Evolution and diversification within the intertidal brown macroalgae Fucus spiralis/F. vesiculosus species complex in the North Atlantic

We examined 733 individuals of Fucusspiralis from 21 locations and 1093 Fucusvesiculosus individuals from 37 locations throughout their northern hemisphere ranges using nuclear and mitochondrial markers. Three genetic entities of F. spiralis were recovered. In northern and sympatric populations, the presence of "F. spiralis Low" in the mid-intertidal and "F. spiralis High" in the high-intertidal was confirmed and both co-occurred with the sister species F. vesiculosus. The third and newly-discovered entity, "F. spiralis South", was present mainly in the southern range, where it did not co-occur with F. vesiculosus. The South entity diverged early in allopatry, then hybridized with F. vesiculosus in sympatry to produce F. spiralis Low. Ongoing parallel evolution of F. spiralis Low and F. spiralis High is most likely due to habitat preference/local selection and maintained by preferentially selfing reproductive strategies. Contemporary populations of F. spiralis throughout the North Atlantic stem from a glacial refugium around Brittany involving F. spiralis High; F. spiralis South was probably unaffected by glacial episodes. Exponential population expansion for F. vesiculosus began during the Cromer and/Holstein interglacial period (300,000-200,000 yrs BP). Following the last glacial maximum (30,000-22,000 yrs BP), a single mtDNA haplotype from a glacial refugium in SW Ireland colonized Scandinavia, the Central Atlantic islands, and the W Atlantic.     

Post-ice age recolonization and differentiation of Fucus serratus L. (Phaeophyceae; Fucaceae) populations in Northern Europe

The seaweed Fucus serratus is hypothesized to have evolved in the North Atlantic and present populations are thought to reflect recolonization from a southern refugium since the last glacial maximum 18 000-20 000 years bp. We examined genetic structure across several spatial scales by analysing seven microsatellite loci in populations collected from 21 localities throughout the species' range. Spatial auto-correlation analysis of seven microsatellite loci revealed no evidence for spatial clustering of alleles on a scale of 100 m despite limited gamete dispersal in F. serratus of approximately 2 m from parental individuals. Pairwise theta analysis suggested that the minimal panmictic unit for F. serratus was between 0.5 and 2 km. Isolation by distance was significant along some contiguous coastlines. Population differentiation was strong within the Skagerrak-Kattegat-Baltic Seas (SKB) (global theta= 0.17) despite a short history of approximately 7500 years. A neighbour-joining tree based on Reynold's distances computed from the microsatellite data revealed a central assemblage of populations on the Brittany Peninsula surrounded by four well-supported clusters consisting of the SKB, the North Sea (Ireland, Helgoland), and two populations from the northern Spanish coast. Samples from Iceland and Nova Scotia were most closely aligned with northwest Sweden and Brittany, respectively. When sample sizes were standardized (N = 41), allelic diversity was twofold higher for Brittany populations than for populations to the north and threefold higher than southern populations. The Brittany region may be a refugium or a recolonized area, whereas the Spanish populations most likely reflect present-day edge populations that have undergone repeated bottlenecks as a consequence of thermally induced cycles of recolonization and extinction.     

A mtDNA-based phylogeny of the brown algal genus Fucus (Heterokontophyta; Phaeophyta)

Species of Fucus are among the dominant seaweeds along Northern Hemisphere shores, but taxonomic designations often are confounded by significant intraspecific morphological variability. We analyzed intra- and inter-specific phylogenetic relationships within the genus (275 individuals representing 16 taxa) using two regions of the mitochondrion: a variable intergenic spacer and a conserved portion of the 23S subunit. Bayesian ML and MP analyses verified a shallow phylogeny with two major lineages (previously reported) and resolved some intra-lineage relationships. Significant species-level paraphyly/polyphyly was observed within lineages 1A and 2. Despite higher species richness in the North Atlantic, a North Pacific origin of the genus is supported by a gradient of decreasing haplotype and nucleotide diversities in F. distichus from the North Pacific to the East Atlantic.     

Arsenic binding to Fucus vesiculosus metallothionein

The seaweed Fucus vesiculosus is a member of the brown algae family. Kille and co-workers [Biochem. J. 338 (1999) 553] reported that this species contains the gene for metallothionein. Metallothionein is a metalloprotein having low molecular weight, and high cysteine content, which binds a range of metals. F. vesiculosus bioaccumulates arsenic from the aquatic environment [Mar. Chem. 18 (1986) 321]. In this paper we describe arsenic binding to F. vesiculosus metallothionein, characterized by electrospray ionization mass spectrometry. Five arsenic-MT species were detected with increasing As to protein ratios. These results provide important information about the metal-chelation behaviour of this novel algal metallothionein which is a putative model for arsenic binding to F. vesiculosus in vivo.     

