Discrimination among and variation within species of Pseudocalanus based on the GPI locus

Patterns of allozyme variation at the GPI (glucose phosphate isomerase) locus showed that the recently described or clarified Pseudocalanus newmani, P. acuspes, P. moultoni and P. minutus are genetically isolated from each other even though morphologically they are very similar, and in places sympatric. This genetic isolation was inferred from the presence of private alleles in some species, and from differences in their degrees of observed heterozygosity and in the observed frequencies of shared alleles in all the species examined. Temporal variations were not detected in P. newmani, P. acuspes and P. minutus. Populations of P. newmani and P. moultoni from the Atlantic and Pacific coasts of North America have apparently diverged. No such divergence was detected among samples of P. acuspes from Nova Scotia, the Canadian Arctic and the Baltic sea, and of P. minutus from Nova Scotia and Hudson Bay. P. elongatus collected in the English Channel differed from P. acuspes from the Baltic Sea.     

Interspecific variation in thermal denaturation of proteins in the congeneric musselsMytilus trossulus andM. galloprovincialis: evidence from the heat-shock response and protein ubiquitination

The genetic population structure of the precominant zooplankter, the copepod Calanus finmarchicus (Gunnerus), was examined to determine whether genetically distinct populations exist in the Gulf of Maine. C. finmarchicus was sampled in three regions of the Gulf of Maine (Great South Channel, spring 1989; northern Gulf of Maine, winter 1990; Great South Channel and Georges Bank, spring 1990). Copepods from seven locations in the Great South Channel, five in the northern Gulf of Maine and four on or near Georges Bank were assayed for allozyme variation and mitochondrial DNA variation of amplified 16S rRNA and cytochrome b genes. Restriction fragment length polymorphism (RFLP) analyses of both mitochondrial DNA genes revealed no variation among any of the individuals assayed. Analysis of five polymorphic allozyme loci revealed that genetic variation among the three geographic regions was low, and genetic identities were high between all locations (I>0.97). Most of the genetic variation was among locations regardless of region. Chi-square tests were used to examine genetic similarity between specific pairs of locations within and between regions. In the northern Gulf of Maine, genetic homogeneity occurred over larger spatial scales (hundreds of km) than in either the Great South Channel or Georges Bank (tens of km). Only copepods from the Bay of Fundy and Nova Scotian Shelf locations were genetically distinct from Wilkinson Basin copepods at two loci. Copepod populations from the northern locations may have been partially isolated or they may represent immigrant populations (e.g., from the Gulf of St. Lawrence). Several pairs of locations were genetically distinct at one or more loci in the two southern regions. Differences between locations in these regions may represent distinct populations advected into the areas at different times or from different sources (e.g., genetic variation may represent a mixture of genetically distinct northern and southern copepod populations). These results suggest extensive gene flow among populations of C. finmarchicus in the Gulf of Maine with some evidence of genetic population subdivision near the Gulf's northeastern and southern boundaries.     

Molecular phylogeny of mud crabs (Brachyura: Panopeidae) from the northwestern Atlantic and the role of morphological stasis and convergence

 Mud crabs of the family Panopeidae are common organisms in coastal soft-bottom, vegetated, rubble, and oyster-bed communities along the temperate and tropical coastlines of the American continent. Similar morphology among many species renders their distinction and classification difficult. Here, we present phylogenies of western Atlantic Panopeidae based on DNA sequences of the mitochondrial large subunit rRNA (16S; 529 basepairs) and cytochrome oxidase I (COI; 640 basepairs) genes. Results suggest that the speciose genera Panopeus and Eurypanopeus are not monophyletic and that their taxonomy does not accurately reflect evolutionary partitions. In two cases (P. herbstii complex and E. depressus and allies), the molecular findings strongly support sister-species relationships that differ from previous morphology-based assumptions. We suggest that convergence or morphological stasis are responsible for the phenotypic similarities between divergent evolutionary lineages. Received: 23 July 1999 / Accepted: 5 April 2000     

