Glucosephosphate isomerase genotype frequencies,homozygous excess and size relationships in the sand flounder Rhombosolea plebeia

Genetic variation was studied at two polymorphic loci for 3 yr (November 1978–February 1982) in juvenile sand flounder (Rhombosolea plebeia) in Wellington Harbour, New Zealand. The Gpi-1 locus showed a heterogeneity in genotype frequencies, but this was not clearly related to season or to fish length. At the Gpi-2 locus, genotype frequencies were dependent upon length and showed a significant excess of homozygotes in juveniles but not in adults. This latter phenomenon has been reported previously in several species of marine molluscs, and so may be common to marine organisms producing large numbers of pelagic larvae. Reasons for the excess of homozygotes are discussed, and it is suggested that assortative mating is the most likely explanation and that this is an area of marine population genetic research which has been over-looked.     

Combined effects of temperature and salinity on embryos and larvae of the northern bay scallop Argopecten irradians irradians

The combined effects of temperature and salinity on embryonic development and on larval survival and growth to setting size of the northerm bay scallop Argopecten irradians irradians (Lamarck) were studied in the laboratory. A 6x6 complete factorial design was used; temperatures ranged from 10° to 35°C, at 5C° intervals, and salinities ranged from 10 to 35S, at 5S intervals. Response-surface contour diagrams were generated to provide estimates of conditions for optimal responses. Normal development of embryos occurred over a very narrow range of temperature and salinity. Survival of larvae occurred over a wider range of temperature and salinity than did embryonic development or growth of larvae. Satisfactory growth (>70% of the maximum observed value) occurred only at high temperature-high salinity conditions; optimal conditions for survival occurred at similar salinities, but at slightly lower temperatures. Temperatures of 35°C or greater and/or salinities of 10S or less were lethal for all life stages studied. Both salinity and temperature exerted significant effects on development and survival, but temperature was clearly the dominant factor influencing growth. It is suggested that northern bay scallop embryos and larvae be reared at their respective optimal temperature-salinity levels so as to increase efficiency of aquaculture operations.This paper is adapted from a thesis submitted to the College of Fisheries, University of Washington, in partial fulfillment of the requirements for the MS degree. This study was conducted at the NMFS Laboratory in Milford, Connecticut, USA     

A genetic basis for geographic variation in shell morphology in the bay scallop, Argopecten irradians

The bay scallop, Argopecten irradians, exhibits extensive variation in morphology among geographically separated populations, resulting in the recognition of three major subspecies (A. i. irradians, A. i. concentricus, A. i. amplicostatus). The extent to which morphological variation results from differing environmental conditions is unknown. In the present study, bay scallops from Massachusetts, North Carolina, Florida, and Texas were collected, spawned and the offspring reared in a common garden experiment to determine if scallops cultured under similar environmental conditions exhibited the morphology expected given the geographic origin of their parents. Significant differences among populations were indicated by ANOVA in both the wild-caught (13/14 morphological characters) and cultured (11/14 characters) scallops. Principal components analysis clustered wild-caught scallops according to geographic origin and cultured scallops according to geographic ancestry. The morphological characters most influential in resolving groups were plical width, plical spacing, number of plicae and valve convexity. Geographic variation in morphology apparently has a strong genetic basis, and reflects significant differentiation among disjunct populations of bay scallops. Received: 12 September 1996 / Accepted: 15 October 1996     

Comparative survival of bay scallops in eelgrass and the introduced alga, Codium fragile, in a New York estuary

Eelgrass, Zostera marina, is generally regarded as the preferred habitat of bay scallops, but in some cases scallop populations have persisted or increased in areas lacking eelgrass. This suggests that some other substrate(s) may serve important ecological functions for bay scallops. One candidate is Codium fragile, a macroalgal species with which bay scallops are known to associate and in which we commonly find juvenile and adult bay scallops in eastern Long Island, New York. In this study, we examined whether survival of planted bay scallops differed in Codium, eelgrass, and Codium + eelgrass substrates at two sites during August and October of 2 years. Survival of tethered scallops and recoveries of live free-planted individuals varied with scallop size, planting season and year, but no differences were observed between the three substrates for a given scallop size and planting date. Crab (particularly Dyspanopeus sayi) and whelk predation were implicated as important causes of tethered scallop mortalities while emigration and removal by predators likely contributed to scallop losses. Densities of naturally recruited 0+ years scallops recovered by visual and suction dredge sampling were similar in the eelgrass and Codium substrates. While our results suggest that Codium may offer some degree of predation refuge for bay scallops, further work needs to weigh the potential disadvantages of this substrate (such as low DO levels, potential attachment and transport of scallops, and differences in current flow, food availability and sedimentation relative to eelgrass) to determine if Codium may serve as a valuable habitat for bay scallops throughout their lifespan.     

