edited embryonic neural stem cells

Lizards regenerate amputated tails but fail to recapitulate the dorsoventral patterning achieved during embryonic development. Regenerated lizard tails form ependymal tubes (ETs) that, like embryonic tail neural tubes (NTs), induce cartilage differentiation in surrounding cells via sonic hedgehog (Shh) signaling. However, adult ETs lack characteristically roof plate-associated structures and express Shh throughout their circumferences, resulting in the formation of unpatterned cartilage tubes. Both NTs and ETs contain neural stem cells (NSCs), but only embryonic NSC populations differentiate into roof plate identities when protected from endogenous Hedgehog signaling. NSCs were isolated from parthenogenetic lizard embryos, rendered unresponsive to Hedgehog signaling via CRISPR/Cas9 gene knockout of smoothened (Smo), and implanted back into clonally-identical adults to regulate tail regeneration. Here we report that Smo knockout embryonic NSCs oppose cartilage formation when engrafted to adult ETs, representing an important milestone in the creation of regenerated lizard tails with dorsoventrally patterned skeletal tissues.

Organisms with regenerative capacity typically regrow organs with correct axial patterning, however, regrown lizard tails lack this feature. Here the authors used neural stem cells to induce patterning in regenerating lizard tails and rescued normal skeletal morphology.

First record of the invasive gecko, Lepidodactylus lugubris Duméril & Bibron, 1836 in mainland Chile (Squamata, Gekkonidae)

In Chile, the presence of Mourning Gecko, Lepidodactylus lugubris Duméril & Bibron, 1836 has been recognized for Easter Island (Rapa Nui) from late 19th century. Here, we report the first observation of a juvenile specimen of L. lugubris in an urban zone of Santiago, Región Metropolitana, mainland Chile, representing the southernmost non-insular record in America for this invasive species. Moreover, an updated distributional map of L. lugubris for South America and the Antilles is provided.

Pet snakes illegally marketed in Brazil: Climatic viability and establishment risk

Invasive species are one among many threats to biodiversity. Brazil has been spared, generically, of several destructive invasive species. Reports of invasive snakes’ populations are nonexistent, but the illegal pet trade might change this scenario. Despite the Brazilian laws forbid to import most animals, illegal trade is frequently observed and propagules are found in the wild. The high species richness within Brazilian biomes and accelerated fragmentation of natural reserves are a critical factors facilitating successful invasion. An efficient way to ease damages caused by invasive species is identifying potential invaders and consequent prevention of introductions. For the identification of potential invaders many factors need to be considered, including estimates of climate matching between areas (native vs. invaded). Ecological niche modelling has been widely used to predict potential areas for invasion and is an important tool for conservation biology. This study evaluates the potential geographical distribution and establishment risk of Lampropeltis getula (Linnaeus, 1766), Lampropeltis triangulum (Lacépède, 1789), Pantherophis guttatus (Linnaeus, 1766), Python bivittatus Kuhl, 1820 and Python regius (Shaw, 1802) through the Maximum Entropy modelling approach to estimate the potential distribution of the species within Brazil and qualitative evaluation of specific biological attributes. Our results suggest that the North and Midwest regions harbor major suitable areas. Furthermore, P. bivittatus and P. guttatus were suggested to have the highest invasive potential among the analyzed species. Potentially suitable areas for these species were predicted within areas which are highly relevant for Brazilian biodiversity, including several conservation units. Therefore, these areas require special attention and preventive measures should be adopted.

Experimental Crossing of Two Distinct Species of Leopard Geckos, Eublepharis angramainyu and E. macularius: Viability, Fertility and Phenotypic Variation of the Hybrids

Hybridization between distinct species of animals and subsequent genetic introgression plays a considerable role in the speciation process and the emergence of adaptive characters. Fitness of between-species hybrids usually sharply decreases with the divergence time of the concerned species and the divergence depth, which still allows for a successful crossing differs among principal clades of vertebrates. Recently, a review of hybridization events among distinct lizard species revealed that lizards belong to vertebrates with a highly developed ability to hybridize. In spite of this, reliable reports of experimental hybridizations between genetically fairly divergent species are only exceptional. Here, we show the results of the crossing of two distinct allopatric species of eyelid geckos possessing temperature sex determination and lacking sex chromosomes: Eublepharis macularius distributed in Pakistan/Afghanistan area and E. angramainyu, which inhabits Mesopotamia and adjacent areas. We demonstrated that F₁ hybrids were viable and fertile, and the introgression of E. angramainyu genes into the E. macularius genome can be enabled via a backcrossing. The examined hybrids (except those of the F₂ generation) displayed neither malformations nor a reduced survival. Analyses of morphometric and coloration traits confirmed phenotypic distinctness of both parental species and their F₁ hybrids. These findings contrast with long-term geographic and an evolutionary separation of the studied species. Thus, the occurrence of fertile hybrids of comparably divergent species, such as E. angramainyu and E. macularius, may also be expected in other taxa of squamates. This would violate the current estimates of species diversity in lizards.

