The hydrozoan coral<Emphasis Type="Italic"> Millepora dichotoma</Emphasis>: speciation or phenotypic plasticity?

This article describes ecological and biological differences between two morphs of the Red Sea fire coral Millepora dichotoma. The species is divided into two main morphs: branching and encrusting, which were found to differ both in color and morphology. Each morph has two or more sub-morphs. A total of 372 M. dichotoma colonies were examined in a census at two study sites in the Gulf of Elat. Colony size and abundance of the two morphs were found to differ significantly between sites. Experimental examination of each morph's morphological plasticity revealed different growth rates and difference in growth plasticity between the branching and the encrusting morph. Most of the fragments from the branching colonies (94%) attached to experimentally placed Plexiglas substrate, compared with much less attachment by the encrusting fragments (11%). The growth form of the branching morph on the Plexiglas switched to encrusting, spreading over and covering the substrate. When the new encrusting colony reached the edge of this substrate, it started to produce tips, and returned to growth in the classic branching form. The encrusting morph did not change its growth form. Following attachment of the original fragments of the branching morph to the substrate, 8.1% of them produced new tips. When the original branches were removed, after converting to encrusting growth form, 19% of the fragments produced new tips. The capsule size of nematocysts of the two morphs was also significantly different (t-test, P<0.05). Molecular data (ITS region) clearly demonstrate that these two M. dichotoma morphs differ considerably. Molecular evidence (srRNA) from the symbiotic zooxanthellae also shows a different pattern of clades in the hosts. The ecological, biological and molecular data thus attest to the two morphs being distinguishable. Contrary to previous reports, we consequently suggest that the two morphs of M. dichotoma found in the Gulf of Elat are actually two distinct species.Communicated by O. Kinne, Oldendorf/Luhe     

Ecological and physiological differences between two colour morphs of the coral Pocillopora damicornis

Pocillopora damicornis (Linnaeus) is a ubiquitous branching coral found throughout the Indo-Pacific region. Like many other species of coral, P. damicornis displays a large range of morphologies. At One Tree Island, it occurs as two distinct morphs that are easily distinguished by the presence or absence of pink pigmentation. The two colour morphs of P. damicornis were found to differ in their distribution and abundance in the One Tree Island Lagoon. The brown morph was more abudant than the pink morph in the shallows (<1 m),whereas the pink morph was more abundant at deeper sites (>3 m). The two morphs also differed physiologically. The brown morph tended to have a greater calcification rate than the pink morph, regardless of environmental conditions. However, the difference in the calcification rate between the two morphs became non-significant under shaded conditions (5% full sunlight), indicating some degree of physiological plasticity of the morphs. The pink colour in P. damicornis was due to a hydrophilic pigment with a major peak absorbance at 560 nm. The expression of pink pigment had both genetic and phenotypic components. The brown morph has a reduced genetic capacity to express the pigment relative to the pink morph. On the other hand, pigment expression could be induced by light in the pink morph. Although genetic differences ultimately determine the differences between the two morphs of P. damicornis, the extent of pigment expression is under some degree of environmental influence.     

Allozyme electrophoresis demonstrates that the scleractinian coral Montipora digitata is two species

Allozyme electrophoresis at five loci was used to clarify the species status of two morphs of the scleractinian coral Montipora digitata (Dana, 1846), using specimens collected from three locations off the Queensland coast between October 1991 and April 1993. The two morphs, occurring sympatrically, were distinguished by one fixed gene difference at Locus LT-2 and frequency differences at three other loci, indicating reproductive isolation between them. Populations of both morphs were generally in Hardy-Weinberg equilibrium, suggesting that sexual reproduction does occur. Despite sampling designed to reduce the chance of collecting clonemates, the genetic diversity ratio (G _O:G_E) indicated that asexual reproduction also occurs. This is in agreement with the known modes of reproduction for this species. There was significant genetic differentiation between populations of one of the morphs of M. digitata. This could have been influenced by greater degrees of asexual reproduction in this morph, selection within sites, or variation in larval survival and recruitment patterns. Relatively low F _st (differentiation among populations) values found for a broadcast spawning species during this study are in accordance with the hypothesis that brooded planulae are adapted for rapid settlement, whereas planulae produced by broadcast spawners are adapted for widespread dispersal.     

