Reproductive cycles of male and female tuatara (Sphenodon punctatus) on Stephens Island, New Zealand

Cycles in gonadal activity and plasma sex steroid concentrations were investigated in wild female and male tuatara on Stephens Island, New Zealand. Females nest once every four years on average. Vitellogenesis is spread over the first three years, and mating, ovulation and nesting occur in the fourth. Oviducal eggs are carried for6–8 months before nesting. Although the length of this ovarian cycle is unparalleled among oviparous reptiles, the associated cycles in plasma concentrations of sex steroids are similar to those in other reptiles. Mean plasma concentrations of oestradiol increase during vitellogenesis, peak at mating, fall rapidly before or around ovulation, are low during most of gravidity, and rise slightly during late gravidity-nesting. Plasma concentrations of testosterone show a similarcycle. Mean plasma concentrations of progesterone are low during vitellogenesis and peak around ovulation. This periovulatory surge falls within1–2 months, and mean concentrations are low during the final 5–6 months of gravidity. Male tuatara show an annual, pre-nuptial reproductive cycle. Mean plasma concentrations of testosterone are low during winter, rise during spring, peak during midsummer-early autumn, when pre-nuptial displays and mating occur, and fall in mid autumn. Limited histological data indicate that spermiogenesis occurs during midsummer-early autumn, and also support a previous study suggesting that there may be no period of complete testicular and epididymal regression. In comparison with the pre-nuptial cycles of other temperate-zone reptiles, the cycle in male tuatara shows a more prolonged duration of testicular activity and of rising or elevated plasma testosterone concentrations. The prolonged reproductive cycles of male and female tuatara may be adaptations to a temperate environment with cool summers and cool, but not freezing, winters.     

Eggshell formation during prolonged gravidity of the tuatara Sphenodon punctatus

Scanning electron microscopy (SEM) was used to examine the process of shell formation in tuatara. Tuatara carry eggs in the oviducts for ∼ 7–8 mo before nesting, a period of gravidity more than three times as long as in any other oviparous reptile. Our aim was to determine whether shell formation occurred rapidly after ovulation, or whether it occurred gradually throughout gravidity. Eggs were obtained from females in early gravidity (May, ∼ 1 mo after ovulation), midgravidity (August and September, 4–5 mo after ovulation), and late gravidity, immediately prior to nesting (December, 8 mo after ovulation). The shell membrane (fibrous layer) was well formed by May, but calcification of the outer surface had only just begun. Vertical columns of calcium carbonate were embedded in the shell membrane and appeared to erupt through the outer surface between early and midgravidity. Changes in the appearance of the outer calcareous layer were evident as gravidity progressed. In all shells, calcium carbonate was present as calcite. The appearance of the inner boundary (innermost layer of eggshell) was variable; some shells had a smooth and amorphous inner boundary as previously reported for tuatara and other reptiles, whereas other shells had an inner boundary composed of small spherical granules on the inner surface of which small calcareous spicules were scattered. A previously published model of the process of shell formation in tuatara eggshells is refined in light of our observations. We interpret the ability of female tuatara to shell their eggs gradually during winter as further evidence of their unusual physiological tolerance of cold conditions. © 1996 Wiley-Liss, Inc.     

Corpus luteum size and plasma progesterone concentration in cows

It is often assumed that a larger corpus luteum will produce more progesterone and generate higher circulating plasma concentrations. The aim of the study was to determine whether the size of the corpus luteum does actually determine circulating plasma progesterone concentrations. Data were collated from a number of studies on various aspects of luteal function in non-lactating dairy cows to allow comparisons to be made between corpus luteum weight and plasma progesterone concentration across the luteal phase. In these studies oestrous cycles had been synchronised and animals slaughtered on day 5, day 8 or day 16 following oestrus. Both corpus luteum weight and plasma progesterone concentration increased between day 5 and day 8. Plasma progesterone concentration but not luteal weight also increased between day 8 and day 16. On day 5 there was a strong relationship between corpus luteum weight and plasma progesterone (R² = 0.64; P < 0.001). However, no such relationship was present on day 8 or day 16. These results indicate that while during the early stage of corpus luteum development a relationship between size and progesterone is present, by day 8 of the cycle, the size of the corpus luteum is no longer of importance in determining circulating progesterone concentrations.     

