Bay scallops, Argopecten irradians (Lamarck), from populations with low rib number (Texas) and high rib number (Virginia) were bred separately and also hybridized. The results suggest that rib number is under genetic control and that the two populations are genetically differentiated. Scallops taken from a population polymorphic for shell color (Massachusetts) were bred in groups, each group containing a single color. The results suggest that color is also under genetic control and is not strongly influenced by the environmen

Adamkewicz, Laura

Castagna, Michael

Karney, Richard

Kraeuter, John

Wall, Robert

English

College of William & Mary: W&M Publish

W&M ScholarWorks VIMS Articles Virginia Institute of Marine Science 1984 Rib number and shell color in hybridized subspecies of the Atlantic bay scallop, Argopecten irradians John Kraeuter Laura Adamkewicz Michael Castagna Robert Wall Richard Karney Follow this and additional works at: https://scholarworks.wm.edu/vimsarticles  Part of the Aquaculture and Fisheries Commons RIB NUMBER AND SHELL COLOR IN HYBRIDIZED SUBSPECIES OF THE ATLANTIC BAY SCALLOP, ARGOPECTEN IRRADIANS 1 John Kraeuter2, Laura Adamkewicz3, Michael Castagna, Robert Wall, and Richard Karney" ABSTRACT Bay scallops, Argopecten irradians (Lamarck), from populations with low rib number (Texas) and high rib number (Virginia) were bred Se'f)arately and also hybridized. The results suggest that rib number is under genetic control and that the two populations are genetically differentiated. Scallops taken from a popula-tion polymorphic for shell color (Massachusetts) were bred in groups, each group containing a single color. The results suggest that color is also under genetic con-trol and is not strongly influenced by the environment. The Bay Scallop, A rgopecten irradians (Lamarck), occurs in disjunct populations from Massachusetts to the Texas gulf coast. Three subspecies are recognized: A rgopecten irra-dians irradians (Lamarck) from Massachusetts to New Jersey, Argopecten irradians concen-tricus (Say) from New Jersey to Louisiana, and Argopecten irradians amplicostatus (Dall) from Galveston to Laguna Madre along the Texas coast (Waller, 1969). Clarke (1965) has sug-gested that the Texas populations should be con-sidered a separate species distinguished by fewer ribs per shell and more inflated valves than other populations. However, the genetic basis, if any, of these shell characteristics is not known. Struhsaker (1968) has found a genetic •Contribution No. 1157 from Virginia Institute of Marine Science, College of William and Mary, Wachapreaque, VA 23480. d El t · 'Crane Aquaculture Center, Baltimore Gas an ec n c Company, P.O. Box 1475, Baltimore, MD ~120~. . >Department of Biology, George Mason Umvers1ty, Fairfax, VA 22030. •Martha's Vineyard Shellfish Group, Box 1552, Oak Bluffs , MA 02557. basis for shell sculpture in the gastropod Lit-torina picta and Staiger (1957) has demon-strated that shell thickness is genetically con-trolled in the gastropod Nucella lapillus (formerly Purpura lapillus). The subspecies A. i. irradians is known to be polymorphic for shell color and pattern. One or both valves can be orange, brown, yellow or white and the color can be distributed as solid, banded or mottled. Shell color has been shown to be controlled by a single gene in the mussel Mytilus edulis (Innes and Haley, 1977) as has the color pattern notata in the clam Mercenaria mercenaria (Chanley, 1961). However, diet is also known to influence shell color and banding in some mollusks (Moore, 1936; Underwood and Creese, 1976). Genetic and environmental influ-ences on shell color have not been investigated in A . irradians. When shell characteristics are used to distin-guish populations of mollus~s'. informat~on on the genetic control of the trait is very desirable. We report the results of several_ exp~rimental crosses made to investigate the mheritance of rib number and shell color in A. irradians. 