Sexual reproduction and external brooding by the Caribbean gorgonianBriareum asbestinum

The reproductive biology of the gonochoricBriareum asbestinum (Pallas), a common Caribbean gorgonian, was studied in the San Blas Islands (Panama), La Paguera (Puerto Rico) and the Bahamas. Of 721 colonies examined at the height of the reproductive season, during the summers of 1985 to 1988, all were either male or female. No hermaphroditic colonies or polyps were observed. The sexratio of Panama populations was significantly biased in favor of males (2.1:1,n=454) over all four years of the study. A significant male bias was also found in populations sampled in Puerto Rico (2.3:1,n=143) and in the Bahamas (2.5:1,n=124). The consistency of this geographically widespread skewed sex-ratio is unique among octocorals and scleractinians. Ooyctes appear annually in September and reach maximum diameter (600 to 900µm) in June and July of the following year. The 3 to 5 mo developmental cycle of spermaries is shorter than that of females and begins in March. Spawning in males is synchronous and occurs following the full moons of June and July. Fertilization is internal. Embryos are released from polyps very early in development, often whilst still in the process of cleaving. Embryos remain attached to the outside of the colony for 3 to 5 d, many becoming entrapped in mucous sheets secreted by the colonies. Larvae are negatively buoyant and settle rapidly once displaced from the colony. Males become reproductive at smaller branch sizes than females. Reproductive effort (gonads polyp^–1 and total gonad volume polyp^–1) for both males and females increased with increasing branch size and in polyps away from the tip and base of the branch.Please address all correspondence and requests for reprints to Dr Brazeau at his present address: Department of Biology, University of Houston, Houston, Texas 77204-5513, USA     

Genetic divergence between colour morphs in populations of the common intertidal sea anemones Actinia equina and A. prasina (Anthozoa: Actiniaria) in the Isle of Man

A distinctive morph ofActinia equina (L.) is found at low frequency among populations on intertidal hard substrata on some shores on the Isle of Man. This morph is red with rows of green oval spots or elongate markings running longitudinally down the column. Starch gel electrophoresis of 21 allozyme loci was used to compare samples of this morph from two localities with other sympatricActinia spp. Collections were made in early summer 1986. For one sampling site the comparison was with redA. equina and greenA. prasina Gosse, whilst at the other site with redA. equina only. At both sites significant genetic differences in allele frequencies at several loci were found between the new morph and sympatricA. equina andA. prasina. The results also confirm the reproductive isolation ofA. prasina. As with much previous work on sea anemones, levels of mean heterozygosity per locus (H) were found to be high (H=0.157 to 0.342). A surprising feature of the results, although bearing out earlier unpublished data, is that high levels of genetic differentiation are found between populations of what appear to be the same morphs collected from shores only a few km apart. Among theActinia spp. studied, differentiation between populations of the same morph on different shores was of the same order as between sympatric, reproductively isolated populations.     

Reproductive success in the Caribbean octocoral Briareum asbestinum

For most sessile marine invertebrates the number of offspring produced by an individual is often determined indirectly from counts of eggs present, with the assumption that all or most become viable offspring. Few field data on the actual number of offspring produced per individual (reproductive success) have been reported. We examined reproductive success in the octocoral, Briareum asbestinum (Pallas), by measuring embryo densities on 40 female colonies on two reefs (Pinnacles and House reefs) in the San Blas Islands, Panama from 1986 to 1988. The percentage of female colonies with mature eggs which subsequently released embryos was low, ranging from 46.6% in 1986 to 5.0% in 1988. Reproductive success was significantly different between reefs. Pinnacles reef had significantly more successful colonies (those releasing embryos) than House reef in all three years and significantly higher embryo densities in 1986 and 1987. There was a significant positive correlation between female reproductive success and the density and proximity of nearby males in both 1986 and 1987. In addition, fertile female branches placed 25 cm away from male branches produced significantly more embryos than female branches placed 50 cm away. In 1988 two groups of female branches were placed at distances of <50 cm and 5 m from four large male colonies at Pinnacles reef. Of the 20 female branches placed 5 m from the males none released embryos while 35% (7 of 20 branches) of the branches <50cm from males released embryos. These data indicate that simple counts of mature eggs present within female colonics prior to the reproductive season provide a poor estimate of reproductive success in B. ashestinum and that female reproductive success is positively influenced by the close proximity of males.     

