Upper lethal temperatures of Northern Bobwhite embryos and the thermal properties of their eggs

Abstract

Northern Bobwhite eggs in the southern United States are often exposed to ambient temperatures in excess of their normal incubation temperature when unattended during their typical extended preincubation period. In drought years, typified by high ambient temperatures, Bobwhite eggs are often exposed to temperatures > 45°C, well-above the upper lethal temperature of most other birds. Because the upper lethal temperature of Bobwhite embryos is not currently known, simulated clutches of eggs were exposed to preincubation temperatures ranging from 39 to 52°C for exposure times of 1, 3, or 6 h. The upper lethal temperatures and the temperatures resulting in ≥ 50% death of Northern Bobwhite embryos were recorded in addition to the time to thermal equilibrium of Bobwhite eggs. The upper lethal temperature for 1, 3, and 6 h of preincubation exposure was 51, 49, and 46°C, respectively. The temperatures resulting in ≥ 50% death were 46, 44, and 40°C for eggs exposed to elevated temperatures for 1, 3, and 6 h, respectively. The mean time for the inner-egg temperature to reach the ambient temperature was 38 ± 1 min (± SE). The thermal tolerances of Northern Bobwhite embryos were much higher than expected, and among the highest reported for birds, indicating an adaptation to the naturally occurring temperature extremes that often occur in the Bobwhite's semi-arid southern range. However, as the temperature increased above the incubation temperature, hatching success declined, showing that increased thermal tolerance has a cost. Although Bobwhite producers, managers, and researchers will find this information useful, it seems most interesting that high temperatures could plausibly have contributed to the population decline observed in the Bobwhite's semi-arid range.

A Draft De Novo Genome Assembly for the Northern Bobwhite (Colinus virginianus) Reveals Evidence for a Rapid Decline in Effective Population Size Beginning in the Late Pleistocene

“…This range-wide decline in bobwhite abundance across most of the U.S. is still ongoing today [22]–[23]. The precise reasons for recent population declines in the U.S. appear to be a complex issue, and have been attributed to factors such as variation in annual rainfall [2], [12]–[13], thermal tolerances of developing embryos within a period of global warming [24]–[25], shifts in land use and scale coupled with the decline of suitable habitat [2]–[3], [14], [20]–[21], red imported fire ants ( Solenopsis invicta ) [26]–[27], sensitivity to ecotoxins [28]–[29], and harvest intensity by humans [30]–[32], particularly during drought conditions [3], [13]. Population declines have prompted intense recent efforts to translocate bobwhites to fragmented parts of their historic range where modern abundance is low.…”

Plasticity in incubation behavior and shading by king rails Rallus elegans in response to temperature

“…Avian clutches are expected to respond to temperature extremes differently based on the structure and composition of the eggs and the nest, as well as parental care strategies (McClintock et al , Coe et al ). Maximum temperature tolerance is likely to vary among species, with egg size, and with the duration of exposure (Webb , Reyna and Burggren ). At one extreme of the tolerance spectrum, embryo mortality in cold‐adapted Adelie penguins Pygoscelis adeliae can occur between 38 and 39°C (Webb ), whereas at the other, northern bobwhite Colinus virginianus embryos can survive temperatures up to 50°C for up to one hour (Reyna and Burggren ).…”

Cardio-respiratory development in bird embryos: new insights from a venerable animal model

“…Bird embryos chronically incubated under hypothermia (35.5 ºC) not unexpectedly show significant retardation of embryonic development (Tazawa, 1973;Boehm et al, 1987;Lourens et al, 2007;Reyna and Burggren, 2012). Additionally, acute hypothermia increases the P O2 and pH and decreases the P CO2 of both arterialized blood and mixed venous blood and creates cardiac hypotrophy in chicken embryos (Boehm et al, 1987;Tazawa, 1973;Tazawa and Mochizuki, 1978).…”

“…Additionally, acute hypothermia increases the P O2 and pH and decreases the P CO2 of both arterialized blood and mixed venous blood and creates cardiac hypotrophy in chicken embryos (Boehm et al, 1987;Tazawa, 1973;Tazawa and Mochizuki, 1978). On the other hand, hyperthermia during incubation decreases hatching success in the chicken and the bobwhite quail (Colinus virginianus) (Stoleson and Beissinger, 1999;Reyna, 2010;Reyna and Burggren, 2012) and alters hemodynamics beyond the expected rate function increases with elevated temperature (Lee and Lee, 2010). Prenatal incubation temperature affects many aspects of post-natal performance.…”

“…Interestingly, temperature disruption also had disproportionately larger effects on soft tissues compared to long bones and skull in zebra finch (Olson et al, 2008). Even pre-incubation storage temperatures at the early blastocyst stage of bird embryos can affect viability (Reyna and Burggren, 2012;Branum et al, 2016). While many species are continuously incubated by a parent (e.g., chicken), other species may leave the eggs exposed to the environment either upon first laying or later during incubation while parents are off foraging (e.g., ratites, quail, etc.).…”