Date of Graduation

Summer 2014


Master of Science in Biology



Committee Chair

Brian Greene


Nerodia sipedon, gestation temperature, phenotype, performance, viviparity

Subject Categories



Temperature during embryonic development can strongly influence the developmental trajectory of reptiles. In snakes, offspring morphology, locomotor speed, anti-predator behavior, and growth are known to be affected by developmental temperature and are likely to have important fitness consequences. I explored the influence of gestation temperature on offspring phenotypes produced by gravid Northern Watersnakes (Nerodia sipedon) maintained at constant temperatures of 23, 26, and 29°;C. Swimming speed, defensive strikes, and flight response were tested at 1 and 26 weeks of age, and growth was measured until 30 weeks of age. The number of ventral scale rows was higher in snakes from the 26°;C group than from the 29°;C group. Thermal influences were persistent over time across temperature treatments. Snakes from the 23°;C treatment swam slower at both testing ages, exhibited lower defensive behavior scores at 1 week of age, and exhibited lower embryonic survival than snakes from the other treatments. Growth in body length, head length, and head width for snakes from 23°;C was higher than for other treatments, but was possibly influenced by feeding regime. The results of my study are consistent with embryonic thermal sensitivity in other reptile taxa in suggesting that thermoregulatory precision by gravid female N. sipedon affects fecundity and measures of performance that likely influence offspring survival.


© Zachary Charles Wrensch

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