Oviductal Eggs Research Articles

Reproductive activity of two sympatric lizard species, Ameivula ocellifera and Glaucomastix itabaianensis (Squamata: Teiidae), from Northeastern Brazil

ABSTRACT Reproductive strategies may vary among lizard species, considering environmental as well as phylogenetic effects. Ameivula ocellifera and Glaucomastix itabaianensis are two sympatric lizard species belonging to the family Teiidae, and therefore we assume they exhibit similarities in their reproductive patterns. The objective of the present study was to describe the reproductive activity and evaluate the influence of environmental variables and the body fat cycle on the reproductive activity of these two lizard species. The research was carried out in Pirambu Restinga, Sergipe state, Northeastern Brazil, between 2017 and 2018. Glaucomastix itabaianensis and A. ocellifera displayed seasonal and continuous reproduction, respectively. In both sexes of G. itabaianensis, the lowest fat values coincided with the peak of reproductive activities. The fat body mass of A. ocellifera remained low throughout the year, coinciding with its continuous reproductive activity. Females of A. ocellifera with oviductal eggs were observed in both seasons. The egglaying of G. itabaianensis occurred in the transition period between the dry and rainy seasons, which may be associated with the presence of microclimatic conditions favourable to the embryonic development and survival of the offspring. Despite both belonging to the family Teiidae and being sympatric, the two species showed different reproductive patterns.

Sexual dimorphism and reproductive biology of commercially harvested oriental rat snakes (Ptyas mucosa: Colubridae) from West Java

Large (>3 m) slender-bodied rat snakes are abundant in agroecosystems of southern Asia and are heavily exploited for their skins and meat. We examined 216 specimens killed at commercial facilities in Cirebon, West Java, to quantify morphological and reproductive traits and evaluate harvest sustainability by comparing this sample to one taken 25 years previously. The snakes we examined were mostly adults, and mostly male. Females were less heavy-bodied than males of the same body length, matured at a larger size than males, but attained smaller maximum sizes. Reproduction and energy (fatbody) storage was seasonal in both sexes, with females containing oviductal eggs primarily during the annual wet season. Clutch size averaged 12.6 eggs and increased with maternal body size. Comparison of the two samples taken 25 years apart revealed strong similarity in sex ratio, the numerical preponderance of adults, body sizes at sexual maturation and mean adult body sizes, sexual dimorphism in body length and mass, reproductive seasonality in females, mean fecundity, and the relationship between fecundity and maternal body size. That consistency suggests that commercial harvesting over the intervening period has not affected the biological traits of rat snake populations, consistent with a sustainable level of offtake.

Sexual Cycle of the Mediterranean Pond Turtle, <i>Mauremys leprosa</i> (Testudines: Geoemydidae) in West Central Morocco

We studied the reproductive cycle of male and female Mauremys leprosa in central Morocco. The cycle for males starts in the spring with warming temperatures and the beginning of the dry-season with testicular enlargement and a decrease in epididimydes size accompanied by sperm production. The epididymis contains sperm mainly in winter, spring and summer. Females exhibited follicular enlargement from November reaching a peak in February when a maximum follicle size of 38.5 mm was observed. Ovulation appears to begin in April or May and oviductal eggs were present in our samples from April – July. Suspected mating activity occurred from January – March when environmental temperatures were lowest and the wet-season peaked. Sexual activity was coincident with the onset of maximum storage of sperm in the epididymis. The overall reproductive cycle of this species is similar to that of other Temperate Zone turtles with the exception that mating occurs in the winter, not in the spring and fall. Winter mating may be a response to the wet-season Mediterranean climates. Rain connects isolated pools in ephemeral rivers and streams in Morocco that form during the dry season, thus providing greater opportunities for access to mates.

The Fecundity Characteristics and Spawning Strategy of Uroteuthis edulis in the East China Sea.

