Theriogenology

Scott J. Stahl , Dale F. DeNardo , in Mader's Reptile and Amphibian Medicine and Surgery (Third Edition), 2019

Oviparity

Oviparity represents the ancestral manner of reproduction in reptiles and characterizes all living chelonians, crocodilians, the tuatara, and most squamates ( Fig. eighty.seven). Once ovulation takes place, usually lilliputian transfer of nutrients is thought to occur between the female and the ova. Withal in squamates embryos have often completed 25% to 30% of their development at oviposition. This is clinically relevant because the health of the offspring is dependent not only on environmental conditions during (external) egg incubation but too (equally with viviparous species) on the conditions a female experiences post-ovulation and prior to oviposition. The ovum becomes an egg when albumin and a shell are added in the oviduct. The degree of beat out calcification varies among species, ranging from minimal, resulting in pliable eggs (snakes, most lizards, and some turtles) to pronounced, resulting in rigid eggs (crocodilians, tortoises, and many geckos). An example of the variation in vanquish rigidity is axiomatic in geckos, in which egg type is phylogenetically based. Geckos in the family Gekkonidae have rigid eggs, nonetheless, Diplodactlidae (i.east., Australian and New Zealand geckos) and Eublepharidae (eye-lid geckos) have pliable eggs. Clinically, ultrasonography tin can be used to distinguish the general stages of gonadal inactivity, early on previtellogenic follicle growth, vitellogenesis, ovulation, and either shelling or fetal development. Encounter ultrasonography afterward in this chapter and in Affiliate 58.

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Comparative Reproduction

Marvalee H. Wake , in Encyclopedia of Reproduction (2nd Edition), 2018

Oviparity

Oviparity, egg-laying, is considered to be the bequeathed fashion of reproduction for vertebrates. Ova (eggs) develop in the females' ovaries (in rare exceptions in males, such as a clade of toads, and pathologically in other vertebrates), mediated by such hormones as estrogen and progesterone, luteinizing hormone, etc., usually cyclically and ofttimes determined by seasonality (light, moisture, etc.). Egg sizes vary enormously, often within classes, families, and genera, merely size usually characterizes each species. A major feature of egg development is vitellogenesis, the deposition of yolk in each ovum. The ancestral status is characterized by the development of yolky eggs that are laid externally (in h2o or on country), often in large numbers, and fertilized externally during a variety of forms of interactions with males. The yolk mass present in each ovum is typically sufficient to maintain the developing embryo until it hatches, when it becomes a gratis-living, usually aquatic, larva that can forage on its own until it metamorphoses. However, in direct-developers (see beneath) eggs sizes are usually large, so that the embryo is provisioned with enough yolk to carry information technology through metamorphosis to hatch equally a juvenile. Conversely, many viviparous species (run across below) have very small eggs with fiddling yolk, correlated with their providing other forms of nutrition to the developing immature (east.g., via a placenta, etc.). Numbers of eggs (clutch size) laid vary enormously; some fishes and frogs lay hundreds, even thousands, of eggs that are fertilized in water by one, sometimes more than, males. While egg-laying is the ancestral condition retained past some members of all classes of vertebrates, (most fishes, most amphibians, about squamates, all turtles and crocodiles, all birds, and both species of monotremes amidst mammals), some are live-bearers (meet below). Also, internal fertilization via a multifariousness of ways of sperm transfer has evolved in virtually lineages – some fishes, using modified fins, a very few frogs, most salamanders, and all caecilians amid amphibians, and all of the amniotes – those vertebrates (reptiles and birds, mammals) that surround their developing embryos with actress-embryonic membranes and then either lay the eggs/embryos or retain them in their oviducts for part or all of their evolution.

