Variation in eggshell characteristics and in intrauterine egg retention between two oviparous clades of the lizard Lacerta vivipara: insight into the oviparity-viviparity continuum in squamates

The concept of the oviparity-viviparity continuum refers to the wide range in the length of intrauterine egg retention and, hence, in the stage of embryonic development at oviposition existing in squamates. The evolutionary process underlying this continuum may involve not only a lengthening of egg retention in utero, but also a marked reduction in the thickness of the eggshell. The idea that there may exist a negative correlation between the developmental stage reached by the embryo at oviposition and the eggshell thickness within squamates, although supported by the comparison of oviparous vs. viviparous species, has seldom been evaluated by comparing eggshell thickness of oviparous forms with different lengths of intrauterine egg retention. Eggs of two distinct oviparous clades of the lizard Lacerta vivipara were compared. The eggs laid by females from Slovenian and Italian populations have thicker eggshells, contain embryos on average less developed at the time of oviposition, and require a longer incubation period before hatching than the eggs laid by females from French oviparous populations. Our data and several other examples available from the literature support the idea that the lengthening of intrauterine retention of eggs and the shortening of the subsequent external incubation of eggs are associated with reduction in the thickness of the eggshell, at least in some lineages of oviparous squamates. The current hypotheses that may account for this correlation are presented and a few restrictions and refinements to those hypotheses are discussed. In particular, other changes, such as increased vascularization of the oviduct and of the extraembryonic membranes, may play the same role as the decrease of eggshell thickness in facilitating prolonged intrauterine egg retention in squamates. Future studies should also consider the hypothesis that the length of intrauterine retention might directly depend on the extent of maternal-fetal chemical communication through the eggshell barrier.     

Comparison of the cold hardiness capacities of the oviparous and viviparous forms of Lacerta vivipara

The lizard Lacerta vivipara has allopatric oviparous and viviparous populations. The cold hardiness strategy of L. vivipara has previously been studied in viviparous populations, but never in oviparous ones. The present study reveals that both the oviparous and viviparous individuals of this species are able to survive in a supercooled state at -3 degrees C for at least one week when kept on dry substrates. The mean crystallisation temperatures of the body, around -4 degrees C on dry substrata and -2 degrees C on wet substrata, do not differ between oviparous and viviparous individuals. All the individuals are able to tolerate up to 48-50% of their body fluid converted into ice, but only viviparous individuals were able to stabilize their body ice content at 48%, and hence were able to survive even when frozen at -3 degrees C for times of up 24 hours. Ice contents higher than 51% have been constantly found lethal for oviparous individuals. This suggests that, in L. vivipara, the evolution towards a higher degree of freezing tolerance could parallel the evolution of the viviparous reproductive mode, a feature believed to be strongly selected under cold climatic conditions. This is the first report, among reptiles, of an intraspecific variation regarding the freeze tolerance capacities.     

Comparisons of mitochondrial DNA (mtDNA) sequences (16S rRNA gene) between oviparous and viviparous strains of Lacerta vivipara: a preliminary study

The lizard Lacerta vivipara has allopatric oviparous and viviparous populations. The mitochondrial DNA (mtDNA) gene coding for the 16S rRNA was sequenced for several viviparous lizard populations from France, Switzerland, Bulgaria, Czech Republic, The Netherlands, Sweden, and for oviparous lizard populations from the Pyrenean and Cantabric Mountains. Seven distinct groups (three oviparous and four viviparous) were identified. The net nucleotide divergence between oviparous and viviparous haplotypes was 1.3% +/- 0.5 (mean +/- standard deviation). These results on mtDNA, together with other data obtained previously, led us to formulate a biogeographical scenario that could be tested by further research.     

Evolutionary and biogeographical implications of the karyological variations in the oviparous and viviparous forms of the lizard Lacerta (Zootoca) vivipara