Trans‐Pacific and trans‐Arctic pathways of the intertidal macroalga Fucus distichus L. reveal multiple glacial refugia and colonizations from the North Pacific to the North Atlantic

Aim We examined the phylogeography of the cold‐temperate macroalgal species Fucus distichus L., a key foundation species in rocky intertidal shores and the only Fucus species to occur naturally in both the North Pacific and the North Atlantic. Location North Pacific and North Atlantic oceans (42° to 77° N). Methods We genotyped individuals from 23 populations for a mitochondrial DNA (mtDNA) intergenic spacer (IGS) (n = 608) and the cytochrome c oxidase subunit I (COI) region (n = 276), as well as for six nuclear microsatellite loci (n = 592). Phylogeographic structure and connectivity were assessed using population genetic and phylogenetic network analyses. Results IGS mtDNA haplotype diversity was highest in the North Pacific, and divergence between Pacific haplotypes was much older than that of the single cluster of Atlantic haplotypes. Two ancestral Pacific IGS/COI clusters led to a widespread Atlantic cluster. High mtDNA and microsatellite diversities were observed in Prince William Sound, Alaska, 11 years after severe disturbance by the 1989 Exxon Valdez oil spill. Main conclusions At least two colonizations occurred from the older North Pacific populations to the North Atlantic between the opening of the Bering Strait and the onset of the Last Glacial Maximum. One colonization event was from the Japanese Archipelago/eastern Aleutians, and a second was from the Alaskan mainland around the Gulf of Alaska. Japanese populations probably arose from a single recolonization event from the eastern Aleutian Islands before the North Pacific–North Atlantic colonization. In the North Atlantic, the Last Glacial Maximum forced the species into at least two known glacial refugia: the Nova Scotia/Newfoundland (Canada) region and Andøya (northern Norway). The presence of two private haplotypes in the central Atlantic suggests the possibility of colonization from other refugia that are now too warm to support F. distichus. With the continuing decline in Arctic ice cover as a result of global climate change, renewed contact between North Pacific and North Atlantic populations of Fucus species is expected.     

Drifting fronds and drifting alleles: range dynamics,local dispersal and habitat isolation shape the population structure of the estuarine seaweed Fucus ceranoides

Aim The seaweed Fucus ceranoides is restricted to spatially discrete estuarine habitats and lacks planktonic dispersal phases; it is therefore expected to exhibit strong population differentiation. Its cold‐temperate affinities and mtDNA variation imply that the northern part of the species’ range, where F. ceranoides is now ubiquitous, was recently colonized after the onset of the last deglaciation, potentially resulting in areas with greater genetic homogeneity. Here we examine the population structure of F. ceranoides to test these predictions, emphasizing the contrasting genetic signatures of limited dispersal in refugial versus recently colonized regions. Location North‐eastern Atlantic estuaries from Portugal to Norway. Methods A total of 504 individuals from 21 estuarine sites spanning the entire range of F. ceranoides were sampled and genotyped for nine microsatellite loci. Population structure was inferred from several genotypic and allele‐frequency analyses. Geographical patterns of genetic diversity were used to reconstruct the historical biogeography of the species. Results Genetic diversity and regional population differentiation showed a consistent decline with increasing latitude. Southernmost populations harboured most of the endemic variation, whereas the northern populations (> 55° N) were almost fixed for the same alleles across loci. In southern and central regions of its distribution, F. ceranoides showed striking population subdivision, with many of the sampled estuaries corresponding to coherent genetic units that were easily discriminated from one another with standard clustering methods. Main conclusions The geographical pattern of genetic diversity supports the long‐term refugial status of Iberia and a post‐glacial range expansion of F. ceranoides into previously glaciated latitudes. Despite the species’ capacity to colonize newly available habitats, the genetic structure of F. ceranoides outside the recently (re)colonized range reveals that gene flow between populations is extremely low. This study provides a remarkable example of how infrequent and spatially limited dispersal can have contrasting effects at the scales of meta‐population (connectivity) versus range dynamics (habitat tracking), and of how dispersal restrictions can result in either genetic divergence or homogeneity depending on the maturity and demographic conditions of the populations.     

