In view of its fundamental and pervasive influences and impacts on organism physiology and ecology, body size is recognized as a key component of evolutionary fitness and serves as the cornerstone of a seminal contribution in freshwater zooplankton ecology-the Size Efficiency Hypothesis (SEH) of Brooks & Dodson (Science 150:28-35, 1965). While the roles and implications of body size in predation and competition-central tenets of the SEH-have been widely considered and reviewed, no broader integrated synthesis exists of the collective array of body size determinants and their implications in the ecology in crustacean zooplankton-a numerically and functionally dominant group of aquatic organisms. Focusing on planktonic Cladocera and Copepoda in inland waters, in particular, we provide a wide-ranging overview of the direct and/or indirect effects of environmental conditions, consumable resources and biotic interactions that independently and/or collectively influence the phenotypic expression of body size (particularly as length), both within and between species. Some indirect ultimate evolutionary consequences of body size are considered, and we identify some controversies and unresolved issues related to this biologically crucial trait. While by no means exhaustive, our overview reveals a complex nexus of extrinsic proximate abiotic and biotic factors and interactions that influence body size, the phenotypic expression of which in natural systems commonly reflects contrasting outcomes related to conflicting direct and/or indirect selective pressures. In general, however, body size (both interand intra specifically) declines with rising temperature and increases with rising food supply (depending on its quality), although both temperature and food supply exert contrary influences on particular taxa (or life history stages) under certain environmental circumstances. Predation undoubtedly has an overriding influence on body size selection. Depending on its mechanistic basis (visual, tactile or both in tandem), it selectively favours either small or large body size, both within (adults vs. juveniles) and between prey species, which are accordingly often 'size-trapped' between contrasting selective pressures, with consequent indirect effects. The bioenergetics of fundamental physiological processes undoubtedly set constraints on body size and serve as the primary determinant. However, within such

Daphnia magna is a common crustacean that is adapted to brief spells of fasting. Lipids are naturally a major component of their diet and are stored as energy reserves. However, there has been some controversy in the literature on the extent to which dietary lipids are used directly for complex lipid formation in Daphnia. We examined lipid metabolism in D. magna by labeling the animals using [1-14C]acetate and then followed the turnover of radiolabeled lipids during a pulse chase. Daphnia were either fed or maintained without food during the chase period. The decrease in radioactivity during the chase was relatively unaffected by feeding, although there were some differences in the distribution of radioactivity between lipid classes or individual FA. The polar lipids, which were four times better labeled than nonpolar lipids, contained the most radioactivity in the zwitterionic phosphoglycerides, PE and PC. Under the experimental conditions, the turnover of the polar membrane lipids was unaffected by feeding. Within nonpolar lipids, TAG accounted for up to about 80% of the label, followed by DAG. Overall, our data show that D. magna is capable of high rates of lipid radiolabeling de novo and, in addition, is able to use--and indeed may be dependent on--some dietary components such as the PUFA linoleate and alpha-linolenate. The results also clearly show that Daphnia is able to tolerate brief spells of fasting (24 h) with very little change to its lipid metabolism.

We review the patterns of recent range expansions and the biology of the invasive PontoCaspian predatory onychopod cladocerans: Cercopagis pengoi, Evadne anonyx, Podonevadne trigona, Cornigerius maeoticus and Cornigerius bicornis.

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Lipids and fatty acids from the lichen Rhizoplaca peltata, growing either high in the mountains or in nearby foothills, were analysed and compared. It was shown that the same lichen species had considerable differences in the content of triacylglycerols, free sterols, wax esters, steryl esters, glycolipids, betaine and phospholipids, as well as in fatty acid content, depending on altitude.

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