bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the origin of feathers
Authors: Brush A. H. 
Published: December 2004

AbstractThe appearance of feathers defines the appearance of birds. A number of changes defined, preceded or accompanied the event. The changes were hierarchical in nature and included revolutions in genomic organization (i.e., HOX and the feather keratin genes), protein sequence and shape, the large scale organization of proteins into filaments, and in the geometry of the cells and their roles in the follicle. Changes at each of these levels differ or produced different products than found in its analog in reptiles. They are essentially unique to birds and produced an evolutionary novelty. I used analysis of extant structure and information on development to reconstruct key events in the evolution of feathers. The ancestral reptilian epidermal structure, while probably a scale or tubercles, is still unidentified. The structural genes of feather proteins (φ‐keratin) are tandem repeats probably assembled from pre‐existing exons. They are unlike the alpha‐keratin of vertebrate soft epidermis. Amino‐acid composition, shape, and behavior of feather keratins are unique among vertebrates. The 3‐dimensional organization of the follicle and the developmental processes are also unique.Although we lack a complete understanding of the appearance and early role of feathers, they are clearly the results of novel events.
Pharyngeal biting mechanics in centrarchild and cichlid fishes: insights into a key evolutionary innovation
Authors: Galis F. , Drucker E. G. 
Published: December 2004

AbstractThis study compares the pharyngeal biting mechanism of the Cichlidae, a family of perciform fishes that is characterized by many anatomical specializations, with that of the Centrarchidae, a family that possesses the generalized perciform anatomy. Our objective was to trace the key structural and functional changes in the pharyngeal jaw apparatus that have arisen in the evolution from the generalized to derived (cichlid) perciform condition.We propose a mechanical model of pharyngeal biting in the Centrarchidae and compare this with an already existing model for pharyngeal biting in the family Cichlidae. Central to our centrarchid model is a structural coupling between the upper and lower pharyngeal jaws. This coupling severely limits independent movement of the pharyngeal jaws, in contrast to the situation in the speciose Cichlidae, in which the upper and lower pharyngeal jaw movements are to a large extent independent. We tested both models by electrically stimulating nine muscles of the branchial and hyoid apparatuses in three centrarchild and three cichlid species. The results confirmed the coupled movement of the upper and lower pharyngeal jaws in the Centrarchidae and the independence of these movements in the Cichlidae.We suggest that the key structural innovation in the development of the functionally versatile cichlid (labroid) pharyngeal jaw apparatus was the decoupling of epibranchials 4 from the upper pharyngeal jaws. This structural decoupling implies the decoupling of the movements of the upper and lower pharyngeal jaws and leads to a cichlid (labroid) type of pharyngeal bite. The initial decoupling facilitated a cascade of changes, each leading to improved biting effectiveness and/or to increased mobility and mechanical flexibility of the pharyngeal jaws. The shift of insertion of the m. levator externus 4 which has been considered the primary innovation in the transformation probably arose secondarily.The transformation of the pharyngeal biting mechanism in the perciforms is an excellent example of decoupling of structures associated with diversification of form and function and with increased speciation rates.
Within population genetic differentiation in traits affecting clonal growth: Festuca rubra in a mountain grassland
Authors: Skálová H. , Pecháčková S. , Suzuki J. , Herben T. , Hara T. , Hadincová V. , Krahulec F. 
Published: December 2004

Abstract Festuca rubra , a clonal grass of mountain grasslands, possesses a considerable variability in traits related to spatial spreading (rhizome production, length and branching; tussock architecture). Since these traits highly influence the success of the species in a spatially heterogeneous system of grasslands, a combined field and growth chamber approach was adopted to determine the within‐population variation in these parameters. Clones were sampled in a mountain grassland (The Krkonoše Mts., Czech Republic); the environment (mean neighbour density) of individual clones varied highly. Before the clones were collected, shoot demography and tussock architecture within these clones were recorded in the field for four seasons. Their clone identity was determined using DNA RAPD. Vegetatively propagated plants from these clones were cultivated in a common garden experiment to demonstrate variation in tussock growth and architecture. Their response to change in red/far red light ratio was determined in the growth chamber.Highly significant variation among clones was found in almost all parameters. In the common garden, the clones differed in tussock growth (mean tillering rate), architecture (mean shoot angle, mean tussock density) and proportion of flowering shoots. In the growth chamber, both the aboveground parameters and parameters of the rhizome system were strongly affected by red/far red ratio; among‐clone variation was also almost always significant. The genotype × environment interaction was significant for tillering rate and rhizome architecture. The structure of the rhizome system (which is the major component of clonal spread in space) is a complex result of several components whose inter‐clone variations differ: (i) genetically determined mean rhizome system size, (ii) overall plasticity in rhizome system size (with no significant genetic variation in plasticity), and (iii) genetically determined plasticity in rhizome architecture. Because of the variation in plasticity in rhizome architecture, some c lones seemed to possess the ability to exploit a favourable habitat patch by producing short branches when there; whereas the remaining clones appeared to possess only a simple escape mechanism from unfavourable patches.Environmental variation in the light levels in the studied grassland is fine grained; horizontal growth rates of F. rubra are sufficient to make genets experience different patches in their lifetime. The high variation in both genotype means and plasticities is likely to be due to selection early in genet life in an environment which is heterogeneous at a fine scale.
Herbivores and the evolution of the semelparous perennial life‐history of plants
Authors: Klinkhamer P. G. L. , Kubo T. , Iwasa Y. 
Published: December 2004

