Cyclic histological changes of the oviductal-cloacal junction in the viviparous snake Toluca lineata

The structure and seasonal changes of the oviductal-cloacal junction remain poorly understood in most squamates. This study was undertaken to describe the histology of the oviductal-cloaca junction of a female viviparous snake Toluca lineata, during gestation, previtellogenesis, and vitellogenesis. The oviductal-cloacal junction exhibits a wider lumen and thicker layers of connective tissue, smooth muscle layers, and total wall width compared to the posterior vagina. The lining is characterized by thick, short longitudinal mucosal folds. The luminal epithelia differ morphologically from anterior to posterior portions of the oviductal-cloacal junction. The anterior portion is lined with a simple columnar epithelium composed of nonciliated cells. The middle portion is lined with stratified epithelium that contains an apical columnar cell layer that undergoes morphological changes coincident with the reproductive cycle. The posterior portion is lined with a stratified squamous epithelium. The connective tissue underlying the epithelium contains numerous ovoid cells having abundant acidophilic cytoplasmic granules—eosinophils. Copulation occurs during the previtellogenic stage, as evidenced by the presence of abundant spermatozoa in the lumen of the anterior portion and of a copulatory plug in the middle and posterior portion of the oviductal-cloacal junction. J. Morphol. 237:91–100, 1998. © 1998 Wiley-Liss, Inc.     

Reproductive biology of the viviparous scorpion,Liocheles australasiae (Fabricius) (Arachnida,Scorpiones, Scorpionidae). I. Absence of males in two natural populations

Summary

Sex of the viviparous scorpion, Liocheles australasiae, collected in two localities in Asia at various seasons during the years 1977 to 1983, was examined on the basis of morphology of gonads and germ cells. A total of 569 specimens consisted of 408 pregnant and 7 interpregnant adult females, 126 immature or nymphal females, and 28 young nymphs in which the sex was not distinguishable. Distinct males were never collected in either locality at any season. No spermatozoa were found in any region of the female reproductive systems. Judging from these results, males do not occur in these populations, and it is presumed that these populations reproduce by thelytokous parthenogenesis.     

Seasonal spermatogenic cycle and morphology of germ cells in the viviparous lizard Mabuya brachypoda (Squamata,Scincidae)

We describe seasonal variations of the histology of the seminiferous tubules and efferent ducts of the tropical, viviparous skink, Mabuya brachypoda, throughout the year. The specimens were collected monthly, in Nacajuca, Tabasco state, Mexico. The results revealed strong annual variations in testicular volume, stages of the germ cells, and diameter and height of the epithelia of seminiferous tubules and efferent ducts. Recrudescence was detected from November to December, when initial mitotic activity of spermatogonia in the seminiferous tubules were observed, coinciding with the decrease of temperature, photoperiod and rainy season. From January to February, early spermatogenesis continued and early primary and secondary spermatocytes were developing within the seminiferous epithelium. From March through April, numerous spermatids in metamorphosis were observed. Spermiogenesis was completed from May through July, which coincided with an increase in temperature, photoperiod, and rainfall. Regression occurred from August through September when testicular volume and spermatogenic activity decreased. During this time, the seminiferous epithelium decreased in thickness, and germ cell recruitment ceased, only Sertoli cells and spermatogonia were present in the epithelium. Throughout testicular regression spermatocytes and spermatids disappeared and the presence of cellular debris, and scattered spermatozoa were observed in the lumen. The regressed testes presented the total suspension of spermatogenesis. During October, the seminiferous tubules contained only spermatogonia and Sertoli cells, and the size of the lumen was reduced, giving the appearance that it was occluded. In concert with testis development, the efferent ducts were packed with spermatozoa from May through August. The epididymis was devoid of spermatozoa by September. M. brachypoda exhibited a prenuptial pattern, in which spermatogenesis preceded the mating season. The seasonal cycle variations of spermatogenesis in M. brachypoda are the result of a single extended spermiation event, which is characteristic of reptilian species. J. Morphol. © 2012 Wiley Periodicals, Inc.     