The fecundity characteristics and spawning strategy of Uroteuthis edulis in the East China Sea were investigated by observing the potential fecundity (PF), relative fecundity by dorsal mantle length (PFML) and relative fecundity by body weight (PFBW). The relationship between fecundity and a single biological indicator was measured, and generalized additive models (GAMs) were fit by adding environmental variables to help better understand this comprehensive relationship. The long diameter and short diameter of the ovarian oocytes ranged from 0.72 mm to 4.74 mm and from 0.46 mm to 3.67 mm, respectively. The long and short diameters of oviducal eggs ranged from 0.61 mm to 5.12 mm and from 0.39 mm to 3.81 mm, respectively. The egg diameter had a unimodal distribution. The PF, PFML and PFBW ranged from 540 to 13,743 cells, 5 to 86 cells/mm and 6 to 53 cells/g, respectively. Three fecundity indicators were unimodally distributed, and the PFBW was more stable than the PFML (δ2PFBW < δ2PFML). The fecundity and single biological indicators were fitted, and it was found that the PF and PFML were positively correlated with dorsal mantle length (ML) and body weight (BW). The generalized additive model (GAM) fitting showed that when considering the interaction between dorsal mantle length and sea surface height (M13), the deviation explanation rate of the PF and PFML was the highest. Studies have shown that the ovary oocytes of U. edulis mature in batches, and then the eggs are laid in batches. The dorsal mantle length (ML), water temperature at 25 m depth (T25) and sea surface height (SSH) are important indicators to measure the fecundity of U. edulis. These findings allow for a deeper understanding of the U. edulis population dynamics for the future management of this economically and ecologically important species.

Seasonal Reproductive Cycle of Wild Alligator Snapping Turtles (Macrochelys temminckii) in Southwest Georgia

We studied the reproductive cycle of wild Macrochelys temminckii (Alligator Snapping Turtle) in southwest Georgia from March 2008 to September 2010. We measured plasma testosterone (T), estradiol (E2), and corticosterone (C). Seasonal changes in T were observed in males, with maximum concentrations occurring in October. Evidence of mating and male combat were seen in April. Females displayed seasonal changes in T and E2 concentrations, with peaks occurring in March and April, respectively, (in association with mating and ovulation) and again in September and October, respectively, (in association with follicular development and vitellogenesis). We observed oviductal eggs (mean clutch size = 28.5) in April. Concentrations of C were not significantly different between months. Reproductive patterns coincided with seasonal variation in temperature and water level.

Smaller size of harlequin toads from populations long exposed to the fungal disease chytridiomycosis

AbstractPathogens can exert great selective pressures on the life history traits of their hosts. Species experiencing high mortality throughout their adulthood can benefit from breeding earlier. Chytridiomycosis, a fungal disease caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), has been a major driver of extinction for harlequin toads (Atelopus) and continues to be frequent cause of adult mortality for species persisting with endemic infections. We compared the body size of Atelopus cruciger between a remnant population long exposed to Bd (post‐epidemic) and populations sampled before the presumed Bd outbreak in the late 80s (pre‐epidemic). Reproductive female and male toads from pre‐epidemic populations were significantly bigger than those from post‐epidemic populations at similar altitudes, suggesting that toads from post‐epidemic populations are breeding earlier. A significant positive relationship between body size and the number of eggs in oviducts suggests a trade‐off between the benefit of breeding earlier and the cost of smaller clutch sizes. This cost–benefit relationship is likely to change along elevation gradients because the number of eggs relative to body size tends to be lower at higher elevations. By breeding earlier harlequin toad populations long exposed to Bd can increase their demographic competence, particularly in lowland habitats, where the cost–benefit relationship of breeding earlier tends to be more favorable.Abstract in Spanish is available with online material.

