Article

Population genetics of two allopatric (North Sea and Baltic Sea) populations of Evadne nordmanni (Podonidae): Similarities and differences

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

This study assessed the genetic relationship between Evadne nordmanni of the Baltic Sea and the North Sea from sequence variation of the mitochondrial cytochrome c oxidase subunit I gene (COI) of 88 specimens from 13 different sites, and from further published data from the Atlantic and Pacific basins. The COI sequences of E. nordmanni from the North and Baltic Seas were represented by a coherent cluster of 28 haplotypes dominated by a central haplotype that accounted for over half of the individuals from these seas, from all samples except one from the Arkona Basin (Baltic Sea). Overall, the North and Baltic Sea populations appear relatively homogenous and the North Sea plausibly represents the source population for the Baltic one. However, the haplotype network also involved a haplogroup of exclusively Baltic Sea haplotypes, comprising four haplotypes represented by 21 individuals and strongly dominated by specimens from the Arkona basin. This inspires discussion about the post‐glacial evolution of a genetically distinct Baltic Sea group, related to a special local salinity regime. Partly as a reflection of the presence of the unique haplogroup, the mean haplotype diversity in the Baltic was twice as high as the mean diversity in the North Sea, h = 0.64 versus h = 0.30.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

Article
Full-text available
Environmental gradients have emerged as important barriers to structuring populations and species distributions. We set out to test whether the strong salinity gradient from the marine North Sea to the brackish Baltic Sea in northern Europe represents an ecological and genetic break, and to identify life history traits that correlate with the strength of this break. We accumulated mitochondrial cytochrome oxidase subunit 1 sequence data, and data on the distribution, salinity tolerance, and life history for 28 species belonging to the Cnidaria, Crustacea, Echinodermata, Mollusca, Polychaeta, and Gastrotricha. We included seven non‐native species covering a broad range of times since introduction, in order to gain insight into the pace of adaptation and differentiation. We calculated measures of genetic diversity and differentiation across the environmental gradient, coalescent times, and migration rates between North and Baltic Sea populations, and analyzed correlations between genetic and life history data. The majority of investigated species is either genetically differentiated and/or adapted to the lower salinity conditions of the Baltic Sea. Species exhibiting population structure have a range of patterns of genetic diversity in comparison with the North Sea, from lower in the Baltic Sea to higher in the Baltic Sea, or equally diverse in North and Baltic Sea. Two of the non‐native species showed signs of genetic differentiation, their times since introduction to the Baltic Sea being about 80 and >700 years, respectively. Our results indicate that the transition from North Sea to Baltic Sea represents a genetic and ecological break: The diversity of genetic patterns points toward independent trajectories in the Baltic compared with the North Sea, and ecological differences with regard to salinity tolerance are common. The North Sea–Baltic Sea region provides a unique setting to study evolutionary adaptation during colonization processes at different stages by jointly considering native and non‐native species. Environmental gradients have emerged as important barriers to structuring populations and species distributions. Using ecological and genetic data, we show that marine invertebrates exhibit significant structure across a strong salinity gradient from marine to brackish water. The length of the planktonic larval phase may be the sticking point for the colonization of brackish environments, as species with long‐lived planktonic larvae did not occur at lower salinities.
Preprint
Full-text available
Aim Environmental gradients have emerged as important barriers structuring populations and species distributions. We set out to test whether a strong salinity gradient from marine to brackish, represented in a marginal northern European sea, should be considered a diversification hotspot or a population sink, and to identify life history traits that correlate with either evolutionary trajectory. Location The Baltic Sea, the North Sea and their transition zone. Methods We accumulated mitochondrial cytochrome oxidase subunit 1 sequence data and data on the distribution, salinity tolerance and life history for 28 species belonging to the Cnidaria, Crustacea, Echinodermata, Mollusca, Polychaeta and Gastrotricha, including seven non-native species. We calculated measures of genetic diversity and differentiation across the environmental gradient, coalescent times and migration rates between North and Baltic Sea populations, and analysed correlations between genetic and life history data. Results The majority of investigated species is either genetically differentiated and/or is adapted to the lower salinity conditions of the Baltic Sea. Moreover, the species exhibiting population structure have a range of patterns of genetic diversity in comparison to the North Sea, from lower in the Baltic Sea to higher in the Baltic Sea, or equally diverse in North and Baltic Sea. Main conclusions Our results indicate that the Baltic Sea should be considered a diversification hotspot: The diversity of genetic patterns points towards independent trajectories in the Baltic compared to the North Sea. At the same time, we found limited evidence for the traditional scenario of the Baltic Sea as a population sink with lower diversity and strong gene flow. The North Sea - Baltic Sea region provides a unique setting to study evolutionary adaptation during colonization processes at different stages by jointly considering native and non-native species.
Article
Full-text available
We present the latest version of the Molecular Evolutionary Genetics Analysis (MEGA) software, which contains many sophisticated methods and tools for phylogenomics and phylomedicine. In this major upgrade, MEGA has been optimized for use on 64-bit computing systems for analyzing bigger datasets. Researchers can now explore and analyze tens of thousands of sequences in MEGA. The new version also provides an advanced wizard for building timetrees and includes a new functionality to automatically predict gene duplication events in gene family trees. The 64-bit MEGA is made available in two interfaces: graphical and command line. The graphical user interface (GUI) is a native Microsoft Windows application that can also be used on Mac OSX. The command line MEGA is available as native applications for Windows, Linux, and Mac OSX. They are intended for use in high-throughput and scripted analysis. Both versions are available from www.megasoftware.net free of charge.