AbstractThe relationship between a plant and its potential enemies changes drastically after reproduction has started. Using a dynamic modelling approach we study the effects of herbivores and pathogens, that are attracted by reproducing plants, on optimal allocation of resources, and life‐history strategies. We assume that the level of attack increases with the investment in reproduction, which may lead to a reduction of current years reproductive success, a reduction of storage efficiency or an increase of plant mortality. If herbivores or pathogens attracted by flowering plants mainly reduce current years reproductive success, the optimal life‐history is annual or iteroparous perennial if the attack is an all or nothing event. If the level of consumption increases with the number of herbivores attracted, the optimal life‐history is most likely iteroparity with or without mast years. Only under very restricted conditions this may lead to semelparity. If herbivores mainly reduce the efficiency of the resources stored for next year, the optimal life‐history is iteroparity. If herbivores mainly reduce survival, the optimal solution is likely to be mast years or semelparity. For parameter values that are realistic for Cynoglossum officinale, a semelparous perennial from calcereous soils, the model predicts that reproduction should start in the third year and that 99% of the available resources at the end of season should be invested in reproduction and only 1% saved for growth next year. With such an investment only c. 1% of the plants would survive after reproduction, so the optimal life‐history is close to semelparity. For the small fraction of plants that reproduce more than once, years of vegetative growth only and years with reproduction should alternate. Multiple reproduction is rare in C. officinale. However, such a life history is very common for plants known as semelparous perennial. Although the available empirical evidence is, as yet, circumstantial rather than conclus ive we propose that reproduction related mortality mediated through herbivores or pathogens may play a role in the evolution of the semelparous perennial life‐history.
Consequences of Wolbachia transmission process on the infection dynamics
Authors: Guillemaud T. , Rousset F. 
Published: December 2004

AbstractIn some species displaying Wolbachia‐induced cytoplasmic incompatibility, the intensity of incompatibility depends on the density of symbionts in both parents. Although modalities of the transmission process are poorly known, it appears that the density of Wolbachia within the offspring of a female is variable and is correlated with that of the mother. Assuming that the infection level of an host is a continuous trait, we examine some theoretical consequences of the Wolbachia transmission process on the evolution of the infection level within a population. The hypotheses of this model concern two main points: the transmission of Wolbachia is affected by stochastic processes and a deterministic bias, and the bacterial load of the parents of a cross affects their compatibility relationships. It is shown that the variance of the number of bacteria transmitted induced by the stochastic processes tends to counteract the effect of bacterial curing on the dynamics of infection. A general consequence of the model is that the extinction of Wolbachia is possible even if there is strong incompatibility and no selective disadvantage for the host to bear the bacteria. The model indicates that the evolution of bacterial mutants does not depend on the level of incompatibility they induce, but that mutants with higher transmission variance can be selected for. Moreover, the mean infection level of the host population increases in the presence of such bacteria.
Lerista bougainvillii, a case study for the evolution of viviparity in reptiles
Authors: Qualls C. P. , Shine R. 
Published: December 2004

AbstractMany factors, both environmental and biotic, have been suggested to facilitate or hinder the evolution of viviparity (live‐bearing) in reptiles. Viviparity has evolved recently within the Australian scincid lizard Lerista bougainvillii and the species includes oviparous, viviparous, and reproductively intermediate (with prolonged egg retention) populations; thus, it offers an exceptional opportunity to evaluate the validity of these hypotheses. We carried out such tests by (i) comparing environmental conditions over the geographic ranges occupied by oviparous, viviparous, and intermediate populations (to identify possible selective forces for the evolution of viviparity), and (ii) comparing morphological, reproductive and ecological traits of L. bougainvillii with those of other sympatric scincid species (to identify traits that may have predisposed this taxon to the evolution of viviparity). The areas occupied by viviparous L. bougainvillii are significantly colder than those occupied by both their intermediate and oviparous conspecifics, in accord with the “cold‐climate” hypothesis for reptilian viviparity. Rainfall is similar over the ranges of the three forms. Climatic unpredictability (as assessed by the magnitude of year‐to‐year thermal variation) is lower for viviparous animals, in contradiction to published speculations. Comparison with 31 sympatric scincid species showed that L. bougainvillii is not atypical for most of the traits we measured (e.g., body size, clutch size, thermal preferenda and tolerances). However, oviparous L. bougainvillii do display several traits that have been suggested to facilitate the evolution of viviparity. For example, pregnancy does not reduce locomotor ability of females; the lizards are semi‐fossorial; even the oviparous females produce only a single clutch of eggs per year; and they ovulate relatively late in summer, so that the time available for incubation is limited.
Precise control of sex allocation in pseudo‐arrhenotokous phytoseiid mites
Authors: Nagelkerke C. J. , Sabelis M. W. 
Published: December 2004

