bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of habitat saturation on the number and turnover of queens in the polygynous ant, Myrmica sulcinodis
Authors: Pedersen J.S. , Boomsma J.J. 
Published: March 2003

Abstract
In polygynous social insects more than one queen reproduces in a colony. In such populations ecological factors affecting survival and reproduction of queens are likely to be of prime importance for social organization. In particular, habitat saturation leading to severe limitations in the availability of nest sites has been suggested to promote high queen number. In this study we examine the social and genetic structure of colonies in the polygynous ant Myrmica sulcinodis. We investigated a single breeding population in two adjacent habitats which differed markedly in the availability of nest sites. In the main habitat M. sulcinodis occupied almost all suitable nest sites, whereas in the other (marginal) habitat most sites were unoccupied by ants, due to a recent fire. In support of the habitat saturation hypothesis, the number of queens per colony which could explain the estimated relatedness among workers was almost five times higher for the main habitat than for the marginal habitat. This is the first demonstration that the kin structure of a social insect population is plastic and responds adaptively to short-term changes in ecological constraints such as nest site availability. Based on combined genetic and demographic data we discuss queen reproductive strategies and suggest that a special class of queen ‘floaters’ only stays ephemerally in the colonies, thus causing a substantial turnover of reproducing queens across years.
Genetic differentiation between individuals
Authors: Rousset  
Published: March 2003

Abstract
I describe a method of analysis of genetic differentiation which is suitable for the comparison of genetic and demographic estimates of the ‘neighborhood size’– more precisely the product of density and second moment of dispersal distance σ2– in continuous populations sampled at the smallest scale. This method is based on results of models of isolation by distance common to a wide variety of dispersal distances. The performance of this method is tested by simulation for some highly leptokurtic dispersal distributions, and it is applied to a previous study of a kangaroo-rat (Dipodomys spectabilis) population. In this case, genetic and demographic estimates are within a factor of two from each other. Thus, in line with some previous examples, this study shows that a better agreement may be attained than is usually recognized between genetic and demographic estimates.
The evolution of courtship display repertoire size in the dabbling ducks (Anatini)
Authors: Johnson  
Published: March 2003

Abstract
Many animals possess multiple ornaments or behaviours that seem to have evolved via sexual selection. A complete understanding of sexual selection requires an explanation for such multiple traits. The dabbling ducks (Tribe: Anatini) exhibit considerable variation among species in the number of displays in the male courtship repertoire. I tested five hypotheses concerning the evolution of the variation in display repertoire size of dabbling ducks: (1) species recognition, (2) courtship habitat, (3) sexual selection intensity, (4) display media tradeoff and (5) time constraints on pair formation. I tested these hypotheses, using an explicit phylogenetic hypothesis developed from DNA sequences for the dabbling ducks, with two types of statistical comparative methods (discrete and continuous character). The variation observed in male courtship display repertoire size in dabbling ducks was consistent with the courtship habitat and sexual selection intensity hypotheses. Specifically, the size of the display repertoire was larger in species that exhibit courtship exclusively on water and larger in species with dimorphic plumage. These results suggest that ecological (habitat) as well as social (sexual selection) factors may be important in driving the evolution of displays in the dabbling ducks.
The fitness of twin mothers: evidence from rural Gambia
Authors: Sear R. , Shanley D. , Mcgregor I. A. , Mace R. 
Published: March 2003

Abstract
We used a longitudinal database from a natural fertility population in rural Gambia to compare the overall fertility of mothers who had given birth to twins at some point in their reproductive history and mothers who had only ever given birth to singletons. We found that twin mothers had shorter birth intervals, higher age-specific fertility and more surviving children than singleton mothers. This suggests that, despite the considerably higher mortality of twins found in this population, twin mothers have a fitness advantage over singleton mothers, even in the absence of modern medical care. We ran a simple simulation model to estimate the relative fitness of twin and singleton mothers, and found that the model also estimated higher fitness for twin mothers. Further, girls who went on to become twin mothers were of higher anthropometric status during their teenage years than those who became singleton mothers.
Low relatedness among cooperatively breeding workers of the greenhead ant Rhytidoponera metallica
Authors: Chapuisat M. , Crozier R. 
Published: March 2003