DNA barcoding of Pacific Canada’s fishes

DNA barcoding—sequencing a standard region of the mitochondrial cytochrome c oxidase 1 gene (COI)—promises a rapid, accurate means of identifying animals to a species level. This study establishes that sequence variability in the barcode region permits discrimination of 98% of 201 fish species from the Canadian Pacific. The average sequence variation within species was 0.25%, while the average distance separating species within genera was 3.75%. The latter value was considerably lower than values reported in other studies, reflecting the dominance of the Canadian fauna by members of the young and highly diverse genus Sebastes. Although most sebastids possessed distinctive COI sequences, four species did not. As a partial offset to these cases, the barcode records indicated the presence of a new, broadly distributed species of Paraliparis and the possibility that Paraliparis pectoralis is actually a species pair. The present study shows that most fish species in Pacific Canadian waters correspond to a single, tightly cohesive array of barcode sequences that are distinct from those of any other species, but also highlights some taxonomic issues that need further investigation.     

Comparative analysis on the genetic population structures of the deep-sea whelks <Emphasis Type="Italic">Buccinum tsubai</Emphasis> and <Emphasis Type="Italic">Neptunea constricta</Emphasis> in the Sea of Japan

The population structures of Buccinum tsubai and Neptunea constricta were compared using partial sequences of the mitochondrial COI gene. B. tsubai included four genetically distinguishable subpopulations (Hokkaido, Yamagata-Toyama, Yamato Bank, and San’in), which is consistent with the results of our previous study using mitochondrial 16SrRNA sequences. The genetic structure of N. constricta was also clear, but the lineage sorting corresponding to the geographical distribution was not as clear as that of B. tsubai. The difference between the genetic structures of these two species might be due to a difference in either their dispersal abilities or the historic distribution patterns in the Sea of Japan. The fossil record and nested clade analyses support the latter alternative. The four subpopulations of B. tsubai are estimated to have diverged 0.42–1.46 million years ago, providing support for the existence of intermediate water of normal salinity and oxygen concentration capable of sustaining B. tsubai between the low-salinity surface water and anoxic deep water during the Pleistocene glacial periods. The genetic diversity of the Yamato Bank subpopulation of B. tsubai was lower than that of the other subpopulations, which is likely attributable to the small size of the Yamato Bank subpopulation.     

Molecular relationships and species divergence among <Emphasis Type="Italic">Phragmatopoma</Emphasis> spp. (Polychaeta: Sabellaridae) in the Americas

Phragmatopoma spp. are marine, reef-building polychaetes that inhabit the intertidal and shallow subtidal zones of both coasts of the Americas. Phragmatopoma californica is found in the Pacific Ocean along the California coast south to Mexico, while Phragmatopoma caudata inhabits the Caribbean islands and Atlantic Ocean from the Florida coast south to Brazil. Although apparently geographically isolated, P. californica and P. caudata have been found to interbreed (Pawlik 1988a) and thus their specific taxonomic relationship has been unclear. In this study, two genes, cytochrome c oxidase subunit I (COI) and the first internal transcribed spacer region (ITS-1), were sequenced to assess the specific status of P. californica and P. caudata as well as Phragmatopoma virgini. Comparison of sequences revealed that samples of P. californica shared no COI haplotypes or ITS-1 sequences with P. caudata. Phylogenetic analyses, including maximum parsimony and Bayesian methods, clustered each species in separate, well-supported clades with genetic distances between them being greater than between either contested species or the uncontested, valid species, P. virgini. Thus, the molecular data support that P. californica and P. caudata are separate species. However, the sample of individuals of P. virgini included one genetically divergent individual, whose morphology was found to match that of a species formerly recognized as P. moerchi but since synonymized with P. virgini. Divergences among lineages were dated using the COI sequences, after adjustment for non-clock-like behavior. Consequently, we suggest that P. virgini and P. caudata are sister taxons and that P. californica diverged from the P. virgini/P. caudata clade ∼5.7 mya with P. virgini diverging from P. caudata ∼3 mya.     