Cadmium accumulation and toxicity in the kidney of the bay scallop Argopecten irradians

Specimes of bay scallops, Argopecten irradians, collected from shallow-water eel-grass beds near Beaufort, North Carolina (USA) in September 1979, were exposed to 0.7 ppm cadmium in flowing seawater for 5 d. This exposure resulted in a massive extrusion of the calcified concretions of most of the kidney epithelial cells, although marked morphological damage consisting of cytoplasmc degeneration was apparent in only a few focal areas of the kidney. In addition, unique cytoplasmic membrane-bound bodies were observed in epithelial cells of cadmium-treated but not control scallop kidneys. In some cells, these bodies appeared to fuse with the main concretion vacuole. Kidneys of cadmium-treated scallops accumulated cadmium to 200 ppm on a wet wt basis; of this 60% was associated with concretions (2 000 ppm dry wt) and 38% with the membranous pellet obtained after ultracentrifugation at 105 000 g for 1 h. Approximately 2% of total kidney cadmium was associated with the cytosolic fractions but, unlike zinc or manganese, which were bound to either high or low molecular weight species, a large component of the cadmium in this fraction was bound to a protein peak of approximately 21 000 daltons. Results of this study indicate that kidney concretions of A. irradians play a major role in the control of renal cadmium accumulation and excretion and hence the toxicity of cadmium to this organism.     

Genetic subdivision within the eastern Australian population of the sea anemoneActinia tenebrosa

An electrophoretic survey of allozyme variation revealed substantial genetic differentiation within the eastern Australian population ofActinia tenebrosa. This differentiation appears to reflect the effects of both asexual reproduction and limited gene flow among local populations separated by up to 1050 km. Variation was assessed within groups of 27 to 55 adults sampled between September 1985 and December 1988 collected from small areas of shore within each of 24 local populations. All individuals were collected from stable rock platforms, with the exception of Boulder Bay, where some sea anemones were removed from small mobile boulders. High levels of variability were detected for each of seven enzyme-encoding loci. The patterns of genotypic variation detected imply that local populations are maintained by predominantly asexually generated recruitment. Levels of multi-locus genotypic diversity within samples were consistently less than 50% of the level expected for sexual reproduction with free recombination. This was reflected by the detection of relatively low numbers of multi-locus genotypes and significant departures from expectations for single-locus Hardy-Weinberg equilibria within 17 of the 24 local populations. Standardised genetic variances (F _ST ), calculated from the genotypes of all individual adults were typically much greater than those expected for marine organisms with widely dispersed larvae. The former values were reduced, but were still extremely large when clonal genotype frequencies were substituted into the calculation. These data imply that although widely dispersed larvae may be an important source of initial colonists, levels of gene flow among established local populations are low. Furthermore, cluster analysis revealed a clear subdivision of the population into northern and southern groups. However, this subdivision was largely explained by strong clinal variation at a GPI-encoding locus. For this locus, allele frequencies ranged from fixation of the A allele in samples from the 12 most northern sites to near fixation of the alternative B allele in southern samples. Subdivision of the eastern Australian population is consistent with the predicted off-shore movement of the Eastern Australian Current close to the border between Victoria and New South Wales. However, the split into northern and southern regions, as evidenced by the variation forGpi, could reflect patterns of gene flow and/or other factors such as natural selection or the recent patterns of colonisation.Contribution No. 78 from the Ecology and Genetics Group of the University of Wollongong     

Effects of an Odh null allele and a GPI low-activity allozyme on shell length in laboratory-reared Mytilus edulis

Mytilus edulis L. heterozygotes with a null allele at the octopine dehydrogenase (Odh) locus or an allele coding for low activity at the glucose phosphate isomerase (Gpi) locus were found to grow significantly faster (p(0.05) than other juvenile mussels in the same laboratory cultures. Odh null homozygotes were not significantly different in growth from mussels with active Odh alleles. No additive effects were seen in individuals which had both the Odh null allele and the allele coding for low GPI activity. These results do not support the contention that null alleles are a significant cause of the observed correlation between multiple-locus heterozygosity and fitness in mussels. The apparent deficiencies of heterozygotes against Hardy-Weinberg expectations observed at the Odh locus in two Netherlands M. edulis populations can be more than accounted for by the null-allele frequency calculated, assuming Hardy-Weinberg equilibrium, from the observed frequency of null homozygotes in these populations.     