18 THE NAUTILUS January 30, 1984 Vol. 98 (1) Materials and Methods All the adult scallops were mated and their offspring reared at the Virginia Institute of Marine Science (VIMS) Eastern Shore Labora-tory using methods described by Castagna (1975). For the investigation of rib number, scallops were imported from Laguna Madre, Texas. These were mated among themselves (Texas cross) as were animals from a native Virginia stock (Virginia cross). Individuals from the two stocks were mated to produce an F 1 (hybrid cross). All three matings were made at the same time and all · offspring were the same age when scored for rib number. During the growth period, conditions were kept as uniform as possible. Scallops for the shell-color matings were ob-tained from Sengekontacket Pond on Martha's Vineyard, Massachusetts. The animals were sorted into three groups based on the. colors of their top and bottom valves: orange top-orange bottom (o/o, 18 scallops), brown-white (b/w, 21 scallops), and white-white (w/w, 32 scallops). Each group was mass spawned. When the off-spring were 1.5 to 2.0 cm long, they were scored for top and bottom valve color. Results and Discussion Table 1 shows the distribution of shell colors among the offspring of each color group. As ex-pected in mass crosses of wild-caught individ-uals, no Mendelian ratios occur. However, the distribution of colors was completely different in each of the matings and no single parental phenotype produced the entire range of colors among its offspring. All of the white offspring and none of the orange ones came from the mating of white-shelled parents. One phenotype (both valves brown), that was not present in any of the parents, appeared among the progeny of TABLE 1. Distribution of shell colors in offspring of mass matin~s of single colors. Colors are o = orange, b = brown, w=wh1te, y=yellow. Top valve is listed first, bottom valve second. Offspring Phenotypes Parental Phenotype olo bib b/w w/w y/y TOTAL olo 1671 413 197 0 0 2281 b/w 30 143 760 0 25 958 w/w 0 124 137 949 0 1210 all three crosses and the phenotype "striped yellow", also not present in the parents, ap-peared in the b/w cross. These results are not compatible with any hy-pothesis that the environment, particularly the diet, has a strong influence on shell color. All three crosses were reared in natural sea water from a common source. Furthermore, the off-spring were reared in Virginia where the native population is not polymorphic for these shell colors. The results are compatible with the hy-pothesis that shell color is genetically con-trolled, possibly by only a few genes. Because none of the parental phenotypes produced uni-form progeny none of the three phenotypes tested can represent a single, homozygous genotype. Table 2 presents the data on number of ribs per top valve in the Texas and Virginia crosses and their F 1 hybrid. The Texas and Virginia off-spring were distinctly different with no overlap in number of ribs. The maximum number of ribs for a Texas shell was 18 and the minimum for a Virginia shell was 19. The mean rib number for the Texas scallops was 15.96 and for the Virginia scallops it was 20.39. Clearly the hybrid cross was intermediate both in range of rib num-bers, 17 to 21, and in mean rib number, 18.90. However, the hybrid mean of 18.90 differed TABLE 2. Distribution of rib number on the top valves of A. irradians from experimental crosses. Number of Ribs 14 15 16 17 18 19 20 21 22 23 24 TOTAL ANIMALS MEAN VARIANCE STD. ERROR OF MEAN Texas 8 25 34 29 4 100 15.96 1.029 0.101 CROSS Hybrid 7 28 37 24 4 100 18.90 0.960 0.098 Virginia 25 36 23 9 5 2 100 20.39 1.473 0.121 Vol. 98 (1) January 30, 1984 THE NAUTILUS 19 significantly from the mid-parent value of 18.18 and was closer to the Virginia mean than to the Texas mean. A one-way analysis of variance showed a highly significant difference in rib number among the three crosses (F ratio = 440 with d.f. 2 and 297, error mean square = 1.15, p<0.0001). These results are exactly what one expects for a polygenic trait when two geneti-cally distinct strains, or in this case subspecies, are crossed (Falconer, 1981). An examination of size differences among the three crosses also supports the hypothesis that differences in rib number are genetically deter-mined. Figure 1 shows the mean and range of shell length (lip to hinge) for each of the rib numbers in each of the crosses. The three crosses were significantly different in shell length with the Texas scallops smallest and the hybrids exactly intermediate (mid-parent = 32.3). A one-way analysis of variance of shell length among crosses gave an F ratio of 40 with 2 and 169 degrees of freedom, p < 0.001. However, when each cross was examined separ-ately, there was no tendency