Meeting Abstract

115.6  Tuesday, Jan. 7 11:30  Differential growth rates of body segments explain ontogenetic shifts in heart position ANDERSON, GE*; SECOR, SM; University of Alabama; University of Alabama ganderson@crimson.ua.edu

Relative heart position in snakes has been hypothesized to be adaptively correlated with habitat and shown to be conserved phylogenetically. For snakes, relative heart position also shifts ontogenetically, becoming relatively closer to the head with size. We asked whether the shift in heart position occurs independently of body segment or is fixed to body segment and segments develop differentially with age. To explore this question we used the diamondback water snake (Nerodia rhombifer), a medium sized colubrid snake that experiences a noted shift in heart position with length (from 23% to 17% of snout-vent length). From the dissections of over 100 snakes (18.5 – 107cm SVL), we found that the heart was closely aligned with the 26th to 29th vertebrae with no trend between vertebrate number and body size. From the prepared skeletons of over 100 snakes (18.5 – 118cm SVL) we measured the length, width, height, and mass of eight vertebra positioned at equal intervals of the snake’s body. We found that the vertebra in the middle region of snakes grew 75.5% faster than vertebra of the anterior body. We conclude that heart position is largely fixed to body segment and that the ontogenetic shift in heart position is due to the differential growth of body segments. Body segments grow relatively larger in the middle portion of the body compared to near the head, resulting in a seemingly anterior movement of the heart with increased snake length.