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Measures Only (measure + only)
Selected AbstractsWidespread hermaphroditism in freshwater gastrotrichsINVERTEBRATE BIOLOGY, Issue 4 2001Mitchell J. Weiss Abstract. Freshwater members of the phylum Gastrotricha were long thought to lack male gametes and to exist exclusively as parthenogenetic females. The surprising 1978 discovery of sperm in the common species Lepidodermella squamata raised the question of how many other freshwater gastrotrichs might likewise be hermaphroditic. In a comparative study of species from across both major families, sperm have been found in every species examined intensively. They were detected in 19 species of Chaetonotidae (from Aspidiophorus, Chaetonotus, Heterolepidoderma, Ichthydium, Lepidodermella, and Polymerurus) and 3 species of Dasydytidae (from Haltidytes, Setopus, and Stylochaeta), characteristically occurring ventrally in single unilateral or (more often) 2,12 bilateral packets. Their shape ranges from filiform (length in Chaetonotus bisacer, ,40 ,m) to rodlike, spindlelike, oval, and possibly spherical (some in Stylochaeta scirtetica measure only 1 ,m). With light microscopy, a dense nucleus appears to fill the entire volume of these aflagellate cells. Spermatogenesis within cysts (maximally, 16 sperm/clone) is evidently characteristic of both families, each cyst generating one large residual body. Sperm-bearers display oocytes with sometimes distinctive cytoplasmic elements and a posterior X-organ whose organization can be complex. Evidence supports an unusual life cycle in which parthenogenesis is followed by simultaneous hermaphroditism. These findings may illuminate the reproductive characters as well as ancestry of marine and brackish-water taxa of Chaetonotida. [source] Population dynamics of fisheries stock enhancementJOURNAL OF FISH BIOLOGY, Issue 2004K. Lorenzen The population dynamics of fisheries stock enhancement, and its potential for generating benefits over and above those obtainable from optimal exploitation of wild stocks alone are poorly understood and highly controversial. I extend the dynamic pool theory of fishing to stock enhancement by unpacking recruitment, incorporating regulation in the recruited stock, and accounting for biological differences between wild and hatchery fish. I then analyse the dynamics of stock enhancement and its potential role in fisheries management, using the candidate stock of North Sea sole as an example. Enhancement through release of recruits or advanced juveniles is predicted to increase total yield and stock abundance, but reduce abundance of the naturally recruited stock component through compensatory responses or overfishing. Release of genetically maladapted fish reduces the effectiveness of enhancement, and is most detrimental overall if fitness of hatchery fish is only moderately compromised. As a temporary measure for rebuilding of depleted stocks, enhancement can not substitute for effort limitation, and is advantageous as an auxiliary measure only if the population has been reduced to a very low proportion of its unexploited biomass. Quantitative analysis of population dynamics is central to the responsible use of stock enhancement in fisheries management, and the necessary tools are available. [source] Inference of parasite local adaptation using two different fitness componentsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2007D. REFARDT Abstract Estimating parasite fitness is central to studies aiming to understand parasite evolution. Theoretical models generally use the basic reproductive rate R0 to express fitness, yet it is very difficult to quantify R0 empirically and experimental studies often use fitness components such as infection intensity or infectivity as substitutes. These surrogate measures may be biased in several ways. We assessed local adaptation of the microsporidium Ordospora colligata to its host, the crustacean Daphnia magna using two different parasite fitness components: infection persistence over several host generations in experimental populations and infection intensity in individual hosts. We argue that infection persistence is a close estimator of R0, whereas infection intensity measures only a component of it. Both measures show a pattern that is consistent with parasite local adaptation and they correlate positively. However, several inconsistencies between them suggest that infection intensity may at times provide an inadequate estimate of parasite fitness. [source] The Use of HOS Test to Evaluate Membrane Functionality of Boar Sperm Capacitated in vitroREPRODUCTION IN DOMESTIC ANIMALS, Issue 6 2002D Lechniak Contents The functional and structural integrity of sperm membrane are crucial for the viability of spermatozoa. The commonly used staining test (eosin + nigrosin) for assessing sperm membrane measures only its structural integrity. The hypoosmotic swelling test (HOS) originally developed for human sperm (Jeyendran et al. 1984) has been also applied to several species of domestic animals (bull, pig, horse, dog). The test enables to evaluate the functional status of the sperm membrane. The principle of HOS is based on water transport across the sperm tail membrane under hypoosmotic conditions. It has previously been used to assess the semen quality (Revell and Mrode 1994), to analyse fertilizing capacity (Rota et al. 2000; Perez-Llano et al. 2001) and also to detect viable, immotile cells for ICSI (Intra-cytoplasmic sperm injection) in human (Zeyneloglu et al. 2000). There are two procedures commonly used for sperm capacitation in the pig-sperm washing and incubation before insemination (Nagai 1994). Capacitation involves several changes like removing molecules coating the sperm head membrane, changes in membrane fluidity and intracellular ion concentration (Green and Watson 2001). Thus the membrane integrity as well as functionality may be affected as shown by Harrison (1996). The aim of the present study was to analyse changes in sperm membrane integrity after in vitro capacitation by use of the HOS test. [source] High-pressure neutron diffraction study of l -serine-I and l -serine-II, and the structure of l -serine-III at 8.1,GPaACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2006Stephen A. Moggach The hydrostatic compression of l -serine- d7 has been studied to 8.1,GPa by neutron powder diffraction. Over the course of this pressure range the compound undergoes two phase transitions, the first between 4.6 and 5.2,GPa, yielding l -serine-II, and the second between 7.3 and 8.1,GPa, yielding l -serine-III. All three polymorphs are orthorhombic, P212121, and feature chains of serine molecules connected via head-to-tail ND,O hydrogen bonds formed between ammonium and carboxylate groups. The chains are linked into a ribbon by a second set of ND,O hydrogen bonds. The hydroxyl moieties are distributed along the outer edges of the ribbon and in phase I they connect the ribbons into a layer by chains of OD,OD hydrogen bonds. The layers are connected together by a third set of ND,O hydrogen bonds, forming rings with substantial voids at their centres. In the transition from phase I to II these voids begin to close up, but at the cost of breaking the OD,OD chains. The OD,OD hydrogen bonds are replaced by shorter OD,O hydrogen bonds to carboxylate groups. At 7.3,GPa the O,O distance in the OD,O hydrogen bonds measures only 2.516,(17),Å, which is short, and we propose that the phase transition to phase III that occurs between 7.3 and 8.1,GPa relieves the strain that has built up in this region of the structure. The hydroxyl D atom now bifurcates between the OD,O contact that had been present in phase II and a new OD,O contact formed to a carboxylate in another layer. Hirshfeld surface fingerprint plots show that D,D interactions become more numerous, while hydrogen bonds actually begin to lengthen in the transition from phase II to III. [source] | ||||||||||