PARENTAL INVESTMENT, EMBRYO GROWTH, AND HATCHLING LIPID RESERVES IN SOFTSHELL TURTLES (APALONE MUTICA) FROM ARKANSAS

The smooth softshell Apalone mutica is a North American trionychid turtle typically found in moderate to fast moving rivers and streams. Such habitats contrast with more resource rich environments (e.g., marshes and swamps) inhabited by other turtle species for which parental investment and egg and hatchling components have been studied. We measured components of eggs, embryos, and hatchlings and determined levels of pre-ovulatory parental investment in Apalone mutica from Arkansas. Eggs averaged 7.34 g wet mass and 28.8% non-polar lipids (NPL) by dry mass. Triacylglycerol, an energy storage lipid, was the major lipid class component of eggs, averaging 82% of total egg lipids. Levels of structural (mostly polar) lipid classes were generally similar to those found in eggs of other turtle species, although proportions of phophatidylethanolamine were higher and increased with egg size. Incubation time averaged 55 ± SE 3.4 d. At 18 and 36 d of development, embryo dry mass represented 11% and 34%, respectively, of embryo dry mass at hatching. Thus, approximately two-thirds of the total increase in embryo dry mass occurred during the final one-third (18 d) of development. Hatchlings averaged 6.60 g wet mass and 25.9% NPL by dry mass. The index of parental investment in care (hatchling NPL/egg NPL) averaged 75.4%, the highest such index reported among turtles. High levels of pre-ovulatory, parental investment in trophic care of neonates appear to be a factor important to hatchling survival during early life stages such as dispersal from the nest, movement to aquatic habitats, and the period prior to which hatchlings attain a positive energy balance in relatively low resource environments.