Common lizard primary oviduct cell culture: A model system for the genetic and cellular basis of oviparity and viviparity

Reproduction by egg-laying (oviparity) or live-bearing (viviparity) is a genetically determined trait fundamental to the biology of amniotes. Squamates are an emerging model for the genetics of reproductive mode yet lack cell culture models valuable for exploring molecular mechanisms. Here, we report a novel primary culture model for reproductive biology: cell cultures derived from the oviduct tissues (infundibulum, uterus and vagina) of oviparous and viviparous common lizards (Lacertidae: Zootoca vivipara). We maintained and expanded these cultures for over 100 days, including repeated subculturing and successful revival of cryopreserved cells. Immunocytochemical investigation suggested expression of both epithelial and fibroblast-like proteins, and RNA sequencing of cultured cells as compared to in vivo oviduct tissue showed changes in gene expression in response to the cell culture environment. Despite this, we confirmed the maintenance of distinct gene expression patterns in viviparous and oviparous cells after 60+ days of cell culture, finding 354 differentially expressed genes between viviparous and oviparous cells. Furthermore, we confirmed the expression of 15 viviparity-associated candidate genes in cells maintained for 60+ days in culture. Our study demonstrates the feasibility and utility of oviduct cell culture for molecular analysis of reproductive mode and provides a tool for future genetic experiments.

Microscopic Analysis of Nuclear Speckles in a Viviparous Reptile

Nuclear speckles are compartments enriched in splicing factors present in the nucleoplasm of eucaryote cells. Speckles have been studied in mammalian culture and tissue cells, as well as in some non-mammalian vertebrate cells and invertebrate oocytes. In mammals, their morphology is linked to the transcriptional and splicing activities of the cell through a recruitment mechanism. In rats, speckle morphology depends on the hormonal cycle. In the present work, we explore whether a similar situation is also present in non-mammalian cells during the reproductive cycle. We studied the speckled pattern in several tissues of a viviparous reptile, the lizard Sceloporus torquatus, during two different stages of reproduction. We used immunofluorescence staining against splicing factors in hepatocytes and oviduct epithelium cells and fluorescence and confocal microscopy, as well as ultrastructural immunolocalization and EDTA contrast in Transmission Electron Microscopy. The distribution of splicing factors in the nucleoplasm of oviductal cells and hepatocytes coincides with the nuclear-speckled pattern described in mammals. Ultrastructurally, those cell types display Interchromatin Granule Clusters and Perichromatin Fibers. In addition, the morphology of speckles varies in oviduct cells at the two stages of the reproductive cycle analyzed, paralleling the phenomenon observed in the rat. The results show that the morphology of speckles in reptile cells depends upon the reproductive stage as it occurs in mammals.

Effects of testosterone on urogenital tract morphology and androgen receptor expression in immature Eastern Fence lizards (Sceloporus undulatus)

In non-avian reptiles, the onset of sexual dimorphism of the major structures of the urogenital tract varies temporally relative to gonadal differentiation, more so than in other amniote lineages. In the current study, we used tonic-release implants to investigate the effects of exogenous testosterone (T) on postnatal development of the urogenital tract in juvenile Eastern Fence Lizards (Sceloporus undulatus) to better understand the mechanisms underlying the ontogeny of sexual differentiation in reptiles. We examined gonads, mesonephric kidneys and ducts (male reproductive tract primordia), paramesonephric ducts (oviduct primordia), sexual segments of the kidneys (SSKs), and hemiphalluses to determine which structures were sexually dimorphic independent of T treatment and which structures exhibited sexually dimorphic responses to T. To better understand tissue-level responsiveness to T treatment, we also characterized androgen receptor (AR) expression by immunohistochemistry. At approximately 4 months after hatching in control animals, gonads were well differentiated but quiescent; paramesonephric ducts had fully degenerated in males; mesonephric kidneys, mesonephric ducts, and SSKs remained sexually undifferentiated; and hemiphalluses could not be everted in either sex. Exogenous T caused enlargement, regionalization, and secretory activity of the mesonephric ducts and SSKs in both sexes; enlargement and regionalization of the oviducts in females; and enlargement of male hemipenes. The most responsive tissues exhibited moderate but diffuse staining for AR in control lizards and intense nuclear staining in T-treated lizards, suggestive of autoregulation of AR. The similarity between sexes in the responsiveness of the mesonephric ducts and SSK to T indicates an absence of sexually dimorphic organizational effects in these structures prior to treatment, which was initiated approximately 2 months after hatching. In contrast, the sex-specific responses in oviducts and hemipenes indicate that significant organization and/or differentiation had taken place prior to treatment.