Reproductive and Morphological Characteristics of Hemidactylus turcicus (Squamata: Gekkonidae) and Tarentola annularis (Squamata: Phyllodactylidae) in Southern Egypt

Hemidactylus turcicus and Tarentola annularis are occasionally sympatric and are ecologically similar in vertical wall microhabitat. For this reason, I studied their sexual, fat-body, and liver cycles for three years. All morphological variables are male-biased in T. annularis, unlike male H. turcicus, which showed significant differences in head sizes only. Females exhibited a spring to summer vitellogenic period with ovulation occurring during mid-spring to mid-summer in T. annularis and from late spring to late summer in H. turcicus. The mean clutch size of oviductal eggs (1.86) and relative clutch mass (0.188) was higher in H. turcicus than in T. annularis (1.67 and 0.132). Relative clutch mass was negatively correlated with snout–vent length in T. annularis but was not in H. turcicus. Sperm were present in the epididymis for eight months in H. turcicus while year-round in T. annularis. Post-breeding, masses of liver and fat body increased in both sexes of both species. There were significant differences in fat body and liver masses between the sexes of both species. Based on the liver-mass cycle, the energy expenditure on reproduction in male and female T. annularis was high compared with the corresponding sexes of H. turcicus. Testicular recrudescence began in late fall or early winter corresponding to lower temperatures, photoperiod, and precipitation. Testicular regression occurred at the highest temperatures in late summer and early fall.

Reproductive Phenology and Output in Florida Box Turtles (Terrapene bauri) in Southwestern Florida

Box turtle (Terrapene spp.) reproduction has been relatively well studied in northern populations inhabiting more seasonal climates but is much less understood in the subtropics. We assessed female reproduction of T. bauri in southwestern Florida by quantifying courtship, mating, seasonal timing of nesting, clutch frequency, and clutch size. Box turtles were observed courting or mating in 10 out of 12 mo. Radiographs revealed oviducal eggs from January to August. To our knowledge, this is the earliest recorded detection of eggs in wild box turtles. Individual turtles produced 2–4 clutches of 1–5 eggs in a nesting season. This study provides further evidence that turtle populations at warmer climates exhibit extended reproductive seasons compared with similar populations in cooler climates.

Egg retention in wild-caught [i]Python bivittatus[/i] in the Greater Everglades Ecosystem, Florida, USA

Retention of eggs in oviducts beyond the normal oviposition period is a common problem for captive reptiles, but the occurrence of egg retention in wild populations is largely unknown. The Burmese python (Python [molurus] bivittatus; Kühl 1820) is an oviparous snake native to south-eastern Asia that is now established in southern Florida. From 2011–2019, invasive Burmese pythons were opportunistically removed from Everglades National Park and Big Cypress National Preserve, humanely euthanised, and necropsied to determine reproductive condition. A total of 258 females of reproductive size were found to exhibit various stages of oviposition which generally aligned with purported annual reproductive timing. However, we encountered five pythons during the post-ovulatory period (Aug–Feb) showing signs of recent oviposition with retained eggs. Most of these cases comprised a small number of retained eggs, likely representing some portion of the total clutch. Because this condition is nearly absent in wild animal literature, our observations suggest retained eggs in wild snakes may be more common than previously assumed, possibly slowing or otherwise impacting population growth. However, we recognise that for an invasive species like the Burmese python in Florida, the egg retention rate may be higher in the non-native range compared to the native range due to maladaptation to novel habitats or environmental conditions. Additional research is needed to determine the exact causes of egg retention and investigate the implications for population dynamics on this and other snake species. Keywords: invasive species, dystocia, snakes, Burmese, reproduction

Bioaccumulation and impact of maternal PFAS offloading on egg biochemistry from wild-caught freshwater turtles (Emydura macquarii macquarii)