Sexual maturity and hermaphroditism of the red porgy Pagrus pagrus (Teleostei: Sparidae)

Gonadal changes related to sexual maturity were examined by histology in reared populations of the red porgy Pagrus pagrus L., aged 0.5 to 6.5 years. More than 50% of red porgies were mature at the age of 4 years although some individuals were already mature at the age of 3, as indicated by changes in the gonadosomatic index, plasma levels of vitellogenin, 17β-estradiol and testosterone in females and males. Sex frequency distribution analysis in relation to the age and histological analysis of the gonads indicated the presence of males originated from the sex change of adult functional females. P. pagrus is a protogynous species. Some females had not changed sex up to the age of 6.5 years. Received: 16 July 1998 / Accepted: 29 April 1999     

Metabolic transformations of acquired lucibufagins by firefly “femmes fatales”

Summary. Female Photuris fireflies sequester defensive steroidal pyrones (lucibufagins) from male fireflies of the genus Photinus. Lucibufagin analyses of Photuris females and Photinus ignitus males show that the lucibufagin mixtures of predator and prey differ in their composition. Analyses of whole body extracts showed that P. ignitus males contain a mixture of eight non-glycosylated lucibufagins, composed mostly of compounds with two oxygenated positions in the steroidal A-ring (C-3, C-5). After feeding on P. ignitus males, Photuris females contain six major lucibufagins. Three of these compounds are not present in the prey, including the novel lucibufagin glycoside 5β,11α-dihydroxy-12-oxo-3β-O-β-D-xylopyranosylbufalin, and two other lucibufagins with a trioxygenated A-ring (C-2, C-3, C-5). These results indicate that Photuris females transform the sequestered lucibufagins both by glycosylation and oxidation, which could affect the systemic transportability of these compounds due to an increase in their polarity. Received 18 February 1999; accepted 19 April 1999.     

Invasion patterns inferred from cytochrome oxidase I sequences in three bryozoans, Bugula neritina, Watersipora subtorquata, and Watersipora arcuata

Nucleotide variation in cytochrome c oxidase subunit I (COI) was used to examine population structure in three invasive bryozoans: Bugula neritina (Linnaeus, 1758), Watersipora subtorquata (d’Orbigny, 1852), and W. arcuata (Banta, 1969). These species are found on ship hulls and have a short (≤2 days) larval phase. Samples were collected from 1998–2001 at multiple sites in Australia, and in Hong Kong, New Zealand, Hawaii, California, Curaçao, and England. B. neritina is known to include three cryptic species, including species Type S (Davidson and Haygood in Biol Bull 196:273–280, 1999) which occurs on the east and west coasts of the USA. One haplotype recorded previously in the USA, S1, was found to be widespread, occurring throughout Australia and in Hong Kong, Curaçao, Hawaii, and England. W. subtorquata, a Caribbean–Atlantic species which has invaded southern Australia, New Zealand, and California, had low nucleotide diversity in these areas (π=0.0016±0.0014), consisting of three haplotypes connected by one or two nucleotide mutations. W. arcuata, an Eastern-Pacific native, had comparatively high diversity (π=0.0221±0.0115) in introduced populations from Australia and Hawaii. In each species, identical haplotypes were identified on separate coastlines providing evidence of widespread, rather than genetically independent, introductions. The major contrast in nucleotide diversity suggests that different propagule-source models explain introductions.     

Spatial and temporal distributions of copepods to leeward and windward of Oahu, Hawaiian Archipelago

The spatial and temporal distributions of two island-associated copepod species, Undinula vulgaris Dana and Labidocera madurae Scott, were compared to the distributions of two open ocean species, Cosmocalanus darwinii Lubbock and Scolecithrix danae Lubbock, along 28-km windward and leeward transects off the island of Oahu, Hawaii. Samples were taken in September and December 1985 and April and June 1986. A warm, low salinity pool on the leeward side was a prominent feature during all transects except December. The abundances of the two oceanic species did not change significantly between leeward and windward stations, with distance from shore, or between September 1985 and April 1986 samples. As expected, very high abundances of U. vulgaris occurred at some nearshore stations, up to 3 g dry wt m⁻² for adults alone. Calculations of respiratory loss at these densities (0.7 g C m⁻² d⁻¹) suggest a high local productivity would be required to meet these demands. L. madurae, a surface-dwelling species normally restricted to within 1 km of shore, was an effective indicator species of nearshore water movement. It was more common in offshore samples on the leeward transects, rarely being found offshore on the windward side, consistent with prevailing currents and the presence of the leeward warm, low salinity pool. The occurrence of a strong mixing event in April 1986 resulted in L. madurae being distributed throughout the upper 100 m of the water column. The presence of oceanic species close to shore on the windward side also coincided with this wind-driven event. The primary environmental influence on vertical distributions was daytime cloud cover, with U. vulgaris tending to be found shallower on cloudy days. Of the two oceanic species, S. danae exhibited the most pronounced vertical migration, however, vertical distributions were not significantly correlated with environmental factors for either species. The abundant nearshore U. vulgaris population cannot be explained by differences in vertical distribution between it and the two oceanic species that might allow a physical mechanism to concentrate U. vulgaris. A high population growth rate is likely necessary to explain U. vulgaris' dominance. Received: 26 June 1998 / Accepted: 31 March 1999     

