Meeting Abstract

P1-104   -   Heart position is associated with regional boundaries of vertebral shape in snakes Hampton, PM*; Meik, JM; Colorado Mesa University; Tarleton State University pahampton@coloradomesa.edu

Relative heart position varies greatly among snakes yet the developmental and selection forces driving this variation have not been thoroughly investigated. In this study, we evaluated the correlation in vertebral morphology and heart position of over 45 species representing 10 families of snake. Using geometric morphometrics on the cranial aspect of the vertebrae, we identified two transitions in pre-cloacal vertebral shape using segmented regression. The positions of the apex of the heart was determined using scale counts. A positive correlation was observed between the first transition in vertebral shape and the apex of the heart among all sampled taxa. A similar relationship was observed when the families were analyzed separately, however the y-intercepts varied among families. These results first indicate that the position of the heart is associated with the first major transition point in vertebral regions. However, the proximity of the heart to the transition appears to vary among snake families, suggesting that the heart can experience minor shifts along the anteroposterior axis independent of the vertebral column. We conclude that heart position in snakes is the result of both homeotic shifts in the heart and evolutionary changes in the proportion of vertebral numbers in the different regions of the pre-cloacal vertebral column.