Article
Full-text available
Arlequin ver 3.0 is a software package integrating several basic and advanced methods for population genetics data analysis, like the computation of standard genetic diversity indices, the estimation of allele and haplotype frequencies, tests of departure from linkage equilibrium, departure from selective neutrality and demographic equilibrium, estimation or parameters from past population expansions, and thorough analyses of population subdivision under the AMOVA framework. Arlequin 3 introduces a completely new graphical interface written in C++, a more robust semantic analysis of input files, and two new methods: a Bayesian estimation of gametic phase from multi-locus genotypes, and an estimation of the parameters of an instantaneous spatial expansion from DNA sequence polymorphism. Arlequin can handle several data types like DNA sequences, microsatellite data, or standard multilocus genotypes. A Windows version of the software is freely available on http://cmpg.unibe.ch/software/arlequin3.
Article
Full-text available
The study of the copepod Eurytemora affinis has provided unprecedented insights into mechanisms of invasive success. In this invited review, I summarize a subset of work from my laboratory to highlight key insights gained from studying E. affinis as a model system. Invasive species with brackish origins are overrepresented in freshwater habitats. The copepod E. affinis is an example of such a brackish invader, and has invaded freshwater habitats multiple times independently in recent years. These invasions were accompanied by evolution of physiological tolerance and plasticity, increased body fluid regulation, and evolutionary shifts in ion transporter (V-type H+ ATPase, Na+, K+-ATPase) activity and expression. These evolutionary changes occurred in parallel across independent invasions in nature and in laboratory selection experiments. Selection appears to act on standing genetic variation during invasions, and maintenance of this variation is likely facilitated through “beneficial reversal of dominance” in salinity tolerance across habitats. Expression of critical ion transporters is localized in newly discovered Crusalis leg organs. Increased freshwater tolerance is accompanied by costs to development time and greater requirements for food. High-food concentration increases low-salinity tolerance, allowing saline populations to invade freshwater habitats. Mechanisms observed here likely have relevance for other taxa undergoing fundamental niche expansions.This article is protected by copyright. All rights reserved.
Article
Full-text available
The ctenophore Mnemiopsis leidyi is one of the most successful marine bioinvaders on record. Native to the Atlantic coast of the Americas, M. leidyi invaded the Black Sea, Caspian and Mediterranean Seas beginning the in late 1980s, followed by the North and Baltic Seas starting in 2006, with major concomitant alterations in pelagic ecology, including fishery collapses in some cases. Using extensive native range sampling (21 sites), along with 11 invasive sites in the Black, Caspian, Mediterranean, North and Baltic Seas, we examined M. leidyi worldwide phylogeographic patterns using data from mitochondrial cytochrome b (cytb) and six nuclear microsatellite loci. Cytb and microsatellite data sets showed different levels of genetic differentiation in the native range. Analyses of cytb data revealed considerable genetic differentiation, recovering three major clusters (northwestern Atlantic, Caribbean, and South America) and further divided northwestern Atlantic sampling sites into three groups, separated approximately at Cape Hatteras on the US Atlantic coast and at the Floridian peninsula, separating the Gulf of Mexico and Atlantic coasts. In contrast, microsatellite data only distinguished samples north and south of Cape Hatteras, and suggested considerable gene flow among native samples with clear evidence of isolation by distance. Both cytb and microsatellite data sets indicated that the northern invaders (North/Baltic Seas) originated from north of Cape Hatteras, with cytb data pointing to Delaware and north. Microsatellite data indicated a source for the southern invaders (Black, Caspian and Mediterranean Seas) to be south of Cape Hatteras, while cytb data narrowed the source location to the Gulf of Mexico region. Both cytb and microsatellite data sets suggested that the southern invasion was associated with genetic bottlenecks while evidence was equivocal for the northern invasion. By increasing the native range spatial sampling, our dataset was able to sufficiently characterize patterns and levels of genetic differentiation in the native range of M. leidyi and identify likely biogeographic boundaries, allowing for the most complete characterization of M. leidyi’s invasion histories and most realistic estimates of its source region(s) to date.
Article
Full-text available
Invasive species are often in focus in the non-indigenous species (NIS) research while low-abundance species receive relatively little attention. However, tracking NIS dynamics since the early stages of an invasion provides valuable information on the ecology of invasions. In the current paper, we investigated the invasion history and population dynamics of the small-bodied cladoceran Evadne anonyx G. O. Sars, 1897 in the Gulf of Riga (Baltic Sea) almost since its first detection in 2000. The species already was widespread the Gulf of Riga in 2001 and has been found in nearly every subsequent sample collected during summer months. However, the abundance of the species remained low, seldom 100 individuals m- 3 . Both, salinity and water temperature affected the spatial distribution and population abundance of E. anonyx. The species was found to occur only sporadically at salinities below ca. 6. To obtain reliable presence/absence and density estimates on this small-bodied cladoceran, the entire zooplankton sample needed to be analysed.