Numerical taxonomy of some taxa of the genus Fucus in the Iberian Peninsula

A study of morphological variation patterns in three Iberian Fucus species has been carried out. Data on 36 features from 113 specimens have been studied by numerical methods (PCA, discriminant analysis and ANOVA).The PCA ordination displayed a continuous trend of variation in the following Fucus species: F. ceranoides, F. vesiculosus and F. spiralis. However, no obvious morphological discontinuities have been observed. In addition, three varieties of F. spiralis and five of F. vesiculosus have been identified.At the varietal level discriminant functions could be used for identifying 93–100% of the individuals within F. vesiculosus and 72–91% of F. spiralis.The most discriminating diagnostic character appeared to be the midrib size, as detected by ANOVA procedures.Some qualitative characters, such as presence of vesicles, dioecious-monoecious character and receptacle edge shape, frond and receptacle shape, have been also important for discriminating specific and infraspecific taxa.A nomenclatural discussion of varietal taxa is also included.     

Cadmium tolerance and adsorption by the marine brown alga Fucus vesiculosus from the Irish Sea and the Bothnian Sea

Cadmium (Cd) uptake capacities and Cd tolerance of the marine alga Fucus vesiculosus from the Irish Sea (salinity 35 psu) and from the Bothnian Sea (northern Baltic, 5 psu) were quantified. These data were complemented by measurements of changes in maximal photosynthetic rate (P(max)), dark respiration rate and variable fluorescence vs. maximal fluorescence (F(v):F(m)). At concentrations between 0.01 and 1 mmol Cd l(-1), F. vesiculosus from the Bothnian Sea adsorbed significantly more (about 98%) Cd compared with F. vesiculosus from the Irish Sea. The photosynthetic measurements showed that the Bothnian Sea F. vesiculosus were more sensitive to Cd exposure than the Irish Sea algae. The algae from the Irish Sea showed negative photosynthetic effects only at 1 mmol Cd l(-1), which was expressed as a decreased P(max) (-12.3%) and F(v):F(m) (-4.6%). On the contrary, the algae from the Bothnian Sea were negatively affected already at Cd concentrations as low at 0.1 mmol Cd l(-1). They exhibited increased dark respiration (+11.1%) and decreased F(v):F(m) (-13.9%). The results show that F. vesiculosus from the Bothnian Sea may be an efficient sorption substrate for Cd removal from Cd contaminated seawater and this algae type may also have applications for wastewater treatment.     

Phenotypic and genotypic analysis of Flavobacterium psychrophilum isolates from Ontario salmonids with bacterial coldwater disease

Flavobacterium psychrophilum is the causative agent of bacterial coldwater disease (BCWD) and rainbow trout fry syndrome. BCWD has a considerable economic impact on aquaculture operations in Ontario, Canada, and our limited understanding of the population structure and epidemiology of F. psychrophilum isolates is an impediment to the development of improved management strategies. Seventy-five 16S rRNA gene and gyr polymerase chain reaction positive isolates of F. psychrophilum that had been collected over a 16-year period from farmed salmonids with tail rot, necrotic myositis, and osteochondrosis were characterized morphologically, biochemically, and genotypically. Although the isolates were homogeneous by preliminary biochemical and phenotypic characterization, two distinct biovars were found by API ZYM testing. As well, four restriction pattern types were detected by 16S rRNA polymerase chain reaction - restriction fragment length polymorphism analysis and there was a significant (P < 0.001) correlation between biovar I and digestion with MaeIII and between biovar II and digestion with MnlI or no site (P < 0.05). Further heterogenity was detected by sequence analysis of a 194 bp stem loop 3 region of rRNA. Nine sequence types were identified; 40/46 biovar I isolates were sequence type "a", while 21/32 biovar II isolates belonged to either sequence type "c" or "d". More than one biovar and genotype was identified among the strains recovered from separate fish sampled from three groups of rainbow trout (Oncorhynchus mykiss) experiencing BCWD mortality events. No association was found between genotype or biovar and type of disease. Taken together, these data suggest that F. psychrophilum from Ontario can be grouped into two major lineages based on biovar and 16S rRNA polymorphisms, and although three major strain types were most frequently isolated in this study, it appears that the population of F. psychrophilum with pathogenic potential is quite heterogeneous.     

Molecular markers reveal genetic isolation and phylogeography of the S and F intersterility groups of the wood-decay fungus Heterobasidion annosum

The root-rot fungus Heterobasidion annosum (Fr.) Bref. species complex consists of three intersterility groups (S, F, and P), separated by their host affinity. The phylogenetic relationship of the species complex was studied, with the focus on the S and F groups, by comparing DNA sequences of four nuclear gene fragments: calmodulin, glyceraldehyde 3-phosphate dehydrogenase, heat stress protein 80-1, and elongation factor 1-alpha, and one anonymous locus, from 29 fungal isolates originating from Europe, Asia, and North America. The phylogeny of each separate gene locus as well as the combined dataset consisted of three main clades: European F group isolates, Euroasian S group isolates, and North American S group isolates, suggesting them to be separated into phylogenetic species. The results also support the hypothesis of an early separation between the S and F groups, indicating that their distribution have followed their host tree species for a considerable time period.     