The ultrastructural features of the infundibulum of the green iguana, Iguana iguana

The purpose of this study is to describe, in detail, the ultrastructure of the infundibulum of the sexually mature and active female green iguana, Iguana iguana. The infundibulum of five iguanas was remarkably distinct from the uterus, and was also clearly demarcated into cranial (expanded v-shaped) and caudal (tubular) divisions. Tissue samples obtained from five portions (three from the cranial division and two from the caudal division) of the infundibulum were processed conventionally for light and electron microscopy. The epithelial lining of the most anterior, middle, and posterior, parts of the cranial division displayed nonciliated cells predominantly, and occasionally ciliated cells. The numerous secretory granules in nonciliated type 1 cell found in the fimbrial aspect of the infundibulum were homogenous and deeply electron-dense, but those in the other two regions were variants of this cell type because they contained variably electron-dense secretory granules. Two main types of nonciliated cells (type 2 and its variant, type 3, as well as type 4) occurred in the epithelial lining of the caudal division of the infundibulum, but they, clearly, showed no dense secretory granules. Whereas the nonciliated type 2 cell and its variant (type 3 cell) contained large glycogen deposits, the type 4 cell lacked these deposits but its apical part contained large lipid-like droplets and, remarkably, blebbed into the duct lumen. The nonciliated cells lining the mucosal tubular glands contained highly electron-dense secretory granules, which were similar to those found in the nonciliated type 1 cell in the epithelial lining of the fimbrial part of the cranial division of the infundibulum.

Heads or tails first? Evolution of fetal orientation in ichthyosaurs, with a scrutiny of the prevailing hypothesis

According to a longstanding paradigm, aquatic amniotes, including the Mesozoic marine reptile group Ichthyopterygia, give birth tail-first because head-first birth leads to increased asphyxiation risk of the fetus in the aquatic environment. Here, we draw upon published and original evidence to test two hypotheses: (1) Ichthyosaurs inherited viviparity from a terrestrial ancestor. (2) Asphyxiation risk is the main reason aquatic amniotes give birth tail-first. From the fossil evidence, we conclude that head-first birth is more prevalent in Ichthyopterygia than previously recognized and that a preference for tail-first birth likely arose in derived forms. This weakens the support for the terrestrial ancestry of viviparity in Ichthyopterygia. Our survey of extant viviparous amniotes indicates that fetal orientation at birth reflects a broad diversity of factors unrelated to aquatic vs. terrestrial habitat, further undermining the asphyxiation hypothesis. We propose that birth preference is based on parturitional mechanics or carrying efficiency rather than habitat.

Placentation in the Mexican scincid lizard Plestiodon brevirostris (Squamata: Scincidae)

Viviparity is the reproductive pattern in which females gestate eggs within their reproductive tract to complete their development and give birth to live offspring. Within extant sauropsids, only the Squamata (e.g., snakes, lizards, and amphisbaenians) evolved viviparity, representing 20% of the existing species. The genus Plestiodon is represented by 43 species and is one of the most widely distributed genera of the Scincidae in Mexico. The goal of this research has been to determine the placental morphology and ontogeny during gestation in the lizard Plestiodon brevirostris. Specimens were dissected to obtain the embryonic chambers and the embryos were categorized to carry out the correlation between the development stage and the placenta development. The embryonic chambers were processed using the conventional histological technique for light microscopy. The identified embryonic stages were 4, 29, 34, 36, and 39. A thin eggshell surrounds the egg in early developmental stages; however, this structure is already absent in the embryonic hemisphere during the developmental stage 29. The results revealed that P. brevirostris is a lecithotrophic species, but a close maternal-fetal relationship is established by tissue apposition. Ontogenically, the placental types that form in the embryonic hemisphere are the chorioplacenta, choriovitelline placenta, and chorioallantoic placenta; whereas the omphaloplacenta is formed in the abembryonic hemisphere. The structure of the chorioallantoic placenta in P. brevirostris suggests that it may play a role during gas exchange between the mother and the embryo, due to the characteristics of the epithelia that comprise it. The structure of embryonic and maternal epithelia of the omphaloplacenta suggests a role in the absorption of the eggshell during gestation and possibly in the transport or diffusion of some nutrients. In general, it is evident that ontogeny and placental characteristics of P. brevirostris match those of other species of viviparous lecithotrophic scincids.

