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A surprisingly large number of fish and amphibian species reproduce terrestrially despite the absence of the key evolutionary innovation of the amniotic egg. In contrast with shelled eggs of reptiles and birds, eggs of teleost fish and amphibians are typically much smaller and enclosed in relatively simple chorionic membranes. Incubation times may be brief or prolonged, and resultant hatchlings typically require the return to an aquatic habitat. Advantages of terrestrial incubation include the increased availability of warmer temperatures and avoidance of aquatic hypoxia, whereas disadvantages include desiccation, exposure to novel predators, and the risk of hatching into a hostile habitat. Hatching may be environmentally cued. Use of energy in the yolk may require trade-offs between growth of the embryo and extended incubation, as exemplified by a case study of the California Grunion. The physical challenges of terrestrial incubation, constraints for hatching, effects of egg size, and parental care are explored. Eight different types of early life history among anamniotic embryos incubating in a terrestrial environment are identified, with examples of these alternate routes to the invasion of land by vertebrates.

California grunion Leuresthes tenuis synchronize spawning with tidal cycles, so the embryos incubate in a terrestrial environment, delay hatching until cued by a specific environmental trigger, and may extend incubation for up to an additional four weeks. These adaptations, however, do not appear to alter the morphology or sequence of early developmental stages as compared to other Atherinomorph fishes in the Orders Beloniformes and Cyprinodontiformes. Embryonic development is described in a series of 30 stages based on morphology observed by light microscopy. Stages are placed in five periods: zygote and cleavage, blastula, gastrula, segmentation and organogenesis, and hatching competence. Embryos from a southern population of L. tenuis in Los Angeles are compared with embryos found > 560 km north in San Francisco Bay. Northern L. tenuis embryos developed more slowly at several stages than southern embryos and reached hatching competence later, but both locations maintained synchrony with the tidal cycle for both spawning and hatching. The variation in rates of development and stage at hatching readiness are forms of developmental heterochrony that may be associated with evolutionary adaptation or morphological plasticity within this highly successful clade.

Background: The aim of this study is to model the processes of early embryopathy seen in human pregnancy complicated by maternal hyperglycemia secondary to maternal diabetes using a mouse embryo culture system., Methods: Female mice were superovulated and mated in pairs. Two-cell embryos were harvested from the oviducts and cultured in vitro in KSOM medium (synthetic oviductal medium enriched with potassium) supplemented with 0.2, 5.56, 15.56 or 25.56 mM d-glucose. Cell proliferation, differentiation and apoptosis were assessed. Experiments were performed in constant, embryos exposed to a particular concentration of glucose (0.2, 5.56, 15.56 or 25.56 mM) from harvest to either Day 5 post fertilization (pf) or Day 8 pf, and fluctuating, embryos exposed to alternate high 25.56 mM and normal 5.56 mM concentrations of glucose between harvest and Day 5 pf, glycemic culture., Results: Expected levels of blastocyst formation and hatching were seen at 0.2 and 5.56 mM concentrations of glucose but both were impaired at higher concentrations (chi(2), P < 0.005; P < 0.001). Total cell numbers (P < 0.002) and cell allocation to the inner cell mass (P < 0.01) were reduced, but with no evidence of enhanced apoptosis in the hyperglycemic cultures. Variation in hyperglycemic exposure of the embryos on Days 2, 3 and 4 showed no adverse effects of hyperglycemia up to 24 h, but 48 and 72 h exposures were equally embryopathic (P < 0.01)., Conclusions: Hyperglycemic exposure for >24 h is toxic to early embryo development. These findings may explain the lower than expected implantation rates and higher than expected rates of congenital abnormality and early pregnancy loss seen in patients with diabetes, particularly those with poor diabetic control.

Preimplantation mouse embryos, cultured in vitro and those freshly flushed from the reproductive tract, exhibit a switch in energy substrate preference, from pyruvate during the early preimplantation stages, to glucose at the blastocyst stage. Although the biochemical basis of this phenomenon is quite well characterized, its timing and possible association with developmental factors have not been considered. We have therefore examined the role of five developmental factors in determining the timing of the switch, namely: (1) embryo age (in hours post hCG); (2) developmental stage; (3) cytokinesis; (4) cell number; and (5) activation of the embryonic genome. One-cell embryos, which develop more slowly than 2-cell embryos in vitro, were used to investigate the role of embryo age and developmental stage. Cytochalasin D, which inhibits cytokinesis and delays the timing of compaction and cavitation, was used to investigate the role of cell division and developmental stage. Finally, transcription of the embryonic genome was examined with the inhibitor, alpha-amanitin. Pyruvate and glucose consumption by single embryos were measured using a noninvasive ultramicrofluorometric technique. The results showed that the timing of the switch in energy substrate preference is precisely regulated in the mouse preimplantation embryo. Activation of the embryonic genome is a prerequisite for the switch and its timing is closely associated with developmental stage, specifically compaction and/or cavitation. Cell number, cytokinesis and embryo age appeared to be unrelated to the timing of the switch. These conclusions may well be extrapolated to other species, since an increase in net glucose uptake, if not always at the expense of pyruvate, is a feature of preimplantation embryo metabolism in all mammals studied.

The effects of two metabolic inhibitors, methyl palmoxirate (MP) and amino-oxyacetate (AOA), on mouse preimplantation embryo development and cell number, and inner cell mass. (ICM) cell metabolism have been examined. Two-cell embryos were cultured in media supplemented with either MP, which inhibits fatty acid oxidation, or AOA, which inhibits the transamination of glutamate into alpha-ketoglutarate. Embryos were scored for development daily. On day 5, expanded blastocysts were differentially labeled with fluorochromes to visualize TE and ICM cell nuclei, or the ICMs isolated by immunosurgery and their energy metabolism determined using microfluorometric methods. Embryos exposed to the two inhibitors developed into fully expanded blastocysts, although cell numbers of both the TE and ICM cells were significantly reduced compared to controls. The uptake of glucose in the presence of 1 mM MP or AOA did not differ from the controls, but less glucose was accountable for by lactate production. MP significantly reduced lactate production. In the presence of 4 mM AOA, the amount of glucose oxidized and the amount of lactate formed by ICMs were significantly reduced. The results indicate that the fuels used by isolated mouse ICMs vary in response to substrate availability and that fatty acids may be a potential energy source.