Kosteletzkya virginica, a halophytic species with potential for agroecotechnology in Jiangsu Province, China

Kosteletzkya virginica (L.) Presl. is a perennial dicot halophytic species, that grows in brackish portions of coastal tidal marshes of the mid-Atlantic and southeastern United States. New saline mudflats have been increasing every year in Northern Jiangsu, China. In 1993, we introduced K. virginica (L.) into China from the Halophyte Biotechnology Center (University of Delaware, USA) as a potential species to improve the soil and develop ecologically sound saline agriculture. Our nearly 10 years of experimental research, both in a test garden and in the field, indicated that K. virginica adapts excellently to the heavy saline soils of Jiangsu Province, China. The average seed yield of K. virginica in 2001 at Yancheng was 638 kg/ha from 1-year old seedlings. There were significant variations among individuals from the unselected population of K. virginica on growth, quality, and seed yield traits. There is great potential to increase the seed yield if superior clones are selected. The seed yield of 35 selected individuals was six times greater than that of the average. Four growth traits of K. virginica were found to have a significant correlation with seed yield. However, there was no strong positive or negative correlation among seed quality traits. The mean seed weight and the germination ratio of the 35 selected individuals of K. virginica were 16.36±0.32 g and 76.11±1.82%, respectively. The percentage content of oil and crude protein in the seeds was 11.28±0.67 and 8.17±0.19%, respectively. The percentage of seed vigor of the selected individuals was 99%, as determined by soft X-ray radiography.     

Extraction,Antioxidant Activity and Identification of Flavonoids from Root Tubers of <i>Kosteletzkya virginica</i>

Kosteletzkya virginica (K. virginica) is used for revegetation of salt-affected coastal tidal flats and as a raw material of biodiesel. K. virginica root tuber, a biowaste with low economic value, is rich in bioactive compounds. This study aimed to extract and identify flavonoids from K. virginica root tubers. The optimal extraction conditions were 1/25 (w/v) solid/liquid ratio, 40% ethanol concentration at 40°C for 60 min. Under these conditions, 65.2 ± 3.7 mg/g total flavonoid content was extracted from the roots, which were collected from salinized soil in late autumn of the third year. Antioxidant activity was evaluated through 1,1-diphenyl-2-picrylhydrazyl, hydroxyl radical, and superoxide anion scavenging assays. The extracted flavonoids exhibited antioxidant activity in a dose-dependent manner. Five flavonoids, glucoliquiritin apioside, licoisoflavone B, 5-methoxy-7,8-diprenyl- flavone, 7,2′-dihydroxy-6,8-dimethyl-4′,5′-methylenedioxyflavan, and 5,7,4′-trihydroxy-3′-methoxy-6,8-di-Cmethylflavanone, were identified by ultra-performance liquid chromatography–tandem mass spectrometry. Our results suggest that the flavonoids of K. virginica root tubers might be potent antioxidants and can be effectively applied as an ingredient in food and natural medicine.     

Spread of Exotic Cordgrasses and Hybrids (Spartina sp.) in the Tidal Marshes of San Francisco Bay, California, USA

Four species of exotic cordgrass (Spartina sp.) occur in the San Francisco estuary in addition to the California native Spartina foliosa. Our goal was to map the location and extent of all non-native Spartina in the estuary. Hybrids of S. alterniflora and S. foliosa are by far the most numerous exotic and are spreading rapidly. Radiating from sites of deliberate introduction, S. alterniflora and hybrids now cover ca. 190 ha, mainly in the South and Central Bay. Estimates of rate of aerial increase range from a constant value to an accelerating rate of increase. This could be due to the proliferation of hybrid clones capable of rapid expansion and having superior seed set and siring abilities. The total coverage of 195 ha by hybrids and other exotic cordgrass species is slightly less than 1% of the Bay's tidal mudflats and marshes. Spartina anglica has not spread beyond its original 1970s introduction site. Spartina densiflora has spread to cover over 5 ha at 3 sites in the Central Bay. Spartina patens has expanded from 2 plants in 1970 to 42 plants at one site in Suisun Bay. Spartina seed floats on the tide, giving it the potential to export this invasion throughout the San Francisco estuary, and to estuaries outside of the Golden Gate. We found isolated plants of S. alterniflora and S. densiflora in outer coast estuaries north of the Bay suggesting the likelihood for the San Francisco Bay populations to found others on the Pacific coast.     