Article
Full-text available
The chapter discusses the reproductive biology of marine cladocerans. Marine cladocerans are seasonally abundant and widely distributed in continental shelf waters, estuaries, the open ocean, the Baltic, the Mediterranean, and inland seas. Marine cladocerans, like most of their freshwater counterparts, exhibit direct development, alternation of gamogenesis (amphimixis), and diploid parthenogenesis (apomixis) and padogenesis, or the initiation of reproduction by young individuals during their own early development. The chapter summarizes the life cycle of a podonid cladoceran, using Evadne nordmanni as an example. Physiology and nutrition of marine cladocerans is discussed. Ovaries in cladocerans are elongated, spindle-shaped organs located on each side of the intestine. In Evadne nordmanni, the ovary extends nearly the length of the thorax at maturity. Oogenesis occurs in this species at the narrow anterior end of the ovary, while mature eggs accumulate at the broader and more rounded posterior end. The sex of a marine cladoceran may be recognized on the basis of body size, body shape and other secondary sexual characteristics. The paired testes of marine podonids are located in the hemocoel on both sides of the intestine. Fertilization in marine cladocerans probably occurs before the gamogenic egg moves from the ovary into the brood chamber. Annual cycles of abundance have been recorded for many populations of marine cladocerans. Marine cladocerans exhibit distinct patterns of abundance in relation to temperature and salinity.
Article
Full-text available
To evaluate the influence of the ice ages on patterns of genetic diversity and to test generally accepted perspectives related to glacial refugia and proposed post-glacial colonization pathways in the North Atlantic area, we sequenced a portion of the mitochondrial cytochrome c oxidase subunit I of two amphi-Atlantic distributed amphipods, Gammarus duebeni (n = 418) and Gammarus oceanicus (n = 242). Both species showed several populations with a combination of highly reduced levels of genetic diversity and significant demographic expansion in previously glaciated sites, consistent with an expected extinction and recolonization scenario. Within G. oceanicus, two reciprocally monophyletic clades were found. One clade consisted of the specimens from populations of the American St. Lawrence River and two populations south of it. The other clade included specimens from populations of Europe, Greenland, Iceland and Svalbard, as well as from the Hudson Bay. For G. duebeni, we found no private American haplotypes, and post-glacial colonization from two founder populations is likely. A fixed genetic discontinuity was observed in both species between Iceland and Greenland on the one hand and Europe on the other hand. Our data hence indicate that the proposed postglacial colonization of America from Europe via the Faroe Islands, Iceland and Greenland could be more complex than previously thought and that parts of the North Atlantic region were not colonized from the Eastern Atlantic coasts. Unlike other studies, we speculate that there must be a Nordic glacial refugium for both species, which could be located in Greenland. The Greenlandic populations of both species exhibited private haplotypes, but signals of demographic expansion, conflicting with our theory. It is possible that the refugial character of the Greenlandic populations was erased by the LGM. Furthermore, we found evidence for glacial refugia along the Norwegian coast, the English Channel (G. duebeni) and on the Faroe Islands (G. oceanicus).
Article
Full-text available
More than 140 aquatic alien species (AAS) have been reported from coastlines of the North Sea and the Baltic Sea and from inland waters within the national borders of Germany. The majority of these species has established self-sustaining populations. The most important vectors of introduction are shipping, species imports for aquaculture purposes and species imports as part of the ornamental trade. Several AAS have reached German waters via shipping canals. Many species show a locally limited distribution, but almost half of all AAS have spread successfully across larger areas. Several introduced species are abundant and approximately 20 % of all AAS in Germany can be considered as invasive. Prime source regions are the north-western Atlantic, the Indo-Pacific, and the Ponto-Caspian region. For all source regions considered, the invasion rate has been increasing since the end of the last century.
Article
Full-text available
We examined the population genetics of six species of marine cladocerans, using a ~600bp fragment of the cytochrome oxidase subunit I gene sequence. Phylogenetic analysis revealed significant intraspecific, semi-allopatric phylogenetic breaks in four out of five species belonging to the Podonidae, supporting an ancient radiation and oceanic expansion for this group. By contrast, Penilia avirostris (Sididae) displayed no phylogeographic structure across a global sampling, suggesting a recent worldwide expansion. Our results also show a transoceanic distribution of identical or very similar haplotypes in several species of marine Cladocera, which may be interpreted as either natural transport or evidence of recent anthropogenic transport. If the latter is the case, marine cladocerans represent one of the first genetically documented cases of exotic or invasive marine zooplankton, likely an underreported group.
Article
Full-text available
Long-term dynamics (1960–1997) of the cladoceran species Bosmina coregoni maritima, Evadne nordmanni and Podon spp. are described for the Gdansk Deep and the Gotland Basin (Central Baltic Sea). By using correlation analyses on seasonal time-series, the influence of temperature and salinity on the abundance of cladoceran species was investigated. A clear affinity to higher temperature was found for B. coregoni maritima in summer as well as for E. nordmanni and Podon spp. in spring. In addition to temperature, association tests with salinity revealed besides species-specific preferences, regional and temporal differences. Contrary to B. coregoni maritima, both other species were positively associated to salinity in summer and autumn in the Gdansk Deep. In the Gotland Basin only E. nordmanni was positively correlated to salinity in autumn. Differences in the response to hydrographic variables are possibly stage specific, i.e. between resting eggs and adults, or due to a different adaptation to the abiotic environment.
