The effects of variation in egg water loss on the chick embryo and its fluid compartments

The rates of water loss of domestic chicken eggs were varied during incubation to measure the osmoregulatory ability of the avian embryo. Egg water loss was increased by drilling holes in the eggshell over the airspace on day 13 (I = 21 days) and then placing these eggs in a low relative humidity (r.h; 0-10%) incubator until hatch. Egg water loss was decreased by placing other eggs in a high r.h. (85%) incubator on day 0. Eggs that lost 25% of initial fresh mass (IFM) produced embryos with smaller wet masses than control eggs that lost 12.5% of IFM. However, water-stressed embryos did not differ from control embryos in dry body mass indicating the water-stressed embryos were dehydrated. Hatching success was 20.5% and 85% for high and control water loss eggs respectively. These results show that increased water loss during the last week of incubation produces embryos that weigh less because they have a lower water content, not because they grow more slowly. Eggs that lost 6% of IFM produced embryos and yolks that were not different in wet or dry mass compared to control eggs that lost 11% of IFM. However, 1-4 gm of excess albumen were left in these eggs on day 21. Hatching success was 71% and 89% for low and control eggs respectively. Low egg water loss did not disturb embryonic growth;Allantoic fluid volume declined faster with high and slower with low rates of water loss. Millimolar allantoic Na[superscript]+ and Cl[superscript]- ion levels declined at faster rates with high water loss after day 12. Thus, excess water is lost as a result of increased movement of water out of allantoic fluid. High egg water loss (\u3e20% of IFM) caused elevated Cl[superscript]- ion levels after day 17 in plasma and amniotic fluid which indicated a period of osmotic stress after depletion of allantoic fluid between day 18 and hatch. The decrease in wet embryo mass measured in embryos from high water loss eggs was due to dehydration of skin which may serve as an emergency water reservoir during osmotic stress. Dehydrated chicks from high water loss eggs regained the water deficit 7 days after hatch and grew at a rate similar to controls through 6 weeks of age. These results show that the regulation of allantoic fluid volume and ion content and the action of the chorioallantoic membrane surrounding it are the integral components of the osmoregulatory system of the chick embryo

Neonatal growth of Steller sea lion (Eumetopias jubatus) pups in Alaska

The growth rate of Steller sea lion (Eumetopias jubatus) pups was studied in southeast Alaska, the Gulf of Alaska, and the Aleutian Islands during the first six weeks after birth. The Steller sea lion population is currently stable in southeast Alaska but is declining in the Aleutian Islands and parts of the Gulf of Alaska. Male pups (22.6 kg [±2.21 SD]) were significantly heavier than female pups (19.6 kg [±1.80 SD]) at 1−5 days of age, but there were no significant differences among rookeries. Male and female pups grew (in mass, standard length, and axillary girth) at the same rate. Body mass and standard length increased at a faster rate for pups in the Aleutian Islands and the western Gulf of Alaska (0.45−0.48 kg/day and 0.47−0.53 cm/day, respectively) than in southeast Alaska (0.23 kg/day and 0.20 cm/day). Additionally, axillary girth increased at a faster rate for pups in the Aleutian Islands (0.59 cm/ day) than for pups in southeast Alaska v(0.25 cm/day). Our results indicate a greater maternal investment in male pups during gestation, but not during early lactation. Although differences in pup growth rate occurred among rookeries, there was no evidence that female sea lions and their pups were nutritionally stressed in the area of population declin