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Paralia (Bacillariophyta) stowaways in ship ballast: implications for biogeography and diversity of the genus.

MacGillivary ML, Kaczmarska I - J Biol Res (Thessalon) (2015)

Bottom Line: Frustule morphology did not segregate species, however, comparisons of sequence fragments and ITS2 secondary structures yielded a new species from North American waters, P. guyana (with four genodemes), and another widely-distributed species, P. marina.Despite this, as of 2009, P. marina was found only in Cheticamp, Nova Scotia, Canada.Second, genetic analysis readily segregated cryptic and semi-cryptic taxa of Paralia, highlighting the usefulness of the molecular approach to species recognition, e.g., in programs monitoring alien introductions.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Mount Allison University, 63B York Street, Sackville, NB E4L 1G7 Canada.

ABSTRACT

Background: The genus Paralia Heiberg is one of the most recognizable, widely distributed and commonly reported diatoms from contemporary coastal marine environments and ship ballast. Species discovery has historically been made in diatoms through the recognition of morphological discontinuities between specimens, first using light and later electron microscopy. However, recently, morphologically semi-cryptic species of Paralia were delineated using genetic analyses, among mostly tropical and subtropical sites.

Results: Ten morphological characters of the frustules and sequence fragments from the nuclear genome (conserved 18S regions of ribosomal RNA and the variable internal transcribed spacer [ITS]), and from the RuBisCo large subunit (rbcL) gene of the chloroplast genome were examined. Frustule morphology did not segregate species, however, comparisons of sequence fragments and ITS2 secondary structures yielded a new species from North American waters, P. guyana (with four genodemes), and another widely-distributed species, P. marina. The latter was lecto- and epitypified here because it is most similar to specimens in the type preparation BM1021 representing Smith's concept of the species. Paralia marina and certain genodemes of P. guyana were morphologically cryptic. Only those genodemes of P. guyana that possess prickly separation valves could be morphologically distinguished from P. marina with relative confidence in SEM preparations. All clones established from chains isolated from the ballast sediment of the ships sailing along the Atlantic coast of North America belonged to P. guyana. All DNA sequences of preserved Paralia chains recovered from the three trans-Atlantic voyages (TAVs) samples arriving to eastern Canada from Europe shared 100% identity with P. marina.

Conclusion: First, if the [Formula: see text] = 130592 P. marina cells per ballast tank at the end of the TAVs represents their abundance in ballast tanks of similar crossings and following mid-ocean ballast water exchange, then this diatom, if de-ballasted, exerts a strong and continued propagule pressure on Eastern Canadian coasts. Despite this, as of 2009, P. marina was found only in Cheticamp, Nova Scotia, Canada. Second, genetic analysis readily segregated cryptic and semi-cryptic taxa of Paralia, highlighting the usefulness of the molecular approach to species recognition, e.g., in programs monitoring alien introductions.

No MeSH data available.


Related in: MedlinePlus

ITS2 rRNA transcript secondary structure model ofParalia marina(strain Helgo3). Sequence orientation (5′ to 3′) and helix numbering (I, II, III, IV and V) are specified. An arrowhead shows the pyrimidine-pyrimidine mismatch (CxU) on Helix II, the ultra-conserved UGGU motif on the 5′ side of Helix III is indicated by an ellipse and areas of relative conservation between P. marina and P. guyana are boxed. CBCs between P. guyana and P. marina are shaded gray across the entire base pair. HCBCs between P. guyana and P. marina are shaded only on the changed base of the base pair.
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Fig11: ITS2 rRNA transcript secondary structure model ofParalia marina(strain Helgo3). Sequence orientation (5′ to 3′) and helix numbering (I, II, III, IV and V) are specified. An arrowhead shows the pyrimidine-pyrimidine mismatch (CxU) on Helix II, the ultra-conserved UGGU motif on the 5′ side of Helix III is indicated by an ellipse and areas of relative conservation between P. marina and P. guyana are boxed. CBCs between P. guyana and P. marina are shaded gray across the entire base pair. HCBCs between P. guyana and P. marina are shaded only on the changed base of the base pair.

Mentions: Folding of ITS2 rRNA transcripts revealed two very different secondary structures in Paralia marina and P. guyana with five helices in the former and four in the latter (Figures 11 and 12). Nonetheless, they both demonstrated the hallmarks of ITS2 structures seen in many eukaryotes such as Helix II being relatively short and harbouring a pyrimidine-pyrimidine mismatch; here different for each species with C:U in P. marina and U:C and C:C in P. guyana (depending on genodeme, arrowheads in Figures 11 and 12). Helix III was the longest and carried known variants of the ultra-conserved motif at the distal end of the 5΄ side of the Helix (UGGU for P. marina and AGGA for P. guyana, surrounded by ellipses in Figures 11 and 12). These two Paralia species also showed other, albeit very few, areas of conservation (boxes in Figures 11 and 12). These included: (1) a six nucleotide sequence which preceded Helix I, (2) five basal pairs of Helix I, (3) part of the spacer between Helix I and Helix II, (4) two basal pairs of Helix II, (5) two base pairs near the terminal loop in Helix II, (6) two base pairs near the base of Helix III, (7) a base pair immediately below the super-conserved motif in Helix III, and (8) the basal part of Helix IV which contained three base pairs. Some of these areas were also conserved between the two species discussed here and species in the P. longispina species-complex [6] and some other algae [49,50].Figure 11


Paralia (Bacillariophyta) stowaways in ship ballast: implications for biogeography and diversity of the genus.