Genetic and environmental effects on the growth rate of Littorina saxatilis

Transfer experiments with two morphs of Littorina saxatilis Olivi (=L. rudis) typically inhabiting exposed and sheltered localities, showed a between-morph difference in shell growth in the same type of habitat, and a withinmorph difference between exposed and sheltered environments. The former indicates a genetic difference between the two morphs, although growth rate has an environmental component as shown by the latter. Juvenile snails of the exposed morph were on average slightly larger than sheltered morph juveniles on hatching, but at 20 wk, when raised in identical environments, the sheltered morph juveniles had grown significantly larger than the exposed ones. A rise in temperature from 5° to 10°C enhanced growth rate for snails raised in the laboratory. Temperature alone could not however explain increased growth during the spring and summer in natural populations.     

Genetic connectivity among color morphs and Pacific archipelagos for the flame angelfish, <Emphasis Type="Italic">Centropyge loriculus</Emphasis>

Color variation is used in taxonomic classification of reef fishes, but it may not reliably indicate evolutionary divergence. In the central Pacific, there are three color morphs of the flame angelfish, Centropyge loriculus: a red morph that occurs primarily in the Hawaiian archipelago, the endemic Marquesan color morph with reduced black markings, and an orange morph that occurs throughout the rest of Oceania. The red and orange morphs co-occur at Johnston Atoll (1,300 km south of Hawai’i), but intermediate forms have not been reported. To determine whether the three color morphs represent distinct evolutionary lineages, we compared 641 base pairs of mitochondrial cytochrome b. Forty-one closely related haplotypes were observed in 116 individuals. Analysis of molecular variance (AMOVA) indicated no significant genetic structure among color morphs (Φ_ST = 0.011, P = 0.147). Likewise, there was no significant pairwise structure between sampling locations, separated by up to 5,700 km, after a Bonferroni correction (Φ_ST = 0.000–0.080, P = 0.0130–0.999). Genetic studies in conjunction with larval distribution data indicate that Centropyge species are highly dispersive. While there is a strong geographic component to the distribution of color morphs in C. loriculus, we find no evidence for corresponding genetic partitioning. We do not rule out an adaptive role for color differentiation, but our data do not support emerging species.     

Morphological divergence of Eastern Pacific and Caribbean isopods: effects of a land barrier and the Panama Canal

The Isthmus of Panama rose approximately 3 million years before the present (mybp) and isolated biotas in the tropical eastern Pacific from those in the Caribbean Sea. Populations that were split by the Isthmus and have evolved in allopatry since that time are known as geminates. The surf zone/beach isopod Excirolana braziliensis Richardson was examined between 1984 and 1989 to test the hypothesis that divergence in geminate isopod morphology has occurred, and that geminate divergence is greater than divergence between local populations from the same coastline. Three morphs of Excirolana braziliensis, one in the Caribbean and two in the eastern Pacific, were discovered using numerical taxonomic methods that adjust for body size. The two Pacific morphs have overlapping large-scale distributions, but those morphs are segregated on a smaller scale by beach. We inferred that one Pacific morph and one Caribbean morph were geminates, based on their relative similarity in shape, their geographical ranges, and natural history information about the organism's dispersal capabilities. The origin of the third morph probably predates the Isthmus of Panama, given its relative dissimilarity from the geminate morphs. The presumed geminates differ primarily with respect to the rostrum, antennae and one male reproductive structure. Divergence between geminates is greater than divergence between local populations of any morph along a coastline. Because only one morph occurs in the Caribbean, that region contains less morphological variation than the eastern Pacific, which contains two morphs. There was weak evidence that some introductions may have taken place in the last century from the Caribbean to the Pacific; however, introductions have not masked the pattern of divergence that has developed over millions of years.     

