The genus Frustulia on Gough Island (Tristan da Cunha archipelago).

Abstract

Gough Island (40°21’ S, 9°53’ W), part of the Tristan da Cunha archipelago, is a small, uninhabited island, situated in the cool-temperate zone of the southern Atlantic Ocean. Large parts of the island are quite mountainous with most of the island above 400 m. This volcanic island is typically oceanic and has never been part of a continental landmass. The climate is cool and wet, with a mean annual temperature (at sea level) of 11° C, a mean annual precipitation in excess of 3000 mm and with frequent gale-force winds. Despite its very interesting geographical position, its oceanic origin and the number of interesting habitats, the non-marine diatom flora of Gough Island is only poorly known. Carter published in 1966 on the diatom flora from the Tristan da Cunha Island group, reporting the presence of a very diverse diatom flora with a large number of new taxa that so far have been rarely observed elsewhere. Recently, a new survey of the moss-inhabiting diatoms on Gough Island has started. During this survey, several taxa were discovered belonging to the genera Pinnularia, Eunotia and Frustulia, that could not be identified using the currently available literature. The poster illustrates and discusses the diversity within the genus Frustulia. Apart from the presumably cosmopolitan species F. vulgaris (Thwaites) De Toni, six unknown Frustulia taxa were observed. Based on detailed LM and SEM observations, it is highly likely that these six taxa need to be described as new species. They differ from each other and from already described taxa by a series of morphological features such as the overall valve outline, the shape and structure of the helictoglossa, the structure of the central area and the external proximal and distal raphe endings. All differentiating characters are highlighted on the poster. Brief notes on the ecology of the six taxa are added. References: Carter, J. (1966) Some freshwater diatoms of Tristan da Cunha and Gough Island. Nova Hedwigia 9: 443-492.

Full text

Although we have already examined the genus Frustulia in the most
detailed way, possible new taxa are highly similar in some
ultramorphological features. In Figure 1 we can see a fusion of the ribs to
a linear-shaped helictoglossa and to form a less distinct porte-crayon
structure. Striae circumpolar composed of one to two areolae,
sometimes are also elongated on the top where also a clear space is
always present. Internally (Fig.2)we can see not only fused ribs to form
a central nodule, but also smaller, rounded areolae increasing in size
towards the margins. Striae are straight and parallel although often
wavy in the central area. Externally, we can see not only elongated
areolae in both the apex (Fig.3)and the central area (Fig.4) but also a
reduction in areola size. T-shaped raphe endings are present on both
distal and proximal sides, often more curved in the central area,
resembling more an umbrella or mushroom hat.
The genus Frustulia on Gough Island
(Tristan da Cunha archipelago)
Vinšová, Petra1*, Kopalová, Kateřina1,2, Gremmen, Niek J.M.3, de Haan, Myriam4& Van de Vijver, Bart4,5
1Charles University in Prague, Faculty of Science, Depart ment of Ecology, Viničná 7, CZ-12844 Prague 2, Czech Republic (vinsova@gmail.com), 2Institute of Botany, Academy of
Sciences of the Czech Republic, Centre for Phycology, Dukel ská135, 379 82, Třeboň, Czech Repub lic, 3Data-Analyse Ecologie, Hesselsstraat11, 7981 CD Diever, The Nethe rlands,
4Botanic Garden Meise, Department of Bryophyta & Thallop hyta, Nieuwelaan 38, B-1860 Belgium, 5University of Antwerp, Department of Biology-ECOBE, Universiteitsplein 1,
B-2610 Wilrijk, Belgium
INTRODUCTION
REFERENCES:
CARTER,J. (1966) Some freshwater diatoms of Tristan da Cunha and Gough Island. Nova Hedwigia9: 443–492.
VESELÁ,J., URBÁNKOVÁ,P., ČERNÁ,K. & NEUSTUPA,J. (2012) Ecological variation within traditional diatom morphospecies: diversity of Frustulia rhomboides sensu lat o (Bacillariophyceae) in European freshwater habitats. Phycologia 51(5): 552–561.
Gough Island (40°21’S, 9°53’W), part of the Tristan da Cunha archipelago, is a
small, uninhabited island situated in the cool-temperate zone of the southern
Atlantic Ocean. So far, only Carter (1966) focused on its diatom flora, reporting
the presence of a very diverse diatom flora that has been rarely observed
elsewhere. Recently, a new survey of the moss-inhabiting diatoms on this
isolated island has started.
This poster illustrates and discusses the diversity within the genus Frustulia.In
the past decade, a lot of new species have been described and recent genetic
results pointed to a hidden diversity within this genus (Veselá et al. (2012).
Although the species recorded on Gough Island bear some similarity to
previously described ones, small morphological differences may point to more
cryptic diversity within Frustulia. Therefore, we differentiate several
morphologically different and most likely new taxa.
Possible new taxa from Gough Island
Frustulia sp. E
Lenght range: (44.7) 56.3–79.9
Width Range: 9.9–13.7
Central Nodulus: 4.2–5.5
Striae in 10 µm: 33–36
Frustulia sp. P
Lenght range: 50.2–83.3
Width Range: 11.6–15.1
Central Nodulus: 3.8–5.9
Striae in 10 µm: 31–33
Frustulia sp. V
Lenght range: 38.1–75.2
Width Range: 9.7–13.5
Central Nodulus: 3.1–5.9
Striae in 10 µm: 31–33
Frustulia sp. L
Lenght range: 83.1–100
Width Range: 16–17.3
Central Nodulus: 5.6–7.3
Striae in 10 µm: 31–32
Frustulia sp. H
Lenght range: 36.9–51.7
Width Range: 9.7–11.3
Central Nodulus: 3.1–4.3
Striae in 10 µm: 32–34
Frustulia sp. N
Lenght range: 39–41.5 (54.1)
Width Range: 9–9.7 (11.3)
Central Nodulus: 2.93–4.27
Striae in 10 µm: 36 – 37
ULTRAMORPHOLOGY OF FRUSTULIA FROM GOUGH ISLAND
1 2
3 4
DISCUSSION
CONCLUSION
The diatom flora on Gough Island is highly interesting not only from the taxonomic, but also the biogeographic point of view. A lot of
taxa from different genera will have to be described as new to science. Similar trends are observed within the genera Frustulia, Eunotia &
Pinnularia, suggesting that this might reflect the isolated position of the island and (recent) allopatric speciation. Genetic analysis and
morphometrics on more samples will be necessary to confirm these statements.
The genus Frustulia was found in relatively large populations in 29 samples from Gough island, making it an important element of the
diatom flora on the island. Basic LM observations such as valve outline, size range and number of striae, proved to be the most distinctive
tool to discriminate these six (most likely new) taxa. Although some features, such as more elongated areolae
(sp. H) or a stria inclination towards the apexes (sp. P) can be observed, more SEM photos will be needed to confirm these differences.
These six taxa always differ in valve outline, especially in the shape of neck, shoulder, and head structures, although occasionally
overlap in size or shape throughout the samples can be observed. Further data will be needed to determine the impact of ecological
plasticity on valve shape prior to the description of new taxa. So far, we noticed a higher number of taxa in river beds, with valves being
slightly larger than those from other habitats.
Figure 5: Position of Gough Island in the southern
Atlantic Ocean.
Scale bar represents 10 µm.
Figure 6: SEM photos of discussed
Frustulia taxa. Scale bar represents 10 µm.
Frustulia sp. E
Frustulia sp. L
Frustulia sp. N
Frustulia sp. H
Frustulia sp. P
Frustulia sp. V