Low levels of global genetic differentiation and population expansion in the deep-sea teleost <Emphasis Type="Italic">Hoplostethus atlanticus</Emphasis> revealed by mitochondrial DNA sequences

The orange roughy Hoplostethus atlanticus is a well-known commercial species with a global distribution. There is no consensus about levels of connectivity among populations despite a range of techniques having been applied. We used cytochrome c oxidase subunit I (COI) and cytochrome b sequences to study genetic connectivity at a global scale. Pairwise Φ_ST analyses revealed a lack of significant differentiation among samples from New Zealand, Australia, Namibia, and Chile. However, low but significant differentiation (Φ_ST = 0.02–0.13, P < 0.05) was found between two Northeast Atlantic sites and all the other sites with COI. AMOVA and the haplotype genealogy confirmed these results. The prevalent lack of genetic differentiation is probably due to active adult dispersal under the stepping-stone model. Demographic analyses suggested the occurrence of two expansion events during the Pleistocene period.     

Life under Arctic sea ice – reproduction strategies of two sympagic (ice-associated) amphipod species, Gammarus wilkitzkii and Apherusa glacialis

The reproductive strategies of two gammaridean amphipod species, Gammarus wilkitzkii and Apherusa glacialis, that permanently inhabit the Arctic sea ice were investigated. G. wilkitzkii reaches sexual maturity at an age of 2 years and produces 128 ± 54 eggs fem.⁻¹ yr⁻¹. Mating takes place during fall and winter, and the development of the large eggs (0.60 to 0.80 mm diam.) lasts 6 to 7 months. The sex ratio of G. wilkitzkii was dominated by males in a proportion of 1.5:1. In vivo studies showed that juveniles are released in batches from the brood pouches of the females during April and May. A. glacialis reaches sexual maturity at the age of 1 year and produces 555 ± 151 eggs fem.⁻¹ yr⁻¹. The eggs are between 0.18 and 0.23 mm in diameter, and are the smallest known for gammaridean amphipods. Eggs are kept in packages of two to eight in the brood pouches of females. The sex ratio of A. glacialis was dominated by females in a proportion of 3:1. The high fecundity of both amphipod species, the release of juveniles in batches over a period of time, a high proportion of females (A. glacialis), and an elongated life-span with multiple spawnings (G. wilkitzkii) are discussed as possible adaptations to the specific and highly variable conditions under Arctic sea ice. Received: 29 December 1999 / Accepted: 8 March 2000     

Evidence of limited gene flow in three species of coral reef fishes in the lagoon of New Caledonia

Allozyme variation was used to investigate the genetic structure of the coral reef fishes Stegastes nigricans, Epinephelus merra and Acanthurus triostegus around New Caledonia. Each species was sampled from each of three sites in the ≃1000 km circumference of the lagoon of New Caledonia. Allelic variation was recorded for each species at 14, 13 and 17 loci, respectively, and heterozygosity diversity (H s) was 0.082, 0.065 and 0.116, respectively. Analysis of genetic differentiation between sites produced inconsistent results between species, with spatial heterogeneity in two species (S. nigricans, F st  = 0.038; A. triostegus, F st = 0.049) and homogeneity in one species (E. merra, F st = 0.000). Hydrological and climatic data from the lagoon suggest that the eastern and western sides of the lagoon are isolated, since they lie in water masses of different origin. This may explain the genetic differentiation and restricted gene flow found at a local scale for S. nigricans and A. triostegus. Homogeneity in populations of E. merra is discussed in relation to its low genetic diversity and its reproductive behaviour. Received: 23 April 1997 / Accepted: 25 September 1997     