<Emphasis Type="Italic">Kosteletzkya virginica</Emphasis> displays mixed mating in response to the pollinator environment despite strong inbreeding depression

Mixed mating systems often evolve despite strong inbreeding depression, but there have been few experimental tests of this observation. Kosteletzkya virginica, a perennial dicot halophytic species of the Family Malvaceae, is native to brackish portions of coastal tidal marsh in the United States of America and was introduced into China in 1993. Pollination of K. virginica occurs through insect vectors and by delayed self-pollination via stylar movement. In the same two naturalized populations of K. virginica during 2005–2007, we measured (i) inbreeding depression across a range of life-cycle stages, (ii) pollination failure rate, and (iii) selfing rate estimated by AFLP markers. Results indicate that inbreeding depression values for the two naturalized populations during 2005–2007 ranged from 0.620 ± 0.036 to 0.656 ± 0.032, and mean inbreeding depression was 0.640 ± 0.006. Pollinator failure rates at the two naturalized K. virginica populations during 2005–2007 ranged from 0.091 ± 0.039 to 0.174 ± 0.061, and selfing rate ranged from 0.247 ± 0.018 to 0.468 ± 0.031. Population selfing rates are significantly and positively correlated with field estimates of pollinator failure (P = 0.008 < 0.01, R ² = 0.857). Our data provide an empirical demonstration of a mixed mating system response to the pollinator environment in the presence of strong inbreeding depression.     

Occurrence of symbiotic turbellarians in the oyster,Crassostrea virginica

Crassostrea virginica was collected from several locations where it is cultured, both along the Northumberland Strait of New Brunswick and Malpeque Bay on the coast of Prince Edward Island. The oysters were found with two turbellarians on their gills. Urastoma cyprinae (Graff) was found in the oysters mostly during the warmer months of the year in numbers averaging as high as 50 worms per host (N = 50) and with as much as 78% of the host population infected (N = 100). Paravortex gemellipara (Linton) was also found during warmer months, but much less frequently or abundantly.Both male and female oysters were found to have U. cyprinae. No eggs or recent young of U. cyprinae were found in hosts; female-mature individuals of P. gemellipara with young were found from June through August.     

Degradation and corrosive activities of fungi in a diesel–mild steel–aqueous system

The fungi Aspergillus fumigatus, Hormoconis resinae and Candida silvicola were isolated from the fuel/water interfacial biomass in diesel storage tanks in Brazil. Their corrosive activities on mild steel ASTM A 283-93-C, used in storage tanks for urban diesel, were evaluated after various times of incubation at 30 °C in a modified Bushnell–Haas mineral medium (without chlorides) with diesel oil as sole source of carbon. Their ability to degrade diesel oil was evaluated after growth for 30 and 60 days. The fungus Aspergillus fumigatus and the consortium of all three organisms showed the highest production of biomass; A. fumigatus gave the greatest value for steel weight loss and produced the greatest reduction in pH of the aqueous phase. Solid phase microextraction (SPME) showed that the main acid present in the aqueous phase after 60 days incubation with A. fumigatus was propionic acid. Polarization curves indicated that microbial activity influenced the anodic process, probably by the production of corrosive metabolites, and that this was particularly important in the case of A. fumigatus. This fungus preferentially degraded aliphatic hydrocarbons of chain lengths C₁₁--C₁₃ in the diesel, producing 47.7, 37.5 and 51% reductions in C₁₁, C₁₂ and C₁₃, respectively. It produced more degradation than the consortium after 60 days incubation. It is likely that the presence of other species in the consortium inhibited the growth of A. fumigatus, thus resulting in a lower rate of diesel fuel degradation.     

Seed viability and seed dormancy of non-native Phragmites australis in suburbanized and forested watersheds of the Chesapeake Bay, USA

The non-native, invasive haplotype of Phragmites australis is rapidly invading tidal and non-tidal wetlands across North America. Phragmites has the potential to spread by seeds and rhizomes. Seed viability and dormancy differences were quantified among 18 patches of non-native Phragmites in subestuarine wetlands in developed (i.e., suburbanized) vs. forested watersheds of the Chesapeake Bay. We used tetrazolium and germination assays to assess seed viability and compared germination percentages and rate of germination among fresh seeds, cold–moist treated seeds, and warm–dry treated seeds to evaluate seed dormancy. Seed viability was <1% in most patches but a few patches produced abundant viable seeds (5–21%). Seed viability, however, did not differ significantly between wetlands in forested vs. developed watersheds. Contrary to studies of Phragmites seed dormancy in European populations, some Phragmites seeds were dormant at maturity; cold–moist treated seeds germinated faster and to higher percentages than fresh seeds or warm–dry treated seeds.     

