Peter A. Siver

Complex phylogeographic patterns in the freshwater alga Synura provide new insights into ubiquity vs. endemism in microbial eukaryotes

The global distribution, abundance, and diversity of microscopic freshwater algae demonstrate an ability to overcome significant barriers such as dry land and oceans by exploiting a range of biotic and abiotic colonization vectors. If these vectors are considered unlimited and colonization occurs in proportion to population size, then globally ubiquitous distributions are predicted to arise. This model contrasts with observations that many freshwater microalgal taxa possess true biogeographies. Here, using a concatenated multigene data set, we study the phylogeography of the freshwater heterokont alga Synura petersenii sensu lato. Our results suggest that this Synura morphotaxon contains both cosmopolitan and regionally endemic cryptic species, co‐occurring in some cases, and masked by a common ultrastructural morphology. Phylogenies based on both proteins (seven protein‐coding plastid and mitochondrial genes) and DNA (nine genes including ITS and 18S rDNA) reveal pronounced biogeographic delineations within phylotypes of this cryptic species complex while retaining one clade that is globally distributed. Relaxed molecular clock calculations, constrained by fossil records, suggest that the genus Synura is considerably older than currently proposed. The availability of tectonically relevant geological time (107–108 years) has enabled the development of the observed, complex biogeographic patterns. Our comprehensive analysis of freshwater algal biogeography suggests that neither ubiquity nor endemism wholly explains global patterns of microbial eukaryote distribution and that processes of dispersal remain poorly understood.

Development of paleolimnological inference models for pH, total nitrogen and specific conductivity based on planktonic diatoms

Canonical correspondence analysis (CCA was used to explore and identify statistically significant relationships between the distributions of planktonic diatoms and the physical and chemical properties of 50 Connecticut lakes. Six variables (pH, total nitrogen, calcium, sulfate, potassium and chlorophyll- a concentrations) were found to be significantly correlated with either or both of the first two extracted axes. The pH and calcium concentration, and to a lesser extent total nitrogen concentrations, were the most important variables controlling the distributions of planktonic diatoms in this suite of lakes. Paleolimnological inference models were developed for pH, total nitrogen (TN) and specific conductivity. Weighted averaging with (WAtol) and without (WA) tolerance downweighting, with and without bootstrap resampling techniques, and using either classical or inverse deshrinking methods were used to develop inference models for each variable. The pH and TN yielded sufficiently high λ1/λ2 ratios and a highly significant first (constrained) axis when entered as single variables in both constrained and partially constrained CCA analyses, supporting the idea that reliable inference models could be developed for these variables. The r2 and RMSE of prediction values ranged from 0.73 to 0.86 and 0.37 to 0.6, respectively for pH, and from 0.4 to 0.64 and 59 μg/l to 95 μg/l, respectively for TN. Inference models for specific conductivity also yielded significant goodness-of-fit statistics. However, because specific conductivity was removed from the CCA analysis due to its high variance inflation factor and did not yield a significant relationship when entered as the sole variable in a partial constrained CCA, inference models for this variable will probably not yield any additional environmental information. The use of only planktonic diatoms in construction of inference models is discussed.

Forensic Limnology: The Use of Freshwater Algal Community Ecology to Link Suspects to an Aquatic Crime Scene in Southern New England

During July, 1991, two young boys were brutally attacked by multiple teenaged assailants while fishing at a suburban Connecticut pond. After being accosted at knife point, the victims were bound with duct tape, beaten with a baseball bat and dragged into the pond to drown. One victim managed to free himself, rescue his colleague, and summon help from local residents. An exhaustive investigation led to the rapid apprehension of three suspects. In an effort to link the suspects to the crime scene, sediment encrusted sneakers were seized from both assailants and victims, and analyzed for aquatic microorganisms. Numerous species of diatoms and scaled chrysophytes (planktonic algae) were recovered from the sneakers and from reference samples of pond sediment. The marked similarities in the algal communities present on the sneakers indicated exposure to a common freshwater habitat, most probably the crime scene pond. Additional analyses revealed that Mallomonas caudata was the dominant scaled chrysophyte species in each sample, and that there was no significant difference in the ratios of three species of the diatom Eunotia between all samples examined. These findings further supported the idea that all of the samples originated from a common, if not the same, locality. This case further exemplifies the applicability of aquatic community ecology to forensic investigations.