AbstractCan sex allocation be controlled by haplo‐diploid organisms where both males and females arise from fertilised eggs but males become effectively haploid by paternal genome loss (pseudo‐arrhenotoky)? If so, how does the control of mean and variance of sex allocation compare with haplo‐diploids where males arise from unfertilised eggs (arrhenotoky)? These questions are addressed by experiments with two species of pseudo‐arrhenotokous plant‐inhabiting predatory mites: Typhlodromus occidentalis Nesbitt and Phytoseiulus persimilis Athias‐Henriot (Acari: Phytoseiidae).It is shown that females conditionally adjust offspring sex ratio in response to the presence of conspecifics or their cues. The sex ratios are precise in that their variance is less than expected from a binomial distribution. Because eggs are produced one‐by‐one at regular intervals, it is not possible to designate separate clutches, thus rendering conventional clutch‐based estimates of precision inadequate. To remedy this a range of time scales was investigated and this showed an increase in precision with time scale (and hence “clutch” size). Markovian analysis of son‐daughter sequences showed that this increase arises only if the predator “memorizes” the mean sex ratio of all eggs laid before.Control of mean and variance of sex allocation is selectively advantageous when local mating groups vary in size and are usually small, as is the case for the phytoseiid mites under study. Predictions of the optimal sex ratio from local mate competition models were in agreement for T. occidentalis. However, P. persimilis, exhibited a stronger female bias than predicted. We suggest that this may be due to selection levels operating at a larger spatial scale than the local mating group.Control of sex allocation seems as good as in arrhenotokous arthropods, suggesting that — in this respect — pseudo‐arrhenotoky is not at a disadvantage compared to arrhenotoky.
Mate recognition in a freshwater fish: geographical distance, genetic differentiation, and variation in female preference for local over foreign males
Authors: Wong B. B. M. , Keogh J. S. , Jennions M. D. 
Published: December 2004

Abstract
It often is assumed that more distant allopatry should reflect reduced rates of contemporary gene flow and/or greater divergence in mate recognition systems. This assumption, however, is rarely tested and may not always be appropriate. Here we investigated female preference for local and foreign males in a morphologically variable Australian freshwater fish, the Pacific blue-eye Pseudomugil signifer. Using a multidisciplinary approach that combined molecular phylogeography with conventional mate choice experiments, we found female blue-eyes spent more time in association with local males only when the alternative was a foreigner from a geographically and genetically more distant population. When offered the choice between two foreign males, females associated more with males from the population that was more closely adjacent to their own. Our results suggest that female preference for local over foreign males in blue-eyes may depend on how genetically and geographically separated populations are from one another.
Transport of l‐arginine and nitric oxide formation in human platelets
Authors: Signorello Maria G. , Pascale Raffaele , Leoncini Giuliana 
Published: December 2004

The results of the present study show that human platelets take up l‐arginine by two transport systems which are compatible with the systems y+ and y+L. These Na+independent transporters have been distinguished by treating platelets with N‐ethylmaleimide that blocks selectively system y+. System y+, that accounts for 30–40% of the total transport, is characterized by low affinity for l‐arginine, is unaffected by l‐leucine, is sensitive to changes of membrane potential and to trans‐stimulation. The other component of l‐arginine transport identified with the system y+L (approximately 60–70% of the total flux) shows high affinity for l‐arginine, is insensitive to N‐ethylmaleimide treatment, unaffected by changes in membrane potential, sensitive to trans‐stimulation and inhibited by l‐leucine in the presence of Na+.Moreover a strict correlation between l‐arginine transport and nitric oxide (NO) production in whole cells was found. N‐ethylmaleimide and l‐leucine decreased NO production as well as cGMP elevation, and the effect on NO and cGMP were closely related. It is likely that the l‐arginine transport systems y+ and y+L are both involved in supplying substrate for NO production and regulation in human platelets.
Pair Bonding and Multiple Paternity in the Polygamous Common QuailCoturnix coturnix
Authors: Rodríguez‐Teijeiro J. D. , Puigcerver M. , Gallego S. , Cordero P. J. , Parkin D. T. 
Published: December 2004