A genetic analysis of the pea crabs (Decapoda: Pinnotheridae) of New Zealand

Seven populations of the pea crabPinnotheres atrinicola Page were sampled from around the North Island of New Zealand from February to October 1987, and individuals were scored at 23 presumptive enzymatic loci. For a brachyuran crab,P. atrinicola revealed high levels of polymorphism and heterozygosity. Of the loci scored, phosphoglucose isomerase (Gpi) and phosphoglucomutase (Pgm) were distinguished by high variability ( =0.602 and 0.526, respectively). A clinal variation in electromorph frequency was evident at several loci, and atGpi in particular. Statistical analyses revealed that, despite relatively small genetic distance separation, a high degree of structuring was present between the geographic populations. The degree of population subdivision observed in this study is atypical of brachyuran crabs. It is suggested that the genetic differentiation observed between pea crab populations is maintained by life-history attributes and current movements which restrict gene flow between populations and, to some extent, by random genetic drift.Publication No. 41 from the Evolutionary Genetics Laboratory, University of Auckland     

Size-dependent, spatial and temporal genetic variation at a leucine aminopeptidase (LAP) locus among blue mussel (Mytilus galloprovincialis) populations along a salinity gradient

Biochemical genetic variation at a leucine aminopeptidase (LAP) locus is related to salinity variation in several marine bivalve molluscs. This paper details an investigation of the Long Island Sound model of LAP selection (LAP genotype-dependent mortality occurring among newly settled Mytilus edulis mussels) carried out in 1997 among three M. galloprovincialis mussel populations along the salinity gradient of Wellington Harbour, New Zealand. Significant LAP genotypic heterogeneity was observed at the LAP locus between small (<25 mm shell length) and large (>25 mm shell length) M. galloprovincialis from Petone and Eastbourne (the two sites experiencing the greatest salinity variation), whereas genotypic heterogeneity was not significantly different between small and large mussels from Seatoun (the site experiencing the least salinity variation). The Lap ³ allele decreased in frequency and the Lap ⁴ allele increased in frequency at Petone and Eastbourne, whereas the Lap ³ and Lap ⁴ allele frequencies remained effectively constant at Seatoun. Both these findings are consistent with the Long Island Sound model of selection. At all three locations, the Lap ^3,3 genotype decreased in frequency from small to large mussels, whereas the Lap ^3,4 genotype increased in frequency from small to large mussels. All other LAP genotypes occurred at low frequencies (<0.10) at all three locations and showed no evidence of frequency change from small to large-size mussels nor evidence of clinal change among the three locations. These genotype frequency data possibly indicate that the Lap ^3,3 genotype is at a selective disadvantage compared to the Lap ^3,4 genotype at all three locations, and that this selective disadvantage is related to the extent of salinity variation which exists at each location. Further investigation is required before it can be determined if the Long Island Sound model of selection best describes the size-dependent and location-specific changes in LAP allele and genotype frequencies along this salinity gradient. Comparison of the population genetic structure at the LAP locus in 1995 and in 1997 revealed a profound change from heterozygote excesses to heterozygote deficiencies for all three M. galloprovincialis populations. The reason for the change is unknown, but the change indicates that population genetic structure at the LAP locus is highly variable in time, but consistent in space, among these M.␣galloprovincialis populations. Received: 5 February 1998 / Accepted: 27 May 1998     

Substrate catabolism related to reproduction in the bay scallop Argopecten irradians concentricus,as determined by O/N and RQ physiological indexes

Weight specific rates of oxygen consumption carbon dioxide production, and ammonia-N excretion, measured for a Florida population of the bay scallop Argopecten irradians concentricus between May and September, 1982 and October and November, 1983 were significantly correlated (P<0.0005) to environmental factors that co-varied seasonally with metabolic shifts related to reproduction. Mean O/N and CO₂/O₂ (RQ) molar ratios indicates that scallop energy metabolism varied over the course of the reproductive cycle. Resting stage individuals (May-early June) had RQ values close to 0.7, indicative of a predominantly lipid-based metabolism. During the initial stages of gametogenesis (late June-early July) scallops catabolized primarily carbohydrate, as evidenced by maximum O/N (>22) values and RQ values close to 1.0 RQ values >1.0 indicated a possible carbohydrate to lipid conversion during the period of cytoplasmic growth (late July-early September). As gametes matured and spawning commenced (late September-November), metabolism became primarily protein based, as indicated by O/N and RQ values around 9.0 and 0.8, respectively. This pattern of substrate catabolism supports existing data on the storage and utilization of specific energy reserves with respect to reproduction in this species.     

