Martinez MCDiMichele L2010-02-152010-02-151992 199http://hdl.handle.net/1969.3/23047-Laguna Madre (LM), Texas, has unique populations of oysters, Crassostrea virginica , that are genetically distinct from all other Atlantic populations. The LM is also a unique environment, characterized by extreme hypersalinities and high summer temperatures. The authors examined growth of LM oysters relative to Galveston Bay (GB) oysters to determine if this genetic differentiation is correlated with oyster physiology. Oysters were acclimated to a common environment and mass spawned to produce two pure populations and the reciprocal crosses. The paternal GB crosses grown in 40 ppt died at the larval stage. Spat from surviving groups were grown in LM and GB. At both locations, LL sub(40ppt), and LL sub(20ppt), spat grew significantly faster than GG sub(20ppt) spat. Growth of all reciprocal crosses were intermediate and showed significant parental effects. LL sub(20ppt) growth was similar in both locations. GG sub(20ppt) spat in LM grew faster than siblings in GB, but significantly slower than any LL cross. LM populations may have genetically adapted to their environment, or drift isolation may be responsible for the observed differentiation. Results are consistent with the isolation hypothesis but indicate that some physiological differentiation may have occurred as wellASW,USA,TexasASW,USA,Texas,Galveston BayASW,USA,Texas,Laguna MadreCrassostreaCrassostrea virginicafishGalveston Baygrowthgrowth rateOyster cultureOysterspopulation geneticsPopulationsQ1 01265 Genetics and evolutionQ1 01443 Population geneticsQ1 01583 Shellfish cultureQ3 01583 Shellfish cultureselective breedingsubpopulationsSurvivalTemperatureTexasUSACONF