Polycross Seed of Genetically Diverse Smooth Cordgrass (Spartina alterniflora) for Erosion Control and Habitat Restoration

Although seed‐based planting is common in crop systems, it is relatively a new concept in coastal erosion control and habitat restoration. This paper discusses the potential use of seed‐based revegetation to accommodate large‐scale erosion control using a highly diverse population of smooth cordgrass (Spartina alterniflora) from controlled polycross to attain desirable genetic diversity suitable for habitat restoration. Seed‐based restoration provides a more versatile alternative approach to the current clonal revegetation technique in many regions, including the Gulf Coast of the United States. The objectives of this study were to (1) describe seed production and cultural aspects of the polycross population and (2) discuss the potential use of polycross seeds for direct seeding applications and other innovative restoration approaches using seed‐derived planting materials. The polycross population was produced using 15 genetically diverse and high‐seed producing smooth cordgrass lines selected from native populations. The average seed set of the polycross population was 58.5 ± 6.3% with an average germination rate of 82.2 ± 9%. As comparison, Vermilion, the only available smooth cordgrass cultivar, has a seed set of 20.6 ± 5% and a germination rate of 35 ± 8%. The average yield of S. alterniflora seed from the polycross population was 277.5 kg/ha, which is equivalent to approximately 26 million viable seeds. Seed can be stored in 100% humidity at a temperature of 2 ± 1°C for 6–9 months.     

Soybean and sunflower oils increase the infectivity of Colletotrichum gloeosporioides f. sp. aeschynomene to Northern Jointvetch

Soybean and sunflower oils increased the level of infection of northern jointvetch, Aeschynomene virginica, plants by Colletotrichum gloeosporioides f. sp. aeschynomene. Inoculation of seedlings with spore suspensions containing 10% (v:v) soybean oil or 10% sunflower oil resulted in more disease than when inoculated with suspensions of spores in water alone. The lengths of the dew periods required to establish equivalent levels of disease by spore suspensions containing 10% soybean or 10% sunflower oil were approximately 4–8 h less compared to aqueous suspensions. Incubation of spores in 10% soybean oil followed by removal and resuspension in water did not affect the infectivity of spores when compared to spores incubated in aqueous suspensions. Spore germination and appressoria formation were unaffected by either of the oils tested in in vitro assays; however, in in vivo assays, 10% soybean oil and 10% sunflower oil increased spore germination in comparison to spores that were suspended in water.     

Seed dispersal and vegetation development on a debris avalanche on the Ontake volcano,Central Japan

Seed dispersal and early revegetation processes were studied in an area devastated by a debris avalanche that occurred on volcano Ontake, Central Japan in 1984. The avalanche was initiated by a volcanic earthquake, and a 3.4 x 10⁷ m³ land mass destroyed the vegetation over 700 ha. The revegetation of the first five years was slow in the area of higher elevation (subalpine area). Both the speed of revegetation and the species richness of trapped seeds varied with the elevation. The post-disturbance vegetation on the deposit with surface soil or plant fragments was richer in species than that without any surface soil. Almost all of the seeds caught by sticky traps and most of the species with frequent occurrence in the vegetation after disturbance were wind dispersed. Wind dispersal was especially important on the deposit without surface soil or plant fragments.     

Two newhalophytophthora species,H. tartarea andH. masteri,from intertidal decomposing leaves in saltmarsh and mangrove regions

Two new pythiaceous fungi were obtained from decaying leaves submerged in saltmarsh environments of the east coast of the U.S.A., or fringing mangroves in the Bahama Islands, and are described here asHalophytophthora tartarea andH. masteri. The two species have superficially similar zoosporangia whose dehiscence tubes have ragged-looking apices. However, differences in fine structures and development of the dehiscence tube and plug, characteristics of the dehiscence plugs, and presence or absence of vesicles clearly distinguish the two species.Halophytophthora masteri is the only species ofHalophytophthora that has a zoospore release mechanism involving both an extruded plug and a vesicle. Cultural properties concerning growth and asexual reproduction at various salinities and temperatures are also different between the two, probably reflecting adaptation to their respective habitats. Though zoospore release inH. masteri occurs spontaneously from mature zoosporangia, it is remarkably enhanced inH. tartarea and alsoH. masteri by mildly dehydrating mature zoosporangia followed by rewetting with seawater, which suggests a possible relation between the asexual reproduction of these oomycetes and the tidal rhythm in their natural habitats.     

