Showing papers in "Biological Reviews in 1996"

Locomotor activity and non-photic influences on circadian clocks

Abstract: Some of the main themes in this review are as follows. 1. The notion that non-photic zeitgebers are weak needs re-examining. Phase-shifts to some non-photic manipulations can be as large as those to light pulses. 2. As well as being able to phase-shift and entrain free-running rhythms, non-photic events have a number of other effects: these include after-effects of entrainment, period changes, and promotion of splitting. 3. The critical variable for non-photic shifting is unknown. Locomotor activity is more likely to be an index of some other necessary state rather than being causal itself. This index may be better when tendencies to move are channelled into easily measured behaviours like wheel-running. 4. Given ignorance about the critical variable, quantification of activity may be the best presently available measure of zeitgeber intensity. Therefore, the behaviour during non-photic manipulations must be examined as carefully as the shifts themselves. When no phase-shifting follows manipulations such as IGL lesions or serotonin depletion, if the animals are inactive, then little can be inferred. 5. Lack of information on the critical variable(s) for non-photic shifting makes it problematic to compare data from studies using different non-photic manipulations. However, the presence of locomotor activity (or its correlate) does appear to be necessary for triazolam to produce shifts. 6. Novelty-induced wheel-running in hamsters depends on the NPY projection from the IGL to SCN. It remains to be determined how important NPY is in other species or in clock-resetting by other manipulations, but methods are now available to study this. 7. Interactions between photic and non-photic zeitgebers remain virtually unexplored, but it is evident that photic and non-photic stimuli can attenuate the phase-shifting effects of each other. Interactions are not purely additive or predictable from PRCs. 8. The circadian system does more than synchronize free-running rhythms to the solar day. Its non-photic functions and their interactions with photic inputs probably account for some of the anatomical complexity of circadian circuitry.

Sexually transmitted diseases in animals: ecological and evolutionary implications.

Abstract: Sexually transmitted diseases (STDs) have been generally thought of as a small subset of infectious diseases, rather than as an important group of diseases that occur in numerous species. In this paper, we have (1) briefly reviewed theoretical studies on the dynamics of STDs; (2) documented the distribution of STDs in the animal kingdom; and (3) investigated whether STDs have characteristics which distinguish them from other infectious diseases. The dynamics of STDs should differ from those of ordinary infectious diseases because their transmission depends on the frequency rather than density of infectives. With this type of transmission, there is no threshold density for disease spread, and the conditions for host-pathogen coexistence are more restrictive. Nevertheless, a wide variety of disease characteristics may allow a sexually transmitted pathogen to coexist with its host. We found over 200 diseases for which there was evidence of sexual transmission. They occurred in groups as diverse as mammals, reptiles, arachnids, insects, molluscs and nematodes. Sexually transmitted pathogens included protozoans, fungi, nematodes, helminths, and cancerous cell lines, as well as bacteria and viruses. Detailed comparison of the characteristics of sexually transmitted mammalian diseases with those that are transmitted by non-sexual means, showed that STDs cause less mortality, are longer-lived in their hosts, are less likely to invoke strong immune responses, have narrower host-ranges, and show less fluctuation in prevalence over time. These shared features are related to mode of transmission rather than either host or pathogen taxonomic affiliation. This suggests an evolutionary explanation based on shared ecologies rather than one based on phylogenetic history.

The evolution of host-feeding behaviour in insect parasitoids

Abstract: CONTENTS

The evolution of soldiers in aphids.

Abstract: 1. Defensive individuals, termed soldiers, have recently been discovered in aphids, Soldiers are typically early instar larvae, and in many species the soldiers are reproductively sterile and morphologically and behaviourally specialized. 2. Since aphids reproduce parthenogenetically, we might expect soldier production to be more widespread in aphids than it is. We suggest that a more useful way to think about these problems is to attempt to understand how a clone (rather than an individual) should invest in defence and reproduction. 3. Known soldiers are currently restricted to two families of aphids, the Pemphigidae and Hormaphididae, although they are distributed widely among genera within these families. We discuss the use of a phylogenetic perspective to aid comparative studies of soldier production and we demonstrate this approach using current estimates of phylogenetic affinities among aphids. We show that the distribution of soldier production requires a minimum of six to nine evolutionary origins plus at least one loss. 4. At least four main types of soldiers exist and we present and discuss this diversity of soldiers. 5. Most soldier-producing species produce soldiers within plant galls and we discuss the importance of galls for the evolution of soldiers. 6. We summarize the evidence on the interactions between soldiers and predators and between soldier-producing aphids and ants. 7. We present an optimality model for soldier investment strategies to help guide investigations of the ecological factors selecting for soldiers. 8. The proximate mechanisms of soldier production are currently very poorly understood and we suggest several avenues for further research.