The lizard Lacerta ( Zootoca ) vivipara has two modes of reproduction and is variable karyologically. We describe its karyological variation from literature data and from new data on two viviparous populations from France, on two oviparous populations from the Pyrenees in south-western France and on three oviparous populations recently discovered in Slovenia. Males have 36 chromosomes, whereas females have only 35 chromosomes in all viviparous populations and in the Pyrenean oviparous populations. This karyotype has been interpreted to result from a fusion of an ancestral sexual W chromosome with an autosome from the Zl or from the Z2 pair. The karyotype formula is 32 autosomes + ZIZ2W for the female and 32 autosomes + Z1Z1Z2Z2 for the male. The karyotype of the Slovenian oviparous populations, 34 autosomes + ZW in the male and 34 autosomes +ZW in the female, represents an evolutionary stage that preceded the chromosomal fusion. There is minor karyological variation, mainly concerning the W and Z2 chromosomes, within the Pyrenean oviparous populations. This parallels the geographic variation of the W-linked alleles of the MPI enzyme and suggests that allopatric differentiation of these oviparous populations might have occurred in the vicinity of the Pyrenees during the Pleistocene.
The viviparous populations from western Europe carry a metacentric W chromosome, whereas oviparous populations from south-western Europe and eastern viviparous populations both show an acrocentrie, or a subtelocentrie. W chromosome. This suggests that the acrocentric-subtelocentric W is a primitive character and that viviparity probably arose in an eastern lineage of the species.     

Experimental evidence of early costs of reproduction in conspecific viviparous and oviparous lizards

Reproduction entails costs, and disentangling the relative importance of each stage of the reproductive cycle may be important to assess the costs and benefits of different reproductive strategies. We studied the early costs of reproduction in oviparous and viviparous lizard females of the bimodal reproductive species Zootoca vivipara. Egg retention time in oviparous females is approximately one-third of the time in viviparous females. We compared the vitellogenesis and egg retention stages that are common to both reproductive modes. Precisely, we monitored the thermoregulatory behaviour, the weight gain and the immunocompetence of the females. Moreover, we injected an antigen in half of the females (immune challenge) to study the trade-offs between reproductive mode and immune performance and between different components of the immune system. Finally, we experimentally induced parturition in viviparous females at the time of egg laying in oviparous females. Oviparous and viviparous females did not show strong differences in response to the immune challenge. However, viviparous females spent more time thermoregulating while partially hidden and gained more weight than oviparous females. The greater weight gain indicates that the initial period of egg retention is less costly for viviparous than for oviparous females or that viviparous females are able to save and accumulate energy at this period. This energy may be used by viviparous females to cope with the subsequent costs of the last two-third of the gestation. Such an ability to compensate the higher costs of a longer egg retention period may account for the frequent evolution of viviparity in squamate reptiles.     

Reproductive biology of viviparous and oviparous species of the leaf beetle genus Oreina

In five species of the genus Oreina Chevrolat (Coleoptera, Chrysomelidae) we compared the size of offspring, the fecundity of the females, the timing of offspring production and female investment over the season. Two of the species, O. elongata and O. luctuosa, laid eggs, while O. cacaliae, O. gloriosa and O. variabilis gave birth to larvae. Offspring size corrected for female size was similar in the two oviparous species and in the viviparous O. cacaliae. In the two other viviparous species the larvae were two to three times bigger in relation to the female. The greater size of the offspring was not traded off for lower fecundity in these latter two species, yet the production of bigger larvae was associated with a longer laying period and thereby a spreading of reproductive investment over the season. The prediction of life history theory that higher investment in individual offspring should be traded off for lower fecundity could not be confirmed. The investigation of egg and larval development showed that in one of the oviparous species, O. luctuosa, the length of the egg stage was more variable. This corroborates the view that in this species the eggs can be retained for varying times before being laid. Greater size at birth does not necessarily lead to shortened developmental times: the larval periods of O. cacaliae, O. elongata, O. gloriosa and O. variabilis were all comparable although the larvae of the first two species were relatively smaller when laid; only the small larvae of O. luctuosa needed significantly longer for their development. For all growth parameters examined the differences between species were larger than the differences between populations. A comparison of larval growth of the oligophagous species O. cacaliae on three plant genera showed that larval growth rate is influenced by the food plant. However, the plant on which the larvae grew worst is apparently not chosen for oviposition in the field. A comparison with a phylogeny of the species based on allozymes suggests that species with similar reproductive parameters are closely related, yet that viviparity evolved independently in O. cacaliae on one hand and O. variabilis and O. gloriosa on the other.     