Directional asymmetry in gonad length indicates moray eels (Teleostei, Anguilliformes, Muraenidae) are "right-gonadal"

Directional asymmetry indicates a unidirectional deviation from perfect bilateral symmetry, which was rarely examined in the inner organs of the teleost (Teleostei) compared to external traits. This study examines the directional asymmetry in the gonad length of 20 species of moray eels (Muraenidae) and two outgroup species with 2959 individuals. We tested three hypotheses: (1) moray eel species did not exhibit directional asymmetry in the gonad length; (2) the directional asymmetry pattern was the same for all selected species; (3) the directional asymmetry was not related to the major habitat types, depth and size classes, and taxonomic closeness of the species. Moray eels were generally "right-gonadal", the right gonad length being constantly and significantly longer than the left one in all studied Muraenidae species. The degree of asymmetry varied among species and was not significantly related to taxonomic closeness. The habitat types, depth, and size classes had intermingled effects on observed asymmetry without a clear correspondence. The directional asymmetry in the gonad length is a unique and widely occurring phenomenon in the Family Muraenidae, which was likely a by-product in the evolutionary history without significant disadvantage in survival.

Neuronal control of the vagina in vertebrates: A review

BACKGROUND

At present, there is an increased interest in the vaginal microbiome. It is believed that microbes play equally important roles in the vagina, including the modulation of neuronal pathways, as in the gut. However, in man as well as in animals, the vagina is the least well-studied part of the female reproductive system. The vagina, a fibromuscular tract, having two main functions, i.e., childbirth and sexual intercourse, is mainly innervated by the pudendal nerve and the pelvic splanchnic nerves (the uterovaginal nerve plexus) containing sympathetic, parasympathetic and nociceptive nerve fibers. Innervation density in the vaginal wall undergoes significant remodeling due to hormonally mediated physiological activity. Knowledge about expression and function of neuropeptides and neurotransmitters in the vaginal fibers is incomplete or not established. Most research concerning the neuroregulation of the vagina and the function and expression of neuropeptides and neurotransmitters, is performed in several vertebrate species, including large farm animals, rodents, domestic fowl and lizards.

METHODS

This review summarizes, on a bibliographic basis, the current knowledge on vaginal innervation and function of neuropeptides and neurotransmitters expressed in vaginal nerve fibers in several vertebrate species, including humans. The presence and role played by the local microbioma is also explored.

CONCLUSION

A thorough knowledge of the vaginal innervation is necessary to unravel the putative communication of the vaginal microbiome and vaginal nerve fibers, but also to understand the effects of vaginal pathologies and of administered drugs on the neuroregulation of the vagina.

Reproductive Biology, Sperm storage, and Sexual Maturity of Thamnodynastes strigatus (Serpentes: Dipsadidae)

Life history strategies determine and influence many aspects of species fitness. In this study, we describe the reproductive biology - reproductive cycle, sperm storage, and sexual maturity - of Thamnodynastes strigatus in South Brazil. We analyzed 49 individuals (25 males and 24 females) from herpetological collections. The reproductive cycle of males and females was described considering the morpho-anatomical and histological changes in the testes, ductus deferens, and kidney, as well in the ovary and oviduct. The age at the onset of sexual maturity was determined by skeletochronology of the caudal vertebra. The reproductive cycle is seasonal semi-synchronous and most individuals have a reproductive peak in spring and summer. The seasonal biennial reproductive cycle and viviparity are two phylogenetically conserved characters in Tachymenini snakes. Thamnodynastes Strigatus females store sperm in the utero-vaginal junction furrows during autumn. There were no differences between the ages of sexual maturity of males (4-11y) and females (4-12y). Females reach sexual maturity at larger body sizes, and this may confer an adaptive advantage due to a higher fecundity potential. Herein, we confirmed the previously described seasonal biennial reproductive cycle of T. strigatus through histological analysis.

Histological findings of sperm storage in green turtle (Chelonia mydas) oviduct

Green turtles (Chelonia mydas) are seasonal breeders with a time lag between mating and nesting periods. We therefore investigated whether female turtles store sperm like some other animals by histologically and ultrastructurally analyzing oviducts collected from three mature female free-ranging green turtles during the breeding season in the Ogasawara Islands, Japan. The oviduct comprised an infundibulum, magnum, isthmus, uterus, and vagina. Sperm was found in the isthmus of all turtles examined. Some spermatozoa were found in the duct and acini of glands in the isthmus of two turtles with oviducts containing eggs, and a few were also located in the transition area between the uterus and vagina of one of the turtles. On the other hand, we also found abundant spermatozoa on the luminal surface of the isthmus of one turtle captured during mating. In most reptiles, fertilization occurs in the infundibulum or albumen region, and thus the isthmus near those areas might be suitable for storing sperm in female turtles.