Distribution pattern, reproductive traits, and molecular analysis of two coexisting vermetid gastropods of the genus Petaloconchus: a Caribbean endemic and a potential invasive species

Vermetid gastropods are characterized by complex taxonomy and unusual ecology. A survey of the fouling community in the intake channel at the Planta Centro Power Plan in Puerto Cabello, Venezuela, found massive colonies of vermetid gastropods of the genus Petaloconchus. We arbitrarily named two prevalent varieties as black and brown-orange morphs, distinguishing based on the color of their soft bodies. Spatial distribution was different for the morphs. The black morph was present along the jetty, with higher average densities in the shallower intertidal area (410 vs. 143 ind m⁻²), while the brown-orange morph was only present at the initial part of the channel (μ = 83 ind m⁻²). Both produced small eggs (142 vs. 180 μm diameter on average), with the orange-brown eggs being slightly larger, but the morphs differed in other reproductive aspects. The brown-orange morph produced significantly fewer capsules (up to nine simultaneously per female) with fewer embryos (average of 27 viable embryos/capsule) that hatched at a larger size (577 μm on average), allocating about 17.64% of the initial egg production to nurse eggs. In contrast, the black morph produced up to 14 capsules simultaneously, hatched an average of 178 veligers of 212 μm, and produced no nurse eggs. The intra-capsular development reached a more advanced stage in the brown-orange morph than in the black one. Several cytochrome subunit I (COI) and 16S rRNA (16S) haplotypes were found for the black morph, when compared to only one haplotype for both genes present for the brown-orange morph. Preliminary phylogenetic analyses separated the morphs into different clades, supported by robust bootstrap values and posterior probabilities (>98). Our results indicate that the morphs are two different species: the black morph was identified as Petaloconchus cf. varians and the brown-orange morph as a non-described species, Petaloconchus sp. (orange). The first is endemic to the Caribbean, while the second is potentially an introduced species.     

Genetic differentiation between morphotypes of the marine sponge Suberites ficus (Demospongiae: Hadromerida)

Sponges of three morphotypes of Suberites ficus (Johnston, 1842) were collected during February and March 1985 off the south-west of the Isle of Man, and were compared by using spicule size distributions and genetic allele frequencies of isozyme loci. The populations did not show any significant differences of spicule size or type, but could be easily differentiated into three separate species based on isozyme patterns. Samples of pale orange S. ficus growing on gastropod shells inhabited by hermit crabs (Pagurus spp.) were reproductively isolated from the redorange and the pale yellow colour morphs encrusting the bivalve Chlamys opercularis. These latter two colour morphs were genetically similar, but significant differences were observed at two of the 19 gene loci assayed. All the sponges studied were sympatric, and therefore the genetic differences, indicating reproductive isolation, are strong evidence for separate gene pools and, hence, that they are different species. The genetic identity between the two colour morphs of S. ficus on C. opercularis shells was 0.977, whilst between each of these and S. ficus on hermit crabs it was about 0.65. In all three species genetic variability was high, with mean expected and observed heterozygosity values per locus ranging from 0.17 to 0.36.     

<Emphasis Type="Italic">Symbiodinium</Emphasis> sp. associations in the gorgonian<Emphasis Type="Italic"> Pseudopterogorgia elisabethae</Emphasis> in the Bahamas: high levels of genetic variability and population structure in symbiotic dinoflagellates