Per- and polyfluoroalkyl substances (PFAS) are persistent synthetic contaminants that are pervasive in the environment. Toxicity resulting from elevated PFAS concentrations in wildlife has been studied, yet evidence of their accumulation, developmental toxicity and maternal offloading in egg-laying species is limited. Here we show the maternal offloading of PFAS in freshwater short-necked turtles (Emydura macquarii macquarii) exposed to elevated PFAS and the resulting biological impact on oviducal eggs. Total PFAS concentrations were determined in serum from adult females and harvested oviducal eggs collected from euthanised turtles exposed to low and high levels of PFAS and compared against turtle serum and eggs collected from a suitable reference site. Multi-omics assays were utilised to explore the biochemical impact of elevated PFAS on egg albumen, yolk and eggshell using a range of metabolomics, lipidomics, and proteomics techniques. Eggshells were also screened for metals by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Analysis of the serum collected from adult female turtles and their oviducal eggs demonstrated PFAS offloading and transference that is 1.6 and 5.3 times higher in the low and high PFAS impacted eggs, respectively, compared to maternal serum concentrations. Oviducal egg yolk comprised >90% of the bioaccumulated PFAS load. Multi-omic analysis of the dissected egg fractions illustrated PFAS impacted eggs are significantly elevated in purine metabolism metabolites, which are tied to potential biological dysfunctional processes. The yolks were significantly depleted in lipids and lipid quality tied to growth and development. The high PFAS impacted oviducal eggshells were lower in calcium, important developmental and immune response proteins, and higher in glycerophosphoethanolamines (PE) lipids and histidine metabolism metabolites that are tied to a weakened physical structure. Further investigation is needed to establish the rate of PFAS offloading and quantify the developmental impact on hatchling and hatchling success to fully demonstrate PFAS-developmental toxicity linkages.

Reproductive phenology in a Neotropical aquatic snake shows marked seasonality influenced by rainfall patterns

ABSTRACT Reproductive phenology of snakes varies widely among species, likely influenced by biotic and abiotic factors related to seasonality. In Neotropical regions, where seasonal variation in temperature and photoperiod is minimal, the factors regulating the reproductive phenology of snakes remain poorly known, despite the great diversity of species found in this region. We hypothesise that the phenology of tropical aquatic snakes is directly influenced by local precipitation patterns and resulting water levels. We studied for the first time the reproductive cycle of a neotropical aquatic oviparous snake, Helicops pastazae, in a mountain river in the Andean foothills of Colombia. To do so, we sampled 212 snakes from 2013 to 2017 and classified the monthly reproductive stages of the adult snakes. In females we observed follicular development and presence of oviductal eggs, in males we performed histological analyses of testes, kidney, and deferent ducts. Females showed a marked seasonal reproductive cycle, with secondary vitellogenic individuals mainly clustered during the high precipitation months, ovigerous stages found throughout low precipitation months, and with egg-laying occurring from low precipitation to the early dry seasons. Males produced spermatozoa throughout the year indicating year-round reproduction at a population level. We found sexual dimorphism in tail length, with both juvenile and adult males showing significantly longer tails than females, while adult females were larger than males and showed greater midbody width, head length, and head width. The reproductive activity of H. pastazae is highly seasonal in females, driven by regional rainfall patterns, whereas males are reproductive thorough the year, being a permanent resource for females.

Aspidoscelis costatus costatus (Squamata, Teiidae): high elevation clutch production for a population of whiptail lizards

Clutch size and number of clutches per reproductive cycle are important life history traits that can be influenced by anatomical, physiological, evolutionary, and ecological factors. This report on the clutch size and number of clutches of an endemic Mexican whiptail lizard, Aspidoscelis costatus costatus (Cope, 1878), is based on a study of population at an unusually high elevation for a member of this genus. The study site is located in Ixtapan de la Sal, southeastern Estado de México, Central Mexico, at 2090 m a.s.l. Lizards were sampled in June 2006, and from May to July 2007, where females of Aspidoscelis costatus costatus were collected by hand along a drift fence. Female reproductive condition was evaluated based on abdominal palpation for presence of developing eggs; clutch size was determined by actual counts of either vitellogenic follicles or oviductal eggs. The smallest reproductive female was 77 mm snout-vent length; females produced a minimum of two clutches during the breeding season, the mean clutch size of 6.5 eggs (n = 33) was one of the largest reported for the genus. However, both length and width of its eggs, and the relative clutch mass have not been diminished by development of a large clutch. Additionally, comparisons of clutch size were undertaken within the polytypic A. costatus complex, within the genus Aspidoscelis, and between certain genera of whiptail lizards. This apparently represents the first study of whiptail lizards (genus Aspidoscelis), assessing the aforementioned reproductive characteristics, in a population above 2000 m.

Reproductive cycle and maturation of Swinhoe's tree lizard (Diploderma swinhonis (Günther, 1864)) in Hyuga City, Miyazaki Prefecture, Japan.