Mode of larval development and genetic population structure inNodilittorina africana knysnaensis (Prosobranchia: Littorinidae)

We examined electrophoretic variation in the supralittoral gastropod,Nodilittorina africana knysnaensis, along the coast of South Africa in 1989. There was little allozyme variation in nine samples collected over 1 500 km for three highly polymorphic loci,Est, Gpi, andPgm, and Wahlund's effect was absent in the pooled sample. A gene diversity analysis showed that 98.1% of total genic diversity, on average, was contained within populations, and that only 1.9% was due to allozyme frequency differences among populations. Since the mode of larval development has not yet been described for this species, we suggest that the lack of strong allozyme frequency differences over long distances indicates thatN. a. knysnaensis has a planktonic mode of larval development.     

Muscle esterase variation and size variation in the sand launce Ammodytes dubius

Esterase variation detected in homogenates of muscle tissue taken from the sand launce Ammodytes dubius in April, 1970 and 1971 is described. Eight alleles were found segregating at a single locus, and the frequencies of these alleles were homogenous in population samples taken on the Emerald Bank, off Nova Scotia, Canada, in successive years. When ordered by their electrophoretic mobility, the profile of the frequencies of these alleles was unimodal and symmetric. In both of the population samples, there were significant excesses of homozygotes and deficencies of heterozygotes. There was an association between genotype and size of individuals among homozygous genotypes; individual homozygous for the most common, intermediately-migrating allele were larger than homozygotes bearing alleles with relatively fast or slow mobilities.     

Temporal stability of gene frequencies within genetically heterogeneous populations of the queen scallop Aequipecten (Chlamys) opercularis

The widely held assumption that gene frequencies within samples of multi-aged organisms are temporally stable has rarely been tested. In order to test this assumption in the commercially exploited bivalve scallop Aequipecten (Chlamys) opercularis (L.), 12 populations were sampled from around the UK over the period 1988–1990 and each was assayed at four putative polymorphic enzyme loci. Most populations were comprised of 3 to 4 year-classes, distinguishable by annual rings laid down on the shell. Three alleles from each locus were used as discriminant-function variables. Discriminant-function analysis based on allele frequencies averaged for each inividual year-class (45 demes) revealed highly significant inter-site heterogeneity. A posteriori classification of individual year-classes based on the discriminant analysis resulted in assignment of year-classes to the correct home site in 80% of cases. If allozyme neutrality is assumed, the phenomenon of predominant local allele frequency-stability through time within populations which are genetically heterogeneous from one site to another raises the possibility that queen scallop populations may be self-recruiting. Despite a planktonic larval phase lasting up to several weeks, this possibility is not excluded by the available hydrographic data.     

Occurrence and detrimental effects of the bivalve-inhabiting hydroid <Emphasis Type="Italic">Eutima japonica</Emphasis> on juveniles of the Japanese scallop <Emphasis Type="Italic">Mizuhopecten yessoensis </Emphasis>in Funka Bay,Japan: relationship to juvenile massive mortality in 2003