Formation and regression of the corpus luteum of the American alligator (Alligator mississippiensis)

Luteal morphology of the American alligator is unique when compared to other reptiles but is similar to that of its phylogenetic relatives, the birds. The theca is extensively hypertrophied, but the granulosa never fills the cavity formed following the ovulation of the ovum. The formation of the corpus luteum (CL) is correlated with elevated plasma progesterone concentrations, which decline dramatically after oviposition with the onset of luteolysis. Unlike those of most other reptiles, the central luteal cell mass is composed of two cell types; one presumably is derived from the granulosa, whereas the other is from the theca interna. Both cell types are present throughout gravidity but only one cell type is seen during mid to late luteolysis. A significant decline in luteal volume occurs following oviposition and continues throughout the post-oviposition period. The fastest decline in luteal volume occurs in the month immediately after oviposition; this rate then slows. Luteolysis appears to continue for a year or more following oviposition, as distinct structures of luteal origin can still be identified in animals 9 months after oviposition. The size of persistent CL can be used to determine whether a given female oviposited during the previous nesting season. Females with CL having volumes greater than 0.2 cm² or CL diameters greater than 0.4 cm were active the previous season. © 1995 Wiley-Liss, Inc.     

Effects of luteectomy in early pregnancy on the maintenance of gestation and plasma progesterone concentrations in the viviparous temperate lizard <Emphasis Type="Italic">Barisia imbricata imbricata</Emphasis>

Background  

Several studies have shown that the corpus luteum is the principal source of progesterone during the gravidity period in reptiles; however, its participation in the maintenance of gestation in the viviparous squamata is in dispute. The effects of ovariectomy or luteectomy vary according to the species and the time at which the procedure is performed. In this paper, we describe the effects of luteectomy during early pregnancy on the maintenance of gestation and progesterone concentrations in the temperate Mexican viviparous lizard Barisia imbricata imbricata.     

Mutant mouse models and their contribution to our knowledge of corpus luteum development,function and regression

The corpus luteum is a unique organ, which is transitory in nature. The development, maintenance and regression of the corpus luteum are regulated by endocrine, paracrine and autocrine signaling events. Defining the specific mediators of luteal development, maintenance and regression has been difficult and often perplexing due to the complexity that stems from the variety of cell types that make up the luteal tissue. Moreover, some regulators may serve dual functions as a luteotropic and luteolytic agent depending on the temporal and spatial environment in which they are expressed. As a result, some confusion is present in the interpretation of in vitro and in vivo studies. More recently investigators have utilized mutant mouse models to define the functional significance of specific gene products. The goal of this mini-review is to identify and discuss mutant mouse models that have luteal anomalies, which may provide some clues as to the significance of specific regulators of corpus luteum function.     

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.     

Focusing and accommodation in tuatara (Sphenodon punctatus)

Summary Photorefraction and photokeratometry were performed on two juvenile tuatara (Sphenodon punctatus, 7 years of age, total length approx. 27 cm). Sphenodon is the only surviving genus of the Rhynchocephalia, an order of reptiles. Both existing species are endangered and are found only in New Zealand. Even though Walls (1942) has stated that the ciliary muscle is relatively weak in tuataras, we observed 8 D of accommodation. The eyes were found to focus independently and we could induce an anisometropia of 6 D. The average corneal power of the tuatara was found to be 101 D.     

Microvascular endothelial cells of the corpus luteum

The cyclic nature of the capillary bed in the corpus luteum offers a unique experimental model to examine the life cycle of endothelial cells, involving discrete physiologically regulated steps of angiogenesis, blood vessel maturation and blood vessel regression. The granulosa cells and theca cells of the developing antral follicle and the steroidogenic cells of the corpus luteum produce and respond to angiogenic factors and vasoactive peptides. Following ovulation the neovascularization during the early stages of corpus luteum development has been compared to the rapid angiogenesis observed during tumor formation. On the other end of the spectrum, the microvascular endothelial cells are the first cells to undergo apoptosis at the onset of corpus luteum regression. Important insights on the morphology and function of luteal endothelial cells have been gained from a combination of in vitro and in vivo studies on endothelial cells. Endothelial cells communicate with cells comprising the functional unit of the corpus luteum, i.e., other vascular cells, steroidogenic cells, and immune cells. This review is designed to provide an overview of the types of endothelial cells present in the corpus luteum and their involvement in corpus luteum development and regression. Available evidence indicates that microvascular endothelial cells of the corpus luteum are not alike, and may differ during the process of angiogenesis and angioregression. The contributions of vasoactive peptides generated by the luteal endothelin-1 and the renin-angiotensin systems are discussed in context with the function of endothelial cells during corpus luteum formation and regression. The ability of two cytokines, tumor necrosis factor alpha and interferon gamma, are evaluated as paracrine mediators of endothelial cell function during angioregression. Finally, chemokines are discussed as a vital endothelial cell secretory products that contribute to the recruitment of eosinophils and macrophages. The review highlights areas for future investigation of ovarian microvascular endothelial cells. The potential clinical applications of research directed on corpus luteum endothelial cells are intriguing considering reproductive processes in which vascular dysfunctions may play a role such as ovarian failure, polycystic ovary syndrome (PCOS), and ovarian hyperstimulation syndrome (OHSS).     