Swinhoe’s tree lizard (Diploderma swinhonis) is an arboreal agamid that is native to Taiwan. The species has been introduced to some areas of Japan and is regarded as an invasive alien species. In 2016, a nonnative population of D. swinhonis was discovered in Hyuga City, Miyazaki Prefecture, Japan, but little information was available on the ecology of the population at the time. The main purpose of this study was therefore to investigate the reproductive cycle and maturation of this population. Field research was conducted from 2017 to 2019, and 764 lizards were collected. Euthanized lizards were dissected and the reproductive organs were examined to determine the reproductive period, clutch size, clutch frequency and size at sexual maturity. Females with oviductal eggs or vitellogenic ovarian follicles were observed from May to October. Clutch size ranged from 2 to 8, and clutch frequency was more than twice a year. In males, spermiogenesis started in early May and testicular regression was observed in September. Males with spermatozoa in the epididymides were found from May to November. Minimum snout-vent length at sexual maturity was 50.2 mm in females and 53.0 mm in males. Comparisons of the findings of this study and reports from Taiwan suggest that the nonnative population of D. swinhonis in Hyuga City has a higher fecundity than populations in Taiwan. It is therefore considered necessary to exterminate the population in Hyuga City before this species colonizes other areas.

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.

Sexual dimorphism, diet, and notes on reproduction in Oxyrhopus trigeminus (Serpentes: Colubridae) in the semiarid Caatinga of northeastern Brazil

Sexual dimorphism, diet, and notes on reproduction in Oxyrhopus trigeminus (Serpentes: Colubridae) in the semiarid Caatinga of northeastern Brazil. Selected morphological characters, diet, and reproduction of the false-coral snake, Oxyrhopus trigeminus, from several localities in the Caatinga region of northeastern Brazil are described based on examination of preserved specimens. Sexual dimorphism is evident, with females attaining larger body sizes than males, but males have relatively larger heads and tails. A total of 25 prey items was identifed in 23 of the 97 O. trigeminus examined; based on the orientation of the prey in the stomachs, all items were ingested headfrst. Lizards are the most frequent prey (96%) of O. trigeminus, with the lizard Tropidurus hispidus being the most important prey species both in number and in volume; marsupials account for 4% of the diet. Juveniles have a narrower dietary niche width than adults, presumably because they have smaller mouths with a narrower gape. Females have a wider dietary niche than males, but there is a high niche overlap between the sexes; males and females do not differ in prey volumes. The analysis of the gonads showed that 10 females have 4–13 vitellogenic follicles (mean 7.8 ± 2.8 follicles), and 2 females have oviducal eggs, one with only one egg and the other with fve eggs. The estimated minimum size at maturity for female O. trigeminus in the Caatinga is 400 mm.

Comparative impact of coumaphos, amitraz and plant extract of Ageratum conyzoides on the oogenesis of Rhipicephalus microplus

The present experiment was conducted to evaluate and compare the impact of Ageratum conyzoides plant extract (ACE) with routinely used synthetic acaricides i.e., amitraz and coumaphos on the oogenesis of engorged adult females of Rhipicephalus microplus tick. On the day of dropping from the host, panoistic ovary of R. microplus appeared white in colour, horseshoe shaped, hollow tubular organ with immature oocytes predominantly in dorsal groove. Different developmental stages of oocytes (I–V) proceed simultaneously and asynchronously. Oocytes showed gradual increase in size, deep brown colored with accumulation of eggs in oviduct during 24–72 hours of development.At LC90 concentration a highly significant (p < 0.001) cessation of egg laying after exposure to amitraz and ACE while significant reduction (p < 0.01) of egg laying in coumaphos treated ticks was observed. Upon dissection of treated ticks, uterus and oviduct packed with eggs, which failed to pass out was observed. The histo-architectural alterations including presence of extensive vacuolation, alteration of oocyte morphology, deformation of chorion and disorganization of yolk granules were observed in the treated ovaries. Histochemically, low level of storage or synthesis of essential elements viz., proteins, polysaccharides and lipids in treated oocytes responsible for reduction of fertility and inhibition of progress of vitellogenesis was observed.