Article
Full-text available
The Baltic Sea: ed. by A. Voipio, Elsevier oceanography series ; 30, 219-274
Article
Full-text available
Theory predicts that speciation can be quite rapid. Previous examples comprise a wide range of organisms such as sockeye salmon, polyploid hybrid plants, fruit flies and cichlid fishes. However, few studies have shown natural examples of rapid evolution giving rise to new species in marine environments. Using microsatellite markers, we show the evolution of a new species of brown macroalga (Fucus radicans) in the Baltic Sea in the last 400 years, well after the formation of this brackish water body ~8-10 thousand years ago. Sympatric individuals of F. radicans and F. vesiculosus (bladder wrack) show significant reproductive isolation. Fucus radicans, which is endemic to the Baltic, is most closely related to Baltic Sea F. vesiculosus among north Atlantic populations, supporting the hypothesis of a recent divergence. Fucus radicans exhibits considerable clonal reproduction, probably induced by the extreme conditions of the Baltic. This reproductive mode is likely to have facilitated the rapid foundation of the new taxon. This study represents an unparalleled example of rapid speciation in a species-poor open marine ecosystem and highlights the importance of increasing our understanding on the role of these habitats in species formation. This observation also challenges presumptions that rapid speciation takes place only in hybrid plants or in relatively confined geographical places such as postglacial or crater lakes, oceanic islands or rivers.
Article
Full-text available
Within the Cladocera, the water-fleas, four major taxa can be distinguished: Anomopoda, Ctenopoda, Haplopoda, and Onychopoda. Haplopoda and Onychopoda are called "predatory water-fleas." The Haplopoda is monotypic; its only representative, Leptodora kindtii, is common in palearctic and nearctic freshwater bodies. The Onychopoda show a remarkable geographic distribution. Most of the described species are restricted to the Caspian Sea, the Aral Sea, and peripheral areas of the Black Sea, including the Sea of Azov--all remnants of the Eastern Paratethys. The remaining onychopods are either freshwater inhabitants or marine animals, widespread in the world oceans. We present molecular evidence for a sister group relationship between Haplopoda and Onychopoda within the Cladocera. The Onychopoda and its three families are monophyletic. We suggest an independent invasion into the Ponto-Caspian basin at least three times, twice originating in the palearctic freshwater bodies and once starting from the world oceans.
Article
Full-text available
Current efforts to reconstruct the tree of life and histories of multigene families demand the inference of phylogenies consisting of thousands of gene sequences. However, for such large data sets even a moderate exploration of the tree space needed to identify the optimal tree is virtually impossible. For these cases the neighbor-joining (NJ) method is frequently used because of its demonstrated accuracy for smaller data sets and its computational speed. As data sets grow, however, the fraction of the tree space examined by the NJ algorithm becomes minuscule. Here, we report the results of our computer simulation for examining the accuracy of NJ trees for inferring very large phylogenies. First we present a likelihood method for the simultaneous estimation of all pairwise distances by using biologically realistic models of nucleotide substitution. Use of this method corrects up to 60% of NJ tree errors. Our simulation results show that the accuracy of NJ trees decline only by ≈5% when the number of sequences used increases from 32 to 4,096 (128 times) even in the presence of extensive variation in the evolutionary rate among lineages or significant biases in the nucleotide composition and transition/transversion ratio. Our results encourage the use of complex models of nucleotide substitution for estimating evolutionary distances and hint at bright prospects for the application of the NJ and related methods in inferring large phylogenies. • phylogenetics • molecular evolution • distance estimation • tree of life • maximum likelihood
Article
Full-text available
Marginal populations are often isolated and under extreme selection pressures resulting in anomalous genetics. Consequently, ecosystems that are geographically and ecologically marginal might have a large share of genetically atypical populations, in need of particular concern in management of these ecosystems. To test this prediction, we analysed genetic data from 29 species inhabiting the low saline Baltic Sea, a geographically and ecologically marginal ecosystem. On average Baltic populations had lost genetic diversity compared to Atlantic populations: a pattern unrelated to dispersal capacity, generation time of species and taxonomic group of organism, but strongly related to type of genetic marker (mitochondrial DNA loci had lost c. 50% diversity, and nuclear loci 10%). Analyses of genetic isolation by geographic distance revealed clinal patterns of differentiation between Baltic and Atlantic regions. For a majority of species, clines were sigmoid with a sharp slope around the Baltic Sea entrance, indicating impeded gene flows between Baltic and Atlantic populations. Some species showed signs of allele frequencies being perturbed at the edge of their distribution inside the Baltic Sea. Despite the short geological history of the Baltic Sea (8000 years), populations inhabiting the Baltic have evolved substantially different from Atlantic populations, probably as a consequence of isolation and bottlenecks, as well as selection on adaptive traits. In addition, the Baltic Sea also acts a refuge for unique evolutionary lineages. This marginal ecosystem is thus vulnerable but also exceedingly valuable, housing unique genes, genotypes and populations that constitute an important genetic resource for management and conservation.