Molecular phylogeny of vestimentiferans collected around Japan, revealed by the nucleotide sequences of mitochondrial DNA

The phylogenetic relationships among local populations of undescribed vestimentiferan species that belong to the genera Lamellibrachia and Escarpia and had been collected at six sites around Japan were analyzed on the basis of the partial (1023 bp) nucleotide sequences of the mitochondrial gene for cytochrome oxidase I (COI), using a pogonophoran and a polychaete as outgroups. The identical amino acid sequence was deduced from the nucleotide sequence obtained from each of the vestimentiferans analyzed. The strong similarity among deduced amino acid sequences of COI suggested a close relationship between vestimentiferans and pogonophorans. On the basis of the phylogenetic relationships, the analyzed vestimentiferan populations were classified tentatively as five species. The genetic differentiation of vestimentiferans was suggested to occur bathymetrically as well as being a consequence of horizontal segregation. Two of these tentatively identified species inhabit both a hydrothermal area and a cold seep area, as is the case for some species of bivalves that belong to the genera Bathymodiolus and Calyptogena. Received: 28 August 1996 / Accepted: 2 October 1996     

Genetic diversity of Nymphon (Arthropoda: Pycnogonida: Nymphonidae) along the Antarctic Peninsula with a focus on Nymphon australe Hodgson 1902

Sea spiders are conspicuous, and often abundant, members of the Antarctic benthic community. Nymphonidae (Pycnogonida) in Southern Ocean waters comprise over 240 species which are often difficult to assign due to their intraspecific ‘highly variable’ morphology. In particular, Nymphon australe, the numerically dominant species in Antarctic waters is known to have a high level of phenotypic variation in external morphology and is also reported to have a circumpolar distribution. Circumpolarity seems contradictory to the pycnogonid’s brooding lifestyle and presumably limited dispersal. Here we examine the genetic diversity of several Nymphon species collected in the Antarctic Peninsular region. Concomitantly, we assess the genetic structure of N. australe to gain insight into Nymphon dispersal capacity. Cytochrome c oxidase subunit I (COI) and 16S ribosomal gene data suggest a recent common history and/or recent gene-flow of N. australe populations across nearly 800 km of the Antarctic Peninsula. Furthermore, these data support that the Antarctic Peninsula region may hold two previously unrecognized species of Nymphon. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Eurythoe complanata (Polychaeta: Amphinomidae), the ‘cosmopolitan’ fireworm, consists of at least three cryptic species

Eurythoe complanata (Pallas 1766) has been considered a cosmopolitan species with a great morphological similarity across its geographic range. To elucidate whether E. complanata is actually a single species, genetic (cytochrome oxidase subunit I and allozymes) and morphological differences were compared among specimens from the Pacific, Caribbean, and South Atlantic Oceans. Large levels of COI divergence (10–22%) and diagnostic allozyme loci identified three cryptic species: one in the eastern Pacific and two in the Atlantic, with one being morphologically differentiated and found only in islands. COI sequences between Pacific and Atlantic lineages were much more divergent than those of other transisthmian invertebrates, indicating their split before the Panama Isthmus closure or a faster evolutionary rate of COI for this species. The existence of two Atlantic species may be a consequence of parapatric speciation followed by a secondary invasion or even a sympatric speciation in the Atlantic oceanic islands.     

Population structure of Brachidontes pharaonis (P. Fisher, 1870) (Bivalvia, Mytilidae) in the Mediterranean Sea, and evolution of a novel mtDNA polymorphism

Brachidontes pharaonis (Fisher P, 1870) is an Indo-Pacific mussel that has colonized the Mediterranean Sea via the Suez Canal. Mussels may have migrated by natural dispersal of pelagic larvae, or they may have been transported on the hulls of ships, or in ballast water, or by some combination of these. Mitochondrial COI sequences (618 bp) from 101 mussels from six localities in the central and eastern Mediterranean Sea and from one site in the Red Sea were used to describe population structure. Analysis of molecular variance indicated that frequencies differed among populations, and that 92% of the variation resided within populations. The majority of haplotypes were private alleles. No simple pattern of longitudinal variation was detected for haplotype frequencies, haplotype diversity, or nucleotide diversity. A variety of tree-building algorithms (NJ, MP, ME) gave consistent results, showing two sister groups. One clade had a leucine (L-form) and the other one a methionine (M-form) at the 30th amino acid. These sympatric forms were detected within all localities and they had similar frequencies in males and females. The M- and L-form were separated by a 7.3% sequence divergence, indicating that this is an ancient polymorphism. Closely related species of mussels had exclusively the L-form, so we infer that the M-form evolved from the L-form lineage of B. pharaonis, probably in the northern portion of the Red Sea. Neutrality tests detected an excess of rare mutations, a pattern of variation expected in expanding populations. Patterns of variation detected by Tajima’s D suggest that some form of balancing selection has maintained this polymorphism.     

