teeth and a rugose area in each valve; interior smooth, white, often violet 

 color at anterior and posterior margins; pallial sinus small, angular; inner 

 margins crenulate. (Abstracter's note: this description sounds more like 

 M. meroenaria, and the adult illustrated in plate 14, fig. 89 apDears to have 

 the smooth area in the middle of the outer surface of the valve, characteristic 

 of the northern quahogj - J.L.M. 



1460 



Pesch, Gerald. 1972. 



Isozymes of lactate dehydrogenase in the hard clam, Meroenaria meroenaria. 

 Comp. Biochem. Physiol. 43B(1): 33-38. 



M. meroenaria samples were obtained from 4 localities from Prince Edward 

 Island, Canada, to Wadmalaw Island, S.C. For comparison, M. campechiensis 

 from Beaufort, N.C. and Tampa Bay, Fla., were examined. Lactate 

 dehydrogenase occurred as isozymic patterns of 1 or 2 bands , with no 

 phenotypic differences between sexes. The simplest genetic mechanism to 

 explain the observed phenotypes is single-locus autosomal inheritance. Up 

 to 7 different alleles may be found at this locus. Each band was equated 

 with an allele. Homozygotes had one band, heterozygotes had 2. All Canadian 

 clams were of a common phenotype composed of 2 bands. Presence of this 

 double band in the entire population was explained either by duplication of 

 the locus controlling structure of the enzyme, or by complete selection for 

 heterozygotes. The other populations had a variety of single- and double- 

 banded phenotypes showing that gene duplication had not occurred in these 

 populations. The number of different lactate dehydrogenase bands showed a 

 gradual increase from 2 in the Canadian population of M. meroenaria to 7 in 

 the Fla. population of M. campechiensis. Observed and expected phenotypic 

 frequencies fitted poorly. More double-banded patterns were observed than 

 expected in 5 of the 6 populations, and in the other, from N.C, observed 

 numbers were significantly less than expected. M. meroenaria closes its 

 valves at temps below 4°C and is relatively inactive. The Canadian 

 population undoubtedly experiences long periods of anaerobiosis in winter. 

 The single phenotype with 2 bands probably represents an adaptive "optimum" 

 for the rigorous northern environment, in which isozymes necessary for 

 aerobic and anaerobic metabolism are necessary for survival. Florida and 

 N.C. clams respire year-round. Continuous growth attests to their 

 continuous respiration. Under such conditions various phenotypes, including 

 homozygotes, survive well. Homozygotes are favored in the N.C. population, 

 which came from the deepest water sampled (15 m) , which probably has the 

 narrowest range of temp fluctuation. Where shifts from aerobic to long 

 periods of anaerobic metabolism are not necessary, it probably is more 

 efficient metabolically to have only one form of lactate dehydrogenase. 

 Logically, selection favoring homozygotes should lead to predominance of a 

 single allele best suited to that environment. Although homozygotes were 

 most frequent in the N.C. population, they were not exclusive. It is 

 suggested that genetic variability is maintained in that area by transport 

 of larvae of varied genetic background into the Beaufort area. - J.L.M. 



1461 



Pesch, Gerald George. 1972. 



Protein polymorphisms and population genetics of the hard clam, Meroenaria 

 meroenaria (L.). Ph.D. Thesis, Univ. Rhode Island, 59 p. 



Four populations of M. meroenaria were sampled, from the Bideford River, 

 P.E.I. , Canada, Boothbay Harbor, Maine, Narragansett Bay, R.I., and Wadmalaw 

 Island, S.C. Samples of M. campechiensis from Beaufort, N.C. and Tampa Bay, 

 Fla. were obtained for comparison. Electropherograms of tissue proteins were 

 assayed with medium specific for lactate dehydrogenase, NAD-malate 

 dehydrogenase, and 2 enzymes of unknown substrate, tetrazolium oxidase and 

 an esterase. From phenotypic differences in these enzymes it was inferred 

 that genetic differences existed at the loci controlling their primary 

 structure. Three of the 4 enzymes were polymorphic, with an average of 

 3.5 alleles per locus for 4 loci in M. campechiensis and 2.6 alleles per 



408 



