The ostracod species Eucypris virens exhibits geographical parthenogenesis, with rare sexual populations in southern Europe and widespread asexual populations elsewhere. DNA sequence data from the ...nuclear ITS1 and mitochondrial COI regions have been used to estimate genetic variabilities and reconstruct phylogenies. The observed divergence was exceptionally high, with intraspecific maxima of 10.3% (ITS1) and 20.9% (COI) among European lineages, levels reported for interspecific comparisons of other taxa. Phylogenetic reconstructions reveal multiple origins of asexual clones from sexual populations. However, we argue that such data can only provide a lower limit on the number of origins of asexual reproduction, and an upper limit on the age of asexual lineages. Congruence between gene trees for different loci can provide support for the inference of long‐term apomictic reproduction. Nuclear and mitochondrial data differ in their placement of some asexual clones, possibly indicating that genetic exchange has taken place between sexual and asexual lineages. Such intraspecific hybridization is one route to combine the benefits of both reproductive modes, and it might explain how asexuality managed to persist in E. virens even in long, evolutionary terms.
Diatoms (Bacillariophyceae; single-celled algae) and ostracods (Ostracoda; shelled microcrustacea) are known for their sensitivity to salinity. In palaeolimnology, the potential has yet to be tested ...for quantifying past salinity, lake level, and by inference, climate change, by application of multiple-indicator transfer functions. We used weighted averaging techniques to derive diatom (n = 91; r 2 = 0.92) and ostracod (n = 53; r 2 = 0.83) conductivity transfer functions from modern diatom, ostracod and water chemistry data collected in lakes of central, western and northern Turkey. Diatoms were better represented across the full gradient than ostracods, at intermediate levels of conductivity in particular, but both transfer functions were statistically robust. Because transfer functions are not infallible, we further tested the strength and simplicity of salinity response and the potential for identifying characteristic associations of diatom and ostracod taxa in different parts of the salinity gradient, to improve palaeoclimate reconstruction. We identified a subset of 51 samples that contained both diatoms and ostracods, collected at the same time from the same habitat. We used Two-Way Indicator Species Analysis of a combined diatom-ostracod data set, transformed to achieve numerical equivalence, to explore distributions in more detail. A clear ecological threshold was apparent at ~3 g l−1 salinity, rather than at 5 g l−1, the boundary used by some workers, equating to the oligosaline-mesosaline boundary. Other salinity boundaries were poorly defined, indicating lack of a simple, well-defined salinity response. We did, however, define characteristic associations of taxa, to facilitate the distinction to be drawn between a hydrologically open, fresh lake and an oligosaline lake, in palaeoenvironmental reconstruction. Over the rest of the salinity gradient, we highlighted the potential for the multi-proxy approach to strengthen ostracod-based reconstruction in particular, to overcome the problem of broad apparent tolerance ranges in common halophilic taxa such as Limnocythere inopinata, which often dominate in low-diversity fossil assemblages. The combination of multi-proxy quantitative reconstruction, complemented by qualitative understanding of ecological responses generated by the analysis, remains a powerful tool in Quaternary palaeoclimate research.
Middle Pleistocene fluvial deposits of the Corbets Tey Formation at Purfleet, Essex, provide evidence of an un-named and previously poorly recognized interglacial, thought to corrrelate with Oxygen ...Isotope Stage (OIS) 9. Previous attributions of the sediments to the Ipswichian (Last Interglacial) Stage are refuted. New investigations have yielded rich molluscan, mammalian and ostracod assemblages that indicate fully temperate conditions and the distal influence of marine transgression. Pollen analyses suggest a previously unrecorded phase of interglacial vegetational development. Clast composition, geomorphological evidence and the occurrence of molluscs that favour large rivers all point to deposition by the Thames, rather than in a minor tributary, as suggested previously. Three separate Palaeolithic industries in stratigraphical superposition are recognized at Purfleet, these being Clactonian, Acheulean and Levallois. Purfleet is therefore a key locality in the understanding of the early human occupation and exploitation of southern Britain, as well as for the interpretation and correlation of the terrace sequence in the Thames Valley.
The Polymerase Chain Reaction (PCR) was employed to facilitategenetic analyses of Daphnia ephippial egg banks fromsediment sequences from lakes Windermere and Esthwaite in the English LakeDistrict, ...UK. We present a robust DNA extraction technique for resting eggs andan account of genetic characterisation of dated resting eggs from sedimentcores using both mitochondrial and nuclear DNA markers. We also providepreliminary results from genetic analysis of egg banks preserved in shortsediment cores. PCR was employed to facilitategenetic analyses of Daphnia ephippial egg banks collected from both lakes. Thelong-term environmental data available from lake records can provide a backdropagainst which molecular genetic-environmental interactions over time can beexamined, providing a technique for direct assessments of population responseto environmental change in paleolimnological studies of biodiversityhistory.PUBLICATION ABSTRACT
The Ramsar site of Lake Uluabat, western Turkey, suffers from eutrophication, urban and industrial pollution and water abstraction, and its water levels are managed artificially. Here we combine ...monitoring and palaeolimnological techniques to investigate spatial and temporal limnological variability and ecosystem impact, using an ostracod and mollusc survey to strengthen interpretation of the fossil record. A combination of low invertebrate Biological Monitoring Working Party scores (<10) and the dominance of eutrophic diatoms in the modern lake confirms its poor ecological status. Palaeolimnological analysis of recent (last >200
yr) changes in organic and carbonate content, diatoms, stable isotopes, ostracods and molluscs in a lake sediment core (UL20A) indicates a 20th century trend towards increased sediment accumulation rates and eutrophication which was probably initiated by deforestation and agriculture. The most marked ecological shift occurs in the early 1960s, however. A subtle rise in diatom-inferred total phosphorus and an inferred reduction in submerged aquatic macrophyte cover accompanies a major increase in sediment accumulation rate. An associated marked shift in ostracod stable isotope data indicative of reduced seasonality and a change in hydrological input suggests major impact from artificial water management practices, all of which appears to have culminated in the sustained loss of submerged macrophytes since 2000. The study indicates it is vital to take both land-use and water management practices into account in devising restoration strategies. In a wider context, the results have important implications for the conservation of shallow karstic lakes, the functioning of which is still poorly understood.