Ovarian structure and oogenesis of the extremophile viviparous teleost Poecilia mexicana (Poeciliidae) from an active sulfur spring cave in Southern Mexico

The structure of the ovary and oogenesis of Poecilia mexicana from an active sulfur spring cave is documented. Poecilia mexicana is the only poeciliid adapted to a subterranean environment with high hydrogen sulfide levels and extreme hypoxic conditions. Twenty females were captured throughout one year at Cueva del Azufre, located in the State of Tabasco in Southern Mexico. Ovaries were processed with histological techniques. P. mexicana has a single, ovoid ovary with ovigerous lamella that project to the ovarian lumen. The ovarian wall presents abundant loose connective tissue, numerous melanomacrophage centers and large blood vessels, possibly associated with hypoxic conditions. The germinal epithelium bordering the ovarian lumen contains somatic and germ cells forming cell nests projecting into the stroma. P. mexicana stores sperm in ovarian folds associated with follicles at different developmental phases. Oogenesis in P. mexicana consisted of the following stages: (i) oogonial proliferation, (ii) chromatin nucleolus, (iii) primary growth, subdivided into: (a) one nucleolus, (b) multiple nucleoli, (c) droplet oils‐cortical alveoli steps; (iv) secondary growth, subdivided in: (a) early secondary growth, (b) late secondary growth, and (c) full grown. Follicular atresia was present in all stages of follicular development; it was characterized by oocyte degeneration, where follicle cells hypertrophy and differentiate in phagocytes. The ovary and oogenesis are similar to these seen in other poeciliids, but we found frequent atretic follicles, melanomacrophage centers, reduced fecundity and increased of offspring size.     

Anatomical modifications,viviparous reproduction and hydraulic expulsion of larvae by Cephenemyia nasopharyngeal bot flies of deer

Several specialized adaptations of the reproductive and respiratory systems associated with the retention and expulsion of larvae in ovoviviparous Cephenemyia species (Diptera: Oestridae) are described and illustrated. In these flies the anterior section of the common oviduct is modified into a large sac‐like uterus that contains larvae, and the posterior section is modified into a larvipositor with a central tubular vagina. During larviposition, contraction of abdominal muscles forces haemolymph into a perivaginal sinus, causing a hydraulically driven exsertion of the larvipositor. A group of larvae and uterine fluid sealed off within the lumen of the vagina are then expelled from the vulva via hydraulic pressure as the stretched vagina is compressed. A one‐way, non‐return valve between the uterus and vagina prevents a reflux of larvae upward into the uterus during larviposition. All mutually dependent actions associated with larviposition occur almost simultaneously. All species have evolved a similar mechanism of expelling their larvae, but the shape of the non‐return valve is different in each species studied.     

Lipid class composition of the viviparous yellowtail rockfish over a reproductive cycle

Triacylglycerols (TAG) were the dominant lipids in liver tissue of both sexes of the viviparous yellowtail rockfish Sebastes flavidus during the spring and summer when greatest feeding occurred. Significant declines in liver TAG during the winter corresponded to increased concentrations of polar lipids (PL), the main component of cell membranes. Elevated PL in female livers relative to those of males preceded the period of ovarian enlargement and may be attributed to the production of vitellogenin. During late vitellogenesis and gestation, ovaries contained significantly elevated concentrations of PL, TAG, and cholesterol. Since yellowtail rockfish are highly fecund and viviparous, large quantities of ovarian PL are required for proliferation of the cell membranes in developing larval tissues. TAG accumulated in ovaries in lower concentrations than PL and were likely metabolized as the main source of energy during gestation. This pattern of ovarian PL concentrations exceeding those of TAG and the presence of oil globules, may be unique to highly fecund, viviparous teleosts and signify an alternative profile to those previously documented for oviparous species. Testes at maximum I _G were only 7% of maximum ovarian size, composed of mainly PL, and lacked a defined lipid dynamic pattern across the reproductive cycle.     