In November 2003, we first observed prevalent occurrence of a hydroid, Eutima japonica, on soft body tissues of age zero Japanese scallop (Mizuhopecten yessoensis) juveniles cultured in large areas of Funka Bay, Hokkaido. The occurrence coincided with massive death of juvenile scallops. A major objective was to clarify ecological relationships between the symbionts, and to infer the relationship between symbiosis and the massive mortality. To do this, we investigated distributions of association rates of hydroids with juvenile scallops at 15–34 sites over 3 years (2003–2005), with age one adult scallops at 24 sites in 2003, and with mussels at 13 sites in 2004. We studied seasonal changes in association rates with juvenile scallops, and numbers of polyps per juvenile scallop at three sites from November 2003 to June 2004. We also quantified the hydroid impacts on juvenile scallop shell length growth and triglyceride accumulation in the digestive gland. The association rate of E. japonica polyps with juvenile scallops was high in large areas of Funka Bay in 2003, and overlapped the distribution of mussels bearing polyps. Association rates with age one adult scallops were very low in November 2003, even at the sites where polyps were very common on juvenile scallops. Levels of hydroid occurrence in juvenile scallops varies by year. We found that hydroids presence in juvenile scallops declined drastically in 2004 and 2005. The association rates with juvenile scallops, and numbers of polyps per juvenile scallop declined during winter, until they disappeared completely in the following June. Since polyps were rare in adult scallops, we believe that infection of juvenile scallops was probably initiated from the planulae produced by medusae released from polyps growing on Mytilus spp., especially M. galloprovincialis. Subsequently, the inhabitation spread intraspecifically and interspecifically. In juvenile scallops, inhabitation of polyps reduced shell length growth by 43%, and triglyceride accumulation in digestive glands by 24–47%. Inhabitation of E. japonica on juvenile scallop is best regarded as parasitism, rather than inquilinism or commensalism. Occurrence of polyps was probably not a direct lethal factor for juvenile scallops, because there were some sites where association rates were high, but mortalities were low. Massive mortalities in 2003 may have resulted from simultaneous impacts of heavy polyp load and stresses caused by the way in which the animals were handled (transferred from cages for pre-intermediate culture to cages for intermediate culture), because the massive mortality occurred within a month of the transfer. The presence of polyps in juvenile scallops does not affect the quality of the product in Funka Bay, because market size scallops are hydroid-free.     

Inheritance of a nuclear DNA polymorphism assayed in single bivalve larvae

We examined the inheritance of theMytilus edulis CaM-1 Intron 3 locus, a non-coding DNA locus with two potentially neutral length-variants. The polymerase chain reaction (PCR) was used to determine theCaM-1 genotype for 799 larvae obtained from 11 laboratory crosses. Larvae were typed singly only 8 to 24 h after fertilization. We find evidence that each allele can be inherited from either sex, that there are no barriers to fertilization between gametes of different genotypes, and that most larvae have genotypes compatible with Mendelian inheritance of the locus. Deviations from expected genotype frequencies were found in some crosses; we suggest that a contributing factor is aneuploidy in early larvae, but a major cause is more likely to be selection at a locus linked toCaM-1, occurring under the artificial laboratory culture conditions. This study demonstrates the feasibility of applying molecular genetic techniques to early larval stages of marine bivalves, and presents a new non-destructive biopsy method for DNA analysis from living adult mussels.     

Sexual selection on alleles that determine body size in the swordtail Xiphophorus nigrensis

Summary In a natural population, we document changes in the frequencies of alleles influencing body size and size-correlated alternative male reproductive tactics, and we examine the possible role of sexual selection in producing these changes. Male swordtails (Xiphophorus nigrensis, Rio Choy) exhibit three body size classes (small, intermediate, and large) that primarily derive from allelic variation (s, I, L) at the Y-linked pituitary (P) locus. Some XX individuals are male. They are small and can be fathered either by XX or XY males. We compared the frequencies of Y-linked P alleles across two generations in a natural population. There was a significant decrease in the Y-s genotype relative to Y-I and Y-L genotypes. Laboratory experiments suggest that the disadvantage of Y-s resulted, at least in part, from female preference for larger courting males relative to small chasing males. All larger courting males are of the Y-I or Y-L genotypes. Although the frequency of Y-linked P alleles changed across generations, there was no change in the distribution of male body size classes. The stability of the phenotypic distribution across generations, despite changes in P allele frequencies, was maintained by the production of small XX sons by Y-I and Y-L males. Offprint requests to: M.J. Ryan     

Observations on shell deformities,ultrastructure, and increment formation in the bay scallop Argopecten irradians

