Sub-fossil Remains Research Articles

Assessing environmental stressors on a commercial walleye fishery from a large northern ecosystem (Tathlina Lake) using water chemistry and paleolimnology

Abstract Tathlina Lake (Northwest Territories, Canada) is a large, shallow ecosystem in the rapidly warming northern boreal forest. This lake is of considerable cultural and economic significance as it supports a commercially important walleye ( Sander vitreus ) fishery that has experienced large fluctuations since the 1940s, the causes of which are poorly understood. Here we used paleolimnology to describe long-term environmental changes in the lake that may have contributed to recent collapses in walleye populations. The sub-fossil remains of diatoms and chironomids were used to assess changes in turbidity, nutrients, and oxygen levels, all of which are important to walleye. Minimal changes have occurred in diatom assemblages from the early 1920s to present, suggesting that turbidity and nutrients have not changed markedly in the lake. Hypoxia-tolerant chironomid taxa were found throughout the sediment record, and our modern water chemistry showed that oxygen levels were supersaturated in the summer, but close to the lower tolerance limit of walleye in winter. An increase in sedimentary chlorophyll- a since ~ 1940 suggests Tathlina Lake is affected by recent climate warming. Our findings indicate that walleye populations are likely regularly exposed to hypoxic winter conditions, which may increase the sensitivity of the population to other interacting stressors that occur with recent climate warming. Long-term records of environmental change in large, shallow northern lakes are rare, and paleolimnology provides a framework to reconstruct missing monitoring data, especially in lakes that are economically and culturally important to northern communities.

Reconstructing diatom and chironomid assemblages to infer environmental spatiotemporal trends within Lake Diefenbaker, a narrow river-valley reservoir on the Canadian Prairies

Lake Diefenbaker (Saskatchewan, Canada) is a large reservoir in the southern Canadian Prairies. However, limited monitoring data were available to assess long-term trends in environmental quality. Therefore, a paleolimnological study was conducted to investigate temporal trends in the trophic status of the reservoir. Sediment cores were collected along the length of Lake Diefenbaker, and sediment subsections were analyzed for sub-fossil remains of diatoms and chironomid larvae. The compositions of diatom and chironomid communities were consistent over approximately the previous decade at up-reservoir locations, with a meso-eutrophic species, Stephanodiscus parvus, dominating the diatom communities. This taxon also dominated the early down-reservoir diatom communities along the main flow of the reservoir. However, during the 1980s, dominance of the diatom assemblage shifted from S. parvus to a combination of Aulacoseira ambigua and Tabellaria flocculosa in the majority of down-reservoir regions. Based on total phosphorus concentration optima for these species, this shift suggests a reduction in total phosphorus both spatially and temporally. However, these observed shifts could also have been due to increased water clarity or changes to thermal stratification regime both spatially (from up- to down-reservoir) and over time down-reservoir. An increase in relative abundance of the chironomid tribe Tanytarsini, both with distance down-reservoir and over time, was likely due to spatial and temporal changes in benthic habitat (i.e., sediment character). Results highlight the need to interpret temporal trends within the context of spatial gradients in physical processes, chemistry, and biology along the longitudinal axis of narrow river valley reservoirs.

Salvinia natans in medieval wetland deposits in Gdańsk, northern Poland: evidence for the early medieval climate warming

Large numbers of sub-fossil remains of the aquatic fern Salvinia natans (L.) All. have been found in several early medieval sites in Gdansk, N. Poland. This record indicates a population expansion of this species around 7th–8th century A.D., similar to the recently observed rapid spread and high population dynamics of S. natans in northern Poland, which recent studies have attributed to climate warming. Our results suggest that in the Vistula deltaic area the S. natans expansion in the Early Middle Ages (7th–8th century A.D.) was similarly stimulated by climate warming, while its subsequent decline was mainly due to climate cooling, especially during the Little Ice Age. Warmer winters and springs and a longer growing season seem to be the most important factors forcing the expansion of S. natans in medieval times. According to our data, the co-occurrence of S. natans with other aquatic plant species was similar in both the medieval and present-day vegetation. Also, the high density of S. natans in the medieval population caused impoverishment of the local ecosystems in a way that has been observed in recent water bodies affected by invasive pleustophytes (free-floating plants).