An evo-devo perspective of the female reproductive tract

The vertebrate female reproductive tract has undergone considerable diversification over evolution, having become physiologically adapted to different reproductive strategies. This review considers the female reproductive tract from the perspective of evolutionary developmental biology (evo-devo). Very little is known about how the evolution of this organ system has been driven at the molecular level. In most vertebrates, the female reproductive tract develops from paired embryonic tubes, the Müllerian ducts. We propose that formation of the Müllerian duct is a conserved process that has involved co-option of genes and molecular pathways involved in tubulogenesis in the adjacent mesonephric kidney and Wolffian duct. Downstream of this conservation, genetic regulatory divergence has occurred, generating diversity in duct structure. Plasticity of the Hox gene code and wnt signaling, in particular, may underlie morphological variation of the uterus in mammals, and evolution of the vagina. This developmental plasticity in Hox and Wnt activity may also apply to other vertebrates, generating the morphological diversity of female reproductive tracts evident today.

Reproductive cycles of neotropical boid snakes evaluated by ultrasound

Snakes have increasingly been bred as pets around the world. Few studies have addressed the reproduction of boid snakes, and no study has addressed their reproductive cycles in captivity. Thus, this paper describes the reproductive aspects of Brazilian boids in captivity. We used ultrasonography to characterize the reproductive cycle of four boid species in captivity in the Southern Hemisphere: the anaconda (Eunectes murinus), the red-tailed boa (Boa constrictor constrictor), the Amazon tree boa (Corallus hortulanus), and the rainbow boa (Epicrates cenchria). Nonvitellogenic follicles occurred from January to December in anaconda and red-tailed boa and for a shorter period from September to February in Amazon tree boa and from January to May in rainbow boa. Vitellogenesis occurred from late June to late March in E. murinus in year-round (12 months), from March to March in Amazon tree boa, from late September to late March in red-tailed boa, and from late March to late September in rainbow boa. Mating occurred from late March to late September in red-tailed boa and rainbow boa and from late September to late March in Amazon tree boa. No mating was observed in anacondas, but a female probably underwent parthenogenesis. Births occurred in July in anaconda and in March to July in Amazon tree boa and from December to March in red-tailed boa and rainbow boa. In males, increases in testicular size were associated with the mating season. Ultrasonography proved to be a safe and noninvasive technique to study the reproductive cycle of giant snakes in captivity.

Phylogeny and evolutionary history of the amniote egg

We review morphological features of the amniote egg and embryos in a comparative phylogenetic framework, including all major clades of extant vertebrates. We discuss 40 characters that are relevant for an analysis of the evolutionary history of the vertebrate egg. Special attention is given to the morphology of the cellular yolk sac, the eggshell, and extraembryonic membranes. Many features that are typically assigned to amniotes, such as a large yolk sac, delayed egg deposition, and terrestrial reproduction have evolved independently and convergently in numerous clades of vertebrates. We use phylogenetic character mapping and ancestral character state reconstruction as tools to recognize sequence, order, and patterns of morphological evolution and deduce a hypothesis of the evolutionary history of the amniote egg. Besides amnion and chorioallantois, amniotes ancestrally possess copulatory organs (secondarily reduced in most birds), internal fertilization, and delayed deposition of eggs that contain an embryo in the primitive streak or early somite stage. Except for the amnion, chorioallantois, and amniote type of eggshell, these features evolved convergently in almost all major clades of aquatic vertebrates possibly in response to selective factors such as egg predation, hostile environmental conditions for egg development, or to adjust hatching of young to favorable season. A functionally important feature of the amnion membrane is its myogenic contractility that moves the (early) embryo and prevents adhering of the growing embryo to extraembryonic materials. This function of the amnion membrane and the liquid-filled amnion cavity may have evolved under the requirements of delayed deposition of eggs that contain developing embryos. The chorioallantois is a temporary embryonic exchange organ that supports embryonic development. A possible evolutionary scenario is that the amniote egg presents an exaptation that paved the evolutionary pathway for reproduction on land. As shown by numerous examples from anamniotes, reproduction on land has occurred multiple times among vertebrates-the amniote egg presenting one "solution" that enabled the conquest of land for reproduction.