for size to increase with increasing rib number. The regression coefficient of size on rib number was not significantly different from zero in any of the three crosses. One cannot conclude that the Texas progeny have low rib numbers merely because they are small. Interpretation of the size differences them-selves is less clear. The intermediate perfor-24 0::: 22 w co ~ 20 ::> Z 18 c2 16 14 1---+--< ......... .......... t----+---1 ...... f---+-i J-----+-t -t----+--i f---+-i ........... .............. ~ 10 30 50 10 30 50 10 30 50 VIRGINIA HYBRID TEXAS x•38.6 x=32.3 x=26.0 SHELL LENGTH (mm) FIG. 1. The range of shell lengths and the mean for each rib number class in Argopecten irradians. The Virginia, Hybrid and Texas scallops are the same as those described in Table 2. mance of the hybrid cross does suggest that the differences among the crosses is genetic and ad-ditive. However, the stocks may have differed in genes for temperature adaptation rather than in genes for growth rate. The Texas parents were native to an area of higher water temperature than that in which their offspring were raised. Rearing offspring at a temperature other than that to which their parents were adapted has been shown to affect growth rate in clams (Menzel, 1962). Conclusions From this study, shell color appears to be under genetic control, to be insensitive to the environment and, therefore, to be a valid char-acter for distinguishing between individuals and between populations. Rib number also appears to be genetically controlled and a good character for distinguishing individuals and populations. The data on rib number and shell length show that rib number is a valid characteristic for distinguishing two shells regardless of their ab-solute sizes. The data also suggest that popula-tions of different geographical origin are genetically differentiated for rib number. The Texas scallops maintained their characteristical-ly lower number of ribs despite being bred and reared in Virginia. Acknowledgements The authors wish to thank Ronald C. Circe for collecting and shipping the Texas scallops VIMS. We also thank Allan Sherald and Stephan Taub for their critical review of this manuscript. LITERATURE CITED Castagna, M. 1975. Culture of the bay scallop, Argopecten irradians, in Virginia. Mar. Fish. Rev. 37:19-24. Chanley, P . E. 1961. Inheritance of shell markings and growth in the hard clam, Venus mercenaria. Proc. Natl. Shellfish Assoc. 50:163-169 . Clarke, A. H., Jr. 1965: The scallop superspecies Aequi-pecten irradians (Lamarck). Malacologia 2:161-188. Falconer, D. S. 1981. Introduction to Quantitative Genetics, second edition. Longman, Inc., New York. Innes, D. J. and L. E. Haley. 1977. Inheritance of a shell-color polymorphism in the mussel. J. Hered. 68:203-204. Menzel, R. W. 1962. Seasonal growth of northern and south-ern quahogs, Mercenaria mercenaria and M. campechien-sis, and their hybrids in Florida. Proc. Natl. Shellfish Assoc. 53:111-119. 20 THE NAUTILUS January 30, 1984 Vol. 98 (1) Moore, H. B. 1936. The biology of Purpura lapillus. I. Shell variation in relation to environment. J. Mar. Biol. Ass. U.K. 21:61-89. Staiger, H. 1957. Genetical and morphological variation in Purpura lapillus with respect to local and regional dif-ferentiation of population groups. Coll. Intern. Biol. Mar. St. Roscoff. Annee Biol. 33:251-258. Struhsaker, J. W. 1968. Selection mechanisms associated with intraspecific shell variation in Littorina picta (Proso-branchia: Mesogastropoda). Evol. 22:459-580. Underwood, A. J. and R. G. Creese. 1976. Observations on the biology of the trochid gastropod A ustrocochela con-stricta (Lamarck) (Prosobranchia). II. The effect of avail-able food on shell-banding pattern. J. Exp. Mar. Biol. Ecol. 23:229-240. Waller, T. R. 1969. The evolution of the Argopecten gibbus stock (Mollusca: Bivalvia), with emphasis on the Tertiary and Quaternary species of Eastern North America. Paleont. Soc., Mem. 3 (J. Paleont. 43(5 supp.JJl-125. 

Rib number and shell color in hybridized subspecies of the Atlantic bay scallop, Argopecten irradians

https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=3188&context=vimsarticles

Rib number and shell color in hybridized subspecies of the Atlantic bay scallop, Argopecten irradians

Abstract

Similar works

Full text

Available Versions

College of William & Mary: W&M Publish