The occurrence of a new species of <i>Gomphocythere</i> (Ostracoda, Limnocytheridae) in the Holocene of SE Turkey: the northernmost record for the genus

Abstract. A new species of the genus Gomphocythere (Sars, 1924) from SE Turkey extends the known Holocene biogeographical range of this taxon northwards by 500 km although only sub-fossil remains have been discovered so far. The species has been recorded previously in open nomenclature, from a middle Pleistocene site in northern Israel but the genus Gomphocythere is particularly abundant and diverse in the large lakes of South and East Africa (e.g. Lakes Malawi, Tanganyika and Victoria). The closest relative of the new species, based on external carapace characteristics, is known to be alive today along one of the sources of the River Jordan, central Israel. This suggests the presence of a geographically distinct ‘northern group’ of Gomphocythere separated from the majority of known occurrences in eastern and southern Africa.

Modelling the evolution of protein coding sequences sampled from Measurably Evolving Populations.

Models of nucleotide or amino acid sequence evolution that implement homogeneous and stationary Markov processes of substitutions are mathematically convenient but are unlikely to represent the true complexity of evolution. With the large amounts of data that next generation sequencing promises, appropriate models of evolution are important, particularly when data are collected from ancient and sub-fossil remains, where changes in evolutionary parameters are the norm and not the exception. In this paper, we describe a new codon-based model of evolution that applies to Measurably Evolving Populations (MEPs). A MEP is defined as a population from which it is possible to detect a statistically significant accumulation of substitutions when sequences are obtained at different times. The new model of codon evolution permits changes to the substitution process, including changes to the intensity of selection and the proportions of sites undergoing different selective pressures. In our serial model of codon evolution, changes in the selective regime occur simultaneously across all lineages. Different regions of the protein may also evolve under distinct selective patterns. We illustrate the application of the new model to a dataset of HIV-1 sequences obtained from an infected individual before and after the commencement of antiretroviral therapy.

The History and Palaeoclimatic Significance of Subfossil Remains of Pinus Sylvestris in Blanket Peats From Scotland

(1) The results of pollen-stratigraphic, radiocarbon and tree-ring evidence from several sites in the Loch Tulla area, southern Rannoch Moor, western Scottish Highlands, indicate the following regional pine history: (i) major expansion of pine woodland at c. 6800-6600 B.P.; (ii) significant reduction in regional pine cover between 6600 and 4970 B.P.; (iii) a second expansion of pine wood and throughout the region at c. 4970-4660 B.P.; (iv) major differences between the sites in the representation of pine after c. 4660 B.P. (2) These data are compared with evidence from Scotland as a whole for radiocarbon- dated pine macrofossils obtained from Holocene peat deposits and for 'pluvial' climatic episodes identified from previously published stable isotope studies. (3) Collectively the available data indicate that the density and distribution of pine varied significantly in Scotland during the Holocene probably as a result of variations in precipitation levels. Stable isotope variations indicate particularly wet conditions at c. 7500, 6250-5800,4250-3870 and 3300 B.P.; histogram plots of radiocarbon dates of pine macrofossils from Scotland indicate significant troughs at 5700-5250, 3800-3500 and post-3250 B.P. A time-lag between climatic change and consequent pine reduction is indicated.

A Consideration of the Sub-Fossil Remains of 'Vitis vinifera' L. as Evidence for Viticulture in Roman Britain

It has generally been accepted that the Romans cultivated the vine in Britain although evidence for this, from either literary or archaeological sources, is limited. Information on crops cultivated in this country in early historical times must largely be obtained from sub-fossil remains, and the recent finding of mineralized grape-seeds from a mid second-century pit in the vicus at Doncaster resulted in a search of the literature for other records. The main purpose of this article is to evaluate these records as evidence for cultivation of the vine in Roman Britain. There are very few instances of this species being recovered from Roman archaeological deposits. The lack of detailed information in the early records not only renders them virtually worthless as proof of local viticulture but also prevents a reappraisal of the evidence in the light of present knowledge. These records have been listed previously in discussions on Roman viticulture but without much thought to the evidence they contain. It is apparent that this is partly due to a reliance on sources other than the original records, which is also suggested by errors noted in the quoting of these records.

Shufeldt on Subfossil Bird Remains from Bermuda A Comparative Study of Some Subfossil Remains of Birds from Bermuda, Including the "Cahow" R. W. Shufeldt

Shufeldt on Subfossil Bird Remains from Bermuda A Comparative Study of Some Subfossil Remains of Birds from Bermuda, Including the "Cahow" R. W. Shufeldt