Two Chinese scientists Wei Guo Du AND Xiang Ji from Hangzhou Key Laboratory for Animal Sciences and Technology & Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences respectively conducted a series of experiments with Orthriophis taeniurus eggs in the laboratory to examine the effects of incubation temperature on hatching success, embryonic use of energy and hatchling morphology. This report gives an overview of this paper, noting some of the more interesting conclusions that were drawn from their experiments.
Within the temperature parameters known for incubating reptile eggs, cooler incubation temperatures slow embryogenesis and usually have little lethal effects on the embryo, whereas high temperatures result in faster development of the embryo but often increase the occurrence of abnormalities or mortality. The two scientists incubated eggs from 13 Orthriophis taeniurus females collected from a southern population (Guangxi, China). The temperatures they choose were 22, 24, 27, 30 and 32°C to try and determine an optimal temperature and what effect these temperatures had on the developing embryo and subsequent hatchling. The gravid Beauty Snakes were maintained at a temperature of 30C in the lab and fed on eggs of Coturnix coturnix with fresh water being made available ad lib. All the females laid their eggs between 23rd & 3rd July with clutches consisting of between 7 & 11 eggs. From each clutch one egg was dissected to determine the composition of the eggs. The remaining eggs were incubated at the five constant temperatures mentioned above. Each egg was incubated individually in covered plastic jars containing known amounts of vermiculite and distilled water at approx -12 kPa water potential (Vermiculite : Water = 1:2) Each egg was buried one third lengthwise in the substrate, with the surface near the embryo exposed to air inside the jar. The jars were divided between the 5 incubators and rotated daily within them to mimimize any effects of thermal pockets. The jars were weighed every other day and more distilled water was added to the substrate when necessary to compensate for any evaporation loss.
Eggs incubated at 22C typically took 101 days to hatch and a 50% hatch rate was recorded the sex of the resulting hatchlings was 2.4
At 24C the eggs took 86 days to hatch with a 78% hatch rate and a near even split of the sexes was recorded 12.13
The eggs incubated at 27C had a 79% hatching success rate and 13.6 hatchlings emerged after 66 days.
At 30C the eggs hatched after 53 days with a 79% hatchling rate and a sex ratio of 11.12
In the final incubator which was set at 32C only 41% of the eggs hatched after 50 days, producing 2.5 babies.
A brief summary of their findings:
A prolonged exposure of eggs of O. taeniurus to temperatures less than 24°C or higher than 30°C may have a detrimental effect on the developing embryo, as indicated by the fact that hatching success decreases dramatically at temperatures outside this temperature range. The mean incubation length at 30°C is 53.9 days, approximately 3.4 days longer than that at 32°C, so the ecological disadvantage of the increased incubation length (and thus, decreased growth period prior to the onset of the first winter) due to a decrease in incubation temperature from 32°C to 30°C is less pronounced.
Temperature of 32°C is outside the range of optimal temperatures for incubating eggs of O. taeniurus because of the less developed hatchlings that are produced.
Eggs incubated at 24°C exhibit high hatching success and produce well developed hatchlings, however this brings the hatching time to late September - mid October, so the growth prior to the onset of winter for these hatchlings is only about 4-6 weeks.
All hatchlings incubated at 32C were significantly smaller than those that were incubated at the four other temperatures.
The hatchlings incubated at 22C contained lower quantities of energy and non-polar lipids than did those at the other four temperatures. Conversion efficiency of energy during incubation at 22C was lower than those at 32, 30, 27 & 24C.
The tail length of hatchlings incubated at 22 & 32 was shorter than those at other temperatures presumably giving the males a disadvantage during the breeding season.
Incubating eggs at low temperatures or high temperatures may increase energy expenditure for embryonic development due to the increased incubation length and/or embryonic metabolism. Consequently, eggs incubated at moderate temperatures usually produce larger and heavier hatchlings than did those at low or high temperatures.
More yolks remaining unutilized at hatching when eggs are incubated at high temperatures has been reported for nearly all reptiles studied to-date, where it is known that hatchlings exhibit a substantial increase in size (SVL) during the first post-hatching days due to the transfer of resources in the residual yolk into carcass.
Taking the energy expenditure during incubation, the rate of embryonic development and hatchling phenotypes into account, the two scientists consider that temperatures around 27°C are optimal for incubating eggs of O. taeniurus.
The Effects of Incubation Temperature On Hatching Success, Embryonic Use of Energy and Hatchling Morphology in the Stripe-tailed Ratsnake Elaphe taeniura by Wei Guo Du AND Xiang Ji. Asiatic Herpetological Research, Vol. 11 / 2008 pp.24-30
Republished from October 2008 Ratsnakes Digest