Abstract
The greenhead ant Rhytidoponera metallica has long been recognized as posing a potential challenge to kin selection theory, because it has large queenless colonies where apparently many of the morphological workers are mated and reproducing. However, this species has never been studied genetically and important elements of its breeding system and kin structure remain uncertain. We used microsatellite markers to measure the relatedness among nestmates, unravel the fine-scale population genetic structure, and infer the breeding system of R. metallica. The genetic relatedness among worker nestmates is very low but significantly greater than zero (r=0.082 ± 0.015), which demonstrates that nests contain many distantly related breeders. The inbreeding coefficient is very close to and not significantly different from zero, indicating random mating and lack of microgeographic genetic differentiation. On average, closely located nests are not more similar genetically than distant nests, which is surprising, as new colonies form by budding and female dispersal is restricted. Lack of inbreeding and absence of population viscosity indicates high gene flow mediated by males. Overall, the genetic pattern detected in R. metallica suggests that a high number of moderately related workers mate with unrelated males from distant nests. This breeding system results in the lowest relatedness among nestmates reported for social insect species where breeders and helpers are not morphologically differentiated.
Seasonal variation in sex ratio and sexual egg dimorphism favouring daughters in first clutches of the spotless starling
Authors: Cordero P. J. , Viñuela J. , Aparicio J. M. , Veiga J. P. 
Published: March 2003

Abstract
We investigated possible pre-hatching mechanisms of sex-differential investment by females that may contribute to offspring sex-ratio adjustment enhancing the fitness return from reproductive effort in the spotless starling (Sturnus unicolor). We found a seasonal shift in sex ratio from daughters to sons as the season advances. Furthermore, the probability of breeding at 1-year old and recruitment into the breeding population in daughters is associated with laying date but not with mass at fledging. The reverse is true for males which rarely bred at 1-year old. We also found that eggs containing female embryos are significantly heavier than those containing males in spite of the slight sexual dimorphism in favour of males. This suggests maternal control of provisioning, favouring daughters that may balance sibling mortality and competition with their brothers. Our results on seasonal variation in sex ratio and differential egg provisioning are consistent with an adaptive tactic in which mothers increase their reproductive return by enhancing the probability that daughters survive and breed in their first year of life.
Ecomorphology of plesiosaur flipper geometry
Authors: O'Keefe F. R. 
Published: March 2003

AbstractThe Plesiosauria is an extinct group of marine reptiles once common in mesozoic seas. Previous work on plesiosaur hunting styles has suggested that short-necked, large-headed animals were pursuit predators, whereas long-necked, small-headed animals were ambush predators. This study presents new data on the aspect ratios (ARs) of plesiosaur flippers, and interprets these data via comparison with AR in birds, bats and aircraft. Performance trade-offs implicit in AR variation are well-understood in the context of aircraft design, and these trade-offs have direct ecomorphological analogues in birds and bats. Knowledge of these trade-offs allows interpretation of variation in plesiosaur AR. By analogy, short-necked taxa were specialized for manoeuvrability and pursuit, whereas long-necked taxa were generally specialized for efficiency and cruising. These interpretations agree with previous assessments of maximum swimming speed.
The evolutionary transition to coloniality promotes higher blood parasitism in birds
Authors: Tella J. L. 
Published: March 2003