MacGillivary ML, Kaczmarska I - J Biol Res (Thessalon) (2015)

ITS2 rRNA transcript secondary structure model ofParalia marina(strain Helgo3). Sequence orientation (5′ to 3′) and helix numbering (I, II, III, IV and V) are specified. An arrowhead shows the pyrimidine-pyrimidine mismatch (CxU) on Helix II, the ultra-conserved UGGU motif on the 5′ side of Helix III is indicated by an ellipse and areas of relative conservation between P. marina and P. guyana are boxed. CBCs between P. guyana and P. marina are shaded gray across the entire base pair. HCBCs between P. guyana and P. marina are shaded only on the changed base of the base pair.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4389653&req=5

Fig11: ITS2 rRNA transcript secondary structure model ofParalia marina(strain Helgo3). Sequence orientation (5′ to 3′) and helix numbering (I, II, III, IV and V) are specified. An arrowhead shows the pyrimidine-pyrimidine mismatch (CxU) on Helix II, the ultra-conserved UGGU motif on the 5′ side of Helix III is indicated by an ellipse and areas of relative conservation between P. marina and P. guyana are boxed. CBCs between P. guyana and P. marina are shaded gray across the entire base pair. HCBCs between P. guyana and P. marina are shaded only on the changed base of the base pair.
Mentions: Folding of ITS2 rRNA transcripts revealed two very different secondary structures in Paralia marina and P. guyana with five helices in the former and four in the latter (Figures 11 and 12). Nonetheless, they both demonstrated the hallmarks of ITS2 structures seen in many eukaryotes such as Helix II being relatively short and harbouring a pyrimidine-pyrimidine mismatch; here different for each species with C:U in P. marina and U:C and C:C in P. guyana (depending on genodeme, arrowheads in Figures 11 and 12). Helix III was the longest and carried known variants of the ultra-conserved motif at the distal end of the 5΄ side of the Helix (UGGU for P. marina and AGGA for P. guyana, surrounded by ellipses in Figures 11 and 12). These two Paralia species also showed other, albeit very few, areas of conservation (boxes in Figures 11 and 12). These included: (1) a six nucleotide sequence which preceded Helix I, (2) five basal pairs of Helix I, (3) part of the spacer between Helix I and Helix II, (4) two basal pairs of Helix II, (5) two base pairs near the terminal loop in Helix II, (6) two base pairs near the base of Helix III, (7) a base pair immediately below the super-conserved motif in Helix III, and (8) the basal part of Helix IV which contained three base pairs. Some of these areas were also conserved between the two species discussed here and species in the P. longispina species-complex [6] and some other algae [49,50].Figure 11

Bottom Line: Frustule morphology did not segregate species, however, comparisons of sequence fragments and ITS2 secondary structures yielded a new species from North American waters, P. guyana (with four genodemes), and another widely-distributed species, P. marina.Despite this, as of 2009, P. marina was found only in Cheticamp, Nova Scotia, Canada.Second, genetic analysis readily segregated cryptic and semi-cryptic taxa of Paralia, highlighting the usefulness of the molecular approach to species recognition, e.g., in programs monitoring alien introductions.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Mount Allison University, 63B York Street, Sackville, NB E4L 1G7 Canada.

ABSTRACT

Background: The genus Paralia Heiberg is one of the most recognizable, widely distributed and commonly reported diatoms from contemporary coastal marine environments and ship ballast. Species discovery has historically been made in diatoms through the recognition of morphological discontinuities between specimens, first using light and later electron microscopy. However, recently, morphologically semi-cryptic species of Paralia were delineated using genetic analyses, among mostly tropical and subtropical sites.

Results: Ten morphological characters of the frustules and sequence fragments from the nuclear genome (conserved 18S regions of ribosomal RNA and the variable internal transcribed spacer [ITS]), and from the RuBisCo large subunit (rbcL) gene of the chloroplast genome were examined. Frustule morphology did not segregate species, however, comparisons of sequence fragments and ITS2 secondary structures yielded a new species from North American waters, P. guyana (with four genodemes), and another widely-distributed species, P. marina. The latter was lecto- and epitypified here because it is most similar to specimens in the type preparation BM1021 representing Smith's concept of the species. Paralia marina and certain genodemes of P. guyana were morphologically cryptic. Only those genodemes of P. guyana that possess prickly separation valves could be morphologically distinguished from P. marina with relative confidence in SEM preparations. All clones established from chains isolated from the ballast sediment of the ships sailing along the Atlantic coast of North America belonged to P. guyana. All DNA sequences of preserved Paralia chains recovered from the three trans-Atlantic voyages (TAVs) samples arriving to eastern Canada from Europe shared 100% identity with P. marina.

Conclusion: First, if the [Formula: see text] = 130592 P. marina cells per ballast tank at the end of the TAVs represents their abundance in ballast tanks of similar crossings and following mid-ocean ballast water exchange, then this diatom, if de-ballasted, exerts a strong and continued propagule pressure on Eastern Canadian coasts. Despite this, as of 2009, P. marina was found only in Cheticamp, Nova Scotia, Canada. Second, genetic analysis readily segregated cryptic and semi-cryptic taxa of Paralia, highlighting the usefulness of the molecular approach to species recognition, e.g., in programs monitoring alien introductions.

No MeSH data available.


Related in: MedlinePlus