AbstractThe common quail (Coturnix coturnix) is one of the few species in which mate‐switching (when different pair bonds are established within a single breeding attempt), has been recorded. In this study, we report the characteristics of pair bonds (description, number of males per female and duration) by monitoring a wild population of common quail (28 females and 49 males) by radiotracking. 57% of the females studied (n = 14) showed mate‐switching, whereas 22% of the males were serially polygynous, successively forming pairs with a series of females. The fitness of females with mate‐switching, measured in terms of clutch size and hatching success, did not differ from that of females bonded with one male. The analysis of paternity in three families by multilocus DNA fingerprinting revealed genetic polygamy in two of the nests studied. A male sired offspring with two females, and we obtained genetic evidence for intraspecific brood parasitism. We discuss how these behavioural and ecological observations may relate to the particular mating system of the common quail.
Direct vs. Indirect Benefits of Caching by Gray Squirrels (Sciurus carolinensis)
Authors: Spritzer Mark D. , Brazeau Daniel 
Published: December 2004

AbstractIndividuals of many species cache food to gain direct benefits from consuming their own caches, but individuals of a few species also gain indirect benefits by sharing caches with kin. We investigated whether gray squirrels cache primarily to gain direct benefits or if they also gain indirect benefits by sharing caches with kin. If squirrels share caches with kin, then genetically related squirrels should live near one another and cache near one another to facilitate cache sharing. In contrast, if squirrels cache primarily for direct benefits, then they should clump their caches near the center of their ranges to facilitate cache defense. This study was conducted with 140 squirrels in a 10 ha forest. DNA was extracted from blood samples taken from squirrels, and genetic similarity scores from randomly amplified polymorphic DNA (RAPD) loci were used to measure relatedness. Squirrels were given piles of pecans for caching at six sites and observed from a blind. We recorded the direction squirrels took nuts from piles and at one site determined the location of caches. For male–female comparisons, related squirrels lived significantly closer to one another than unrelated squirrels, but this was not the case for female–female and male–male comparisons. The genetic similarity of neighboring squirrels did not influence the location of caches or the direction that squirrels took nuts from piles. Squirrels clumped their own caches and moved nuts toward their own home range centers. These results suggest that gray squirrels cache primarily to gain direct benefits rather than indirect benefits.
A centric fission and heterochromatin polymorphism inEquus asinusSpanish breeds
Authors: Alaoui N. , Jordana J. , Ponsá M. 
Published: December 2004

SummaryIn this work a chromosomal study inEquus asinusis presented. Forty‐two specimens, belonging to five different Spanish breeds in risk of disappearing, have been analysed. Metaphases have been sequentially stained (uniform, G‐banded and C‐banded) and analysed. All specimens, except one, presented 2n = 62 chromosomes. Variation in chromosome number (2n = 63) is because of a fission in one chromosome of pair no. 3, resulting in two acrocentric chromosomes. Polymorphisms affecting the size of heterochromatic C+ bands and the presence of hetrochromatic 1p and 4p arms are also analysed. The results show no polymorphisms which can be attributed to a particular breed. From the chromosomal point of view, all Spanish asinine specimens correspond to a single population. Rearrangements detected suggest a fission tendency in the homologousE. asinusno. 3 chromosome in Equidae species.
Ketamine: Its use in the emergency department
Authors: Cromhout Andries 
Published: December 2004

AbstractKetamine has been known to the medical world for over 30 years, yet is not widely used to its full potential. It is often considered to be a ‘third world’ drug only. In light of a recent increase in interest in its use in the developed world, this review is for emergency physicians to use as a quick reference.
Red‐back spider envenomation in children in Central Australia
Authors: Trethewy Christopher E , Bolisetty Srinivas , Wheaton Gavin 
Published: December 2004

AbstractObjective:   To describe the clinical spectrum of Red‐back spider (RBS) envenomation in children up to 12 years of age.Methods:   Retrospective case notes review of children with a discharge diagnosis of RBS bite from January 1992 to June 2001. The setting was Alice Springs Hospital, the main paediatric hospital for the whole region of Central Australia. The patients were 54 children, comprising 39 Aboriginal and 15 non‐Aboriginal children.Results:  Forty‐six (85%) children had systemic envenomation. The three most common systemic features are irritability, hypertension and sweating; 35 (65%) children had all three systemic features. Forty‐five (83%) received antivenom therapy. The clinical characteristics and outcomes showed no significant difference between children 4 and > 4 years of age.Conclusions:  There is a high incidence of systemic envenomation due to RBS bite in children in Central Australia. The triad of irritability, hypertension and sweating in a previously well child is highly suggestive of latrodectism.