Article
The abilities of Caspian and Aral Ostracoda for 2 different types of osmoregulation (hyperosmotic and amphiosmotic) were shown. The modern fauna of Ostracoda of the Caspian and Aral seas may thus consist of forms of freshwater origin.-from English summary
Article
The pantropical sea urchin genus Eucidaris contains four currently recognized species, all of them allopatric: E. metularia in the Indo-West Pacific, E. thouarsi in the eastern Pacific, E. tribuloides in both the western and eastern Atlantic, and E. clavata at the central Atlantic islands of Ascension and St. Helena. We sequenced a 640-bp region of the cytochrome oxidase I (COI) gene of mitochondrial DNA to determine whether this division of the genus into species was confirmed by molecular markers, to ascertain their phylogenetic relations, and to reconstruct the history of possible dispersal and vicariance events that led to present-day patterns of species distribution. We found that E. metularia split first from the rest of the extant species of the genus. If COI divergence is calibrated by the emergence of the Isthmus of Panama, the estimated date of the separation of the Indo-West Pacific species is 4.7-6.4 million years ago. This date suggests that the last available route of genetic contact between the Indo-Pacific and the rest of the tropics was from west to east through the Eastern Pacific Barrier, rather than through the Tethyan Sea or around the southern tip of Africa. The second cladogenic event was the separation of eastern Pacific and Atlantic populations by the Isthmus of Panama. Eucidaris at the outer eastern Pacific islands (Galapagos, Isla del Coco, Clipperton Atoll) belong to a separate clade, so distinct from mainland E. thouarsi as to suggest that this is a different species, for which the name E. galapagensis is revived from the older taxonomic literature. Complete lack of shared alleles in three allozyme loci between island and mainland populations support their separate specific status. Eucidaris galapagensis and E. thouarsi are estimated from their COI divergence to have split at about the same time that E. thouarsi and E. tribuloides were being separated by the Isthmus of Panama. Even though currents could easily convey larvae between the eastern Pacific islands and the American mainland, the two species do not appear to have invaded each other's ranges. Conversely, the central Atlantic E. clavata at St. Helena and Ascension is genetically similar to E. tribuloides from the American and African coasts. Populations on these islands are either genetically connected to the coasts of the Atlantic or have been colonized by extant mitochondrial DNA lineages of Eucidaris within the last 200,000 years. Although it is hard to explain how larvae can cross the entire width of the Atlantic within their competent lifetimes, COI sequences of Eucidaris from the west coast of Africa are very similar to those of E. tribuloides from the Caribbean. FST statistics indicate that gene flow between E. metularia from the Indian Ocean and from the western and central Pacific is restricted. Low gene flow is also evident between populations of E. clavata from Ascension and St. Helena. Rates of intraspecific exchange of genes in E. thouarsi, E. galapagensis, and E. tribuloides, on the other hand, are high. The phylogeny of Eucidaris confirms Ernst Mayr's conclusions that major barriers to the dispersal of tropical echinoids have been the wide stretch of deep water between central and eastern Pacific, the cold water off the southwest coast of Africa, and the Isthmus of Panama. It also suggests that a colonization event in the eastern Pacific has led to speciation between mainland and island populations.
Book
Initially the details on morphology and ecology are provided, including sections on: internal and external morphology; horizontal distribution; vertical distribution; influence of environmental factors; seasonal population dynamics; vertical migrations; reproduction; feeding; locomotion, behaviour, life strategy; the role of predatory Cladocera in water bodies; and origin and phylogenetic relationships. A key to the families of the superorder Cladocera is then provided. The systematics (including identification keys and morphological aspects) of the following groups are then covered in some detail: Onychopoda, Podonidae, Pleopis, Pseudevadne, Podon, Evadne, Podonevadne, Cornigerius, Caspievadne, Polyphemidae, Polyphemus, Cercopagidae, Bythotrephes, Cercopagis, Halpopoda, Leptodoridae and Leptodora.
Article
Publisher Summary Cells of euryhaline invertebrates, when submitted to osmotic challenges, show volume regulation responses that are most probably of ecological significance. Volume regulatory responses are concomitant with changes in the intracellular levels of different osmotic effectors—essentially inorganic ions and amino compounds. So far as inorganic ions are concerned, K + plays a particularly important role in the early, large volume decrease that immediately follows the osmotically induced swelling. The changes in the level of that ion are related to changes in efflux due to modifications in the activity of leak pathways. The amino compounds most studied to date have been the amino acids. Their intracellular concentration appears to be regulated essentially by control of their output from the pool, this control being achieved mainly by two different mechanisms: (1) control of the efflux from the cells related to changes in permeability and (2) control of the rate of metabolic exit from the pool by modulation of the enzymatic trans-deamination sequence. Nothing is known about the mechanisms of control of the leak pathways for both K + and the amino compounds.
Chapter
The location of the Baltic Sea in the northern high latitudes affects the structure and function of the Baltic ecosystem. There are also large regional differences in surface salinity and chemical properties. The salinity conditions in the Baltic Sea are very stable. No marked tide-induced currents occur in the area. During different marine and fresh-water stages, there has been a succession of ecosystems. Mainly limnic and marine organisms with a wide osmotic tolerance have been able to survive. The number of species is small. Few genuine brackish-water species have evolved in the Baltic Sea as compared to the geologically old, brackish Pontic–Caspian Sea area. The productive system of the Baltic Sea consists of the trophogenic layers of the pelagial system and the littoral system, the latter of which is also of great importance in the northern part of the area, because of the long and relatively shallow coast. The location of the Baltic Sea in high latitudes causes a pronounced maximum of light in summer. The main consuming system, heterotrophic pelagic and benthic organisms is dependent on organic matter sinking from the trophogenic layer.