Improved biodesulfurization of hydrodesulfurized diesel oil using Rhodococcus erythropolis and Gordonia sp.

Substituted benzothiophenes (BTs) and dibenzothiophenes (DBTs) remain in diesel oil following conventional desulfurization by hydrodesulfurization. A mixture of washed cells (13.6 g dry cell wt l⁻¹) of Rhodococcus erythropolis DS-3 and Gordonia sp. C-6 were employed to desulfurize hydrodesulfurized diesel oil; its sulfur content was reduced from 1.26 g l⁻¹ to 180 mg l⁻¹, approx 86% (w/w) of the total sulfur was removed from diesel oil after three cycles of biodesulfurization. The average desulfurization rate was 0.22 mg sulfur (g dry cell wt)⁻¹ h⁻¹. A bacterial mixture is therefore efficient for the practical biodesulfurization of diesel oil.     

Physiological aspects of hydrocarbon emulsification, metal resistance and DNA profile of biodegrading bacteria isolated from oil polluted sites

The production of biosurfactants was evaluated for seven bacterial strains isolated from different oil contaminated sites by the Emulsification Index using diesel oil as the hydrocarbon source. Minimum Inhibitory Concentrations of Mg²⁺, Cr³⁺ and Cu²⁺ were determined to identify the less sensitive bacteria in order to select the best strains for bioremediation. Plasmid extraction was also performed in order to search for gene sequences involved with biosurfactant synthesis. All strains were able to emulsify diesel oil. Rhodococcus ruber AC239 presented the best index (58%), followed by other Rhodococcus strains. Pseudomonas aeruginosa, R. ruber AC239, AC87 and R. erytropolis AC272 presented smallest sensitivities to heavy metals used, being suitable for use in sites contaminated with high concentrations of them. No plasmid DNA was detected showing that biosurfactant coding genes should be in the chromosomal DNA.     

The North-American amphipods, Melita nitida Smith, 1873 and Incisocalliope aestuarius (Watling and Maurer, 1973) (Crustacea: Amphipoda: Gammaridea), introduced to the Western Scheldt estuary (The Netherlands)

The American amphipod species Melita nitida andIncisocalliope aestuarius have been found in the WesternScheldt estuary (the Netherlands). This is the first record of these species inthe north-east Atlantic. Shipping is the most likely vector of introduction.Thedistribution of both species is investigated and compared with the distributionand the microhabitat of co-occurring amphipod species. Melitanitida is known from both the east and west coast of North Americaand I. aestuarius originates from the east coast of NorthAmerica. Until now neither has been reported from other parts of the world. Inthe Netherlands both species are restricted to the mesohaline part of theWestern Scheldt. Melita nitida occurs predominantly underPacific oysters at the underside of boulders, mainly sublittorally.Incisocalliope aestuarius is associated to hydrozoans.Bothmicrohabitats are hardly utilized by other amphipod species. Therefore, thetheory that the existence of many empty niches in north-western Europeanbrackish waters make this environment particularly susceptible to invasions ofalien species is corroborated. The application of hard substrates in a regionoriginally predominated by soft bottoms moreover facilitates the introductionofexotic species. The species community on hard substrates in the mesohaline partof the Western Scheldt contains a high proportion of introduced species:approximately one third of the macrofauna species is of allochthonous origin.     