Comparative Chromosome Painting and NOR Distribution Suggest a Complex Hybrid Origin of Triploid Lepidodactylus lugubris (Gekkonidae)

Parthenogenesis, unisexuality and triploidy are interesting but poorly studied phenomena occurring in some reptile species. The mourning gecko (Lepidodactylus lugubris) represents a complex of diploid and triploid parthenogenetic mostly all-female populations (males occur quite rarely) widely distributed in coastal areas of the Indian and Pacific Oceans. Here, we study karyotypes of a male and two female L. lugubris (LLU) triploid individuals (3n = 66) using comparative painting with Gekko japonicus, Hemidactylus turcicus and H. platyurus chromosome specific probes to visualize the homologous regions and to reveal genus specific rearrangements. Also, we applied a 28S ribosomal DNA probe and Ag-staining to detect nucleolus organizer regions (NORs). Our results suggest that the karyotype of L. lugubris underwent a chromosome fission and a fusion after its divergence from a common ancestor of the Gekko-Hemidactylus group. The NORs were found to be located on one out of three homologs on each of LLU8, LLU15 and LLU18, thus further confirming a hybrid origin of triploid individuals. It seems that three different bisexual populations might have contributed to the origin of this triploid parthenogenetic population. We postulate that the heterozygosity in NOR localization is maintained in the triploid clone studied by the absence of recombination as described in whiptail lizards. The pattern of NOR localizations and homologous regions in males and females, as well as the absence of other detectable karyotypic differences, suggest that males arise spontaneously in all female populations and do not arise from independent hybridizations with different species.

Male Gamete Contributions to the Embryo

During normal fertilization, plasma membranes of a spermatozoon and an oocyte mingle to form a mosaic plasma membrane of a zygote. This may contribute to the polyspermy block of the zygote. Sperm tail components (mitochondria, axonema, and accessory fibers) that enter the oocyte are "digested" without playing major roles in embryo development. The proximal centrosome adjacent to the sperm nucleus may become the center of the sperm aster that brings the male and female pronuclei to the center of the zygote, but it may not be essential for embryonic development per se. Whether sperm RNAs contribute to embryonic development is the subject of controversy. The nucleus is the most important sperm component that enters the oocyte. It is known that 7-15% of the spermatozoa of fertile men are chromosomally abnormal. The proportion of the spermatozoa with subchromosomal abnormalities (including damage at the DNA level) is expected to be even higher. The majority of embryos and fetuses with genomic abnormalities are aborted before reaching term. Structurally abnormal spermatozoa are not necessarily genomically abnormal, even though the incidence of genomically abnormal spermatozoa is higher among structurally abnormal than normal spermatozoa. In mammals, certain genes (estimated to be about 100) in the spermatozoon and oocyte must be "imprinted" in a gender-specific manner to warrant normal embryonic development.

Evidence for a switch in the reproductive biology of Rubus alceifolius (Rosaceae) towards apomixis, between its native range and its area of introduction

We compared the reproductive system of Rubus alceifolius in its native range in Southeast Asia, in Madagascar, where the plant was introduced apparently some centuries ago, and in La Réunion, an Indian Ocean island onto which R. alceifolius was introduced (from Madagascan source populations) around 1850. While tetraploidy makes it impossible to analyze variation in R. alceifolius using classical methods of population genetics, both the patterns of genetic diversity (as revealed by AFLP [amplified fragment length polymorphism] markers) and differences between half-sib progeny and their maternal parents (revealed by microsatellite markers) show that in the plant's native range in southeast Asia, seeds are produced sexually. In contrast, in Madagascar sexual reproduction cannot alone account for the genetic patterns observed with microsatellite markers. Over 85% of the half-sib progeny resulting from open pollination gave multilocus genotypes identical to those of their respective maternal parents, despite the fact that the latter had alleles that were rare in the population. The other progeny differed in having an allele with one motif more or less than that of the maternal parent. Seeds thus appear to be produced mostly or exclusively by apomixis in Madagascar. We present findings suggesting that Madagascan populations result from hybridization of introduced R. alceifolius and native populations of R. roridus, a closely related species of Rubus subgenus Malachobatus, and suggest that apomixis was a consequence of this hybridization. In Reunionese populations of R. alceifolius (derived from Madagascan populations), seeds obtained in controlled pollination experiments were all genetically identical to maternal parents. While genetic variation (microsatellite markers) in Reunionese populations was low, it was sufficient to allow us to demonstrate that seeds could not have resulted from fertilization by the pollen donors chosen for controlled pollinations, or from autogamy, and were produced exclusively by apomixis.

