Biogeography and Phylogenetic Position of a Warm-stenotherm Centric Diatom, Skeletonema potamos (C.I. Weber) Hasle and its Long-term Dynamics in the River Danube

Abstract

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 3 IntroductionThe classic taxonomy of diatoms is morphology-based using features of their characteristic silica cell wall called frustule (e.g. Ettl et al. 1986). Medlin et al. (1988) introduced molecular methods into diatom taxonomy. Based on molecular, morphological and cytological results, Medlin and Kaczmarska (2004) proposed major clades of diatoms including Mediophyceae for bipolar centrics and the Thalassiosirales. Phylogenetic relationships of this latter order were reconstructed by Alverson et al. (2007).Recently, morphological studies are supplemented by molecular investigations on various Skeletonema species (Alverson and Kolnick 2005; Kooistra et al. 2008; Sarno et al. 2005 Sarno et al. , 2007. Medlin et al. (1988) determined the phylogenetic status of the marine diatom Skeletonema costatum among the eukaryotes based on 16S-like (=18S) rDNA. Molecular and/or morphological studies investigated S. costatum or S. costatum-like diatoms and revealed new species, such as S. pseudocostatum (Medlin et al. 1991), S. grevillei (Zingone et al. 2005), S. dohrnii, S. grethae, S. japonicum, S. marinoi (Sarno et al. 2005 and S. ardens (Sarno et al. 2007). Skeletonema was found to be monophyletic and ancestrally a marine genus (Alverson et al. 2007). There are only two non-marine species in this genus: S. subsalsum occurring mainly in saline and brackish waters and occasionally in freshwater habitats ( Aké Castillo et al. 1995; Gibson et al. 1993; Hasle Evensen 1975; Hustedt 1957) and S. potamos that is recorded from freshwater and slightly brackish habitats (Kiss et al. 2012). This latter species was not involved in molecular investigations previously.Microsiphonia potamos C.I. Weber was first collected in 1966 from the Little Miami River, Cincinatti, Ohio and described by Weber (1970). New material from the Little Miami River, 25 May 1973, was observed by Hasle and Evensen (1976) and as they found this species highly similar to species of the genus Skeletonema, suggested its transfer to this genus Page 4 of 42 A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 4 as Skeletonema potamos (C.I. Weber) Hasle in Hasle & Evensen; they found the same taxon in the liquid-preserved sample from the Jensensee, Plön (Germany), 19 August 1922, Hustedt Collection E 4555, which Hustedt (1928 used when preparing the description of the diatom to which he applied erroneously the name Stephanodiscus subsalsus (Cleve-Euler) Hustedt.Skeletonema potamos is a broadly distributed species (Supplementary Material Table S1) and is considered inv...

Potential distribution of the invasive freshwater dinoflagellate Ceratium furcoides (Levander) Langhans (Dinophyta) in South America

“…To our knowledge, studies using modeling approaches for predicting areas susceptible to phytoplankton invasions are virtually nonexistent as most of the studies in this field are descriptive, although with good predictions (e.g., Cylindrospermopsis raciborskii , Prymnesium parvum , Skeletonema potamos ; Padisák , Duleba et al. , Roelke et al. ).…”

Functional diversity of phytoplankton highlights long‐term gradual regime shift in the middle section of the Danube River due to global warming, human impacts and oligotrophication

“…Here, we showed that the characteristic dominance of eutrophic centric diatoms (codon D ) declined in the middle Danube in almost all seasons, except summer. This might be explained by the increasing summer dominance of the stenotherm Skeletonema potamos at this river section (Duleba et al., ). The species is highly adapted to extreme late summer river conditions: increased water temperature, elongated water residence time and high light availability (Kiss et al., ).…”

“…Further details about the sampling can be found in Duleba et al. (); about the entire Danube basin in Sommerwerk et al. () and Liska ().…”

“…Standardised methods of chemical variables were identical to those presented in Duleba et al. (). In our study, Chl‐ a was used as a proxy for phytoplankton biomass.…”

“…In the River Danube basin, altered seasonality in water run‐off has been prognosticated (ICPDR, ), with decrease in summer and autumn flows and increase in winter and early spring (Stagl & Hattermann, ). During the last decades, water temperature raised significantly in the upper (Webb & Nobilis, ) and also in the middle section of the river (Dokulil, ; Duleba et al., ).…”