Incubation

About: Incubation is a research topic. Over the lifetime, 5748 publications have been published within this topic receiving 126541 citations.

Temperature-dependent sex ratio in a bird

Abstract: To our knowledge, there is, so far, no evidence that incubation temperature can affect sex ratios in birds, although this is common in reptiles. Here, we show that incubation temperature does affect sex ratios in megapodes, which are exceptional among birds because they use environmental heat sources for incubation. In the Australian brush-turkey Alectura lathami, a mound-building megapode, more males hatch at low incubation temperatures and more females hatch at high temperatures, whereas the proportion is 1:1 at the average temperature found in natural mounds. Chicks from lower temperatures weigh less, which probably affects offspring survival, but are not smaller. Megapodes possess heteromorphic sex chromosomes like other birds, which eliminates temperature-dependent sex determination, as described for reptiles, as the mechanism behind the skewed sex ratios at high and low temperatures. Instead, our data suggest a sex-biased temperature-sensitive embryo mortality because mortality was greater at the lower and higher temperatures, and minimal at the middle temperature where the sex ratio was 1:1.

Ovarian Progesterone Levels During in vitro Oocyte Maturation and Ovulation in Xenopus laevis

Abstract: Endogenous progesterone was measured in ovaries of the frog Xenopus laevis following the administration of gonadotropins that induce meiotic maturation and ovulation of large oocytes. Ovarian pieces were incubated for 0, 1, 3, 5, or 10 h in Gurdon’s solution in the presence or absence of human chorionic gonadotropin (HCG; 20 lU/mI) or a frog pituitary homogenate (FPH; 0.04 pituitary/mI). Each incubation sample was scored for ovulation and maturation at the end of its incubation period, homogenized in the medium, and extracted for progesterone with petroleum ether. Following purification on Sephadex LH-20, extracts were assayed for progesterone by a radioimmunoassay that was validated for use with frog ovarian tissue. In 13 experiments, mean (! SEM) progesterone concentration in untreated ovarian tissue was 3.7 ± 0.5 ng/gm at time zero and progesterone levels did not change significantly during 10 h of incubation. HCG-treated tissue (n = 6) exhibited a linear, two-fold increase in progesterone for the first 3 h of incubation and maintained that level for the remainder of the incubation. FPH treatment (n = 10) produced a linear six-fold increase in progesterone over the course of 10 h. Mean progesterone content across time was significantly greater (P<0.005) in FPH-treated tissue than in HCG-treated tissue. Both differed significantly (P<0.05) from untreated controls. In tissue treated with HCG the percent oocyte maturation was correlated (P<0.10) with both mean progesterone concentration across time and progesterone concentration at 10 h of incubation; ovulation did not occur. In FPH-treated tissue progesterone concentration was not correlated with percent maturation but was correlated (P<0.05) with the number of ovulations/gm. Treatment of ovarian pieces with the gonadotropins following a 10 h incubation in Gurdon’s solution produced effects similar to those following treatment at time zero. In vivo treatment with HCG prior to in vitro incubation of ovarian tissue with HCG or FPH resulted in an eight- or eleven-fold increase, respectively, in peak progesterone concentration as compared to tissue that was not pretreated in vivo. In two experiments large, preovulatory follicles contained sufficiently more (P<0.05) progesterone following FPH treatment than did smaller follicles. Both large and small FPH-treated follicles had significantly higher levels of progesterone than untreated control tissue.

Cardiovascular development in embryos of the American alligator Alligator mississippiensis: effects of chronic and acute hypoxia

Abstract: Chronic hypoxic incubation is a common tool used to address the plasticity of morphological and physiological characteristics during vertebrate development. In this study chronic hypoxic incubation of embryonic American alligators resulted in both morphological (mass) and physiological changes. During normoxic incubation embryonic mass, liver mass and heart mass increased throughout the period of study, while yolk mass fell. Chronic hypoxia (10%O2) resulted in a reduced embryonic mass at 80% and 90% of incubation. This reduction in embryonic mass was accompanied by a relative enlargement of the heart at 80% and 90% of incubation, while relative embryonic liver mass was similar to the normoxic group. Normoxic incubated alligators maintained a constant heart rate during the period of study, while mean arterial pressure rose continuously. Both levels of hypoxic incubation (15% and 10%O2) resulted in a lower mean arterial pressure at 90% of incubation, while heart rate was lower in the 10%O2 group only. Acute (5 min) exposure to 10%O2 in the normoxic group resulted in a biphasic response, with a normotensive bradycardia occurring during the period of exposure and a hypertensive tachycardic response occurring during recovery. The embryos incubated under hypoxia also showed a blunted response to acute hypoxic stress. In conclusion, the main responses elicited by chronic hypoxic incubation, namely, cardiac enlargement, blunted hypoxic response and systemic vasodilation, may provide chronically hypoxic embryos with a new physiological repertoire for responding to hypoxia.