Predicting the fate of a living fossil: how will global warming affect sex determination and hatching phenology in tuatara?

How will climate change affect species'' reproduction and subsequent survival? In many egg-laying reptiles, the sex of offspring is determined by the temperature experienced during a critical period of embryonic development (temperature-dependent sex determination, TSD). Increasing air temperatures are likely to skew offspring sex ratios in the absence of evolutionary or plastic adaptation, hence we urgently require means for predicting the future distributions of species with TSD. Here we develop a mechanistic model that demonstrates how climate, soil and topography interact with physiology and nesting behaviour to determine sex ratios of tuatara, cold-climate reptiles from New Zealand with an unusual developmental biology. Under extreme regional climate change, all-male clutches would hatch at 100% of current nest sites of the rarest species, Sphenodon guntheri, by the mid-2080s. We show that tuatara could behaviourally compensate for the male-biasing effects of warmer air temperatures by nesting later in the season or selecting shaded nest sites. Later nesting is, however, an unlikely response to global warming, as many oviparous species are nesting earlier as the climate warms. Our approach allows the assessment of the thermal suitability of current reserves and future translocation sites for tuatara, and can be readily modified to predict climatic impacts on any species with TSD.     

The fine structure of the corpus luteum in Hyrax

Summary Hyrax possess luteal cells with many ultrastructural features similar to those described in other mammalian species. The process of luteinization is gradual. Cells with increasing amounts of smooth endoplasmic reticulum become predominant in the developing gland. The luteal cells of Procavia and Heterohyrax show many ultrastructural similarities. In both species the corpus luteum persists throughout pregnancy.     

A scanning electron microscopic study of the luteo-follicular complex

Summary As observed by SEM, the repair of an ovulated mammalian follicle is accompanied by a sequence of morphogenetic processes. In the initial phase, a mass of cells and coagulated fluids forms at the site of rupture. Shortly thereafter, connective cells, recruited from the adjacent and subjacent connective tissue stroma begin to proliferate and to migrate over this mass such that in the rabbit, the entire site of disruption is covered by a layer of connective cells by approximately 2 days following ovulation. Coincident with the migration of the connective tissue, superficial cells from undisturbed lateral and basal areas of an ovulated follicle also proliferate and begin to migrate over the newly established connective tissue matrix. By approximately 4 days following ovulation in the rabbit, the surface of an ovulated follicle is repopulated by elements of the superficial epithelium. The formation of the underlying corpus luteum (corpora luted) involves characteristic morphological changes as granulosa cells transform into steroid secreting luteal cells. The luteal cells become organized into cords of cells which usually surround capillary vessels. When examined by SEM, the smooth-surfaced endoplasmic reticulum of the luteal cell is quite apparent and is observed to form a three-dimension network of anastomosing tubules which are continuous with the nuclear membrane. Variations in the appearance of the surface of the ovary which directly overlies corpora lutea were observed when the mouse, rat and rabbit were compared. The regression of corpora lutea involves the infiltration of the luteal mass by connective tissue and both degeneration and vacuolization of the luteal cells. The regressing corpus luteum is a honey-comb-like structure in which each space is occupied by a degenerating luteal cell.This work was supported by grants from the National Institutes of Health, Public Health Service (to J.V.B., no. HD-04274), and from Consiglio Nationale delle Ricerche (C.N.R., contracts nos. CT 76.01288.04 and CT 77.01921.4)     

Tumor necrosis factor production and accumulation of inflammatory cells in the corpus luteum of pseudopregnancy and pregnancy in rabbits

