Wiley

Among reptiles that show temperature‐dependent sex determination, sex ratios vary across constant incubation temperatures in ways sufficiently predictable to allow classification into patterns. One common pattern shows low temperatures yielding only males and high temperatures yielding only females. Another common pattern has low as well as high temperatures yielding only or mostly females and some intermediate temperatures yielding mostly males. Patterns tend to be associated with the direction of sexual dimorphism in adult size, especially for species with strong dimorphism.

Pivotal temperatures (those yielding 1:1 sex ratios) within the best‐documented species and genera tend to increase with both latitude and longitude across central and southern North America. These geographic trends probably reflect factors that affect nest temperatures (duration of growing season, insolation, and prevailing amounts of shading by vegetation).

Data from a population of the alligator snapping turtle (Macroclemys temminckii) suggest that some embryos are temperature‐independent females because these individuals become females even when they are shifted among male‐producing temperatures during development. These individuals are also more frequent in clutches of small eggs. In this and several other species, no constant incubation temperatures yield more than 75% males. © 1994 Wiley‐Liss, Inc.

To investigate developmental responses to chronic hypoxia, we incubated alligator eggs at 17% O₂ and 21% O₂ for the entire course of embryonic development and for 5 months post‐hatching. Hypoxic‐incubated alligators hatched later and at a smaller size. Hematocrit was significantly higher in hypoxic‐incubated animals immediately post‐hatch. Allosteric modification of hemoglobin oxygen affinity did not appear to play a role in the adaptation to hypoxia, given equal nucleotide triphosphate‐to‐hemoglobin ratios in the hypoxic and normoxic groups. When acutely exposed to 21% O₂, hypoxic‐incubated alligators maintained oxygen consumption relative to their normoxic siblings despite their lower mass. © 1995 Wiley‐Liss, Inc.

In many species of reptiles, sex is determined by the incubation temperature of the egg. In the red‐eared slider turtle (Trachemys scripta), warm incubation temperatures produce females, cool ones produce males, and a narrow range of intermediate temperatures produces both sexes. The mechanism of sex determination has not been established. Some investigators have postulated that both total incubation time and developmental rate during the first third of development are better predictors of sex than is incubation temperature. Here we consider whether various oxygen concentrations might influence sex determination by altering total incubation time. We incubated T. Scripta eggs at various oxygen concentrations, and found that while total incubation times were significantly influenced by oxygen, sex ratios were not. Very low oxygen concentrations inhibited survival to hatching, In addition, total incubation time and the number of days to internalize the yolk after hatching were significantly lengthened by lowered oxygen concentrations. There were also strong effects of clutch on sex determination and physiology, but these effects were apparently not mediated by an effect on total incubation time.

The influences of temperature and water on the ability of turtle embryos to tolerate hypoxia were investigated by measuring critical oxygen tension, P_c, at different levels of temperature (22, 27, and 32°C) and hydric conditions (3 and 13% gravimetric water content). Eggs were half‐buried in sand with 3 or 13% gravimetric water content and incubated at a constant 30°C. Using a closed metabolic chamber, oxygen consumption, \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm V}\limits^{\rm .} $\end{document}, was measured at decreasing oxygen tensions. Embryonic \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm V}\limits^{\rm .} $\end{document} varied as a function of incubation day and temperature, whereas the P_c differed among temperatures but not among incubation days. At a given incubation day, the P_c increased in direct proportion to temperature. Eggs incubated in sand with 13% gravimetric water content achieved greater mass at days 30 and 39 than did those in sand with 3% gravimetric water content. However, \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm V}\limits^{\rm .} $\end{document}, P_c, and masses of yolk‐free hatchlings were similar in the two hydric conditions, indicating that hypoxic tolerance of turtle eggs is not curtailed by excessive water absorption. The similarity in P_c is likely attributable to the small \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm V}\limits^{\rm .} $\end{document}/surface area ratio of turtle eggs. Within the range of parameters studied, temperature, but not water, can modify the P_c of turtle embryos. © 1994 Wiley‐Liss, Inc.

The role of ecdysteroids in crustacean embryo development and the susceptibility of the developing embryo to the antiecdysteroidal properties of an environmental chemical were evaluated. The agricultural fungicide fenarimol was shown to exhibit antiecdysteroidal activity to the crustacean Daphnia magna by lowering endogenous ecdysone levels and delaying molting in a concentration‐dependent fashion that was mitigated by co‐exposure to exogenous 20‐hydroxyecdysone. Exposure of either gravid maternal organisms or isolated embryos to fenarimol resulted in embryo abnormalities ranging from early partial developmental arrest to incomplete development of antennae and shell spines. Developmental abnormalities were associated with suppressed ecdysone levels in the embryos and the abnormalities could be prevented by co‐exposure to 20‐hydroxyecdysone. Developmental abnormalities caused by the antiecdysteroid were associated with reduced fecundity of the parental organisms. These results demonstrate that ecdysteroids are critical to normal crustacean embryo development and environmental antiecdysteroids can disrupt normal embryo development and compromise the production of viable offspring. Antiecdysteroidal activity may provide a means by which environmental chemicals impact crustacean species while not affecting vertebrates. J. Exp. Zool. 292:287–292, 2002. © 2002 Wiley‐Liss, Inc.

The role in food capture of the nematocysts on the filiform and capitate tentacles of Pennaria tiarella is discussed. The feeding response of Pennaria tiarella to Artemia extracts consists of cone bending and mouth opening. A similar feeding response has been demonstrated to be induced by proline at concentration as low as 10⁻⁶M. Pipecolic acid, a proline analog, also elicits a feeding response. Proline causes the head of the capitate tentacles to shrink, thereby causing the cnidocils of the large stenoteles to be prominent.

An analysis of the problem of embryonic differentiation in terms of protein synthesis was carried out in the embryo of Arbacia punctulata. The problem was approached with the technique of ion‐exchange chromatography of the embryonic proteins soluble in 0.5 M sodium chloride. Synthetic activity was measured as the incorporation of radioactive amino acids into protein fractions. It was seen that the complexity of the embryo's protein‐synthetic repertoire increases during early development indicating that differentiation at this level can be detected during early development.

The antibiotic Actinomycin‐D was found to inhibit most of the specific protein syntheses during late development, while inhibiting fewer in early development. This indicates that most of the differential changes in early protein‐synthetic profiles occur under control of the readout of the embryo's stable messenger RNA. However, most differential changes associated with later development seem to be under control exerted at the gene level. Both translation‐level and transcription‐level control mechanisms appear to be active simultaneously at the stages of development analyzed.

The inhibition of DNA‐dependent RNA synthesis, and of further differentiation beyond blastula, was found to be reversible, even after developmental arrest had occurred. The inhibition of protein synthesis was also reversible on removing embryos from the presence of the antibiotic. Since normal development and normal protein‐synthetic profiles are seen following this release of inhibition, it is concluded that there is no stringent requirement for the gene‐directed synthesis of any specific protein during the first 18 hours of development, in order for normal larval development to occur.