KNUTZEN, Melissa S; JANZEN, Fred Janzen; MULLINS, Michael; Iowa State University; Iowa State University; Iowa State University: Initial investigation into the composition of eggs of the smooth softshell turtle, Apalone mutica

Evolution of the cleidoic (amniotic) egg permitted vertebrates to permanently colonize land, yet distinct variation in egg properties has been observed. Rigid-shelled eggs, in contrast to flexible-shelled eggs, are fairly impervious to water exchange with the environment. Studies involving the flexible-shelled eggs of some species have documented the importance of exogenous moisture for embryonic development and survival. How then do embryos in rigid-shelled eggs develop effectively without access to exogenous moisture? We tested the hypothesis that rigid-shelled eggs of the smooth softshell turtle (Apalone mutica) contain disproportionately more water and show more positive allometric relationships in component mass variation than the flexible-shelled eggs of other turtle species. Eggs of A. mutica were separated into yolk, albumin, and shell and fresh and dry weights were recorded. These measures were then compared to observed measures of egg component variation of other turtle species. Contrary to expectation, A. mutica eggs contained a lower percentage of water (~65%)than published estimates for turtles with flexible-shelled eggs (~69-73%). A. mutica eggs did appear to display a more positive allometric relationship between component mass and fresh egg mass than did eggs of other turtle species. Investigation of A.mutica egg properties continues with testing of lipid content and comparison to recorded results for other turtle species.