Geographic variation in fitness‐related traits of the bladderwrack Fucus vesiculosus along the Baltic Sea‐North Sea salinity gradient

In the course of the ongoing global intensification and diversification of human pressures, the study of variation patterns of biological traits along environmental gradients can provide relevant information on the performance of species under shifting conditions. The pronounced salinity gradient, co‐occurrence of multiple stressors, and accelerated rates of change make the Baltic Sea and its transition to North Sea a suitable region for this type of study. Focusing on the bladderwrack Fucus vesiculosus, one of the main foundation species on hard‐bottoms of the Baltic Sea, we analyzed the phenotypic variation among populations occurring along 2,000 km of coasts subjected to salinities from 4 to >30 and a variety of other stressors. Morphological and biochemical traits, including palatability for grazers, were recorded at 20 stations along the Baltic Sea and four stations in the North Sea. We evaluated in a common modeling framework the relative contribution of multiple environmental drivers to the observed trait patterns. Salinity was the main and, in some cases, the only environmental driver of the geographic trait variation in F. vesiculosus. The decrease in salinity from North Sea to Baltic Sea stations was accompanied by a decline in thallus size, photosynthetic pigments, and energy storage compounds, and affected the interaction of the alga with herbivores and epibiota. For some traits, drivers that vary locally such as wave exposure, light availability or nutrient enrichment were also important. The strong genetic population structure in this macroalgae might play a role in the generation and maintenance of phenotypic patterns across geographic scales. In light of our results, the desalination process projected for the Baltic Sea could have detrimental impacts on F. vesiculosus in areas close to its tolerance limit, affecting ecosystem functions such as habitat formation, primary production, and food supply.     

Photosynthesis in relation to D1, PsaA and Rubisco in marine and brackish water ecotypes of Fucus vesiculosus and Fucus radicans (Phaeophyceae)

The aim of this study was to investigate photosynthetic differences between the marine, Norwegian Sea ecotype and the brackish, Bothnian Sea ecotype of F. vesiculosus and F. radicans and to see whether photosynthetic differences could be connected with the relative amounts of D1 protein (PSII), PsaA (PSI) protein and/or Rubisco. For this purpose, we tested if a higher photosynthetic maximum (P _max) in the Atlantic Ocean ecotype of F. vesiculosus relative to the Baltic Sea ecotype, and an increase of the P _max in Baltic Sea ecotype of F. vesiculosus at higher salinity, could be due to an increase in the relative amounts of Rubisco. The proteins have been evaluated on a relative basis. Immunoblot signals showed that the amount of Rubisco was higher in both ecotypes of F. vesiculosus than in F. radicans, but no differences could be detected between the two ecotypes of F. vesiculosus. The results suggest an uneven photosystem protein stoichiometry in Fucus, with more of the PSI protein PsaA relative to the PSII protein D1. The difference in P _max between the two ecotypes of F. vesiculosus might be related to the difficulties for the algae to adapt to the environment in Bothnian Sea.     

Two Theileria cervi SSU RRNA gene sequence types found in isolates from white-tailed deer and elk in North America.

Two Theileria cervi SSU rRNA gene sequence Types, F and G, from white-tailed deer (Odocoileus virginianus) and elk (Cervus elaphus canadensis) isolates in North America were confirmed. Previously, nucleotide sequencing through a single variable (V4) region showed the presence of SSU rRNA gene Types F and G in T. cervi isolates from white-tailed deer and an elk. In this study, both sequence types were found in four T. cervi isolates (two from deer and two from elk). Microheterogeneity only appeared in the Type G gene, resulting in Subtypes G1, G2 and G3. Subtype G1 was found in two elk and one white-tailed deer T. cervi isolate; Subtypes G2 and G3 were found in a white-tailed deer T. cervi isolate. The Type F SSU rRNA genes were identical in nucleotide sequence in both elk and white-tailed deer T. cervi isolates. The high degree of conservation in the Type F variable regions may be exploited to design specific oligonucleotide primers for parasite detection by the polymerase chain reaction in cervine or tick hosts.     