Systematic overview of Krigia (Asteraceae-Lactuceae)

Cytological and morphological variation among Krigia species is examined. Krigia exhibits a broad range of chromosome numbers including n = 4, 5, 6, 9, 10, 15, and 30. Section Krigia is characterized by reflexed phyllaries and a base chromosome number of x = 5, while section Cymbia is characterized by erect phyllaries and chromosome numbers of n = 4, 6, and 9. The micromorphological characteristics of achenes, pappus, styles, corolla, pollen, stomata, and trichomes are documented using scanning electron microscopy. Among these, the pappus shows the greatest diversity and three major types are identified: 1) a pappus of many bristles and scales, as in K. dandelion, K. montana, and K. biflora; 2) a pappus of five bristles and five scales, as in K. virginica and K. occidentalis; and 3) an absent or highly reduced pappus, as in the K. cespitosa complex and K. wrightii. Thirty-five cytological and morphological characters are subjected to phylogenetic analyses. The two sections, Krigia and Cymbia, form monophyletic lineages. Within section Krigia, the annual species, K. virginica, forms an independent clade, while the perennial species, K. dandelion, K. biflora, and K. montana, form a monophyletic clade. Krigia montana and K. biflora are identified as sister species and a hybrid between these has been identified. The hybrid is more similar morphologically to K. montana than K. biflora. Within section Cymbia, phylogenetic relationships among K. wrightii, K. occidentalis, and K. cespitosa are uncertain. Nine taxa of Krigia are herein recognized: K. dandelion, K. biflora, K. biflora var. viridis (comb. nov.), K. montana, K. virginica, K. wrightii (comb. nov.), K. occidentalis, K. cespitosa, and K. cespitosa f. gracilis (comb. nov.). Phylogenetic relationships among 12 taxa of Krigia species are compared using various combinations of morphology, chloroplast DNA, and nuclear ribosomal DNA data. Tree topologies from different combinations of data are largely congruent. The most resolved phylogenetic tree is obtained using the combined data from morphology, chloroplast DNA, and nuclear ribosomal DNA.     

Development and application of LSU rRNA probes for Karenia brevis in the Gulf of Mexico, USA

The brevetoxin producing dinoflagellate, Karenia brevis, is the target of several monitoring and research programs in the Gulf of Mexico, where it forms extensive and frequently long-lived annual blooms that can cause human intoxication and fish kills, as well as severe economic losses to coastal communities. Rapid, reliable methods for the detection and enumeration of K. brevis cells, as well as their discrimination from morphologically similar species, are valuable tools for managers and scientists alike. Our aim was to produce a species-specific molecular probe that would serve as a tool to facilitate the efficient and reliable detection of K. brevis in the Gulf of Mexico. We sequenced a fragment of the large-subunit ribosomal RNA gene (LSU rDNA) from five K. brevis cultures isolated from the Texas Gulf coast, the Florida Gulf coast, and the Atlantic coast of Florida, and detected no differences among these isolates. A consensus sequence was thus compiled and compared to a previously published sequence from Karenia mikimotoi, the closest known phylogenetic relative to K. brevis, for the purpose of identifying unique K. brevis signature sequences. Fluorescently-labeled (FITC) oligonucleotide probes targeting these regions of the K. brevis LSU rRNA were designed to include at least two base pair differences, as compared to K. mikimotoi. Among seven probes designed, one uniquely identified all K. brevis isolates to the exclusion of all other species tested (Kbprobe-7), including a Gulf of Mexico K. mikimotoi isolate (Sarasota, FL) and several additional Gymnodinium species, as well as other dinoflagellate, diatom, and raphidophyte taxa. Importantly, K. brevis cells in samples taken during a 2001 bloom, fixed with a mixture of modified saline ethanol and 10% formalin, and stored at 4 °C for 7 months were successfully labeled with Kbprobe-7. In addition, preliminary analysis of labeled cells by flow cytometry revealed that K. brevis could be distinguished from K. mikimotoi in solution, suggesting other potential applications of this probe.     

Establishment and reproduction of Aeschynomene virginica (L.) (Fabaceae) a rare,annual, wetland species in relation to vegetation removal and water level

Aeschynomene virginica is a rare annual plant found in freshwater tidal wetlands of the eastern United States. We hypothesized that standing vegetation and water inundation were two important environmental factors in its population dynamics. To test these hypotheses, we sowed seeds into plots with undisturbed vegetation or plots with all aboveground vegetation removed in 1998 and 1999. Presence/absence of seedlings was noted and seedling survival to reproduction, final size, and seed set were measured throughout both growing seasons. Seedling establishment from germination to the first true leaf stage increased with decreasing water depth. Vegetation removal plots had greater seedling establishment, higher seedling survival, and higher seed set per plant than non-removal plots. In a greenhouse study designed to test the effects of water level on seed germination and seedling establishment, no seedlings established in submerged soils, and seed germination and seedling establishment were lower in waterlogged soil than in wet soil. Physical stress associated with deeper water likely limits the distribution of A. virginica to higher elevations, where seeds that colonize patches with low vegetative cover are more likely to produce reproductive adults that produce more seeds relative to patches with established vegetation. A. virginica appears to be a fugitive species specializing on open habitat patches in tidal wetlands. This species may be dependent on disturbances for population establishment and maintenance.     