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Comparative Reproduction

Elisabeth Blesbois , in Encyclopedia of Reproduction (2nd Edition), 2018

Determination

Bird reproduction involves oviparity and a very circuitous organization of internal fertilization. If the male shows highly visible external sexual attributes, its internal reproductive system turns toward an expeditious production of a maximum of gametes in a short fourth dimension. By opposite, the female person genital tract is very sophisticated, reaching a very high level of precision of the dissimilar steps leading to the egg production that has been the back up of the development of the poultry productions. Modern laying hens export in their eggs more than 10 times their weight per year for the daily egg production, and the poultry productions constitute nowadays one of the start protein source for the human diet need.

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Viviparity in Reptiles

Lori C. Albergotti , Louis J. Guillette Jr. , in Hormones and Reproduction of Vertebrates: Reptiles, 2011

10 Conclusions

In squamates, the transition from oviparity to viviparity involves changes in the timing of egg retention, thickness of the eggshell, and the development of a placenta. These physiological and morphological requirements of viviparity accept occurred more than 100 times in squamates alone. Therefore, nosotros should not exist surprised to find that many of the required molecular-, cellular-, and organ-level characteristics of viviparity, including endocrine signaling, were likely already present in the oviparous ancestors, allowing them to be modified for a viviparous way of reproduction. Differences in the utilize of various pathways and mechanisms and timing associated with these processes would likely occur.

From the above discussion, nosotros consider the post-obit to accept evolved concurrently with live nascence and to be requirements of viviparity: intrauterine retention of the egg for the duration of embryonic evolution; reduction of the eggshell; and germination of a fully performance placenta that facilitates not only the exchange of gases, waste material, and nutrients but also endocrine signals. In light of our recent findings that steroidogenesis occurs in the CAM of an avian and crocodilian species, it is likely that embryonic endocrine signals from the extraembryonic membranes play a key role in the maternal recognition, establishment, and maintenance of gestation in viviparous squamates. Given that the CAM is present in all birds, reptiles, and mammals, why has viviparity non evolved in birds or in the other reptiles (tuatara, crocodilians, and turtles)? Merely put, the presence of a steroidogenic CAM is not plenty in itself to facilitate a transition from oviparity to viviparity in the absence of extended egg retention in conjunction with connected embryonic evolution and decreased eggshell thickness. Egg retention is brief in birds and crocodilians, whereas egg retention is extended in some species of turtle and in the tuatara (Andrews & Mathies, 2000). Nonetheless, embryonic development is arrested in turtles and presumed to exist so in the tuatara as little embryonic development occurs in utero and embryos are at the gastrula phase at the time of oviposition (Andrews & Mathies, 2000). Thus, oviposition occurs at early on stages of development prior to evolution of the CAM in birds, crocodilians, turtles, and the tuatara. (Andrews, 2000; 2004). In dissimilarity, oviparous squamates typically retain eggs in utero past the time of CAM development, on average for ane third to one half of embryonic development (Andrews, 2000; 2004). Moreover, if the thickness of the eggshell is not reduced in utero, embryonic or extraembryonic signals that might play a role in further extending egg retention will not be in advice with the maternal uterus.

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Development by Reverting to Ancestral Characters

Nelson R. Cabej , in Epigenetic Principles of Evolution (Second Edition), 2019

Reversion of Bequeathed Reproductive Modes in Vertebrates

Amphibians take switched dorsum from viviparity to oviparity but an amphibian species of the Bufonidae family (club Anura), Nectophrynoides viviparus, and at least populations of two salamander species (Salamandra salamandra and Salamandra algira) are viviparous, with larvae remaining in the uteri and immature launched onto the land fully metamorphosed (Kent, 1973b, p. 38).

As already mentioned, in 98 occasions reptiles (specially snakes) nongenetically switched back from oviparity to viviparity.

When ichthyosauri started aquatic life and could not make use of the sunday warmth to hatch their eggs, they also switched back to viviparity, that is, their eggs hatched inside mother's body. However, in some mammals every bit monotremes, reproduction remains oviparous (they lay eggs, which hatch in the environment). And nevertheless college, placental mammals are remarkably adapted to a perfect viviparous evolution.