Article
When the Bering Strait between Alaska and Siberia opened about 3.5 Ma during the early Pliocene, cool-temperate and polar marine species were able to move between the North Pacific and Arctic-Atlantic basins. In order to investigate the extent, pattern, and dynamics of this trans-Arctic interchange, I reviewed the Recent and fossil distributions of post-Miocene shell-bearing Mollusca in each of five northern regions: (1) the northeastern Atlantic (Lofoten Islands to the eastern entrance of the English Channel and the northern entrance of the Irish Sea), (2) northwestern Atlantic (southern Labrador to Cape Cod), (3) northeastern Pacific (Bering Strait to Puget Sound), (4) northwestern Pacific (Bering Strait to Hokkaido and the northern Sea of Japan), and (5) Arctic (areas north of the Lofoten Islands, southern Labrador, and Bering Strait). I have identified 295 molluscan species that either took part in the interchange or are descended from taxa that did. Of these, 261 are of Pacific origin, whereas only 34 are of Arctic-Atlantic origin. Various analyses of the pattern of invasion confirm earlier work, indicating that there is a strong bias in favor of species with a Pacific origin. A geographical analysis of invaders implies that, although trans-Arctic interchange contributed to a homogenization of the biotas of the northern oceans, significant barriers to dispersal exist and have existed for trans-Arctic invaders within the Arctic-Atlantic basin. Nevertheless, trans-Arctic invaders in the Atlantic have significantly broader geographical ranges than do taxa with a pre-Pliocene history in the Atlantic. Among the possible explanations for the asymmetry of trans-Arctic invasion, two hypotheses were explicitly tested. The null hypothesis of diversity states that the number of invaders from a biota is proportional to the total number of species in that biota. Estimates of Recent molluscan diversity show that the North Pacific is 1.5 to 2.7 times richer than is the Arctic-Atlantic, depending on how faunistic comparisons are made. This difference in diversity is much smaller than is the asymmetry of trans-Arctic invasion in favor of Pacific species. Rough estimates of regional Pliocene diversity suggest that differences in diversity during the Pliocene were smaller than they are in the Recent fauna. The null hypothesis was therefore rejected. The hypothesis of ecological opportunity states that the number of invaders to a region is proportional to the number of species that became extinct there. The post-Early Pliocene magnitude of extinction was lowest in the North Pacific, intermediate in the northeastern Atlantic, and probably highest in the northwestern Atlantic. The absolute number and faunistic importance of post-Early Pliocene invaders (including trans-Arctic species, as well as taxa previously confined to warm-temperate waters and western Atlantic species that previously occurred only in the eastern Atlantic) was lowest in the North Pacific, intermediate in the northeastern Atlantic, and highest in the northwestern Atlantic. Further support for the hypothesis of ecological opportunity comes from the finding that hard-bottom communities, especially those in the northwestern Atlantic, show a higher representation of molluscan species of Pacific origin, and are likely to have been more affected by climatic events, than were communities on unconsolidated sandy and muddy bottoms. Support for the hypothesis does not rule out other explanations for the observed asymmetry of trans-Arctic invasion. A preliminary study of species-level evolution within lineages of trans-Arctic invaders indicates that anagenesis and cladogenesis have been more frequent among groups with Pacific origins than among those with Atlantic origins, and that the regions within the Arctic-Atlantic basin with the highest absolute number and faunistic representation of invaders (western Atlantic and Arctic) are the regions in which speciation has been least common among the invaders. The asymmetry of invasion is therefore distinct from the asymmetry of species-level evolution of invaders in the various northern marine regions.
Article
Salinity represents a critical environmental factor for all aquatic organisms, including fishes. Environments of stable salinity are inhabited by stenohaline fishes having narrow salinity tolerance ranges. Environments of variable salinity are inhabited by euryhaline fishes having wide salinity tolerance ranges. Euryhaline fishes harbor mechanisms that control dynamic changes in osmoregulatory strategy from active salt absorption to salt secretion and from water excretion to water retention. These mechanisms of dynamic control of osmoregulatory strategy include the ability to perceive changes in environmental salinity that perturb body water and salt homeostasis (osmosensing), signaling networks that encode information about the direction and magnitude of salinity change, and epithelial transport and permeability effectors. These mechanisms of euryhalinity likely arose by mosaic evolution involving ancestral and derived protein functions. Most proteins necessary for euryhalinity are also critical for other biological functions and are preserved even in stenohaline fish. Only a few proteins have evolved functions specific to euryhaline fish and they may vary in different fish taxa because of multiple independent phylogenetic origins of euryhalinity in fish. Moreover, proteins involved in combinatorial osmosensing are likely interchangeable. Most euryhaline fishes have an upper salinity tolerance limit of approximately 2× seawater (60 g kg(-1)). However, some species tolerate up to 130 g kg(-1) salinity and they may be able to do so by switching their adaptive strategy when the salinity exceeds 60 g kg(-1). The superior salinity stress tolerance of euryhaline fishes represents an evolutionary advantage favoring their expansion and adaptive radiation in a climate of rapidly changing and pulsatory fluctuating salinity. Because such a climate scenario has been predicted, it is intriguing to mechanistically understand euryhalinity and how this complex physiological phenotype evolves under high selection pressure. © 2015. Published by The Company of Biologists Ltd.