Plasticity and limitations of extended egg retention in oviparous Zootoca vivipara (Reptilia: Lacertidae)

The transition between oviparity and viviparity in reptiles is generally accepted to be a gradual process, the result of selection for increasingly prolonged egg retention within the oviduct. We examined egg retention plasticity in an oviparous strain of the lacertid lizard Zootoca vivipara, a species having both oviparous and viviparous populations. We forced a group of female Z. vivipara to retain their clutch in utero by keeping them in dry substrata, and assessed the effect on embryonic development and hatching success, along with offspring phenotype and locomotor performance. Forced egg retention for one additional week affected the developmental stage of embryos at oviposition, as well as hatchling robustness and locomotor performance. However, embryos from forced clutch retention treatment reached one stage unit more than control embryos at oviposition time. Embryos from control eggs were more developed than embryos from experimental eggs after approximately the same period of external incubation, showing that embryonic development is retarded during the period of extended egg retention, despite the high temperature inside the mother's body. Significant differences in external incubation time were only found in one of the two years of study. Hatching success was much lower in the experimental group with forced egg retention (21.1%) than in the control group (95.4%). Therefore, we conclude that there are limitations that hinder the advance of intrauterine embryonic development beyond the normal time of oviposition, and that extended egg retention does not represent clear advantages in this population of Z. vivipara. Nevertheless, the fact that some eggs are successful after forced egg retention could be advantageous for the females that are able to retain their clutch under unfavourable climatic conditions. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 75–82.     

Thermoregulation during gravidity in the children's python (Antaresia childreni): a test of the preadaptation hypothesis for maternal thermophily in snakes

Pregnant squamate reptiles (i.e. lizards and snakes) often maintain higher and more stable body temperatures than their nonpregnant conspecifics, and this maternal thermophily enhances developmental rate and can lead to increased offspring quality. However, it is unclear when this behaviour evolved relative to the evolution of viviparity. A preadaptation hypothesis suggests that maternal thermophily was a preadaptation to viviparity. Oviparous squamates are unique among oviparous reptiles for generally retaining their eggs until the embryos achieve one fourth of their development. As a result, maternal thermophily by gravid squamates may provide the same thermoregulatory benefits, at least during early development, that have been associated with viviparity. Thus, the evolution of viviparity in squamates may reflect an expanded duration of a pre-existing maternal thermoregulatory behaviour. Despite its evolutionary relevance, thermoregulation during gravidity in oviparous squamates has not yet been explored in depth. In the present study, we examined whether gravidity was associated with thermoregulatory changes in the oviparous children's python, Antaresia childreni . First, we discovered that, compared to most snakes, A. childreni is at an advanced stage of embryonic development at oviposition. Second, using surgically implanted temperature loggers, we detected a significant influence of reproductive status on thermoregulation. Reproductive females maintained higher and less variable body temperatures than nonreproductive females and this difference was most pronounced during the last 3 weeks of gravidity. Overall, these results highlight the continuum between oviparity and viviparity in squamate reptiles and emphasize the importance of thermal control of early embryonic development independent of reproductive mode.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 499–508.     

Reproductive isolation between oviparous and viviparous lineages of the Eurasian common lizard Zootoca vivipara in a contact zone

Contact zones between two evolutionary lineages are often useful for understanding the process of speciation because the observed genetic pattern reflects the history of differentiation. The Eurasian lacertid lizard Zootoca vivipara is a potentially interesting model for studying the role of reproductive mode in the speciation of squamate reptiles because it has both oviparous (Zootoca vivipara carniolica) and viviparous (Zootoca vivipara vivipara) populations that have recently been shown to be genetically distinct. We studied a newly‐discovered syntopic area of these two Zootoca subspecies in the central Italian Alps using genetic markers to investigate the level of introgression between them. Patterns of genetic differentiation in a fragment of the mitochondrial DNA cytb gene and a set of nuclear microsatellites show that the speciation process is complete in this area, with no evidence of recent introgression. Phylogenetic and genotypic divergence suggests that the two subspecies have experienced long independent evolutionary histories, during which genetic and phenotypic differences evolved. The possible roles of biogeography, reproductive mode, and cytogenetic differentiation in this speciation process are discussed. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 566–573.     

Changes to the uterine epithelium during the reproductive cycle of two viviparous lizard species (Niveoscincus spp.)