Morphological research on amniote eggs and embryos: An introduction and historical retrospective

Evolution of the terrestrial egg of amniotes (reptiles, birds, and mammals) is often considered to be one of the most significant events in vertebrate history. Presence of an eggshell, fetal membranes, and a sizeable yolk allowed this egg to develop on land and hatch out well-developed, terrestrial offspring. For centuries, morphologically-based studies have provided valuable information about the eggs of amniotes and the embryos that develop from them. This review explores the history of such investigations, as a contribution to this special issue of Journal of Morphology, titled Developmental Morphology and Evolution of Amniote Eggs and Embryos. Anatomically-based investigations are surveyed from the ancient Greeks through the Scientific Revolution, followed by the 19th and early 20th centuries, with a focus on major findings of historical figures who have contributed significantly to our knowledge. Recent research on various aspects of amniote eggs is summarized, including gastrulation, egg shape and eggshell morphology, eggs of Mesozoic dinosaurs, sauropsid yolk sacs, squamate placentation, embryogenesis, and the phylotypic phase of embryonic development. As documented in this review, studies on amniote eggs and embryos have relied heavily on morphological approaches in order to answer functional and evolutionary questions.

Reproductive biology of Erythrolamprus jaegeri coralliventris (Serpentes: Dipsadidae) in the Brazilian Coastal Pampa

We analyzed reproductive biology of Erythrolamprus jaegeri coralliventris, a snake from the Brazilian Pampa. Females presented larger snout-vent length than males, while no significant differences were found in tail length/snout-vent length ratios between sexes. Females attain sexual maturity in larger sizes than males. The reproductive cycle of females presented a seasonal pattern, with advanced vitellogenesis occurring from middle winter to middle spring and oviductal eggs occurring from middle winter to middle summer. The real fecundity ranged from two to eigth eggs and the expected fecundity varied from one to 12 secondary follicles. No significant correlation was found between females body size and the following parameters: real fecundity, length of the largest egg and potential fecundity. Therefore, E. j. coralliventris presents a seasonal reproductive pattern, which seems to follow the rainfall profile observed for the studied region. This may represent a strategy of energy gain associated to the reproductive cycle, considering that the food resources most explored by this species are anurans that present higher activity during rainy periods.

Developmental morphology and evolution of extraembryonic membranes of lizards and snakes (Reptilia, Squamata)

Amniote embryos are supported and nourished by a suite of tissues, the extraembryonic membranes, that provide vascular connections to the egg contents. Oviparous reptiles share a basic pattern of development inherited from a common ancestor; a vascular chorioallantoic membrane, functioning as a respiratory organ, contacts the eggshell and a vascular yolk sac membrane conveys nutrients to the embryo. Squamates (lizards, snakes) have evolved a novel variation in morphogenesis of the yolk sac that results in a unique structure, the yolk cleft/isolated yolk mass complex. This structure is a source of phylogenetic variation in architecture of the extraembryonic membranes among oviparous squamates. The yolk cleft/isolated yolk mass complex is retained in viviparous species and influences placental architecture. The aim of this paper is to review extraembryonic membrane development and morphology in oviparous and related viviparous squamates to explore patterns of variation. The survey includes all oviparous species for which data are available (11 species; 4 families). Comparisons with viviparous species encompass six independent origins of viviparity. The comparisons reveal that both phylogeny and reproductive mode influence variation in extraembryonic membrane development and that phylogenetic variation influences placental evolution. Models of the evolution of squamate placentation have relied primarily on comparisons between independently derived viviparous species. The inclusion of oviparous species in comparative analyses largely supports these models, yet exposes convergent patterns of evolution that become apparent when phylogenetic variation is recognized.

Anatomy of the reproductive system of a population of Amerotyphlops brongersmianus from southeastern Brazil (Serpentes: Scolecophidia)

Amerotyphlops brongersmianus (Vanzolini, 1976) is distributed in Brazil from the Atlantic Rainforest to the Cerrado biome. Only few studies have focused on the gross anatomy, reproductive organs, and histological data of typhlopids. We accessed information from the anatomy of gonads of 95 individuals collected at different months in the Restinga de Jurubatiba National Park, Rio de Janeiro state, Brazil. This included histological sections of the testes, ductus deferens and sexual segment of kidney (SSK) in males, and oviducts in females, from which fecundity was determined. Results revealed a correlation between gross morphology and histology of the reproductive system. Testes volume increased during spermatogenesis, and the ductus deferens diameter increased with the presence of spermatozoa. Additionally, changes occurred in kidney morphology, which showed a smooth or rough surface, the latter corresponding to the development of the SSK. Spermatozoa were found inside the lumen of the SSK of some males. Females lacked left oviducts and showed changes in morphological and histological aspects of the right oviducts throughout the year. In summer and spring the uterus showed undeveloped structures, while during winter this organ showed conspicuously developed glands and appeared pleated and opaque upon gross examination. The infundibulum was pleated in most females throughout the year and one female had spermatozoon in a receptacle located in the posterior infundibulum. In spring, this organ was enlarged compared to winter, with a thinner epithelium. Fecundity corresponded to 7-11 eggs.