Shell morphology and ultrastructure were examined in the bay scallop Argopecten irradians, cultured in recirculating seawater systems under various conditions of feeding, lighting, and handling. On a unialgal diet of Thalassiosira pseudonana, scallop growth ranged from 120 to 183 m d^-1 at 20°C in the laboratory, about two-thirds of the growth rate found in the field. However, shell deposited in the laboratory differed from that in the field in several ways. In the field, scallops formed costae as an unpigmented, corrugated marginal shell layer; shell deposited in the laboratory lacked this layer and was therefore darker. Also, microstructure of the exterior shell surface of field scallops was coarsely granular, while that of cultured scallops was relatively smooth. Excessive handling of scallops in the laboratory resulted in marginal thickening of valves, a deformity which was completely arrested by a change from daily to weekly handling. Scallops cultured in the same tank with oysters developed shell-thickening on the interior of the valves. It is postulated that shell abnormalities in bivalves result from disruption of complex behavioral processes associated with shell deposition and may be elicited by a variety of natural and experimental irritants. Under natural lighting regimes and optimal conditions for growth, scallops deposited exactly one shell increment per day, but under continuous lighting, deposition of growth increments often became aphasic. In one 28-d experiment, there was a strong correlation between number of growth increments formed and increase in shell height, suggesting that shell ridge formation occurred intermittently, rather than daily, when shell growth rates fell below approximately 150 m d^-1.     

Comparisons in demographic rates of bay scallops in eelgrass and the introduced alga, Codium fragile, in New York

Bay scallops, Argopecten irradians, supported vibrant fisheries which subsequently collapsed, as such, they are a focus species for many restoration efforts along the Atlantic and Gulf coasts of the United States. The scallops’ preferred habitat, seagrass, has also dramatically declined, and some scallop populations have increased post-restoration despite reduced seagrass cover. This has led to the hypothesis that macroalgae may serve as suitable alternative habitats for bay scallops. This study is the first to compare demographic rates, such as long-term survival, growth, condition and reproductive potential of scallops between the native eelgrass, Zostera marina, and the introduced alga, Codium fragile. Although long-term survival was not different between habitats, results suggest site-specific and inter-annual variation in the impacts of Codium on scallop growth. While demographic rates did not differ in Shinnecock Bay, in Sag Harbor, growth and/or condition were significantly different between both vegetated habitats depending on the year. However, recruit density, size and condition did not vary significantly, adding to the complexity of this relationship. Despite potential site-specific and inter-annual differences, this study supports the hypothesis that habitats other than eelgrass can benefit bay scallops.     

Allozyme variation in populations of the dog-whelkNucella lapillus (Prosobranchia: Muricacea) from the South West peninsula of England

Four populations of the predatory gastropodNucella lapillus were sampled at sites around the South West Peninsula of England in 1986, and analysed for allozyme variation at 18 enzyme loci. Two of these loci, Gpd-1 andHk-1, exhibited sex-specific phenotypes. An absolute locus association was observed between two other loci,Mdh-1 andEst-3. This association was only found at one site (Prawle), and it is suggested that the presence of chromosomal polymorphisms could explain this finding. As a measure of overall similarity, Nei's genetic identity statistic,I, was calculated; the mean for all populations was 0.989, with values ranging from 0.981 to 0.997. Although similar on this gross level, considerable interpopulation variation was evident. Observed mean heterozygosity (per locus) ranged from 0.043 to 0.104 (mean 0.074). Populations differed also in the loci at which significant heterozygote deficits were seen (of the seven deficits recorded only those at thePep-1 locus were consistent across sites) and in the presence of rare alleles undetected elsewhere. The variation observed showed no correlation to shell morphology or geographical distance and confirmed the conclusion that species of the genusNucella show considerable disjunct variation.     

Quantitative genetic analysis of growth in larval scallops (Placopecten magellanicus)

We estimated the broad-sense heritability of larval size in 20 full-sib families of the giant scallop, Placopecten magellanicus (Gmelin, 1791) grown in laboratory culture in August and September 1991. The goal was to compare scallops with other bivalves which have been shown to have significant heritabilities for larval growth. Secondly, we estimated the lipid content of occytes from female parents, since this is hypothesized to affect larval growth and survival. Finally, we estimated the among-family variation in mortality from 4 to 21 d as a test of possible genetic variation for viability among larval scallops. Significant genetic variation (h²=1.10 to 1.24) was estimated for larval shell length at 4, 14, and 21 d. There was a significant correlation (r=0.66) between larval size at 4 d and lipid content of oocytes, but only when two females with high levels of lipid oocyte^–1 were excluded as outliers. There was no correlation between larval size at 14 and 21 d and lipid content of oocytes. Mortality among families from 4 to 21 d was high (69 to 97%), and was significantly different among families. These results indicate that there is significant heritability for larval growth which is largely independent of the lipid content of the oocytes. A high heritability for larval growth may indicate that this trait is only weakly correlated with fitness.