A paleolimnological assessment of lake acidification in five Connecticut lakes

New England has received significant amounts of precipitation with a pH between 4.2 and 4.6. Paleolimnological studies based on siliceous microalgal remains support the hypothesis that some lakes in northern New England have acidified as a result of the acidic deposition. However, paleolimnological analyses from five software lakes in southern New England suggest that these lakes have not acidified in recent years. In all of the study lakes the inferred pH has remained relatively stable, and in two lakes the pH has actually increased slightly in recent years. Despite the relatively stable inferred pH reconstructions, significant shifts in species assemblages were observed in each lake, many of which are believed to correlate with land use changes. It is possible that effects of land use changes (e.g. increased urbanization) have masked potential effects of acid deposition.

SEASONAL PERIODICITY OF CHRYSOPHYCEAE AND SYNUROPHYCEAE IN A SMALL NEW ENGLAND LAKE: IMPLICATIONS FOR PALEOLIMNOLOGICAL RESEARCH1

The seasonal periodicity of taxa of Chrysophyceae and Synurophyceae from a small New England lake is described for the period September 1983 through June 1988. We found 51 taxa, including 29 that accounted for over 10% of the total in at least one collection. The taxa were fitted into one of five seasonal patterns. Patterns I and II represented taxa restricted to warm (pattern I) or cold (pattern II) months, respectively. Pattern HI represented organisms that began growth in the summer, persisted through autumn and disappeared with the onset of an ice cover. Pattern IV was an extension of pattern III, in which the taxon remained in the plankton throughout the winter and disappeared soon after ice out. Species without a clear seasonal pattern were grouped as pattern V. The seasonal periodicity of the flora, as examined with ordination analyses, was found to remain remarkedly similar during the 58–month study. Except for episodes of low pH during spring snow melt and unseasonally warm or cold weather, sample scores followed a fairly consistent pattern along the first and second primary axes. Water temperature, specific conductance, and pH were important variables that controlled changes in the species composition during the course of a given year. The flora was used to develop an inference model for water temperature. According to the analyses, the remains of a surface sediment sample represented a flora that grew primarily during the late autumn period at 7.6 ° C. Ways in which seasonal data could be utilized to improve paleolimnological inference work are discussed.

Identification of diatoms (Bacillariophyceae) during ecological assessments: Comparison between Light Microscopy and Scanning Electron Microscopy techniques

Abstract Identification of diatom frustules, a vital step during ecological analyses, is greatly influenced by the magnification at which samples are examined. The striking differences between Light Microscopy (LM) and Scanning Electron Microscopy (SEM) reveal inconsistencies in the identification of diatoms at low magnifications. These inconsistencies hinder comparative analyses between data sets collected by several research centers and may be hiding information of potential value in the assessment of ecosystem health. Additionally, SEM research has had a marked impact on diatom taxonomy rendering traditional identification methods insufficient for recognition of newly created taxa. Many diagnostic features of small representatives of these newly erected taxa can not be recognized even at higher LM magnifications. The consequent lack of taxonomic resolution at the LM level may be leading to overestimation of geographical distributions, ranges of tolerance to environmental parameters, and optimal conditions for growth. Qualitative aspects of the differences between LM and SEM approaches are discussed in the present paper.

SEPERATION OF MALLOMONAS DUERRSCHMIDTIAE SP. NOV. FROM M. CRASSISQUAMA AND M. PSEUDOCORONATA: IMPLICATIONS FOR PALEOLIMNOLOGICAL RESEARCH1

A new species, Mallomonas duerrschmidtiae, with characteristics common to both Mallomonas crassisquama (Asmund) Fott and Mallomonas pseudocoronata Prescott, is described from acidic lakes low in specific conductance and total phosphorus concentration. Characteristics of scales, bristles and spines serve to separate the three taxa. The length and area of scales of M. duerrschmidtiae are significantly larger than those of M. crassisquama but smaller than those of M. pseudocoronata. Although the anterior submarginal ribs of scales of M. duerrschmidtiae may become extended to form short wings, the scales lack the large forward projecting anterior wings characteristic of scales of M. pseudocoronata. Features of the dome and junction between the arms of the V‐rib and anterior submarginal ribs also serve to distinguish between the three species. Cells of M. duerrschmidtiae also possess long, smooth and thick spines on their posterior scales and lack helmet bristles. M. duerrschmidtiae has different maxima along pH, temperature, specific conductance, total phosphorus and seasonal gradients than either M. crassisquama or M. pseudocoronata. Discriminant analysis, based on nine morphological characters, was used to successfully classify body scales of the three species. The importance of M. duerrschmidtiae as a bioindicator in future lake monitoring and paleolimnological inference studies is discussed.

