Subspecies, morphs and clines in the amphipod Gammarus duebeni from fresh and saline waters

The nature and extent of morphological variation within populations of Gammarus duebeni are examined. The exceptional tolerance of G. duebeni to salinities that encompass three orders of magnitude was known in the 19th Century, and has attracted considerable attention from physiologists and ecologists in the 20th Century, including the likelihood that populations in freshwater are distinct from those living in more saline environments. It is concluded that gradual evolution into discrete and readily distinguished subspecies is currently underway, eventually producing several new species in freshwater and saline habitats

Reproduction in Gammarus (Crustacea, Amphipoda): basic processes

Research on the basic reproduction processes of Gammarus is summarized and reviewed, reproductive strategies in males and females being left to two later papers. The author describes the reproductive systems, the development of eggs (oocytes) in the ovaries, courtship and precopulatory amplexus, mating and the production of sperms, egg laying, mortality and diapause

British freshwater Malacostracan

This short divertissement touches lightly on the vagaries of vernacular names for culinary and other crustaceans, gives a thumbnail sketch of the distribution of the common and less well-known freshwate

Reproduction in Gammarus (Crustacea, Amphipoda): female strategies

This paper attempts to review the literature on Gammarus and examine how it allocates its internal resources when producing eggs. There is an extensive literature on the fecundity of freshwater species but almost nothing is known about the sizes and energy contents of the eggs. More is known for saltwater species, in which the mean number of eggs per brood is inversely proportional to mean egg size and directly proportional to the female's body size. Theoretical aspects of egg size, numbers and reproductive effort are examined, along with the relation between sizes of eggs, broods and female body size. The reproductive effort and breeding cycles of both saltwater and freshwater species are reviewed, and reproductive strategies assessed

Gone with the wind? Evidence for 19th century

For decades the variety of English spoken by African Americans in the United States has been a major focus of research in linguistics. Despite that, there is still considerable controversy over its past, and specifically whether there had formerly been a plantation creole which shaped the modern African American Vernacular English (AAVE) linguistic system as it emerged. Increasingly abundant evidence has now been assembled on the 19th century in the form of recordings of speakers born in the antebellum period, backed up by data from works of fiction. Taken together, this evidence strongly suggests that a variety of creole was indeed spoken alongside English, perhaps without clear separation, at least until the time of the Civil War

The ionic composition of surface waters in the English Lake District, related to bedrock geology, with some singular facts and speculation on the existence of mineral-rich groundwaters

This article is based on a survey of tarns conducted mainly in the summers of 1983 to 1985, plus a survey made in the winter of 1985, in which streams were sampled on the wide variety of rock-types occurring on the fringes of the Lake District. Differences in composition of major ions and their concentrations in the surface waters of Cumbria reflect the complex geological structure of the region. At altitudes above 300 m, on Borrowdale Volcanics and Skiddaw Slates, surface waters are derived from atmospheric precipitation, with additional inputs of some ions - especially calcium and bicarbonate - from catchment rocks and soils. In some of the low-lying large lakes on the fringes of the central fells, water composition is also dominated by inputs from upper catchments; examples are Wastwater, Ullswater and Haweswater. However in other lakes there is evidence (Derwentwater and Bassenthwaite Lake) of inputs from saline groundwater

The ionic composition of surface waters in the English Lake District, related to bedrock geology, with some singular facts and speculation on the existence of mineral-rich groundwaters

All natural waters are a cocktail of particulate and dissolved substances,including numerous elements that are present in trace amounts, several plant"nutrients" in small to moderate amounts (particularly nitrogen, phosphorusand silicon), and "major ions" or electrolytes (charged solutes) in moderate torelatively large amounts. The major cations are sodium, calcium, magnesiumand potassium, plus hydrogen and aluminium which occur in increasinglygreater amounts in acid waters, especially at pH below ca. 5.0. Major anionsare chloride, sulphate, nitrate and several components representing "alkalinity"- especially bicarbonate and silicates. Although few in number, these ionsdetermine aspects of water quality that are essential for all aquatic organisms.Sodium, potassium and chloride are vital minerals for internal regulation ofblood and tissue cells in animals, and tissues of plants. Calcium, magnesiumand bicarbonate alkalinity are also vital for the biota, and are the principalcomponents of water "softness" and "hardness". Nitrate is an important plantnutrient, together with phosphate (and silicate for diatoms). Sulphate is a majorcomponent of some tissue cells and important in the external environment as aprincipal anion for maintaining charge balance (electroneutrality), especially inproviding a "balance" for hydrogen, calcium and magnesium cations. In thislatter role sulphate is important in acidification processes affecting soils andwaters, although it is frequently present in larger amounts in hard waters

Subspecies, morphs and clines in the amphipod Gammarus duebeni from fresh and saline waters

As a general rule, most species of Gammarus typically live in one of threemajor environments: near-constant salinities of the marine-littoral, fluctuatingbrackish waters in estuaries and saltmarshes, or the low salinities offreshwater streams and lakes. A few straddle two of these majorenvironments, for example G. tigrinus, a North American coastalbrackish water species that is colonising some fresh waters in western Europe(Gledhill et al. 1993). But Gammarus duebeni Liljeborg is outstandinglyversatile, well known for its ability to tolerate and colonise environmentswhere salinities greatly exceed those of normal seawater, as in hypersalinesupralittoral rockpools where the salt content may be doubled due toevaporation. It also occurs in fresh water on peninsulas and islands around thewestern seaboard of Britain, where close proximity to the sea has slightlyraised the concentration of sodium and chloride. Furthermore, G. duebeni iswidespread and indeed the common gammarid in the fresh waters of Irelandand western part of Brittany

Hedge fund strategies, performance & diversification:A portfolio theory & stochastic discount factor approach

For 5500 North American hedge funds following 11 different strategies, we analyse the stand-alone performance of these strategies using a stochastic discount factor approach. Employing the same data, we then consider the diversification benefits of each hedge fund strategy when combined with a portfolio of US equities and bonds. We compute the out-of-sample Black-Litterman portfolios, with Bayes-Stein, higher moments, simulations, desmoothed data and allowance for regimes as robustness checks. All but two hedge fund strategies out-perform the market as stand-alone investments; and all but one provide significant diversification benefits. The higher is an investor’s risk aversion, the more beneficial is diversification into hedge funds