Trophism and the ecology of fungi associated with plants

Abstract: (a ) Predominantly biotrophic hemibioc-rophs . (b ) Predominantly necrotrophic hemibiotrophs . ( I ) Klebs’ Laws . . . . . . . ( 2 ) Parasite host and environment . . . . (a ) Host reproductive physiology . . . (b) Necrogenesis, ripening and senescence . VIII . Known pathosystems . . . . . . ( I ) Advantages of parasitism . . . . . (2) Pathosystems avoiding necrogenesis . . ( 3 ) Hemibiotrophic pathosystems . . . . (a ) Biotrophic phase predominant . . . VII . Regulation of behaviour in plant parasitic fungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474 476 477 477 478 478

Sexual selection in moths: the role of chemical communication

Abstract: CONTENTS . . . . . . . . . . . . . . . I . Introduction 113 ( I ) Mating signals. 114 (2) Female signalling 1x5 (3) Male signalling 115 11. Mate choice 115 111. Moth mating systems . . . . . . . . . . . . . 1x6 117 (2) Why do females mate more than once? . . . . . . . . . 1x8 IV. Female selection . . . . . . . . . . . . . . I 20 (I) Female intrasexual selection . . . . . . . . . . . 120 (2) Female choice . . . . . . . . . . . . . . 121 (3) Courtship . . . . . . . . . . . . . . 122 (4) Leks 123 V. Male selection 123 (I) Male intrasexual selection 124 (2) Male choice 125 VI. Interspecific signal competition . . . . . . . . . . . I 26

Palaeoecology and hominoid palaeoenvironments

Abstract: (c) Dryopithecinae 263 ( d ) Ponginae 263 . . . . . . . . . . . . (b) Kenyapithecinae 263 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ( e ) Homininae 264 111. Palaeoenvironmental reconstructions 264 (I) Taxonomic analysis 264 . . . . . . . . . . . . . . . . . . . . . . (2) Functional analyses . . . . . . . . . . . . 266 (a ) Theory and assumptions . . . . . . . . . . . 266 (b) Examples . . . . . . . . . . . . . . 266 (3) Species diversity . . . . . . . . . . . . . 269 (a ) Species richness 269 (6) Species abundance 27 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (c) Dominance and evenness 27' (d) Abundance distribution models 273 ( e ) Age distribution models 276 (4) Community structure 276 (a ) Size analysis . . . . . . . . . . . . . 277 (b) Ecological diversity 278 (i) Univariate comparisons 279 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The monitoring of ecological quality and the classification of standing waters in temperate regions: a review and proposal based on a worked scheme for british waters

Abstract: This paper reviews the ways that quality can be assessed in standing waters, a subject that has hitherto attracted little attention but which is now a legal requirement in Europe. It describes a scheme for the assessment and monitoring of water and ecological quality in standing waters greater than about I ha in area in England & Wales although it is generally relevant to North-west Europe. Thirteen hydrological, chemical and biological variables are used to characterise the standing water body in any current sampling. These are lake volume, maximum depth, onductivity, Secchi disc transparency, pH, total alkalinity, calcium ion concentration, total N concentration,winter total oxidised inorganic nitrogen (effectively nitrate) concentration, total P concentration, potential maximum chlorophyll a concentration, a score based on the nature of the submerged and emergent plant community, and the presence or absence of a fish community. Inter alia these variables are key indicators of the state of eutrophication, acidification, salinisation and infilling of a water body.