We investigated morphological differences in uterine epithelia of the reproductive cycle between two closely related viviparous skinks, Niveoscincus metallicus (lecithotrophic) and Niveoscincus ocellatus (placentotrophic), which have similar placental complexity but different degrees of placentotrophy. Scanning (SEM) and transmission electron microscopy (TEM) revealed that the uterine surface of non‐reproductive females of both species is mainly covered by ciliated cells. As vitellogenesis begins, the uterine epithelium consists of ciliated and non‐ciliated cells under a thin glycocalyx. Microvilli are greatly reduced at mid‐pregnancy, and the uterus differentiates into two structurally distinct regions: the chorioallantoic and the omphaloplacenta. At late stages of pregnancy, the uterine epithelium of chorioallantoic placenta in both species is further ridged, forming a knobbly uterine surface. The ultrastructural evidence between N. metallicus and N. ocellatus cannot strictly account for the distinct differences in their placentotrophy; as yet unexplored molecular nutrient transport mechanisms that are not reflected in uterine ultrastructure must play significant roles in nutrient transportation. Characteristics consistent with a plasma membrane transformation were confirmed in both species.     

Altitudinal variation in egg retention and rates of embryonic development in oviparous Zootoca vivipara fits predictions from the cold-climate model on the evolution of viviparity

The evolution of reptilian viviparity is favoured, according to the cold‐climate hypothesis, at high latitudes or altitudes, where egg retention would entail thermal benefits for embryogenesis because of maternal thermoregulation. According to this hypothesis, and considering that viviparity would have evolved through a gradual increase in the extent of intrauterine egg retention, highland oviparous populations are expected to exhibit more advanced embryo development at oviposition than lowland populations. We tested for possible differences in the level of egg retention, embryo development time and thermal biology of oviparous Zootoca vivipara near the extreme altitudinal limits of the species distribution in the north of Spain (mean altitude for lowland populations, 235 m asl.; for highland populations, 1895 m asl.). Altitude influenced neither temperature of active lizards in the field nor temperature selected by lizards in a laboratory thermal gradient, and pregnant females selected lower temperatures in the thermal gradient than did males and nonpregnant females across altitudinal levels. Eggs from highland populations contained embryos more developed at the time of oviposition (Dufaure and Hubert's stages 33–35) than eggs of highland populations (stages 30–34) and partly because of this difference incubation time was shorter for highland embryos. When analysed for clutches from both altitudinal extremes at the same embryonic stage at oviposition (stage 33), again incubation time was shorter for highland populations, indicating genuine countergradient variation in developmental rate. Our results indicate that temperature is an environmental factor affecting the geographical distribution of different levels of egg retention in Z. vivipara, as predicted by the cold‐climate hypothesis on the evolution of viviparity.     

Fate of hamster oviductin in the oviduct and uterus during early gestation

Oviductins are a family of glycoproteins which are synthesized and secreted by oviductal secretory cells and which, upon their secretion in the lumen of the oviduct, become associated with postovulatory oocytes and developing embryos. Recently, we showed that hamster oviductin is maximally secreted in the oviduct at the time of ovulation and is later associated with a certain population of uterine epithelial cells, where it is subsequently endocytosed and degraded. In light of these results, this study was conducted to follow the fate of hamster oviductin in the oviduct and uterus during early gestation. Using a monoclonal antibody against hamster oviductin, immunofluorescence and immunogold labeling revealed that during early gestation, immunoreactivity to oviductin in the uterus gradually diminished to an almost total disappearance at time of implantation. However, the strong labeling intensity remained unchanged in the oviduct. Biochemical analyses demonstrated that a degradation of oviductin occurs in the uterus, and a loss of immunoreactivity was also observed as gestation progressed, so that by the time of implantation, immunoreactivity to oviductin was barely detectable. The decrease of oviductin along the uterine epithelium at the time of blastocyst attachment and its final disappearance at implantation suggest that this glycoprotein could be a potential modulator of uterine receptivity. Mol. Reprod. Dev. 46:306–317, 1997. © 1997 Wiley-Liss, Inc.     

Experimental litter size reduction reveals costs of gestation and delayed effects on offspring in a viviparous lizard

Experimental studies have often been employed to study costs of reproduction, but rarely to study costs of gestation. Disentangling the relative importance of each stage of the reproductive cycle should help to assess the costs and benefits of different reproductive strategies. To that end, we experimentally reduced litter size during gestation in a viviparous lizard. We measured physiological and behavioural parameters during gestation and shortly after parturition, as well as survival and growth of females and their offspring. This study showed four major results. First, the experimental litter size reduction did not significantly affect the cellular immune response, the metabolism and the survival of adult females. Second, females with reduced litter size decreased their basking time. Third, these females also had an increased postpartum body condition. As postpartum body condition is positively related to future reproduction, this result indicates a gestation cost. Fourth, even though offspring from experimentally reduced litters had similar weight and size at birth as other offspring, their growth rate after birth was significantly increased. This shows the existence of a maternal effect during gestation with delayed consequences. This experimental study demonstrates that there are some costs to gestation, but it also suggests that some classical trade-offs associated with reproduction may not be explained by gestation costs.     

