bluuebunny/crossref_metadata_2025_split huggingface dataset:
Why pollinators visit only a fraction of the open flowers on a plant: The plant's point of view
Authors: Iwasa Y. , De Jong T. J. , Klinkhamer P. G. L. 
Published: December 2004

AbstractWe analyze the so‐called ‘exponential decay’ model of pollen transfer for the case in which pollinators visit a fraction of the open flowers on a plant. The analysis is limited to the simplest case of a self‐incompatible species, in which self pollen does not interfere with seed set. Plants can manipulate the number of flowers visited per pollinator approach by adjusting attractiveness of flowers so as to maximize pollen export (male fitness). In the model the length of the visitation sequence that is optimal for the plant f̂ always decreases with pollen deposition rate k1, pollen uptake rate k2, and the number of pollinator approaches to the plant X, but increases with the total number of flowers F. We assume that the average number of pollinator approaches X increases with the total number of flowers F, but slower than proportionality. It then follows that the optimal fraction of flowers a pollinator visits after arriving on the plant (f̂/F) decreases with the total number of flowers F. Furthermore, the male fitness gain per flower generally decreases with number of flowers, except for the condition of ‘inefficient’ pollen transfer with very small values of k1, k2, and X, or when the plant has only a few flowers. The latter conditions should favour high nectar production and mass blooming. The known range of parameters suggests that male fitness increases with the total number of flowers slower than proportionality.
Acetic acid tolerance in Drosophila is a prerequisite for ethanol tolerance
Authors: Th. Eisses Karel , Den Boer Ar A. 
Published: December 2004

AbstractAcetic acid tolerance compared with ethanol tolerance of Drosophila simulans and six Drosophila melanogaster strains shows a curvilinear relation with apparent asymptotic hyperbolic profile. The upper limit of acetic acid tolerance is lower than that for ethanol. We compared strains which had pairwise identical alcohol dehydrogenase (ADH) coding regions but different genetic backgrounds. A positive regression existed for ethanol tolerance on ADH activity. Adh‐null mutants with very low ethanol tolerances had appreciable acetic acid tolerances and as a consequence did not fit the curve. ADH‐F and ADH‐S strains selected for high ethanol tolerances had the ability to tolerate high ethanol concentrations even after selection had been relaxed for several years. These selected lines tolerated higher acetic acid concentrations than the non‐selected original strains. We propose that intake of high concentrations of ethanol and oxidation into acetic acid induces esterification of ethanol and acetic acid into ethylacetate. This cannot take place after the intake of acetic acid only, which also gives a lower energy yield.
Epistatic selection opposed by immigration in multiple locus genetic systems
Authors: Slatkin Montgomery 
Published: December 2004

AbstractA model of “complete” epistatis is considered in which all “plus” alleles must be present in an individual before the adaptive phenotype is expressed. The conditions under which the plus alleles and hence the adaptive phenotype can increase and reach a stable equilibrium in the presence of immigration of gametes carrying minus alleles are found. In haploids and diploids in which the plus alleles are recessive, frequencies of the plus alleles are the same at all loci, regardless of the linkage relationships. Tight linkage favors the existence of a locally stable polymorphic equilibrium, but the equilibrium with only minus alleles is locally stable unless there is very tight linkage or very strong selection. Thus, this kind of epistasis, which provides a simple model for a character that requires several components to be present at the same time, is very sensitive to even a small amount of immigration. Hence, the evolution of such characters is likely only in completely rather than partially isolated populations.
An easy method for preserving nucleic acids in field samples for later molecular and genetic studies without refrigerating
Authors: Laulier M. , Pradier E. , Bigot Y. , Périquet G. 
Published: December 2004

AbstractThe nucleic acids in field collected samples of viruses, bacteria, yeasts, invertebrates and vertebrates were well preserved in buffered solution of 4M guanidium‐thiocyanate. This method is particularly suitable for population, epidemiological and parasitological molecular studies. The DNA and RNA from samples kept up to 41 days without refrigeration in this way were suitable for PCR and reverse transcription PCR.
Genetic variation and plasticity of thorax length and wing length in Drosophila aldrichi and D. buzzatii
Authors: Barker J. S. F. , Krebs R. A. 
Published: December 2004