Eocene Scaled Chrysophytes with Pronounced Modern Affinities

This is the first documentation of scaled chrysophytes of Tertiary age. Siliceous scales belonging to four genera (Synura, Mallomonas, Chrysosphaerella, and Spiniferomonas) are preserved in middle Eocene (∼47 Ma) lacustrine mudstones deposited in a posteruptive crater associated with kimberlite intrusion near Lac de Gras, Northwest Territories, Canada. Astonishingly, most of these microfossils have remarkable morphological affinities with extant congeneric taxa, indicating that the unique siliceous ornamentation of the scaled chrysophytes, including scales, spines, and bristles, was fully evolved by the middle Eocene. These observations imply that the scaled chrysophytes experienced prolonged intervals of relative evolutionary stasis during Neogene and Quaternary times and thus provide a new evolutionary milepost for this algal group.

Estimating historical in-lake alkalinity generation from sulfate reduction and its relationship to lake chemistry as inferred from algal microfossils

Sediment cores were used to estimate in-lake alkalinity generation resulting from sulfate reduction relative to inferred changes in lakewater pH and trophic status over the last century in three Connecticut lakes. Despite being situated in geological settings with crystalline bedrock and thin, poorly buffered soils, and being impacted with high rates of acidic precipitation, none of the study lakes have declined in inferred pH based on scaled chrysophyte and diatom remains. In fact, the pH of one of the lakes, Coventry Lake, has significantly increased over the last century. Over the last 44 to 69 years the amount of sulfur stored in the sediments from each lake increased from ~two to three times resulting in mean rates of alkalinity generation ranging from 78 to 145 meq m−2 yr−1, significantly higher than the 45 to 48 meq m−2 yr−1 of hydrogen ions falling directly on the lake surfaces. In-lake alkalinity generation resulting from sulfate reduction has been sufficient to neutralize all of the acid falling directly onto the lake surfaces, as well as between 9% and 25% of the acid deposited onto the surrounding watersheds. Despite the increased importance of in-lake alkalinity generation, our findings support the hypothesis that significant amounts of alkalinity are also being generated in the catchments of the study lakes. The bulk of the increases in stored sulfur in all three lakes were as Fe sulfides and not in the form of organic sulfur, suggesting that the increases were the result of dissimilatory bacterial reduction of sulfate. As a result of the large increases in storage of Fe sulfides the ratio of total iron to chromium reducible sulfur (Fe:CRS) has declined in all cores over time. Despite the overall decline in Fe:CRS in recent sediments, values are still largely above 3 in more recent sediments of two of the lakes. However, values of Fe:CRS have dropped below 1 in surface sediments of Uncas Lake, suggesting that in-lake loading of phosphorus may be responsible for a recent shift in the algal flora towards a slightly more eutrophic condition.

Lead analysis of sediment cores from seven Connecticut lakes

Lead analyses were performed on sediment cores from seven Connecticut lakes by dilute acid leaching. The absolute concentrations of lead varied from core to core, but the lead profiles were similar in all of the cores, and each depicted a point where the concentration of lead sharply increased above background levels. The background lead concentrations observed in the bottom portions of the cores ranged from 12-54 μg Pb/g sediment with a mean of 30 μg Pb/g, and increased to a mean maximum of 310 μg Pb/g. In six of the lakes significant increases above background levels were not noted until between 1924 and 1952, suggesting that, at least for Connecticut lakes, the point in a lake sediment core where the concentration of lead began to increase was after ca. 1924, and on average about 1930. Lead concentrations declined in the surface sediments of only three of the lakes, mostly since the 1980s, and presumably in response to the phasing out of leaded gasoline. However, significant declines in lead concentrations were not observed in the remaining cores, possibly due to increased motor vehicle use within the airshed of the lakes and/or changes in the export of lead to the lakes from their watersheds.