Facultative oviparity in a viviparous skink ( Saiphos equalis)

Facultative changes in parity mode (oviparity to viviparity and vice versa) are rare in vertebrates, yet offer fascinating opportunities to investigate the role of reproductive lability in parity mode evolution. Here, we report apparent facultative oviparity by a viviparous female of the bimodally reproductive skink Saiphos equalis-the first report of different parity modes within a vertebrate clutch. Eggs oviposited facultatively possess shell characteristics of both viviparous and oviparous S. equalis, demonstrating that egg coverings for viviparous embryos are produced by the same machinery as those for oviparous individuals. Since selection may act in either direction when viviparity has evolved recently, squamate reproductive lability may confer a selective advantage. We suggest that facultative oviparity is a viable reproductive strategy for S. equalis and that squamate reproductive lability is more evolutionarily significant than previously acknowledged.

Infundibular sperm storage and uterine muscular twisting in the Amazonian lancehead, Bothrops atrox

Although knowledge about the reproduction of snakes of the genus Bothrops has increased recently, many questions remain regarding sperm storage by these neotropical pitvipers. The relationship between two known sperm storage sites-the nonglandular uterus and the infundibulum-has yet to be detailed for Bothrops. In addition, the formation of uterine muscular twisting (UMT) and its function in sperm storage in the nonglandular uterus have been questioned. This article presents data on both sperm storage sites (posterior infundibulum and nonglandular uterus) in the Amazonian lancehead, Bothrops atrox, aiming to address the role of UMT in bothropoid reproduction considering female reproductive stages, timing of sperm storage, and morphology and histochemistry of sperm receptacles. The oviduct of B. atrox is composed of the infundibulum (anterior and posterior), the glandular uterus, the nonglandular uterus and the pouch. Sperm storage occurs in the posterior infundibulum and nonglandular uterus in vitellogenic females. In the posterior infundibulum sperm is stored in receptacles, while in the nonglandular uterus it is stored in crypts in the UMT of vitellogenic females. Both sperm storage sites possess granules testing positive for neutral mucopolysaccharides in the presence of spermatozoa, possibly favoring the conditions for spermatozoa surveillance during sperm storage in the reproductive tract.

Development and differentiation of the reproductive system of Tropidurus catalanensis (Squamata: Tropiduridae)

Development and differentiation of the reproductive system in lizards begin in the embryonic period, although the stage and time of their occurrence vary according to populations and species. In this study, the events of the development and differentiation of the reproductive system of males and females of Tropidurus catalanensis were characterized during the embryonic, neonatal, and juvenile periods. Embryos at Stages 27, 34, 37, 40, and 41, neonates and juveniles, from Corrientes, Argentina, were analyzed. At Stage 27, the genital ridge was not observed but primordial germ cells were recorded in the yolk sac as well as the mesenteric mesenchyme, indicating the beginning of germ cell migration. Gonadal differentiation commenced at Stage 34. In males from Stage 37, the testes possessed seminiferous cords with Sertoli cells and spermatogonia, while in hatchlings seminiferous tubules and interstitial tissue with mature Leydig cells were present. Spermatogenesis was observed in a specimen of 51.9 mm snout-vent length, corresponding to the minimum reproductive size. In females, from Stage 37 until hatching, the ovaries had a cavernous medulla and a cortex with somatic cells and abundant oogonia. The onset of meiosis and folliculogenesis occurred in the juvenile period.