The potential involvement of macrophages, T lymphocytes, and the cytokine tumor necrosis factor (TNF) in regression of the corpus luteum was investigated at different stages of pseudopregnancy and pregnancy by use of immunocytochemical methods and a TNF bioassay. Few macrophages (11 +/- 6 per high power field of 8-microns frozen sections of corpus luteum, Day 10 of pseudopregnancy) were observed until the very end of pseudopregnancy, when the number of macrophages increased greatly (176 +/- 42 per high power field, Day 19 of pseudopregnancy). Pregnancy, of 32 days duration, delayed large-scale macrophage accumulation until 3 days after parturition (154 +/- 30 per high power field). Low TNF activity (approximately 1.0 U/mg protein) was detected in incubations of luteal tissue at all stages; in response to lipopolysaccharide, TNF values in medium increased 10- to 30-fold at times of luteal regression and macrophage accumulation (1 day postpartum and Day 19 of pseudopregnancy). Class II-positive T lymphocytes were observed in luteal tissue, but unlike macrophages, the number of lymphocytes did not increase at the time of regression of the corpus luteum. These data are consistent with the hypothesis that involution of the corpus luteum is promoted through the interactions of inflammatory cells and action of TNF, although the action of TNF has not been determined in this luteal tissue. Through unknown mechanisms, pregnancy postpones the accumulation of macrophages in the corpus luteum, in association with the prolongation of luteal function until the time of parturition.     

Luteolysis in the rhesus monkey: Ovarian venous estrogen, progesterone, and prostaglandin F2α-metabolite

The role of prostaglandin F₂α (PGF₂α) in luteolysis in the non-human primate is poorly understood. We have recently reported that chronic PGF₂α infusion to the corpus luteum via Alzet pump, induced premature, functional luteolysis in the rhesus monkey. In the present study we sought to determine the ovarian events leading to spontaneous luteolysis in the monkey. Rhesus monkeys underwent laparotomy during the early luteal (4–5 days after the preovulatory estradiol surge, PES), mid-luteal (7–9 days PES), and late luteal (10–14 days PES) phases or at the first day of menses (M). Concentrations of progesterone, estradiol, estrone, and 13, 14-dihydro-15-keto-PGF₂α (PGFM) were measured in the ovarian venous effluents ipsilateral and contralateral to the ovary bearing the corpus luteum. Steroid levels in the ovarian vein on the corpus luteum side were significantly higher than the non-corpus luteum side throughout the cycle. PGFM levels were similar on both sides until the late luteal phase, when the effluent of the ovary bearing the corpus luteum contained significantly more PGFM (206±3) vs. 123±9 pg/ml, mean±sem); this disparity increased further at the time of menses (241±38 vs. 111±22 pg/ml). These data are the first to show an asymmetric secretion of PGFM in the ovarian venous effluent in the primate and suggest that PGF₂α of ovarian and possibly of corpus luteum origin may be directly involved in luteal demise.     

Ovarian steroid hormones and endometrial response

As a bioassay of the steroidogenic function of the corpus luteum, endometrial biopsy has been proposed as the most efficient way of diagnosing corpus luteum insufficiency. However, analysis of our data on luteal phase evaluation in infertility shows that most cases (86%) of endometrial luteal inadequacy are associated with normal hormone (progesterone, estradiol) stimulation. This apparent lack of endometrial progestational response may be explained by an end organ defect localized to the endometrial steroid receptors.     

Lipofuscin in the corpus luteum of macaque ovaries

The present study examined the histochemistry of pigments in the corpus luteum of the ovaries of cynomolgus monkeys (Macaca fascicularis), Japanese monkeys (Macaca fuscata), and rhesus monkeys (Macaca mulatta). Yellowish brown pigments were found in the regressing corpus luteum cells. Histochemical studies revealed that these pigments consisted of lipofuscin, the so-called age pigment. The findings obtained suggest that accumulation of lipofuscin might be related to cellular aging of the corpus luteum.     

Angiogenesis in the corpus luteum

The corpus luteum (CL) is a site of intense angiogenesis. Within a short period, this is followed either by controlled regression of the microvascular tree in the non-fertile cycle, or maintenance and stabilisation of the new vasculature a conceptual cycle. The molecular regulation of these diverse aspects is examined. The CL provides a unique model system in which to study the cellular and molecular regulation of angiogenesis. Vascular endothelial growth factor (VEGF) has been found to have a major role in the CL. By targeting its action at specific stages of the luteal phase in vivo by antagonists, profound inhibitory effects on luteal angiogenesis and function are observed.