The presence or absence of 77 rodent species was scored within 427 squares of 100 × 100 miles. The grid encompassed the entirety of Europe west of the Urals and north of the Caucasus, but excluded ...all offshore islands. Rodent distributional ranges varied between 26 000 and 22 670 000 km2. Very large ranges were uncommon and 53% of species had ranges covering < 20% of the study area. Range size showed no correlation with body size, nor did it depend on taxonomic provenance. However, saltatorial rodents appeared to have the largest median ranges and fossorial species the smallest. Species densities varied between 4 and 26 species/grid square, with the highest densities coinciding broadly with the steppe-deciduous forest ecotone. The degree of endemism showed a different geographic pattern from that of species density, with the highest values at lower latitudes. Forty-nine squares (11% of Europe's surface) identified as species richness and endemism "hot spots" contained > 80% of genera and species, their largest contiguous coincidence being in the southern Balkans, the Carpathian Basin, southern Ukraine and cis-Caucasia.
Slow molecular evolution in an ancient asexual ostracod Schön, Isabelle; Butlin, Roger K.; Griffiths, Huw I. ...
Proceedings of the Royal Society. B, Biological sciences,
02/1998, Letnik:
265, Številka:
1392
Journal Article
Recenzirano
Odprti dostop
Genetic variability of the non-marine ostracod speciesDarwinula stevensoni was estimated by sequencing part of the nuclear and the mitochondrial genome. As Darwinulidae are believed to be ancient ...asexuals, accumulation of mutations should have occurred, both between alleles within lineages and between lineages, during the millions of years of parthenogenetic reproduction. However, our sequence data show the opposite: no variability in the nuclear ITS1 region was observed within or among individuals of D. stevensoni, despite sampling a geographical range from Finland to South Africa. Lack of allelic divergence might be explained by concerted evolution of rDNA repeats. Homogeneity among individuals may be caused either by slow molecular evolution in ITS1 or by a recent selective sweep. Variability of mitochondrial cytochrome oxidase (COI) was similar to intraspecific levels in other invertebrates, thus weakening the latter hypothesis. Calibrating interspecific, genetic divergences among D. stevensoni and other Darwinulidae using their fossil record enabled us to estimate rates of molecular evolution. Both COI and ITS1 evolve half as fast, at most, in darwinulids as in other invertebrates, and molecular evolution has significantly slowed down in ITS1 of D. stevensoni relative to other darwinulids. A reduced ITS1 mutation rate might explain this inconsistency between nuclear and mitochondrial evolution in D. stevensoni.
It is only in recent years that the use of freshwater Ostracoda as biomarkers in Quaternary studies has become developed to a useful level. This new utility stems from recent developments in the ...understanding of the taxonomy, evolution and (palaeo)-ecology of ostracod faunas, particularly those from northern Europe. Patterns of speciation, migration and lineage extinction all contribute to the value of Ostracoda in European biostratigraphies, although the temporal and geographical data presently available remain insufficient for the fully integrated use of ostracods as biostratigraphic indicators. Recent work provides mounting evidence for the migration of species along Quaternary climatic gradients. Such migrations, and subsequent contacts between closely related taxa, allow for the possibility of inter-lineage hybridisation. Hybridisation events may result in the generation of forms with distinctive, stable morphologies, and these may be of particular value in biostatigraphic studies.
Lake Dojran is a Balkan lake which is host to a number of endemic species and is of high conservation concern. We report the results of research into the present ecological status of the lake and its ...comparison with palaeolimnological data for recent human impact, based on modern zoobenthology, diatom and ostracod palaeoecology, sedimentology and
18O/
16O and
13C/
12C stable isotope ratios from shells of
Darwinula stevensoni (Ostracoda) and
Anodonta cygnea glochidia larvae (Mollusca). The results of the modern survey indicate that benthic faunal composition has changed substantially in recent years. However, in spite of documented eutrophication and major, human-induced fluctuations in lake level since the 1950s, the results of palaeoecological analyses indicate that Lake Dojran is still buffered from major ecological impact. The palaeolimnological datasets suggest, however, that an ecological threshold may have been reached, and remedial measures should now be considered. Ecological problems include not only a major decrease in water depth through water abstraction and the diversion of source waters for agricultural purposes, but also recent climatic aridity and anthropogenic pollution. However, geopolitical problems presently conspire against the formulation of a management strategy for the preservation of the lake and its endemic fauna and flora.
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