Intersex, Hermaphroditism, and Gonadal Plasticity in Vertebrates: Evolution of the Müllerian Duct and Amh/Amhr2 Signaling

In vertebrates, sex organs are generally specialized to perform a male or female reproductive role. Acquisition of the Müllerian duct, which gives rise to the oviduct, together with emergence of the Amh/Amhr2 system favored evolution of viviparity in jawed vertebrates. Species with high sex-specific reproductive adaptations have less potential to sex reverse, making intersex a nonfunctional condition. Teleosts, the only vertebrate group in which hermaphroditism evolved as a natural reproductive strategy, lost the Müllerian duct during evolution. They developed for gamete release complete independence from the urinary system, creating optimal anatomic and developmental preconditions for physiological sex change. The common and probably ancestral role of Amh is related to survival and proliferation of germ cells in early and adult gonads of both sexes rather than induction of Müllerian duct regression. The relationship between germ cell maintenance and sex differentiation is most evident in species in which Amh became the master male sex-determining gene.

How Does Oocyte Uptake Occur? A Macroscopic Study of the Ovarian and Oviductal Modifications for Egg Capture in the Coral-Snake Micrurus corallinus

The processes of follicular development, ovulation, egg capture, and egg transport vary among vertebrates. Therefore, analysis of the reproductive tract of several lineages is needed for understanding the evolutionary changes of the reproductive system. In turtles, the ovulated eggs are released into the coelomic cavity and taken up by one of the two oviducts, a phenomenon called extrauterine migration of eggs. However, the process of egg uptake in lizards is different. The egg is ovulated directly into the infundibulum, and oocyte uptake by the contralateral oviduct rarely occurs. The same pattern has been hypothesized to occur in snakes. To test this hypothesis, we analyzed the reproductive tract of female Micrurus corallinus preserved in zoological collections. We examined the anatomical characteristics of the infundibulum and ovary and compared the reproductive output between the ovaries to verify the mechanism of egg capture and the anatomical viability of extrauterine migration of eggs. The reproductive output of the right ovary was higher than that of the left ovary, and the higher number of eggs in the right oviduct is due exclusively to the production of the ipsilateral ovary. Several anatomical features prevent extrauterine migration of eggs, including the asymmetry of the reproductive system, the arrangement of the ovarian follicles in a single row, and the formation of a wrapping around the ovary and infundibulum by the visceral pleuroperitoneum membrane (preventing against ectopic eggs). Therefore, the hypothesis of egg capture by the contralateral oviduct is anatomically infeasible in M. corallinus and possibly in other snakes. Anat Rec, 301:1936-1943, 2018. © 2018 Wiley Periodicals, Inc.

Simultaneously Occurring Elevated Metabolic States Expose Constraints in Maximal Levels of Oxygen Consumption in the Oviparous Snake Lamprophis fuliginosus

African house snakes (Lamprophis fuliginosus) were used to compare the metabolic increments associated with reproduction, digestion, and activity both individually and when combined simultaneously. Rates of oxygen consumption ([Formula: see text]) and carbon dioxide production ([Formula: see text]) were measured in adult female (nonreproductive and reproductive) and adult male snakes during rest, digestion, activity while fasting, and postprandial activity. We also compared the endurance time (i.e., time to exhaustion) during activity while fasting and postprandial activity in males and females. For nonreproductive females and males, our results indicate that the metabolic increments of digestion (∼3-6-fold) and activity while fasting (∼6-10-fold) did not interact in an additive fashion; instead, the aerobic scope associated with postprandial activity was 40%-50% lower, and animals reached exhaustion up to 11 min sooner. During reproduction, there was no change in digestive [Formula: see text], but aerobic scope for activity while fasting was 30% lower than nonreproductive values. The prioritization pattern of oxygen delivery exhibited by L. fuliginosus during postprandial activity (in both males and females) and for activity while fasting (in reproductive females) was more constrained than predicted (i.e., instead of unchanged [Formula: see text], peak values were 30%-40% lower). Overall, our results indicate that L. fuliginosus's cardiopulmonary system's capacity for oxygen delivery was not sufficient to maintain the metabolic increments associated with reproduction, digestion, and activity simultaneously without limiting aerobic scope and/or activity performance.