Abstract
Parasitism has been argued as one of the major costs of breeding sociality in birds. However, there is no clear evidence for an increased parasite pressure associated with the evolutionary transition from solitary to colonial breeding. I used the pairwise comparative method to test whether colonial bird species incur in a greater risk of infection and if they must to face with a greater diversity of blood parasites (Haematozoa), by comparing pairs of congeners that included one solitary and one colonial breeding species. The richness, both in terms of number of species and number of genera, as well as the prevalence of blood parasites resulted higher in colonial species than in their solitary breeding sisters, while controlling for differences in research effort and other potentially confounding effects. These results point towards higher transmission rates of blood parasites among colonial hosts. Given the detrimental effects of blood parasites on their host fitness, the higher risk of infection and the exposition to a more diverse parasite fauna may have imposed an important cost associated to the evolution of avian coloniality. This may help to explain why colonial species have larger immune system organs, as well as to explore differences in other host life history traits potentially shaped by blood parasites.
The experimental evolution of specialists, generalists, and the maintenance of diversity
Authors: Kassen R. 
Published: March 2003

Abstract
Environmental heterogeneity may be a general explanation for both the quantity of genetic variation in populations and the ecological niche width of individuals. To evaluate this hypothesis, I review the literature on selection experiments in heterogeneous environments. The niche width usually – but not invariably – evolves to match the amount of environmental variation, specialists evolving in homogeneous environments and generalists evolving in heterogeneous environments. The genetics of niche width are more complex than has previously been recognized, particularly with respect to the magnitude of costs of adaptation and the putative constraints on the evolution of generalists. Genetic variation in fitness is more readily maintained in heterogeneous environments than in homogeneous environments and this diversity is often stably maintained through negative frequency-dependent selection. Moreover environmental heterogeneity appears to be a plausible mechanism for at least two well-known patterns of species diversity at the landscape scale. I conclude that environmental heterogeneity is a plausible and possibly very general explanation for diversity across the range of scales from individuals to landscapes.
Seed sex ratio in dioecious plants depends on relative dispersal of pollen and seeds: an example using a chessboard simulation model
Authors: De Jong T. J. , Van Batenburg F. H. D. (EKE) , Van Dijk J. 
Published: March 2003

Abstract
Two principles are important for the optimal sex ratio strategy of plants. (1) Sib mating. Because seed dispersal is restricted, sib mating may occur which selects for a female bias in the seed sex ratio. (2) Local resource competition (LRC). If a plant produces pollen its nuclear genes are dispersed in two steps: first through the pollen and then, if the pollen is successful in fertilizing an ovule on another plant, through the seed. If the plant produces an ovule, its genes are dispersed only through the seed. By making pollen instead of ovules the offspring of a single plant is then spread out over a wider area. This reduces the chance that genetically related individuals are close together and need to compete for the same resource. The effect is the strongest if pollen is dispersed over a much wider area than seeds. Less LRC for paternally vs. maternally derived offspring selects for a male bias in sex allocation.
We study the above-mentioned opposite effects in dioecious plants (with separate male and female individuals), with maternal control over the sex ratio (fraction males) in the seeds. In a two-dimensional spatial model female-biased sex ratios are found when both pollen and seed dispersal are severely restricted. If pollen disperses over a wider area than seeds, which is probably the common situation in plants, the seed sex ratio becomes male-biased. If pollen and seeds are both dispersed over a wide area, the sex ratio approaches 0.5. Our results do not change if the offspring of brother–sister matings are less fit because of inbreeding depression.
Consequences of inbreeding for offspring fitness and gender in Silene vulgaris, a gynodioecious plant
Authors: Emery S. N. , McCauley D. E. 
Published: March 2003