Little is known concerning the fine-scale diversity, population structure, and biogeography for Symbiodinium spp. populations inhabiting particular invertebrate species, including the gorgonian corals, which are prevalent members of reef communities in the Gulf of Mexico, the Caribbean, and the western Atlantic. This study examined the Symbiodinium sp. clade B symbionts hosted by the Caribbean gorgonian Pseudopterogorgia elisabethae (Bayer). A total of 575 colonies of P. elisabethae were sampled in 1995 and 1998–2000 from 12 populations lying along an ~450 km transect in the Bahamas and their Symbiodinium sp. clade B symbionts genotyped at two polymorphic dinucleotide microsatellite loci. Twenty-three unique, two-locus genotypes were identified in association with these P. elisabethae colonies. Most colonies hosted only a single Symbiodinium sp. clade B genotype; however, in some instances ( n=25), two genotypes were harbored simultaneously. For 10 of the 12 populations, 66–100% of the P. elisabethae colonies hosted the same symbiont genotype. Added to this, in 9 of the 12 populations, a Symbiodinium sp. clade B genotype was either unique to a population or found infrequently in other populations. This distribution of Symbiodinium sp. clade B genotypes resulted in statistically significant ( P<0.05 or <0.001) differentiation in 62 of 66 pairwise comparisons of P. elisabethae populations. Tests of linkage disequilibrium suggested that a combination of clonal propagation of the haploid phase and recombination is responsible for maintaining these distinct Symbiodinium sp. clade B populations.     

Acanthochromis polyacanthus,a fish lacking larval dispersal,has genetically differentiated populations at local and regional scales on the Great Barrier Reef

Acanthochromis Gill is a monotypic genus within the damselfish family Pomacentridae, erected for an unusual species [A. polyacanthus (Bleeker)] that uniquely lacks larval dispersal. Instead, offspring are reared in the parental territory, in the manner of cichlids, and fledged into the surrounding habitat. Phenotypic and genotypic variation was surveyed on the basis of body colouration and 7 polymorphic loci in 19 populations from 5 regions of the central and southern Great Barrier Reef (GBR). Variation in both characters was found at regional and local scales. Two colour morphs were recognised: a bicoloured morph from the three northern regions and a uniform dark morph from the two southern regions. Isozyme analysis showed a similar pattern with greatest variation between the different morphs, but also with significant variation at both regional and local scales within morphotypes. Heterozygosity was maximal in the central populations, which, together with other measures of variability, suggests a mixing of separate gene pools in this region and denies species status to the two morphotypes despite numerous fixed differences in allele frequencies between the most distant populations. The presence of fixed differences in multiple alleles between populations separated by 1000 km indicates negligible gene flow over such distances and long isolation of these gene pools. These patterns may reflect recolonisation of the GBR after the last sea-level rise by fish from two stocks. Founder effects and random drift in small populations after colonisation are probably the major sources of the local and regional variations observed at smaller spatial scales. This diversity has been maintained among populations at all scales by the very low levels of gene flow possible without an effective strategy for larval dispersal between coral reefs.     

Genetic relationships of the colour morphs of Acanthochromis polyacanthus (Pomacentridae) on the northern Great Barrier Reef

Acanthochromis polyacanthus is an unusual tropical damselfish because it lacks pelagic larvae and has lost the capacity for broad-scale dispersal among coral reefs. On the modern Great Barrier Reef, this fish has multiple colour morphs and we have previously described steep genetic clines in the central region between three colour morphs. A similar transition of colour morphs has been found in the far northern region (Latitude 11°S), where at least five colour morphs and intergrading hybrids were found during a survey of 14 locations on nine adjacent reefs. On two of these reefs, monochromatic white and bicoloured morphs coexist, partitioning the reef slope vertically when sympatric, but occupying the full depth range elsewhere. In areas of overlap, they interbreed, producing hybrids of intermediate colour. Although the discriminatory power of our genetic analysis was weakened by the low level of variability in these populations (only four polymorphic loci), allozyme electrophoresis revealed significant genetic differentiation within and among reefs. There was neither simple linkage between colour and protein variation, nor correlation between genetic similarity and proximity of sampled populations. We suggest that the observed chaotic structure is the result of differences among the founding populations, although the two colour-based stocks have been homogenized through a long history of introgression during multiple episodes of isolation and secondary contact. Despite genetic mixing, phenotypic diversity (i.e. colour morphs) seems to have been preserved in these populations by sexual selection, perhaps reinforced by natural selection. The long-term stability of this outcome, however, is suggested by the presence of unique morphs on two reefs that are detached from the continental shelf and surrounded by very deep water. The strong identity of these populations can be attributed to long occupation of these isolated sites compared with those on the continental shelf which have only been established in the last 15 000 yr and still retain differences arising from the initial founder events. Received: 15 January 1997 / Accepted: 15 August 1997     