Article
A recently discovered paradoxical maximum of planktonic protistan species in the salinity gradient of the Baltic Sea revealed an inverse trend of species number/salinity relation in comparison to the previously accepted species-minimum model for macrozoobenthos. Here, we review long-term data on organisms of different size classes and ecological groups to show that eukaryotic and prokaryotic microbes in plankton demonstrate a maximum species richness in the challenging zone of the critical salinity 5–8, where the large-bodied bottom dwellers (macrozoobenthos, macroalgae and aquatic higher plants) experience large-scale salinity stress which leads to an impoverished diversity. We propose a new conceptual model to explain why the diversity of small, fast-developing, rapidly evolving unicellular plankton organisms benefits from relative vacancy of brackish-water ecological niches and impaired competitiveness therein. The ecotone theory, Hutchinson's Ecological Niche Concept, species–area relationships and the Intermediate Disturbance Hypothesis are considered as a theoretical framework for understanding extinctions, speciation and variations in the evolution rates of different aquatic species in ecosystems with the pronounced salinity gradient.
The interactions of physiological and morphological evolution are discussed in relation to the branchiopod crustaceans. Many branchiopods are morphologically relatively primitive and evade competition from more advanced forms by physiological adaptations which enable them to survive in extreme environments. The most recently evolved group of branchiopods, the Cladocera, or water fleas, have specialisation of morphology and reproduction which have enabled them to return to less extreme freshwater environments. Most recently they have developed physiological adptations which enable them to exploit the marine and other saline environments.
Article
The Quaternary cold periods in Europe are thought to have heavily influenced the amount and distribution of intraspecific genetic variation in both animals and plants. The phylogeographies of 10 taxa, including mammals (Ursus arctos, Sorex spp., Crocidura suaveolens, Arvicola spp.), amphibians (Triturus spp.), arthropods (Chorthippus parallelus), and plants (Abies alba, Picea abies, Fagus sylvatica, Quercus spp.), were analysed to elucidate general trends across Europe. Only a small degree of congruence was found amongst the phylogeographies of the 10 taxa, but the likely postglacial colonization routes exhibit some similarities. A Brooks parsimony analysis produced an unrooted area phylogram, showing that: (i) the northern regions were colonized generally from the Iberic and Balkanic refugia; and (ii) the Italian lineages were often isolated due to the presence of the Alpine barrier. The comparison of colonization routes highlighted four main suture-zones where lineages from the different refugia meet. Some of the intraspecific genetic distances among lineages indicated a prequaternary divergence that cannot be connected to any particular cold period, but are probably related mainly to the date of arrival of each taxon in the European continent. As a consequence, molecular genetics so far appears to be of limited use in dating Quaternary events.
Article
Members of the order Cladocera show remarkable morphological and ecological diversity. One of the most spectacular adaptive radiations in this group has involved species of the suborder Onychopoda, which have adopted a novel feeding strategy, predation, and have colonized habitats with a broad range of salinities. In order to evaluate the origins and systematics of this group, we derived a molecular phylogeny for its three component families including nine of 10 recognized genera based on three mitochondrial (mt) gene sequences: cytochrome c oxidase subunit I (COI), the ribosomal small and large subunits (12S and 16S) and one nuclear gene sequence: the small ribosomal subunit (18S). Maximum-parsimony, maximum-likelihood and neighbour-joining phylogenetic analyses were largely congruent, supporting the monophyly of the suborder and each of its families. Comparative analyses of data based on total evidence and the conditional combination of the ribosomal genes produced relatively congruent patterns of phylogenetic affinity. By contrast, analyses of single gene results were inconsistent in recovering the monophyletic groups identified by the multigene analyses. Based on the reconstructed phylogeny, we discriminate among the existing hypotheses regarding the evolutionary history of the onychopods. We identify a prolonged episode of speciation from the Miocene to the Pleistocene with two pulses of diversification. We discuss our results with reference to the geological history of the Ponto-Caspian basin, the region which fostered the onychopod radiation.
Article
Within the order Cladocera are found almost all varieties of osmotic regulation, which make it possible for them to live in waters of a wide range of salt concentrations. Many Cladocera are very powerful osmoregulators and are comparable to the teleosts and decapod crustaceans in their abilities. The variety of osmoregulatory capacities within the cladocerans are illustrated and discussed. The function of mitochondrion-rich ion transporting cells found in nuchal glands or on epipodites are diseussed and the physiological mechanisms involved in osmoregulation are compared with similar mechanisms in other crustaceans and in teleosts. Data is provided on osinotic regulation in eggs and embryos in open and elosed brood chambers. Other topics include the occurrence of physiological races in some species, recent changes in osmoregulatory abilities following man-induced changes in salinity, the effects of temperature on osmoregulation and the effects of pH.