Scramble competition selects for greater tailfin size in male red-spotted newts (Amphibia: Salamandridae)

Darwin predicted that scramble competition for access to reproductive females would result in sexual dimorphism of locomotory structures, but direct evidence for this is extremely rare. I examined the relationship between variation in tailfin size and mating success in a field and laboratory study of red-spotted newts, Notophthalmus viridescens. Over three breeding seasons, male tailfin size was positively correlated with variation in male amplexus frequency, and indirectly correlated with male insemination frequency. In a laboratory study, I confirmed that males' ability to capture females is affected by variation in tailfin size. This is the first study to show that naturally occurring variation in male locomotory structures affects male mating success. It corroborates the prediction that scramble competition leads to sexual selection on locomotory structures and, potentially, to dimorphism in these structures. Received: 16 April 1999 / Received in revised form: 16 May 1999 / Accepted: 12 June 1999     

The genetic mating system of a sex-role-reversed pipefish (Syngnathus typhle): a molecular inquiry

In the pipefish Syngnathus typhle as in other species of Syngnathidae, developing embryos are reared on the male's ventral surface. Although much laboratory research has been directed toward understanding sexual selection in this sex-role-reversed species, few studies have addressed the mating behavior of S. typhle in the wild, and none has capitalized upon the power of molecular genetic assays. Here we present the first direct assessment of the genetic mating system of S. typhle in nature. Novel microsatellite loci were cloned and characterized from this species, and employed to assay entire broods from 30 pregnant, field-captured males. Genetic analysis of 1340 embryos revealed that 1–6 females (mean = 3.1) contributed to each brooded clutch, the highest rate of multiple maternity yet documented in any pipefish. Evidence of multiple mating by females was also detected. Thus, this population of S. typhle displays a polygynandrous mating system, a finding consistent with previous field and laboratory observations. Our results, considered together with similar studies of other syngnathid species, provide preliminary support for the hypothesis that the genetic mating system is related to the evolution of sexual dimorphism in the fish family Syngnathidae. Received: 19 January 1999 / Received in revised form: 15 April 1999 / Accepted: 9 May 1999     

Phylogeographic patterns of the mysid Mesopodopsis slabberi (Crustacea, Mysida) in Western Europe: evidence for high molecular diversity and cryptic speciation

The phylogeographic patterns among populations of Mesopodopsis slabberi (Crustacea, Mysida), an ecological important mysid species of marine and estuarine habitats, were analysed by means of DNA sequencing of a fragment of the mitochondrial cytochrome c oxidase subunit I (COI) and the 16S ribosomal RNA genes. Samples of M. slabberi collected from five Atlantic and two Western Mediterranean populations were investigated. Very high levels of within-population molecular diversity were observed in all samples (mean h=0.807 and π=0.0083), with exception of the Mediterranean Ebro population which contained only one haplotype. Differentiation among populations was high, and a clear phylogeographic break was observed between the Atlantic and Mediterranean populations. Moreover, a strong differentiation was detected between both populations in the Western Mediterranean Sea (Alicante and Ebro delta), while two divergent lineages occurred in sympatry within the Atlantic Mondego estuary. The high congruence between both the COI and 16S rRNA sequence data, the reciprocal monophyly of the different mitochondrial clades and the levels of nucleotide divergence between them suggest the presence of a complex of cryptic species within M. slabberi. Estimations of divergence time between the different mitochondrial lineages indicate that a split occurred during the late Miocene/early Pliocene. Such a divergence could be concordant with vicariant events during sea-level drops within the Mediterranean region at that time. However, within the Mediterranean Sea, the potential of divergence through ecological diversification cannot be ruled out.