Color patterns of the shrimps Heptacarpus pictus and H. paludicola (Caridea: Hippolytidae)

Color patterns of the shallow-water shrimps Heptacarpus pictus and H. paludicola are formed by chromatosomes (usually termed chromatophores) located beneath the translucent exoskeleton. Development of color patterns is related to size (age) and sex. The color expressed is determined by the chromatosome pigment dispersion, arrangement, and density. In populations with well-developed coloration (H. pictus from Cayucos, California, 1976–1978, H. paludicola from Argyle Channel, San Juan Island, Washington, June–July, 1978), prominent coloration was a characteristic of maturing females, breeding females, and some of the larger males. In the Morro Bay, California, population of H. paludicola (sampled 1976–1978), color patterns were poorly developed except in a few large females. In both species, most shrimp lose color at night because of pigment retraction in certain chromatosomes. In both species, there are 5 basic morphs: 1 transparent and 4 colored morphs. In the colored morphs, the color patterns are composed of bands, stripes, and spots which appear to disrupt the body outline. Each color morph also has a common environmental color in its color pattern, e.g the green of green algae, the whites and pinks of dead and living coralline algae, and various shades of tidepool litter. These shrimps are apparently under heavy predation pressure by fish, and it is suggested that the color patterns are camouflage against such visually-hunting predators.     

Genetic population structure and sociogenetic organisation in Formica truncorum (Hymenoptera; Formicidae)

Summary The genetic population structure and the sociogenetic organization of the red wood ant Formica truncorum were compared in two populations with monogynous colonies and two populations with polygynous colonies. The genetic population structure was analysed by measuring allele frequency differences among local subsets of the main study populations. The analysis of sociogenetic organisation included estimates of nestmate queen and nestmate worker relatedness, effective number of queens, effective number of matings per queen, relatedness among male mates of nestmate queens and relatedness between queens and their male mates. The monogynous populations showed no differentiation between subpopulations, whereas there were significant allele frequency differences among the subpopulations in the polygynous population. Workers, queens and males showed the same genetical population structure. The relatedness among nestmate workers and among nestmate queens was identical in the polygynous societies. In three of the four populations there was a significant heterozygote excess among queens. The queens were related to their male mates in the polygynous population analysed, but not in the monogynous ones. The data suggest limited dispersal and partial intranidal mating in the populations with polygynous colonies and outbreeding in the populations having monogynous colonies. Polyandry was common in both population types; about 50% of the females had mated at least twice. The males contributed unequally to the progeny, one male fathering on average 75% of the offspring with double mating and 45–80% with three or more matings. Correspondence to: L. Sundström     

Fungal disease resistance of Caribbean sea fan corals (Gorgonia spp.)

An on-going, Caribbean-wide epizootic affecting sea fan corals (Gorgonia spp.) is caused by the fungus Aspergillus sydowii (Thom et Church). We examined the role of crude extracts in resistance of two species of sea fans, Gorgonia ventalina (L.) and G. flabellum (L.), against A. sydowii and a bacterial pathogen of fish, Listonella anguillarum (MacDonell et Colwell). Sea fans were collected in January 1997 from San Salvador, Bahamas, and in June 1997 and January 1998 from Alligator Reef, Florida Keys, USA. Crude extracts from both species were tested to determine concentrations inhibiting germination of A. sydowii spores. Crude extracts from both species inhibited spore germination at concentrations as low as 1.5 mg ml⁻¹; most samples were active at 5 to 10 mg ml⁻¹. These concentrations are within the range estimated in living tissue and were higher in healthy colonies suggesting their role in mediating disease susceptibility. We also detected within-colony gradients in antifungal activity, which varied with the disease state of the colony. In healthy sea fans, resistance was highest at colony edges and lowest in medial and central regions of the colony. Among sea fans with lesions in the colony center, resistance in tissue from proximal and medial regions was as high as tissue from the colony edge (i.e. distal region). The increase in antifungal activity suggests an inducible response by the coral host to the fungal pathogen. This response is most evident among sea fans with lesions in the colony center and not among colonies with lesions at the edge. Antibacterial activity of crude extracts against L. anguillarum was highest at the colony edge but did not vary with disease state or tissue location. Received: 10 March 1999 / Accepted: 10 November 1999     