Isolation and cross‐species amplification of microsatellite loci from the fucoid seaweeds Fucus vesiculosus,F. serratus and Ascophyllum nodosum (Heterokontophyta,Fucaceae)

The Fucaceae is a family of brown seaweeds that dominate and frequently co‐occur on North Atlantic rocky shores. We developed nine polymorphic microsatellite markers for the fucoid seaweeds Fucus vesiculosus, F. serratus and Ascophyllum nodosum using a combined, enriched library. Six of these loci were polymorphic in at least two species, showing from two to eight alleles with heterozygosities ranging from 0.41 to 0.85. Loci were also tested on F. spiralis, revealing five polymorphic microsatellite loci in this species.     

Low Divergence in rDNA ITS Sequences Among Five Species of Fucus (Phaeophyceae) Suggests a Very Recent Radiation

Sequences from the two ribosomal DNA internal transcribed spacers (ITS1 and ITS2) were compared among five species of Fucus. Based on the present taxon sampling, parsimony analysis showed that Fucus serratus is the sister-group of the remaining Fucus species when Ascophyllum nodosum was used as an outgroup. The topology of the tree was (Fucus serratus (F. lutarius (F. vesiculosus (F. spiralis+F. ceranoides)))). The extremely low variation observed suggests a very recent radiation of the genus which supports the view widely accepted that the Fucales are among the most evolutionarily advanced of the brown algae. We further note that sequence differences between Fucus and Ascophyllum were 28%: this does not rule out the utility of ITS sequences within the Fucaceae. The very low number of informative positions allows to demonstrate empirically that distance matrix methods group on the basis of symplesiomorphies. Received: 17 February 1997 / Accepted: 17 April 1997     

Genetic structure and the North American postglacial expansion of the barnacle, Semibalanus balanoides

Population genetic characteristics are shaped by the life-history traits of organisms and the geologic history of their habitat. This study provides a neutral framework for understanding the population dynamics and opportunities for selection in Semibalanus balanoides, a species that figures prominently in ecological and evolutionary studies in the Atlantic intertidal. We used mitochondrial DNA (mtDNA) control region (N = 131) and microsatellite markers (～40 individuals/site/locus) to survey populations of the broadly dispersing acorn barnacle from 8 sites spanning 800 km of North American coast and 1 site in Europe. Patterns of mtDNA sequence evolution were consistent with larger population sizes in Europe and population expansion at the conclusion of the last ice age, approximately 20?000 years ago, in North America. A significant portion of mitochondrial diversity was partitioned between the continents (?(ST) = 0.281), but there was only weak structure observed from mtDNA within North America. Microsatellites showed significant structuring between the continents (F(ST) = 0.021) as well as within North America (F(ST) = 0.013). Isolation by distance in North America was largely driven by a split between populations south of Cape Cod and all others (P < 10(-4)). The glacial events responsible for generating allelic diversity at mtDNA and microsatellites may also be responsible for generating selectable variation at metabolic enzymes in S. balanoides.     

Early embryo development in Fucus distichus is auxin sensitive

Auxin and polar auxin transport have been implicated in controlling embryo development in land plants. The goal of these studies was to determine if auxin and auxin transport are also important during the earliest stages of development in embryos of the brown alga Fucus distichus. Indole-3-acetic acid (IAA) was identified in F. distichus embryos and mature tissues by gas chromatography-mass spectroscopy. F. distichus embryos accumulate [(3)H]IAA and an inhibitor of IAA efflux, naphthylphthalamic acid (NPA), elevates IAA accumulation, suggesting the presence of an auxin efflux protein complex similar to that found in land plants. F. distichus embryos normally develop with a single unbranched rhizoid, but growth on IAA leads to formation of multiple rhizoids and growth on NPA leads to formation of embryos with branched rhizoids, at concentrations that are active in auxin accumulation assays. The effects of IAA and NPA are complete before 6 h after fertilization (AF), which is before rhizoid germination and cell division. The maximal effects of IAA and NPA are between 3.5 and 5 h AF and 4 and 5.5 h AF, respectively. Although, the location of the planes of cell division was significantly altered in NPA- and IAA-treated embryos, these abnormal divisions occurred after abnormal rhizoid initiation and branching was observed. The results of this study suggest that auxin acts in the formation of apical basal patterns in F. distichus embryo development.     

Characterization of microsatellite loci in the marine seaweeds,Fucus serratus and F. evanescens (Heterokontophyta; Fucaceae)

Fucus serratus and F. evanescens commonly occur on Northern European shores. Nine microsatellite loci were developed for F. serratus (8–22 alleles, observed heterozygosities = 0.367–0.850) and one for F. evanescens (seven alleles, observed heterozygosity = 0.804). Cross‐amplification was apparent, as five F. serratus loci were polymorphic in F. evanescens and 2–5 were polymorphic in F. vesiculosus, F. distichus, and F. spiralis.