AbstractReaction norms across three temperatures of development were measured for thorax length, wing length and wing length/thorax length ratio for ten isofemale lines from each of two populations of Drosophila aldrichi and D. buzzatii. Means for thorax and wing length in both species were larger at 24 °C than at either 18 °C or 31 °C, with the reduction in size at 18 °C most likely due to a nutritional constraint. Although females were larger than males, the sexes were not different for wing length/thorax length ratio. The plasticity of the traits differed between species and between populations of each species, with genetic variation in plasticity similar for the two species from one locality, but much higher for D. aldrichi from the other. Estimates of heritabilities for D. aldrichi generally were higher at 18 °C and 24 °C than at 31 °C, but for D. buzzatii they were highest at 31 °C, although heritabilities were not significantly different between species at any temperature. Additive genetic variances for D. aldrichi showed trends similar to that for heritability, being highest at 18 °C and decreasing as temperature increased. For D. buzzatii, however, additive genetic variances were lowest at 24 °C. These results are suggestive that genetic variation for body size characters is increased in more stressful environments. Thorax and wing lengths showed significant genetic correlations that were not different between the species, but the genetic correlations between each of these traits and their ratio were significantly different. For D. aldrichi, genetic variation in the wing length/thorax length ratio was due primarily to variation in thorax length, while for D. buzzatii, it was due primarily to variation in wing length. The wing length/thorax length ratio, which is the inverse of wing loading, decreased linearly as temperature increased, and it is suggested that this ratio may be of greater adaptive significance than either of its components.
Heritable allometric variation in bumble bees: opportunities for colony‐level selection of foraging ability
Authors: Owen R. E. , Harder L. D. 
Published: December 2004

AbstractDifferent characters of an organism may be correlated if genes control the allometric relationship between them. If genetic variation exists for such genes then the allometric relation itself is potentially subject to change by selection. In social insects allometric relations represent colony‐level characters. If colonies differ in these relations and this variation leads to differential productivity among colonies, then selection on allometric relations can operate at the level of the colony. We assessed the extent of heritable, between‐colony variation for the allometric coefficients relating proboscis ( = glossa) length to wing length for two bumble bee species (Bombus huntii and B. occidentalis). We found that in both species colonies did not differ significantly in slope (b) but did differ significantly in intercept (a) of the regression of glossa length on wing length. Within‐colony variation of the intercept was estimated by randomly constituting groups of five workers from each colony and calculating the regression for each group. The intraclass correlation was then calculated from the between‐ and within‐colony mean squares. We found significant intraclass correlations in both species, giving heritabilities of 0.5 ± 0.3 in B. hunti and 0.7 ± 0.3 in B. occidentalis. If this allometric relation affects colony foraging success and foraging environments vary geographically, then the intercept should exhibit corresponding geographic variation. We tested this prediction by comparing intercepts calculated using wild‐caught B. vagans workers from Alberta, Ontario and Maine. We found that the intercepts did differ significantly between sites, with the bees from Alberta having a significantly smaller intercept than the bees from eastern North America. Our results illustrate the opportunity for selection on an allometric relation that directly affects the foraging success of individual bumble bee colonies.
Analysis of the relationship between allozyme heterozygosity and fitness in the rare Gentiana pneumonanthe L.
Authors: Oostermeijer J. G. B. , Van Eijck M. W. , Van Leeuwen N. C. , Den Nijs J. C. M. 
Published: December 2004

AbstractEspecially for rare species occurring in small populations, which are prone to loss of genetic variation and inbreeding, detailed knowledge of the relationship between heterozygosity and fitness is generally lacking. After reporting on allozyme variation and fitness in relation to population size in the rare plant Gentiana pneumonanthe, we present a more detailed analysis of the association between heterozygosity and individual fitness. The aim of this study was to test whether increased fitness of more heterozygous individuals is explained best by the ‘inbreeding’ hypothesis or by the ‘overdominance’ hypothesis. Individual fitness was measured during 8 months of growth in the greenhouse as the performance for six life‐history parameters. PCA reduced these parameters to four main Fitness Components. Individual heterozygosity was scored for seven polymorphic allozyme loci.For some of these loci (e.g. Aat3, Pgm1 and 6Pgdh2) heterozygotes showed a significantly higher relative fitness than homozygotes. To test the inbreeding model, regression analyses were performed between each Fitness Component and the number of heterozygous loci per individual. Multiple regressions with the adaptive distance of five loci as independent variables were used to test the overdominance model. Only the inbreeding model was a statistically significant explanation for the relationship between heterozygosity and fitness in G. pneumonanthe.The number of heterozygous loci was significantly negatively correlated with the coefficients of variation of three of the six initially measured fitness parameters. This suggests a lower developmental stability among more homozygous plants and may explain the higher phenotypic variation in small populations of the species observed earlier. The importance of the results for conservation biology is discussed.
Non‐selectivity in extinction of bivalves in the Late Cretaceous of the Atlantic and Gulf Coastal Plain of North America
Authors: McClure M. , Bohonak A. J. 
Published: December 2004