Histology of the reproductive tract of hybrids between gonochoristic males and parthenogenetic females of Lepidodactylus lugubris in French Polynesia (Reptilia, Gekkonidae)

Parthenogenetic populations of the gecko Lepidodactylus lugubris are widespread throughout Polynesia. They often occur parapatrically, and occasionally syntopically, with the increasingly rare bisexual populations. In these instances, a small number of hybrid individuals occur and include both "female" and "male" external phenotypes, both with greatly reduced gonads. Histological examination demonstrates that these hybrids possess small ovotestes. The differentiation of the cortical tissue is identical in both "male" and "female" hybrids, but the medullary tissue is more developed in "males." The remainder of the genital tract in "females" resembles that of fertile females in the parthenogenetic and bisexual populations. By contrast, the "male" hybrids are markedly intersexual. In one of the two specimens autopsied, the hemipenes are more or less the same size as those of bisexual males, and the sexual segment of the kidney is hypertrophied and serous. In the other hybrid "male," the hemipenes have a structure similar to that seen in females, and the sexual segment of the kidney is poorly differentiated. In both hybrid "males," the ductus deferens is extremely narrow and further reduced in its middle portion; oviducts are present and resemble those of normal or hybrid females. Thus, embryonic-like gonads are associated with complete and normal female reproductive ducts in hybrid "females." Hybrid "males" also have embryonic-like gonads and feminized genital ducts but associated with secondary sexual characters that match those of sexually active or quiescent normal males.

Presumptive sex chromosomes of a unisexual homomorphic species of lizards, Lepidodactylus lugubris

Incorporation of 5-bromo-2'-deoxyuridine (BrdU) in prometaphasic chromosomes allows active from inactivated X chromosomes in female mammalian cells to be distinguished. We have applied the technique to the all-female, chromosomally homomorphic gecko Lepidodactylus lugubris. Similar differences to those obtained between the two female sex chromosomes of mammals are observed in the patterns of chromosome pair 1. It is argued that this is more likely to reflect incipient ZW heterogamety than female (XX) homogamety.

Animal parthenogenesis

The available evidence on the ecological factors favoring the existence and origin of natural parthenogenesis is evaluated. Analysis of the geographical distributions of the well-known cases of animal parthenogenesis in nature reveals (i) that most of these species exist in natural disclimax communities and (ii) that within these communities they exist in isolation from closely related congeneric species. Parthenogenesis can only evolve in areas devoid of the generating bisexual species, because such species would prevent newly formed unisexuals from establishing clones due either to hybridization or competition. Furthermore, the two unique features allowing parthenogenetic species to invade and occupy open habitats faster than bisexuals are (i) a double intrinsic rate of increase and (ii) the ability of one individual to establish a new colony.

Parthenogenetic reptiles: new subjects for laboratory research

Problems preventing establishment of laboratory colonies of parthenogenetic lizards have been solved. Now, productive colonies of these lizards, which have remarkably little genetic variation, can be readily established and used not only for research on parthenogenesis but also for many kinds of experiments for which reptile systems are desirable. Research colonies can provide valuable specimens while reducing the exploitation of natural populations.

Intraclonal histocompatibility in a parthenogenetic lizard: evidence of genetic homogeneity

A total of 175 skin grafts were transplanted among 20 individuals belonging to two separate populations of the parthenogenetic lizard Cnemidophorus uniparens. Of these, 98.8 percent were permanently accepted, which indicates that all individuals of each population may be genetically identical. These results further suggest that large populations or the entire species may consist of one clone derived from a single individual.

Natural hybridization between parthenogenetic and bisexual lizards: detection of uniparental source of skin grafting

Skin graft evidence is used to directly identify the unisexual parent of natural hybrids produced between the bisexual species Cnemidophorus inornatus and the unisexual Cnemidophorus neomexicanus. Reciprocal grafts transplanted among there suspected hybrids between Cnemidophorus inornatus and Cnemidophorus neomexicanus are rejected as well as grafts from the hybrids to C. neomexicanus, indicating that the hybrids are each genetically different from each other and that C. neomexicanus has the ability to reject foreign grafts. Allografts among C. neomexicanus and xenografts from C. neomexicanus to the hybrids are not rejected, indicating that C. neomexicanus is genetically homogeneous and that the hybrids possess genomes genetically identical to C. neomexicanus. Electrophoretic analysis of the hybrids and their probable parents supports the evidence obtained from skin grafting that C. neomexicanus is one of the parents, and suggests that C. inornatus, rather than C. tigris, is the bisexual parent. Chromosome spreads obtained from the hybrids reveal a triploid number of 69, a number consistent with their presumed origin from unreduced diploid ova (2N = 46) from C. neomexicanus and haploid serum (N = 23) from C. inornatus. Preliminary evidence is presented of the first hybrids known between Cnemidophorus inornatus and Cnemidophorus uniparens. Histological examination of the tests suggests that these hybrids are sterile. Included is a list summarizing all known hybrids between bisexual and unisexual species of the genus Cnemidophorus.