Acquisition of sperm motility and its maintenance during storage in the lizard, Lacerta vivipara

Lizard spermatozoa, which are non-motile in the testis, develop the ability to swim as they pass along the excurrent duct. The addition of caffeine, a phosphodiesterase inhibitor, induced forward motility in spermatozoa from the caput epididymidis and increased the velocity of spermatozoa from the distal part of the epididymis. Caffeine had no effect on the motility of testicular spermatozoa. This suggests that sperm motility in this species is cyclic AMP-dependent but this factor alone is not sufficient to induce testicular sperm motility. In samples from the distal region of the epididymis, sperm motility was maximal in April just after the breeding season and then decreased significantly during the following months. A parallel can be drawn between these data and the levels of testosterone in the plasma. In the lizard, as in mammals, the epididymis may play an important role in the maturation of spermatozoa.     

Ultrastructure of the eggshell and its formation in Planipapillus mundus (Onychophora: Peripatopsidae)

Although the majority of onychophorans are viviparous or ovoviviparous, oviparity has been described in a number of species found exclusively in Australia and New Zealand. Light microscopy and scanning and transmission electron microscopy were used to examine developing eggs and the reproductive tract of the oviparous Planipapillus mundus. Deposited eggs and fully developed eggs dissected from the terminal end of the uteri have an outer thick, slightly opaque chorion, and an inner thin, transparent vitelline membrane. The chorion comprises an outermost extrachorion, sculptured with domes equally spaced over the surface; a middle exochorion, with pores occurring in a pattern of distribution equivalent to that of the domes of the extrachorion above; and an innermost, thick endochorion consisting of a spongelike reticulum of cavities comparable to the respiratory network found in insect eggs. The vitelline membrane lies beneath the chorion, from which it is separated by a fluid‐filled space. The vitelline membrane tightly invests the developing egg. Examination of oocytes in the ovary and developing eggs at various stages of passage through the uterus indicate that the majority of chorion deposition occurs in the midregion of the uterus, where vast networks of endoplasmic reticulum are present in the columnar epithelium. The vitelline membrane, however, is believed to begin its development as a primary egg membrane, surrounding the developing oocytes in the ovary. The vitelline membrane is transformed after fertilization, presumably by secretions from the anterior region of the uterus; hence, it should be more accurately referred to as a fertilization membrane. Aspects of the reproductive biology of P. mundus are also included. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Development and characterization of 79 nuclear markers amplifying in viviparous and oviparous clades of the European common lizard

The European common lizard (Zootoca vivipara) is a widely distributed species across Europe and Asia exhibiting two reproductive modes (oviparity/viviparity), six major lineages and several sublineages. It has been used to tackle a large variety of research questions, nevertheless, few nuclear DNA sequence markers have been developed for this species. Here we developed 79 new nuclear DNA sequence markers using a clonation protocol. These markers were amplified in several oviparous and viviparous specimens including samples of all extant clades, to test the amplification success and their diversity. 49.4% of the markers were polymorphic and of those, 51.3% amplified in all and 94.9% amplified in 5–7 of the extant Z. vivipara clades. These new markers will be very useful for the study of the population structure, population dynamics, and micro/macro evolution of Z. vivipara. Cross-species amplification in four lizard species (Psammodromus edwardsianus, Podarcis muralis, Lacerta bilineata, and Takydromus sexlineatus) was positive in several of the markers, and six makers amplified in all five species. The large genetic distance between P. edwardsianus and Z. vivipara further suggests that these markers may as well be employed in many other species.     