干旱胁迫下白刺花种子大小与萌发对策

种子大小与种子萌发及其与环境因子的关系是植物种子萌发对策研究中的重要科学问题之一。采用PEG模拟干旱法研究不同干旱胁迫强度(0,5%,10%,15%,20%)下,白刺花(Sophora davidii)种子萌发进程、种子大小与种子萌发及种子命运的关系。结果表明:不同干旱胁迫下,白刺花种子具有相似的萌发进程,但中度干旱处理(10%PEG)萌发率显著高于零干旱(0%PEG)和重度干旱处理(P0.05),重度干旱处理(20%PEG)种子萌发开始时间晚于零干旱和中度干旱处理;种子大小与种子萌发开始时间的关系表现为零干旱处理下呈极显著负线性关系,中度干旱处理(5%PEG,10%PEG)下无相关关系,重度干旱处理(15%PEG,20%PEG)下呈负二次曲线关系;种子大小对种子命运的影响表现为零干旱处理有利于大、小种子萌发和小种子休眠,中度干旱处理(10%PEG)增加中等种子萌发、大种子休眠和小种子死亡风险,重度干旱处理(15%PEG,20%PEG)增加大种子死亡风险、中等种子和小种子休眠。综合分析表明,白刺花种子大小与萌发行为及种子命运的关系具有较强的环境依赖性,即种子萌发行为表现为顺境下种子越大萌发越快,逆境下小种子和大种子较中等种子萌发更快;种子命运表现为顺境增加种子死亡的风险,中度干扰有利于种子萌发,逆境则有利于种子休眠。     

Spread of the introduced tropical green alga Caulerpa taxifolia in northern Mediterranean waters

The first report of Caulerpa taxifolia in the Mediterranean is from 1984. The alga was found on the rocky shore at Monaco, below the Oceanographic Museum, where it had been on display in tropical aquaria. Within five years, there was an abundance of C. taxifolia on the shores around the first point of observation. In 1987, C. taxifolia appeared on the French coast, 3 km east of Monaco, at Cap Martin. By late 1991, 30 ha of shore in the vicinity of Monaco was covered with the alga. New points of colonization were in Livorno, Italy, 240 km east of Monaco, and to the west at Agay, Le Lavandou, Hyères, Toulon, Les Lecques, Saint Cyprien, 50 to 370 km from Monaco. The westernmost point of colonization, noted in September 1992, was 600 km from Monaco, at Majorca (Balearic island, Spain). Most types of substrata, between 0 and 50 m depth, are susceptible to colonization by C. taxifolia. Seaweed and seagrass populations on the coasts of Monaco and Cap Martin have been significantly reduced or destroyed because of invasion by C. taxifolia.     

New Resources for Marine Genomics: Bacterial Artificial Chromosome Libraries for the Eastern and Pacific Oysters (Crassostrea virginica and C. gigas)

Large-insert genomic bacterial artificial chromosome (BAC) libraries of two culturally and economically important oyster species, Crassostrea virginica and C. gigas, have been developed as part of an international effort to develop tools and reagents that will advance our ability to conduct genetic and genomic research. A total of 73,728 C. gigas clones with an average insert size of 152 kb were picked and arrayed representing an 11.8-fold genome coverage. A total of 55,296 clones with an average insert size of 150 kb were picked and arrayed for C. virginica, also representing an 11.8-fold genome coverage. The C. gigas and C. virginica libraries were screened with probes derived from selected oyster genes using high-density BAC colony filter arrays. The probes identified 4 to 25 clones per gene for C. virginica and 5 to 50 clones per gene for C. gigas. We conducted a preliminary analysis of genetic polymorphism represented in the C. gigas library. The results suggest that the degree of divergence among similar sequences is highly variable and concentrated in intronic regions. Evidence supporting allelic polymorphism is reported for two genes and allelic and/or locus specific polymorphism for several others. Classical inheritance studies are needed to confirm the nature of these polymorphisms. The oyster BAC libraries are publicly available to the research community on a cost-recovery basis at