Herbivory and the mechanics of fracture in plants

Abstract: CON’TENTS I . Introduction . . . . . . 11. Fracture mechanics and herbivory. . 111. Herbivores as soft machines . . . IV. Plant mechanics and morphology of teeth V. Validity of tests . . . . . VI. Strength . . . . . . VII. Intake and digestibility . . . . . IX. Conclusions . . . . . . X. References . . . . . . VIII. Plant structure and plant mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401 . 402 . 405 . 406 . 407 . 408 . 409 . 410 . 411 . 411

Ovarian surface epithelium, ovulation and carcinogenesis.

Abstract: It appears that ovarian surface epithelial cells activated by contact with gonadotropin-stimulated preovulatory follicles can release bioactive substances that weaken the tunica albuginea and apical follicular wall (e.g. collagenolytic enzymes) and induce cell death (e.g. apoptotic agents). However, a definitive obligatory role of the ovarian surface epithelium in ovulation remains equivocal. Epithelium exfoliated from the dome of ovulatory follicles is replenished by generative stem cell replication and migration from the wound edges. Mutagenesis has been related to successive bouts of ovulation and mitosis. Common epithelial ovarian cancer is a deadly insidious disease, mainly because it is asymptomatic until the malignancy has reached beyond the ovaries. The most important susceptibility factors are nulliparity and association to an affected first-degree relative. It will be critical to resolve whether parity and oral contraceptive use confer significant protection to women with a family history of ovarian carcinoma. Clearly, innovative approaches to non-invasive screening and treatment are needed. Early detection is the key to saving lives (90% cure by salpingo-ovariectomy alone if diagnosis is at Stage I). Active immunization with defined tumor epitopes or (passive) intraperitoneal administration of effector-functional humanized antibodies may be of special value in the regional management of common epithelial ovarian cancer.

A review of simultaneous visual discrimination as a method of training octopuses.

Abstract: I have presented a review and critique of the procedures employed in simultaneous discrimination training experiments using octopuses as subjects. Procedural variables were analyzed statistically for their influence on experimental outcome. The variables most significantly associated with successful discriminations included use of a specific start location for subjects, shock as negative reinforcement, fewer trials per session, more sessions per day, and discriminations based on stimulus brightness. No experiment controlled all potential sources of inadvertent cues, and subjects' performances appeared to be sensitive to exact procedural details. The most common practice diminishing evidence for learning involved reward that coincided with the subject's pre-existing preferences. I found no evidence that sub-optimal experimental designs biased experimental outcomes in any significant and systematic way. Although there is sufficient reason for rejecting results of published simultaneous discrimination training experiments, careful conclusive experiments remain to be performed.

Structure and function of the salachian egg case

Abstract: CONTENTS

The neuronal role of angiotensin II in thirst, sodium appetite, cognition and memory.

Abstract: Within the past two decades, a great deal has been learnt about the renin-angiotensin system in the brain. The renin-angiotensin system is one of the best-studied enzyme-neuropeptide systems in the brain. The diversity of localization of this peptide throughout the brain has implied a variety of potential functions. Besides its classical role in the regulation of blood pressure and body-fluid homeostasis, it has more subtle functions involving complex mechanisms such as learning and memory. The profound effects on behaviour produced by angiotensin are of broad interest to neuroscientists. The mechanisms of action differ depending on whether angiotensin is locally synthesized and whether regulation is governed by neural or metabolic inputs impinging on the neurones. Its central action is mediated through peptidergic receptors present on neurones. The description of the receptor subtypes AT1 and AT2 for angiotensin II and the development of non-peptidic specific angiotensin receptor subtype antagonists have opened a new area in this field of research. The AT1 site, which preferentially binds to angiotensin II and angiotensin III, appears to mediate the classical angiotensin functions concerned with maintenance of blood pressure and body-fluid control. In addition, most of the behavioural effects described so far are linked with AT1, although so-called psychotropic effects are presumed to be mediated by receptor systems other than the known specific angiotensin receptors. In fact, evidence for the existence of such receptors with high-affinity binding has been reported. The central action of angiotensin II mediated by AT2 is as yet unclear. Most reports concerning this receptor subtype suggest a role in differentiation and development, since the number of binding sites is higher in fetal and young rats than in adults. Furthermore, the neuronal effect of angiotensin II in the inferior olivary nucleus which is blocked specifically by AT2 antagonists suggests an involvement in motor control. Over the next few years we should find answers to many of the questions currently unanswered about angiotensin function and, given the rapid progress in research on this neuropeptide, it may serve as a model for the action of peptides on neuronal function in general.

