Critical developmental windows for morphology and hematology revealed by intermittent and continuous hypoxic incubation in embryos of quail (Coturnix coturnix)

Abstract

Hypoxia during embryonic growth in embryos is frequently a powerful determinant of development, but at least in avian embryos the effects appear to show considerable intra- and inter-specific variation. We hypothesized that some of this variation may arise from different protocols that may or may not result in exposure during the embryo’s critical window for hypoxic effects. To test this hypothesis, quail embryos (Coturnix coturnix) in the intact egg were exposed to hypoxia (~15% O2) during “early” (Day 0 through Day 5, abbreviated as D0-D5), “middle” (D6-D10) or “late” (D11-D15) incubation or for their entire 16–18 day incubation (“continuous hypoxia”) to determine critical windows for viability and growth. Viability, body mass, beak and toe length, heart mass, and hematology (hematocrit and hemoglobin concentration) were measured on D5, D10, D15 and at hatching typically between D16 and D18 Viability rate was ~50–70% immediately following the exposure period in the early, middle and late hypoxic groups, but viability improved in the early and late groups once normoxia was restored. Middle hypoxia groups showed continuing low viability, suggesting a critical period from D6-D10 for embryo viability. The continuous hypoxia group experienced viability reaching <10% after D15. Hypoxia, especially during late and continuous hypoxia, also inhibited growth of body, beak and toe when measured at D15. Full recovery to normal body mass upon hatching occurred in all other groups except for continuous hypoxia. Contrary to previous avian studies, heart mass, hematocrit and hemoglobin concentration were not altered by any hypoxic incubation pattern. Although hypoxia can inhibit embryo viability and organ growth during most incubation periods, the greatest effects result from continuous or middle incubation hypoxic exposure. Hypoxic inhibition of growth can subsequently be “repaired” by catch-up growth if a final period of normoxic development is available. Collectively, these data indicate a critical developmental window for hypoxia susceptibility during the mid-embryonic period of development.

Phenotypic Switching Resulting From Developmental Plasticity: Fixed or Reversible?

“…In contrast, the same hypoxic exposures cause little change in the red blood cell properties, including blood P 50 , of larvae, whereas these variables remain high plastic in the adults (Pinder and Burggren, 1983). In the quail (Coturnix coturnix) and the chicken (Gallus domesticus), hypoxia experienced during different periods of embryonic incubation induces phenotypic switching of some morphological, physiological and hematological characters, but not others (Dzialowski et al, 2002;Chan and Burggren, 2005;Burggren and Elmonoufy, 2017). Certainly, more experiments designed to reveal specific patterns of phenotypic switching are warranted.…”

Survival, Growth, and Development in the Early Stages of the Tropical Gar Atractosteus tropicus: Developmental Critical Windows and the Influence of Temperature, Salinity, and Oxygen Availability

“…Most studies investigating critical windows have targeted morphological and physiological characteristics, maturation, metabolism, etc. across the different animal taxa [12,13,[15][16][17].…”

Responses of developmental and physiological traits to manipulated incubation conditions in broiler embryos at hypoxic high altitude

“…resistance to high temperature during the early embryonic stage when eggs from sea level were incubated in hypoxia caused by 1720 m altitude. On the other hand, Bahadoran et al (2010) indicated that hypoxia due to HA during early embryogenesis may change the endocrine functions of the embryo, enhance embryo growth, or shorten the hatching process of chickens. However, early H treatment at hypoxic HA resulted in an increased egg water loss at day 11 of incubation.…”

“…Oxygen (O 2 ) provides continuity for metabolic functions and biochemical processes in embryonic cells as demanded by the development and growth of embryos (Simon and Keith, 2008). Barometric pressure lowers when altitude increases, while the partial O 2 pressure progressively falls, causing hypoxia, which represents a reduction and insufficiency of the O 2 level in cells and tissues with failure to fulfil their normal function (Carreau et al, 2011). The reduced O 2 availability at high altitude (HA) stimulates a higher respiration rate as the number of O 2 molecules per breath is reduced.…”

“…Organ systems at different embryonic development periods have different "critical windows" (Burggren and Elmonoufy, 2017). Hypoxia occurring in early embryonic developmental stages may have different effects (Decuypere and Bruggeman, 2007) than at later stages of embryonic development.…”