Article
This paper presents facts and problems related to the concept of critical salinity, i.e., the salinity range 5 to 8 S. It points, in particular, to the distribution of marine and freshwater species revealing a faunistic boundary (minimum number of species), organismic resistance to salinity, osmoregulative capacity, physiological activity, electro-chemical properties of tissues, and evolutionary aspects. The concept of critical salinity opens up new perspectives for the understanding of present day salinity effects as well as for the interpretation of animal evolution.
Article
Long-term research in the Baltic Sea revealed the basic trends of zooplankton community variations depending on oceanographic processes. Alternation of the periods of increase and decrease in salinity of the Baltic Sea against the background of climate changes (temperature increase) and eutrophication affect the state of the entire Baltic ecosystem, including zooplankton. For these periods, the dynamics of zooplankton in the Baltic Sea were analyzed based on literature data and results of regular research in the southeastern Baltic Sea during 1998–2007. The changes in the hydrological situation were accompanied by significant changes in the zooplankton community. In the 1990s–2000s, the abundance and biomass of brackish-water and thermophilous species primarily of Cladocera and Copepoda increased markedly. The role of the previously dominant marine copepod Pseudocalanus elongatus decreased due to salinity reduction in the deep-water part of the Baltic Sea. Maximum development of zooplankton occurred in years of the greatest warming-up of the water (2001, 2005–2007) against the background of a general positive trend of zooplankton abundance in the last decade.
Article
Reconstructing phylogenies from intraspecific data (such as human mitochondrial DNA variation) is often a challenging task because of large sample sizes and small genetic distances between individuals. The resulting multitude of plausible trees is best expressed by a network which displays alternative potential evolutionary paths in the form of cycles. We present a method ("median joining" [MJ]) for constructing networks from recombination-free population data that combines features of Kruskal's algorithm for finding minimum spanning trees by favoring short connections, and Farris's maximum-parsimony (MP) heuristic algorithm, which sequentially adds new vertices called "median vectors", except that our MJ method does not resolve ties. The MJ method is hence closely related to the earlier approach of Foulds, Hendy, and Penny for estimating MP trees but can be adjusted to the level of homoplasy by setting a parameter epsilon. Unlike our earlier reduced median (RM) network method, MJ is applicable to multistate characters (e.g., amino acid sequences). An additional feature is the speed of the implemented algorithm: a sample of 800 worldwide mtDNA hypervariable segment I sequences requires less than 3 h on a Pentium 120 PC. The MJ method is demonstrated on a Tibetan mitochondrial DNA RFLP data set.
Article
Global climate has fluctuated greatly during the past three million years, leading to the recent major ice ages. An inescapable consequence for most living organisms is great changes in their distribution, which are expressed differently in boreal, temperate and tropical zones. Such range changes can be expected to have genetic consequences, and the advent of DNA technology provides most suitable markers to examine these. Several good data sets are now available, which provide tests of expectations, insights into species colonization and unexpected genetic subdivision and mixture of species. The genetic structure of human populations may be viewed in the same context. The present genetic structure of populations, species and communities has been mainly formed by Quaternary ice ages, and genetic, fossil and physical data combined can greatly help our understanding of how organisms were so affected.
The genetic legacy of the Quaternary ice ages
  • Hewitt
Die brackwasserfauna (Mit besonderer berücksichtigung der ostsee)
  • Remane
Remane, A. (1934). Die brackwasserfauna (Mit besonderer berücksichtigung der ostsee). Verhandlungen der Deutschen Zoologischen Gesellschaft Leipzig, 36, 34-74.
Life on the margin: Genetic isolation and diversity loss in a peripheral marine ecosystem, the Baltic Sea
  • Johannesson
South atlantic zooplankton
  • T. Onbe
State and evolution of the Baltic Sea
  • H. U. Lass
  • W. Matthäus
Fehmarnbelt Fixed Link EIA. Marine Water & Fauna & Flora − Baseline. Water Quality and Plankton of the Fehmarnbelt Area
  • Fema-Fehy
FEMA-FEHY. (2013). Fehmarnbelt Fixed Link EIA. Marine Water & Fauna & Flora − Baseline. Water Quality and Plankton of the Fehmarnbelt Area. Report No. E2TR0020 − Volume IV, FEMA consortium/co DHI (ed.), Hørsholm, 158 p.
Neobiota indeutschen Küstengewässern − Eingeschleppte und kryptogene Tierund Pflanzenarten an der deutschen Nord-und Ostseeküste. LLUR SH − Gewässer
  • D Lackschewitz
  • K Reise
  • C Buschbaum
  • R Karenz
Lackschewitz, D., Reise, K., Buschbaum, C. & Karenz, R. (2014). Neobiota indeutschen Küstengewässern − Eingeschleppte und kryptogene Tierund Pflanzenarten an der deutschen Nord-und Ostseeküste. LLUR SH − Gewässer; D 25.
Bidrag till Kännedomen af slägtena Campanularia och Syncoryna. Kungliga Svenska Vetenskaps-Akademiens Handlingar för
  • S L Lovén
Lovén, S. L. (1836). Bidrag till Kännedomen af slägtena Campanularia och Syncoryna. Kungliga Svenska Vetenskaps-Akademiens Handlingar för 260-281.
Ctenopoda and onychopoda
  • T Onbe
Onbe, T. (1999). Ctenopoda and onychopoda. In D. Boltovskoy (Ed.), South atlantic zooplankton (pp. 797-813). Leiden: Backhuys.