Matrotrophy and placentation in invertebrates: a new paradigm

Matrotrophy, the continuous extra-vitelline supply of nutrients from the parent to the progeny during gestation, is one of the masterpieces of nature, contributing to offspring fitness and often correlated with evolutionary diversification. The most elaborate form of matrotrophy-placentotrophy-is well known for its broad occurrence among vertebrates, but the comparative distribution and structural diversity of matrotrophic expression among invertebrates is wanting. In the first comprehensive analysis of matrotrophy across the animal kingdom, we report that regardless of the degree of expression, it is established or inferred in at least 21 of 34 animal phyla, significantly exceeding previous accounts and changing the old paradigm that these phenomena are infrequent among invertebrates. In 10 phyla, matrotrophy is represented by only one or a few species, whereas in 11 it is either not uncommon or widespread and even pervasive. Among invertebrate phyla, Platyhelminthes, Arthropoda and Bryozoa dominate, with 162, 83 and 53 partly or wholly matrotrophic families, respectively. In comparison, Chordata has more than 220 families that include or consist entirely of matrotrophic species. We analysed the distribution of reproductive patterns among and within invertebrate phyla using recently published molecular phylogenies: matrotrophy has seemingly evolved at least 140 times in all major superclades: Parazoa and Eumetazoa, Radiata and Bilateria, Protostomia and Deuterostomia, Lophotrochozoa and Ecdysozoa. In Cycliophora and some Digenea, it may have evolved twice in the same life cycle. The provisioning of developing young is associated with almost all known types of incubation chambers, with matrotrophic viviparity more widespread (20 phyla) than brooding (10 phyla). In nine phyla, both matrotrophic incubation types are present. Matrotrophy is expressed in five nutritive modes, of which histotrophy and placentotrophy are most prevalent. Oophagy, embryophagy and histophagy are rarer, plausibly evolving through heterochronous development of the embryonic mouthparts and digestive system. During gestation, matrotrophic modes can shift, intergrade, and be performed simultaneously. Invertebrate matrotrophic adaptations are less complex structurally than in chordates, but they are more diverse, being formed either by a parent, embryo, or both. In a broad and still preliminary sense, there are indications of trends or grades of evolutionarily increasing complexity of nutritive structures: formation of (i) local zones of enhanced nutritional transport (placental analogues), including specialized parent-offspring cell complexes and various appendages increasing the entire secreting and absorbing surfaces as well as the contact surface between embryo and parent, (ii) compartmentalization of the common incubatory space into more compact and 'isolated' chambers with presumably more effective nutritional relationships, and (iii) internal secretory ('milk') glands. Some placental analogues in onychophorans and arthropods mimic the simplest placental variants in vertebrates, comprising striking examples of convergent evolution acting at all levels-positional, structural and physiological.

Eggshell Types and Their Evolutionary Correlation with Life-History Strategies in Squamates

The eggshell is an important physiological structure for the embryo. It enables gas exchange, physical protection and is a calcium reserve. Most squamates (lizards, snakes, worm lizards) lay parchment-shelled eggs, whereas only some gekkotan species, a subgroup of lizards, have strongly calcified eggshells. In viviparous (live-bearing) squamates the eggshell is reduced or completely missing (hereafter “shell-less”). Recent studies showed that life-history strategies of gekkotan species differ between species with parchment- and rigid-shelled eggshells. Here we test if the three different eggshell types found in the squamates are also associated with different life-history strategies. We first investigated the influence of the phylogeny on the trait “eggshell type” and on six life-history traits of 32 squamate species. Phylogenetic principal component analysis (pPCA) was then conducted to identify an association between life-history strategies and eggshell types. Finally, we also considered adult weight in the pPCA to examine its potential effect on this association. Eggshell types in squamates show a strong phylogenetic signal at a low taxonomical level. Four out of the six life-history traits showed also a phylogenetic signal (birth size, clutch size, clutches per year and age at female maturity), while two had none (incubation time, maximum longevity). The pPCA suggested an association of life-history strategies and eggshell types, which disappeared when adult weight was included in the analysis. We conclude that the variability seen in eggshell types of squamates is weakly influenced by phylogeny. Eggshell types correlate with different life-history strategies, and mainly reflect differences in adult weights of species.

Evidence of Egg Diversity in Squamate Evolution from Cretaceous Anguimorph Embryos

Lizards are remarkable amongst amniotes, for they display a unique mosaic of reproduction modes ranging from egg-laying to live-bearing. Within this patchwork, geckoes are believed to represent the only group to ever have produced fully calcified rigid-shelled eggs, contrasting with the ubiquitous parchment shelled-eggs observed in other lineages. However, this hypothesis relies only on observations of modern taxa and fossilised gecko-like eggshells which have never been found in association with any embryonic or parental remains. We report here the first attested fossil eggs of lizards from the Early Cretaceous of Thailand, combining hard eggshells with exquisitely preserved embryos of anguimoph (e.g. Komodo dragons, mosasaurs). These fossils shed light on an apparently rare reproduction strategy of squamates, demonstrate that the evolution of rigid-shelled eggs are not an exclusive specialization of geckoes, and suggest a high plasticity in the reproductive organs mineralizing eggshells.