Production and glycosylation of sperm constitutive proteins in the lizard Lacerta vivipara. Evolution during the reproductive period

From epididymal fluid samples taken at three different times during the reproductive period (early April, late April, mid-May), the soluble proteins were separated with one dimensional electrophoresis on polyacrylamide gel. Their evolution was studied: firstly quantitatively, after staining with Coomassie blue, or, for one protein (the "L" protein), by immunodetection; secondly, according to their glycosylation after transfer to nitrocellulose and treatment with a set of labelled lectins: from Wheat germ, Ricinus communis, Lens culinaris, Asparagus pea or Canavalia ensiformis, with or without use of their specific inhibitor sugars. At least 15 proteins underwent a quantitative and/or qualitative evolution, mainly during the month of April. Protein "L" (19 kDa), which is androgen dependent and which fixates on to spermatozoa during their epididymal transit, appears to be little or not glycosylated. By contrast its accumulation in the epididymal canal increases considerably during the month of April. Five other proteins proved to be especially interesting because of their evolution during this same period, notably the MW 94, 67, 35, 29 and 25.5 kDa proteins. With the exception of the 67 kDa all the others increased quantitatively. All were decisively enriched in mannose or in methyl-mannoside residues. The proteins of MW 29 and 25.5 kDa were also enriched in galactose or N-acetyl galactosamine residues. These findings are of physiological significance since they are set up concomitantly with the acquisition of maximum motility of spermatozoa in the distal segment of the epididymis, and they coincide with a very great increase in testosteronemia.     

Uterine and chorioallantoic angiogenesis and changes in the uterine epithelium during gestation in the viviparous lizard,niveoscincus conventryi (squamata: scincidae)

We used immunofluorescent confocal microscopy and scanning electron microscopy to quantify uterine vascularity and to describe uterine surface morphology during gestation in pregnant females of the lecithotrophic lizard Niveoscincus coventryi. As uterine angiogenesis and epithelial cell morphology are thought to be under progesterone control, we studied the effect of a progesterone receptor antagonist (mifepristone) on uterine and chorioallantoic microvasculature and features of the uterine epithelial surfaces. Although intussuceptive angiogenesis was observed in both, uterine and chorioallantoic, vascular beds during gestation, the only significant increases were in the diameters of the uterine vessels. An ellipsoid vessel‐dense area grows in the mesometrial hemisphere of the developing conceptus, which parallels the expansion of the allantois to form the chorioallantoic placenta. Uterine surface topography changed during gestation. In particular, uterine blood vessels bulge over the luminal surface to form marked ridges on the uterine embryonic hemisphere, especially during the last stage of pregnancy, and ciliated cells are maintained in the embryonic and abembryonic hemispheres but disappear in both the mesometrial and antimesometrial poles. This distinct regionalization of uterine ridges and ciliated cells in the uterine surface and in the shape of the epithelial component of the chorion might be related to the function of both chorioallantoic and yolk sac placentae during gestation. There was no significant difference between females treated with or without mifepristone, which may be related to the partial function of mifepristone as a progestin antagonist and/or with the function and time of action of progesterone in the uterus during gestation in N. coventryi. Differences in the pattern of angiogenesis and uterine surface morphology during gestation among squamates may be related to the functional diversity of the uterine component of the different placentae and probably reflect its diverse evolutionary history. J. Morphol., 2011. © 2011 Wiley Periodicals, Inc.     

Proliferation of Oogonia and folliculogenesis in the viviparous teleost Ilyodon whitei (Goodeidae)

Oogonial proliferation in fishes is an essential reproductive strategy to generate new ovarian follicles and is the basis for unlimited oogenesis. The reproductive cycle in viviparous teleosts, besides oogenesis, involves development of embryos inside the ovary, that is, intraovarian gestation. Oogonia are located in the germinal epithelium of the ovary. The germinal epithelium is the surface of ovarian lamellae and, therefore, borders the ovarian lumen. However, activity and seasonality of the germinal epithelium have not been described in any viviparous teleost species regarding oogonial proliferation and folliculogenesis. The goal of this study is to identify the histological features of oogonial proliferation and folliculogenesis during the reproductive cycle of the viviparous goodeid Ilyodon whitei. Ovaries during nongestation and early and late gestation were analyzed. Oogonial proliferation and folliculogenesis in I. whitei, where intraovarian gestation follows the maturation and fertilization of oocytes, do not correspond to the late oogenesis, as was observed in oviparous species, but correspond to late gestation. This observation offers an example of ovarian physiology correlated with viviparous reproduction and provides elements for understanding the regulation of the initiation of processes that ultimately result in the origin of the next generation. These processes include oogonia proliferation and development of the next batch of germ cells into the complex process of intraovarian gestation. J. Morphol. 275:1004–1015, 2014. © 2014 Wiley Periodicals, Inc.