The foreign loss and reevolution of oviparity, ovoviviparity, and viviparity in vertebrate classes seems neither to take ever been influenced by any evolutionary pressure nor to have gradually arisen as would be predicted from the neo-Darwinian view. The repeated pattern of switching to culling modes of reproduction suggests that vertebrates may have conserved ancestral developmental pathways responsible for ancestral modes of reproduction.

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Development by Reverting to Ancestral Characters

Nelson R. Cabej , in Epigenetic Principles of Evolution, 2012

Reversion of Bequeathed Reproductive Modes in Vertebrates

Amphibians have switched dorsum from viviparity to oviparity (their eggs hatch in the surroundings), only an amphibian species of the Bufonidae family unit (order Anura), Nectophrynoides viviparus, and populations of at least two salamander species (Salamandra salamandra and S. algira) are viviparous, with larvae remaining in the uteri, and young launched onto the land fully metamorphosed (Kent, 1973, p. 38). Salamandra atra secretes nutritive substances and produces eggs on which its viviparous immature feed during the prenatal life.

Equally already mentioned, in 98 occasions reptiles (peculiarly snakes) non-genetically switched dorsum from oviparity to viviparity.

When ichthyosauri started aquatic life and could not brand apply of the dominicus warmth to hatch their eggs, they also switched back to viviparity, i.e., their eggs hatched inside mother's body. However, in some mammals, such as monotremes, reproduction remains oviparous. (They lay eggs, which hatch in the environment.) And still higher, placental mammals are remarkably adapted to a perfect viviparous development.

The strange loss and re-evolution of oviparity, ovoviviparity, and viviparity in vertebrate classes seem neither to accept e'er been influenced past any evolutionary pressure nor to take gradually arisen. The repeated blueprint of switching to culling modes of reproduction suggests that vertebrates may have conserved ancestral developmental pathways responsible for bequeathed modes of reproduction.

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Comparative Reproduction

Alexander V. Ereskovsky , in Encyclopedia of Reproduction (2nd Edition), 2018

Modes of Reproduction

Gonochorism and hermaphroditism also every bit viviparity, oviparity, and ovoviparity occur in sponges. The information on the sex phenotype take been obtained mainly from Demospongiae ( Table i). However, information technology was demonstrated that oviparous sponges are chiefly gonochoric, but viviparous (brooding) sponges chiefly are hermaphrodites.

Table i. Sex phenotype, oviparity & viviparity, larval blazon, and asexual reproduction distribution in the phylum Porifera

Taxa Sexual activity phenotype Reproductive conditions Larval type Asexual reproduction
Form Hexactinellida
  Order Hexactinosida H V ? B
  Order Lyssacinosida H V Tr No
Class Demospongiae
  Order Agelasida G/H O ? No
Fam Astroscleridae ? Five Pa ?
  Guild Axinellida G O ? B
  Society Biemnida G O ? F
  Guild Bubarida M O ? ?
  Social club Chondrosida G O Co F
  Order Chondrillida G O Co No
Fam Halisarcidae G V Di No
  Society Clionaida H O Co One thousand
  Gild Dendroceratida Yard V Pa B/No
  Order Desmacellida ? ? ? ?
  Order Dictyoceratida Chiliad 5 Pa B/No
  Social club Haplosclerida Yard/H V/O Pa F/Chiliad
  Order Merliida ? ? ? ?
  Social club Poecilosclerida H V Pa F
  Order Polymastiida G O Co B
  Social club Scopalinida H V Pa ?
  Order Sphaerocladina ? ? ? ?
  Order Spongillida G V Pa G/F
  Order Suberitida
Family unit Suberitidae G O ? G
Family Halichondriidae H/1000 V Pa F
Family Stylocordylidae ? V/O D ?
  Guild Tethyida G O Pa B
  Order Tetractinellida G O ? B/F
Family Tetillidae Grand 5 D B
Family Thoosidae H Five Ho G
  Order Trachycladida ? ? ? ?
  Social club Verongida G O Co B
Class Homoscleromorpha H V Ci B
Class Calcarea
  Subclass Calcaronea H V Am B
  Subclass Calcinea ? V Ca B