Ribosomal 5s rna: tertiary structure and interactions with proteins

Abstract: . . . . . . . . . (6) Interaction with other ribosomal RNAs . . . . . . (7) Other activities . . . . . . . . . . 111. The structure of 5s rRNA in solution . . . . . . . ( I ) Y-shaped model . . . . . . . . . . (2) Model for E. coli 5s rRNA ( 3 ) Model for yeast 5s rRNA (lollipop) . . . . . . . . . . . . . . IV. The elongated shape model of plant 5s rRNA V. Interaction of 5s rRNA with proteins . . . . . . . . . . . . ( I ) Ribosomal proteins . . . . . . . . . . (2) TF IIIA . . . . . . . . . . . . VI. Crystallization . . . . . . . . . . . VII. Summary and perspectives . . . . . . . . . VIII . Acknowledgements . . . . . . . . . . IX. References . . . . . . . . . . . . . . . I . . . I

Protein targeting and translocation; a comparative survey

Abstract: The last few years has seen enormous progress in understanding of protein targeting and translocation across biological membranes. Many of the key molecules involved have been identified, isolated, and the corresponding genes cloned, opening up the way for detailed analysis of the structure and function of these molecular machines. It has become clear that the protein translocation machinery of the endoplasmic reticulum is very closely related to that of bacteria, and probably represents an ancient solution to the problem of how to get a protein across a membrane. One of the thylakoid translocation systems looks as if it will also be very similar, and probably represents a pathway inherited from the ancestral endosymbiont. It is interesting that, so far, there is a perfect correlation between thylakoid proteins which are present in photosynthetic prokaryotes and those which use the sec pathway in chloroplasts; conversely, OE16 and 23 which use the delta pH pathway are not found in cyanobacteria. To date, no Sec-related proteins have been found in mitochondria, although these organelles also arose as a result of endosymbiotic events. However, virtually nothing is known about the insertion of mitochondrially encoded proteins into the inner membrane. Is the inner membrane machinery which translocates cytoplasmically synthesized proteins capable of operating in reverse to export proteins from the matrix, or is there a separate system? Alternatively, do membrane proteins encoded by mitochondrial DNA insert independently of accessory proteins? Unlike nuclear-encoded proteins, proteins encoded by mtDNA are not faced with a choice of membrane and, in principle, could simply partition into the inner membrane. The ancestors of mitochondria almost certainly had a Sec system; has this been lost along with many of the proteins once encoded in the endosymbiont genome, or is there still such a system waiting to be discovered? The answer to this question may also shed light on the controversy concerning the sorting of the inter-membrane space proteins cytochrome c1 and cytochrome b2, as the conservative-sorting hypothesis would predict re-export of matrix intermediates via an ancestral (possibly Sec-type) pathway. Whereas the ER and bacterial systems clearly share homologous proteins, the protein import machineries of mitochondria and chloroplasts appear to be analogous rather than homologous. In both cases, import occurs through contact sites and there are separate translocation complexes in each membrane, however, with the exception of some of the chaperone molecules, the individual protein components do not appear to be related. Their similarities may be a case of convergent rather than divergent evolution, and may reflect what appear to be common requirements for translocation, namely unfolding, a receptor, a pore complex and refolding. There are also important differences. Translocation across the mitochondrial inner membrane is absolutely dependent upon delta psi, but no GTP requirement has been identified. In chloroplasts the reverse is the case. The roles of delta psi and GTP, respectively, remain uncertain, but it is tempting to speculate that they may play a role in regulating the import process, perhaps by controlling the assembly of a functional translocation complex. In the case of peroxisomes, much still remains to be learned. Many genes involved in peroxisome biogenesis have been identified but, in most cases, the biochemical function remains to be elucidated. In this respect, understanding of peroxisome biogenesis is at a similar stage to that of the ER 10 years ago. The coming together of genetic and biochemical approaches, as with the other organelles, should provide many of the answers.