Reproductive aspects of the semi-aquatic snake Erythrolamprus miliaris (Dipsadidae: Xenodontini) in the state of Rio de Janeiro, southeastern Brazil.

We analyzed some aspects of reproduction and sexual dimorphism of the semi-aquatic dipsadid snake Erythrolamprus miliaris in the state of Rio de Janeiro, southeastern Brazil. We detected sexual dimorphism in body size (snout-vent length), with females averaging larger than males, but no sexual dimorphism in the relative length of the tail. Oviductal eggs and secondary follicles were found in all seasons, suggesting that female reproductive cycles are continuous, in spite of the tropical seasonal climate in the region. Reproductive males were present throughout the year, suggesting a continuous cycle for males as well. Clutch size averaged 10.3 ± 4.8 (range 4-21) and there was a positive and significant relationship between clutch size and female size. Compared to conspecific populations previously studied in other Atlantic Rainforest areas, populations of E. miliaris from the state of Rio de Janeiro appear more similar overall in their reproductive traits to a more northern population from the state of Bahia than to populations from further south in the states of São Paulo and Paraná.

Natural history of the threatened coral snake Micrurus altirostris (Serpentes: Elapidae) in Argentina

The genus Micrurus comprises nearly 80 endemic species in the American continent. Knowledge on its natural history is based on populations from Brazil and Uruguay, making it necessary to intensify ecological research in Argentina. We present data on morphology, diet, and reproduction for a threatened Argentine population of M. altirostris from the Atlantic Forest biodiversity hotspot. Ecological data were obtained from collected specimens and scientific collections. Females attained sexual maturity at a longer body size than males, but the latter reached a larger size, which is related to male-male combat, a behavior reported in this study. We report a female with 3 oviductal eggs, and 2 ovipositions of 4 and 6 eggs in the late spring-early summer period. Males seemed to have a seasonal reproductive cycle. The diet of M. altirostris was based on elongated reptilians and was mostly similar to the diet of populations from Brazil and Uruguay. We reported 4 new prey types for M. altirostris and confirm the consumption of reptile eggs for the genus Micrurus . Our results contribute to a better understanding of the natural history of M. altirostris , providing valuable information for designing strategic conservation plans.

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.

Expression of aquaporin 4 in the chicken oviduct following tamoxifen treatment.

This study was designed to examine whether aquaporin 4 (AQP4) is present in the chicken oviduct, and if so, whether its expression changes during pause in laying induced by tamoxifen (TMX; oestrogen receptor modulator) treatment. The control chickens were injected with a vehicle (ethanol) and the experimental ones with TMX at a dose of 6mg/kg of body weight. Birds were treated daily until complete cessation of egg laying. The oviductal parts, that is the infundibulum, magnum, isthmus, shell gland and vagina were isolated from hens on day 8 of the experiment, and subsequently, the gene and protein expressions of AQP4 in tissues were examined by real-time PCR and Western blot, respectively. Immunohistochemical localization of AQP4 in the wall of the chicken oviduct was also investigated. Both mRNA and protein of AQP4 were found in all segments of the chicken oviduct. The relative expression [RQ] of AQP4 was the highest in the infundibulum and the vagina and the lowest, less detectable, in the magnum and isthmus. The pattern of AQP4 protein expression was similar to that of mRNA. Treatment of hens with TMX decreased the mRNA and protein levels of AQP4 in the oviduct. Immunohistochemistry demonstrated tissue and cell-dependent localization of AQP4 protein in the oviductal wall. The intensity of the immunopositive reaction was as follows: the infundibulum>vagina>shell gland≥isthmus>˃magnum. In the control chickens, the immunoreactivity for AQP4 in all oviductal segments was stronger compared with the TMX-treated hens. The results obtained indicate that AQP4 takes part in the regulation of water transport required for the formation of egg in the chicken oviduct. Moreover, a relationship between oestrogen action and AQP4 gene and protein expression is suggested.