The Affects of Altitude and Temperature on Snake Development

     This article, High temperatures limit developmental resilience to high-elevation hypoxia in the snake Natrix maura (Squamata: Colubridae) by Jérémie Souchet et al. set out to analyze the results of high altitude (low oxygen, hypoxia) and temperature on snake development. It was published in the Biological Journal of the Linnean Society. This is very relevant in our modern climate as temperatures are rising. As a result, certain species are migrating to higher elevations where the temperatures are cooler, however the oxygen content is lower. This change in temperate and oxygen content could have serious impacts on development and fitness for every spices, not just snakes. 

    202 eggs were collected from 17 gravid female viperine snakes. 102 of the eggs were taken to the Observatory Midi-Pyrénées of the Pic du Midi de Bigorre which is located 2877 meters above sea level to test the effects of high-elevation hypoxia. 100 of the eggs remained at the Station d’Ecologie Théorique et Expérimentale du Centre National de la Recherche Scientifique which is located at 436 meter above sea level which is low elevation with normal oxygen levels.

     At both locations, high elevation (EHE) and low elevation (LE), half the eggs were exposed to normal temperatures (C) of 24 C and half were exposed to high temperatures (H) of 32 C during embryonic development. Heart rate and mass were measured until hatching. Egg mass for both groups in high heat decreased from day one all the way to hatching, with the extreme high elevation high heat group decreasing the most. Both of the cool temperature groups gained mass until the 35 day mark where they then decreased a little. Heart rates for both hot groups spiked to over 100 beats per minute, with the low elevation going about 12 bpm greater. The heart rate for the cool group was very stable at around 55-60 bpm until hatching. This experiment shows that embryonic development is more effected by temperature than altitude. 

    After hatching, individuals were measured for snout-ventral length, and total body length. They were also weighted and sex determined. Hatchling success was also determined. All the juveniles were then placed a 20 C which has been a proven temperature for viperine survivorship success. Hatching success was between 90-94% in LEC, LEH, and EHEC, but the EHEH group had a rate of 74%. Elevation and temperature did not affect the sex rate. The cool temperature groups had incubation periods of about 30 days longer than the hot groups. The cold groups also retained about 30% more egg yolk than the hot groups. At 1 day post hatching, the EHEH group was 13% lighter than the other three treatment groups which were all about the same mass. Both cool groups were about 5% longer than the LEH group, which was about 5% longer than the EHEH group. 

    The final experiment was testing swimming speed in the different groups. The snakes were placed in a 5 cm deep swimming track that was 100 x 20 x 20 cm. The water was 25 C and the snakes were acclimated to the water for 30 minutes prior to recording times. The results were measured at 9 days post hatching and 25 days post hatching. Individuals from each group had swimming data recorded at both low and high altitudes at the 25 day mark. At the 9 day mark, individuals from the hot groups were faster than the cool groups, and the EHEH group was the fastest. The real take away is that individuals from the EHEH were the fastest overall when swimming in low elevation. It is predicted that the high temperature and low oxygen could have lowered the optimal temperature performance range. These results are also quite insightful because it's expected that the longer snakes will have the quicker swimming speed, but the smaller snakes from the hot groups were faster overall. 

    This article does a great job of showing the impacts that temperature and elevation have on snakes. These results can be used to estimate the effects on other reptiles. This research is very relevant currently as the affects of climate change are being felt world wide, and species are having to adapt their ecological roles in order to survive. We can clearly see that temperature plays a crucial role in embryonic development, hatching success, and the overall fitness of juveniles. Those changes paired with changes in oxygen content can have critical impacts on individuals. Research in this field needs to be continued to better understand the effects of climate change, and hopefully we can find ways to protect species that are being impacted the most. 

Article link: https://doi.org/10.1093/biolinnean/blaa182