Abbreviations: Sex phenotype – G, gonochorisme; H, hermaphroditisme. Reproductive conditions – O, oviparity; 5, viviparity. Cleavage pattern – Ch, chaotic; Ra, radial-like; In, incurvational; Po, polyaxial. Larval type – Am, amphiblastula; Ca, calciblastula; Ci, cinctoblastula; Co, coeloblastula; D, directly evolution Di, disphaerula; Ho, hoplitomella; Pa, parenchymella; Tr, trichimella. Asexual reproduction – B, Budding; F, fragmentation; Thou, gemmulogenesis; No, absence.

Sequential or successive hermaphroditism (or sex activity reversal) is a type of the hermaphroditism that occurs when the individual changes sexual practice at some period in its life. It can be change from a male to female (protandry), or from a female person to male (protogyny). Successive hermaphroditism has been documented in only a few cases in demosponges and therefore the existent extent of this phenomenon cannot be properly evaluated at the moment. This type of hermaphroditism has been indicated in: Polymastia mammillaris, Suberites massa, Hymeniacidon perlevis, H. heliophila, Chalinula ecbasis, and Spongilla lacustris. A conscientious analysis of the sex bike is also necessary to avert confusion between hermaphrodite species with sexual phases far autonomously in time and gonochoric species.

Contemporaneous hermaphroditism is more than common than successive and well known in many demosponges (gild Poecilosclerida), some Homoscleromorpha and Calcarea. Some species could include more often than not contemporaneous hermaphrodites in a population in co-beingness with a few gonochoristic individuals and vice versa, populations consisting mainly of gonochoristic individuals accept been showed to comprise some contemporaneous-hermaphroditic individuals.

Both oviparity and viviparity (brooding) be in sponges. In dissimilarity to the sex phenotype, oviparity and viviparity are stable features of individuals and species. Viviparous sponges release larvae and the oviparous sponges release zygotes or unfertilized eggs.

Viviparity and oviparity are as widespread reproductive modes in sponges. The embryonic development in the oviparous sponges is always external, leading to free-swimming larvae. Viviparous or ovoviviparous sponges are characterized past brooding of embryos in the mesohyl or within the special temporary structure – follicles. Resulting free-pond larvae release through the canals of the aquiferous system. The direct evolution without larval stage exists in some demosponges. In Demospongiae some orders are completely oviparous (Polymastiida, Clionaida, Tethyida, and Verongida), while other – have but viviparity (Spongillida, Dendroceratida, Dictyoceratida). However, some viviparous representatives tin can exist found in the oviparous orders, for example, the viviparous genera Alectona, Thoosa, Stylocordyla (gild Suberitida), genus Halisarca (lodge Chondrosida), genera Haliclona, Xestospongia (order Haplosclerida).

Viviparity in sponges often correlates with the hermaphroditism. For example, all investigated Hexactinellida, Homoscleromorpha and Calcarea are viviparous and hermaphrodites.

No sexual dimorphism exists in gonochorists or successive hermaphrodites.

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Comparative Reproduction

Mari Kawaguchi , Keiichi Sato , in Encyclopedia of Reproduction (2nd Edition), 2018

Manner of Elasmobranch Reproduction

The strategy of reproduction of elasmobranchs conventionally classified into oviparity and viviparity: viviparity is the major way of reproduction, while oviparity is found but in the demersal groups, such every bit bullhead sharks (Heterodontidae), carpet sharks (Orectolobidae), catsharks (Scyliorhinidae), and skates (Rajidae). These species lay relatively large eggs encased with hard capsules of a species-specific shape, and the embryos swallow diet just from the yolk (i.eastward., are lecithotrophic).

