Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

William B. Stickle


Environmental and genetic effects on salinity adaptation in the southern oyster drill were estimated by their salinity-related genotypic (i.e. determined by electrophoresis) and phenotypic (i.e. determined by salinity tolerance and microcalorimetry) variations. The systematics of Stramonita haemastoma were studied using allozyme, radular and shell characteristics to exclude taxonomic differences which might have obscured variations in salinity adaptation. Radular and shell features are not reliable as systematic characteristics. S. h. canaliculata and S. h. floridana are separable using allozyme characteristics. Nei's genetic distance (D = 0.28) and the fixed allelic differences in Fum, LeuAla, Mdh, and 6-Pgdh indicate that the differences between S. h. canaliculata and S. h. floridana are on the species level and S. h. canaliculata should be named S. canaliculata. 28-day high-salinity LC-50 is lower in four populations of Stramonita canaliculata (44.4 to 51.5 $\perthous$ S) than in the population of S. haemastoma floridana (54.8 $\perthous$S S). In low salinity, S. canaliculata (3.5 to 7.1 $\perthous$ S) is more tolerant than S. h. floridana (7.3 $\perthous$ S). S. canaliculata from medium to high salinity areas exhibit a higher high-salinity LC-50 and shorter adaptation period than populations from low to medium salinity. Low-salinity LC-50 exhibit the opposite trend. Little allelic variation of loci has been found among populations in either species. Heat flux of Stramonita canaliculata was depressed less with a shorter recovery period in snails transferred from normoxic 10 to 30 $\perthous$ S than snails transferred from 30 to 10 $\perthous$ S. Snails transferred to hyperosmotic conditions expended more energy than snails transferred to hyoosmotic conditions under anoxia. Penotypic variations among individuals exist as indicated by the heat flux variability in these experiments. Salinity adaptation in the southern oyster drills is primarily due to environmental effects as observed in the phenotypic variations in salinity tolerance and heat flux with little genetic variation among populations. Their protein-oriented metabolism and avoidance behavior to rapid salinity changes may explain the insignificant genotype specific adaptation to salinity.