Abstract
In gynodioecious plants, hermaphrodite and female plants co-occur in the same population. In these systems gender typically depends on whether a maternally inherited cytoplasmic male sterility factor (CMS) is counteracted by nuclear restorer alleles. These restorer alleles are often genetically dominant. Although plants of the female morph are obligatorily outcrossing, hermaphrodites may self. This selfing increases homozygosity and may thus have two effects: (1) it may decrease fitness (i.e. result in inbreeding depression) and (ii) it may increase homozygosity of the nuclear restorer alleles and therefore increase the production of females. This, in turn, enhances outcrossing in the following generation. In order to test the latter hypothesis, experimental crosses were conducted using individuals derived from four natural populations of Silene vulgaris, a gynodioecious plant. Treatments included self-fertilization of hermaphrodites, outcrossing of hermaphrodites and females using pollen derived from the same source population as the pollen recipients, and outcrossing hermaphrodites and females using pollen derived from different source populations. Offspring were scored for seed germination, survivorship to flowering and gender. The products of self-fertilization had reduced survivorship at both life stages when compared with the offspring of outcrossed hermaphrodites or females. In one population the fitness of offspring produced by within-population outcrossing of females was significantly less than the fitness of offspring produced by crossing females with hermaphrodites from other populations. Self-fertilization of hermaphrodites produced a smaller proportion of hermaphroditic offspring than did outcrossing hermaphrodites. Outcrossing females within populations produced a smaller proportion of hermaphrodite offspring than did crossing females with hermaphrodites from other populations. These results are consistent with a cytonuclear system of sex determination with dominant nuclear restorers, and are discussed with regard to how the mating system and the genetics of sex determination interact to influence the evolution of inbreeding depression.
Evolution in stressful environments II: adaptive value and costs of plasticity in response to low light in Sinapis arvensis
Authors: Steinger T. , Roy B. A. , Stanton M. L. 
Published: March 2003

Abstract
Plants possess a remarkable capacity to alter their phenotype in response to the highly heterogeneous light conditions they commonly encounter in natural environments. In the present study with the weedy annual plant Sinapis arvensis, we (a) tested for the adaptive value of phenotypic plasticity in morphological and life history traits in response to low light and (b) explored possible fitness costs of plasticity. Replicates of 31 half-sib families were grown individually in the greenhouse under full light and under low light (40% of ambient) imposed by neutral shade cloth. Low light resulted in a large increase in hypocotyl length and specific leaf area (SLA), a reduction in juvenile biomass and a delayed onset of flowering. Phenotypic selection analysis within each light environment revealed that selection favoured large SLA under low light, but not under high light, suggesting that the observed increase in SLA was adaptive. In contrast, plasticity in the other traits measured was maladaptive (i.e. in the opposite direction to that favoured by selection in the low light environment). We detected significant additive genetic variance in plasticity in most phenotypic traits and in fitness (number of seeds). Using genotypic selection gradient analysis, we found that families with high plasticity in SLA had a lower fitness than families with low plasticity, when the effect of SLA on fitness was statistically kept constant. This indicates that plasticity in SLA incurred a direct fitness cost. However, a cost of plasticity was only expressed under low light, but not under high light. Thus, models on the evolution of phenotypic plasticity will need to incorporate plasticity costs that vary in magnitude depending on environmental conditions.
24‐hour 51Cr post‐transfusion survival, 51Cr life span and haemolysis of red blood cells stored at 4 °C for 56 days in AS‐3
Authors: Valeri C. R. , Pivacek L. E. , Cassidy G. P. , Ragno G. 
Published: March 2003

Background and ObjectivesRed blood cells (RBC) were collected either by a manual method using a 16‐gauge needle or by an apheresis procedure using an 18‐gauge needle, and were stored at 4 °C in a solution of CP2D (anticoagulant)/AS‐3 (Nutricel) for 56 days. The purpose was to compare the outcome of the autotransfused red cells collected by both techniques.Materials and MethodsFive healthy male volunteers were studied on two occasions.ResultsThe autotransfusions of the manual and apheresed RBC resulted in a mean 24‐h post‐transfusion survival of 71%, a normal mean 51Cr RBC life span, a 2,3 DPG level that was less than 10% of normal, and 0·6% haemolysis.ConclusionsWhether collected manually or by apheresis, the outcomes were similar for RBC stored at 4 °C for 56 days in CP2D/AS‐3.
Bacteria‐induced release of white cell‐ and platelet‐derived vascular endothelial growth factor in vitro
Authors: Nielsen H. J. , Werther K. , Mynster T. , Svendsen M. N. , Rosendahl S. , Elley T. , Skov F. 
Published: March 2003