The cycles of reproduction in elasmobranchs are mostly long and vary between species. The major cycles in viviparous species are annual, biennial, and three-year cycles, and the bicycle type is determined past the periods of vitellogenesis and gestation. Brood size differs for each species and for the body size of each individual: being mostly small in the oophagous or lipid-rich histotrophic species. The species with the smallest brood size are hawkeye rays (Mobulidae and Myliobatidae), generally with simply ane embryo per uterus. The sand tiger shark has the smallest brood size among sharks; usually only one embryo is found in each uterus as a result of embryonic cannibalism. The brood sizes are more often than not big in placental species similar hammerhead sharks (encounter Fig. 5). The largest brood size e'er recorded was a whale shark landed in Taiwan, nurturing 304 embryos. In other groups, the blue sharks (eighty embryos), tiger sharks (70 embryos), and probably the sleeper sharks also produce large broods (Castro, 2011).

Fig. 5

Fig. five. A litter of embryos of the shine hammerhead shark, Sphyrna zygaena. Each embryo has a placental connection to the mother's uterus via an umbilical cord.

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Reproductive Modes

Laurie J. Vitt , Janalee P. Caldwell , in Herpetology (Fourth Edition), 2014

Reptiles

Reptile reproductive modes are defined on the basis of whether they lay eggs (oviparity) or produce live young (viviparity) and whether nutrition is provided exclusively by the yolk (lecithotrophy) or at to the lowest degree partially by the mother (matrotrophy) or father (patrotrophy) ( Tabular array 5.1). All crocodylians, turtles, the tuatara, and a majority of squamates lay eggs. In most of these, hatching of eggs appears to be synchronous (Fig. 5.10). Nearly 20% of squamates are viviparous. In oviparous reptiles, embryo nourishment comes from the yolk (lecithotrophy). Females of some oviparous species, such as the snake Opheodrys vernalis and the lizard Lacerta agilis, retain eggs until the embryos are within only a few days of hatching. Among species that conduct live immature, maternal contribution of nutrients (matrotrophy) to evolution varies considerably. In some viviparous species, evolution of embryos is supported entirely by yolk in the egg (lecithotrophy), but every bit in oviparous species. Examples include the live-bearing horned lizard Phrynosoma douglassi and all snakes in the Boinae. In others, such as the South American skink Mabuya heathi, developmental nutrition derives entirely from the mother via a placenta.

FIGURE 5.x. Synchronous hatching occurs when eggs of the Amazonian lizard Plica plica are disturbed (L. J. Vitt).

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CHONDRICHTHYES | Physiology of Sharks, Skates, and Rays

J.Southward. Ballantyne , J.W. Robinson , in Encyclopedia of Fish Physiology, 2011

Reproduction

All elasmobranchs use internal fertilization and display one of the two types of reproduction (oviparity, i.e., egg laying, and viviparity, i.e., live birth) ( see too SOCIAL AND REPRODUCTIVE BEHAVIORS | Sexual Behavior in Fish). The male has two external intromittent organs called 'claspers' with grooved surfaces to introduce sperm into the female. Seawater is used past the muscles of the claspers to pump sperm into the female. In egg-laying species, a tough leathery egg case is deposited around the egg, and this is released to the surround soon later on fertilization. Amid livebearers (55% of all elasmobranch species and 100% of freshwater species), there are further ii reproductive types (placental and aplacental). The embryos of aplacental forms rely on yolk reserves or eat unfertilized eggs or other embryos. Placental embryos either feed on placental milk produced by a placental analog (uterine epithelium) or form a true placenta with the maternal and embryonic tissues in close contact.

In all cases of viviparity, the embryo is released in a highly developed state and no farther maternal care is given.

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