Differences in reproductive strategies of morphs of the genus Echinaster (Echinodermata: Asteroidea) from the Eastern Gulf of Mexico

Two morphs of the asteroid genus Echinaster, E. Type 1 and E. Type 2, have reciprocal annual cycles of reproduction and nutrient storage. The pyloric caeca (storage organs) reach maximal size over winter then decrease with increasing gametogenic activity in the spring. E. Type 1 broadcasts buoyant eggs in late May to early June. E. Type 2 deposits benthic eggs in late April. Lecithotrophic larval development is similar in both morphs except that larvae of E. Type 1 undergo a brief planktonic phase. E. Type 1 reaches sexual maturity at a larger size, expends a lower reproductive effort but has a greater absolute reproductive output than E. Type 2. E. Type 2 produces fewer, larger eggs and has a greater parental investment per egg. In both morphs, females have much higher gonadal lipid levels than males and expend a higher reproductive effort in terms organic matter and energy. Reproductive effort, reproductive output, nutrient storage in the pyloric caeca and body size varied between populations and between years in each morph. Egg size and parental investment per egg were constant. Within-morph variability is attributed to differences in nutritional state. Differences in reproductive strategy support the hypothesis that the morphs are separate species.     

Population genetics of Crassostrea ariakensis in Asia inferred from microsatellite markers

Crassostrea ariakensis is an important aquacultured oyster species in Asia, its native region. During the past decade, consideration was given to introducing C. ariakensis into Chesapeake Bay, in the United States, to help revive the declining native oyster industry and bolster the local ecosystem. Little is known about the ecology and biology of this species in Asia due to confusion with nomenclature and difficulty in accurately identifying the species of wild populations in their natural environment. Even less research has been done on the population genetics of native populations of C. ariakensis in Asia. We examined the magnitude and pattern of genetic differentiation among 10 wild populations of C. ariakensis from its confirmed distribution range using eight polymorphic microsatellite markers. Results showed a small but significant global θ _ST (0.018), indicating genetic heterogeneity among populations. Eight genetically distinct populations were further distinguished based on population pairwise θ _ST comparisons, including one in Japan, four in China, and three populations along the coast of South Korea. A significant positive association was detected between genetic and geographic distances among populations, suggesting a genetic pattern of isolation by distance. This research represents a novel observation on wild genetic population structuring in a coastal bivalve species along the coast of the northwest Pacific.     

Comparisons of genetic population structures in four intertidal brachyuran species of contrasting habitat characteristics

Genetic population structures along the Japanese coast, analyzed by sequence data from the mitochondrial DNA COI region, were determined for four intertidal brachyuran species in the superfamily Thoracotremata (Ocypode ceratophthalma, Gaetice depressus, Chiromantes dehaani and Deiratonotus japonicus), which were characterized by different habitat requirements. O. ceratophthalma (seashore; supratidal sand) and C. dehaani (estuarine; supratidal marsh) showed no significant genetic differentiation among Japanese populations. The Japanese populations of O. ceratophthalma, however, were found to genetically differentiated from the Philippine population. G. depressus (seashore; intertidal cobbles) exhibited significant genetic differentiation between the Amami-Ohshima population and other local populations. D. japonicus (estuarine; intertidal cobbles) showed significant genetic differentiation among many local populations separated by about 30–1,200 km. The different patterns of genetic population structure recorded for the four species, thus, do not simply correspond to habitat type. An erratum to this article can be found at