Background and ObjectivesPoor prognosis after resection of primary colorectal cancer may be related to the combination of perioperative blood transfusion and subsequent development of infectious complications. White blood cell‐ and platelet‐derived cancer growth substances, including vascular endothelial growth factor (VEGF), may be involved in this process. Therefore, we studied the in vitro release of VEGF from white blood cells and platelets stimulated by bacterial antigens and supernatants from stored red cell components.Materials and MethodsEight units of whole blood (WB) and eight units of buffy‐coat‐depleted red cell (SAGM) blood were donated by healthy blood donors. Subsequently, half of every unit was leucocyte depleted by filtration, and all 32 half‐units were stored under standard conditions for 35 days. Just after storage, and on days 7, 21 and 35 during storage, aliquots of the supernatants were removed from the units and frozen at −80 °C. WB from other healthy donors was stimulated for 2 h with sodium chloride (controls), with Escherichia coli lipopolysaccharide (LPS) alone, or with LPS plus supernatants from the non‐filtered or prestorage leucofiltered WB units (diluted 1 : 10), or from non‐filtered or prestorage leucofiltered SAGM blood units (diluted 1 : 20) stored for 0, 7, 21, or 35 days, respectively. Similar assays were performed using Staphylococcus aureus‐derived protein A as a stimulatory antigen. The concentration of VEGF was determined in supernatants from stored blood and in assay supernatants by using enzyme‐linked immunosorbent assay (ELISA).ResultsThe concentration of VEGF increased significantly (P < 0·0001) in a storage time‐dependent manner in non‐filtered WB and SAGM blood, while the increase was abrogated by prestorage leucofiltration. The supernatant concentration of VEGF was significantly increased in LPS‐stimulated (P = 0·002) and in protein A‐stimulated (P < 0·0001) assays compared with controls. Addition of supernatants from stored, non‐filtered WB or SAGM significantly increased the assay supernatant VEGF concentration storage‐time dependently (P = 0·006) in LPS assays. In protein A assays, only supernatants from non‐filtered WB significantly increased the assay supernatant VEGF concentration storage‐time dependently (P = 0·022). This additional effect by supernatants from stored blood components was not observed with prestorage leucofiltered blood.ConclusionsExtracellular VEGF may accumulate in non‐filtered red cell components, but this can be prevented by prestorage leucocyte depletion using filtration. In addition, bacterial antigens appear to induce release of VEGF from white blood cells and platelets. Addition of supernatants from stored, non‐filtered WB or SAGM blood may increase the VEGF levels in a storage time‐dependent manner, while prestorage leucofiltration may prevent further increase by supernatants.
Detection of enterovirus viraemia in blood donors
Authors: Welch J. B. , McGowan K. , Searle B. , Gillon J. , Jarvis L. M. , Simmonds P. 
Published: March 2003

Background and ObjectivesThe infrastructure established for screening blood donations for hepatitis C virus has enabled large‐scale population testing for other viruses which are potentially transmissible by transfusion of blood components and plasma‐derived blood products. We have measured the frequency of viraemia of enteroviruses and parechoviruses in 83 600 Scottish blood donors to allow an initial assessment of their risk to blood safety.Materials and MethodsPlasma samples collected from blood donors over 7 calendar months were tested anonymously in mini‐pools of 95 donations, by polymerase chain reaction (PCR) for human enterovirus and parechovirus sequences.ResultsA total of 19 mini‐pools, from the 880 that were tested, were PCR‐positive for enterovirus RNA, predicting a donor prevalence of 0·023%. Enterovirus sequences were not detected in factor VIII or IX clotting factor concentrates. None of the 230 mini‐pools or concentrates contained detectable parechovirus RNA.ConclusionsThe prevalence of enterovirus viraemia detected in this study predicts that at least 1000 enterovirus‐contaminated blood components are transfused per year in the UK. The frequency of transmission and clinical outcome after exposure to enterovirus‐contaminated blood components in recipients is unknown.