Aquaculture of Posidonia australis Seedlings for Seagrass Restoration Programs: Effect of Sediment Type and Organic Enrichment on Growth

Seeds of the seagrass Posidonia australis are desiccation sensitive and as there is no seed dormancy seeds cannot be stored for use in restoration projects. To realize the restoration potential of seed‐based restoration of Posidonia, this study investigated preconditioning seedlings of Posidonia in aquaculture facilities before transplanting to extend the restoration window from a few weeks (for fresh seed) to months or even years (for preconditioned seedlings). Here, we tested two levels of organic matter addition, 0 and 1.5% sediment dry weight and three sediment types; two heterogeneous sediments typical of low‐energy marine environments (1) unsorted calcareous and (2) unsorted silica, and a homogeneous sediment typical of high‐energy marine habitats (3) well‐sorted silica. We then evaluated seedling survival, biomass and development over a period of 7 months in tank culture. There was 100% survival over the 7‐month experimental period for seedlings. Seedling leaf, root, rhizome, and total biomass increased when organic matter was added to unsorted calcareous and unsorted silica sediment but not well‐sorted silica sediment, although this increase was significant only after 7 months of growth. The characteristics of the sediment also influenced seedling root length and architecture. Root length and number of lateral root branches were greatest in unsorted sediments and when organic matter was present. This study demonstrates that tank culture of P. australis enabled seedlings to be available for restoration purposes for at least 7 months, and with modification of the sediment composition, larger P. australis seedlings with more substantial root systems can be produced.     

The maize Viviparous10/Viviparous13 locus encodes the Cnx1 gene required for molybdenum cofactor biosynthesis

Abscisic acid (ABA), auxin and nitrate are important signaling molecules that affect plant growth responses to the environment. The synthesis or metabolism of these compounds depends on the molybdenum cofactor (MoCo). We show that maize (Zea mays) viviparous10 (vp10) mutants have strong precocious germination and seedling lethal phenotypes that cannot be rescued with tissue culture. We devised a novel PCR-based method to clone a transposon-tagged allele of vp10, and show that Vp10 encodes the ortholog of Cnx1, which catalyzes the final common step of MoCo synthesis. The seedling phenotype of vp10 mutants is consistent with disruptions in ABA and auxin biosynthesis, as well as a disruption in nitrate metabolism. Levels of ABA and auxin are reduced in vp10 mutants, and vp10 seedlings lack MoCo-dependent enzyme activities that are repairable with exogenous molybdenum. vp10 and an Arabidopsis cnx1 mutant, chlorate6 (chl6), have similar defects in aldehyde oxidase (AO) enzyme activity, which is required for ABA synthesis. Surprisingly, chl6 mutants do not show defects in abiotic stress responses. These observations confirm an orthologous function for Cnx1 and Vp10, as well as defining a characteristic viviparous phenotype to identify other maize cnx mutants. Finally, the vp10 mutant phenotype suggests that cnx mutants can have auxin- as well as ABA-biosynthesis defects, while the chl6 mutant phenotype suggests that low levels of AO activity are sufficient for normal abiotic stress responses.     

食蚊鱼生殖特性的研究

食蚊鱼Gambusia affinis(Baird et Girard)属于鱂形目(Cyprinodontiformes)、胎鱂科(Poeciliidae)。是一种原产北美洲的热带性卵胎生小鱼。这种鱼自1927年从马尼拉引入我国后,已成为遍及我国南方淡水小鱼,并在灭蚊控疟方面发挥一定作用。有关其繁殖生物学Rosen,D.E.et al.（1963）,Resenthal,H.L.（1952）,Turner,C.L.（1937,1941.）曾有过报道,为了补充食蚊鱼繁殖生物学资料,作者在1979—1982年在广州对其生殖特性作了观察研究。