AbstractIt has been suggested that the biogeographic and clade‐level characteristics of marine invertebrate groups important in survival through mass extinctions are different from those important in survival during normal times. The role played by ecologically important characters in survival across mass extinctions, however, has not been well‐studied. We obtained information from the literature about the feeding mode and morphology, burrowing habits, size and depth below sea‐level inhabited, temperature range, shell thickness, species richness and abundance of bivalve genera present in the Late Cretaceous of the Atlantic and Gulf Coastal Plain of North America. Non‐parametric analysis revealed that there were no significant associations between any of these characteristics and survival across the Cretaceous‐Tertiary boundary. This lack of selectivity may be due to varying local conditions, which favor different ecological characteristics in each area and produce no overall pattern of selectivity. It might also be indicative of the severity of this extinction on bivalves — differences in ecological habits may have been virtually irrelevant to survivorship through this event.
A genetic metapopulation model for reef fishes in oceanic islands: the case of the surgeonfish, Acanthurus triostegus
Authors: Planes S. , Galzin R. , Bonhomme F. 
Published: December 2004

AbstractAllozyme data on a surgeonfish, Acanthurus triostegus, were analysed from 10 islands in French Polynesia. We compared estimates of gene flow according to the hypothesis of an equilibrium between genetic drift and migration, and estimated genetic divergence times assuming complete genetic isolation without gene flow since foundation. The significant correlation between genetic divergence and geographic distance, at the within‐archipelago level (r = 0.709, P = 0.024) indicates exchange of individuals mainly between neighbouring populations. The correlation was, however, not significant at the among‐archipelagoes level (r = 0.325, P = 0.330), suggesting that long distance migrations are more sporadic. This addresses the problem of scale in population biology. According to the spatial scale of analysis, results can change from an island model, with no relation between genetic differentiation and geographical distances between archipelagos, to an isolation‐by‐distance model within an archipelago.These factors lead us to propose a “patchy population” model, in which all patches are occupied and reproductively active, though with few successful migrations between neighbouring populations. This model describes a subdivided population that is stable through time, with an amount of gene flow small enough to allow significant local differentiation in neutral gene frequency, but high enough to prevent differential fixation in the long term, and therefore preserving the genetic cohesion of the species.
Frequency dependent selection: I. Rare male phenomenon in D. subobscura dependent on the proportion of Amy genotypes and substrate composition
Authors: Terzić T. , Andjelković M. , Marinković D. , Stamenković‐Radak M. 
Published: December 2004

AbstractAnalysis of the rare male mating advantage in D. subobscura, as a type of frequency dependent selection on maltose and starch media, was done by applying different statistical approaches (χ2, cross‐product ratio, variance and regression analysis). They reveal that mating occurs at random when proportions of prospective mates are equal, and that mating success of the males homozygous for Amy‐locus genotypes (S/S and F/F) depends on their proportion. Regression analysis showed that the F/F males are sexually more active (have higher vigour) than S/S males. Rare male effect is one‐sided and appears in F/F males that partake in more heterogamic matings. Comparison of the number of observed and expected homo‐ and heterogamic matings shows that homogamic matings are more frequent. Multifactorial analysis of variance shows that the number of matings are different for nine pairs of lines and four possible mating types (SfSm, SfFm, FfSm, FfFm). The rare male phenomenon is not dependent on different food composition, but is associated with variations in individual genotypes.
Hybrid zones between two genetically differentiated forms of the pond frog Rana lessonae in southern Italy
Authors: Santucci F. , Nascetti G. , Bullini L. 
Published: December 2004

AbstractTwo distinct population groups of the pond frog Rana lessonae were detected in peninsular Italy and Sicily by multilocus electrophoresis: one group inhabits the peninsula down to northern Calabria, the second occurs in southern Calabria and on Sicily. Fixed alternative alleles distinguish the two groups at 5 of the 25 loci examined; marked allele frequency differences were observed at two additional loci. On average, the two groups differ by a Nei's standard genetic distance of 0.4. A wide hybrid zone (about 120 km) occurs between the two groups, with high genotypic diversity and absence of pure parental genotypes in central Calabria. Patterns of allozyme variation suggest that at least two distinct contact and hybridization events occurred, one in the Catanzaro, the other in the Crati‐Sibari plains, about 70 km to the north. Geological evidence indicates that these areas correspond to two main marine‐flooded grabens that would have repeatedly interrupted or reduced genetic exchange during Plio‐Pleistocene times. The finding of a fixed difference at the Mdhp‐1 locus between Sicilian and Calabrian R. lessonae witnesses their continuing differentiation following their last separation by definitive opening of the Strait of Messina, about 50 000 years ago. The wide hybrid zone, the diversity of genotypes and the agreement with Hardy‐Weinberg expectations suggest complete hybrid fertility. Different patterns of introgression were observed at the various loci. The pattern of allelic variation at loci in R. lessonae is paralleled by the pattern of variation in lessonae genomes of the sympatric hemiclonal hybrid Rana esculenta, into which lessonae genomes are introduced each generation as a result of hybridogenesis.
Hypericum cumulicola demography in unoccupied and occupied Florida scrub patches with different time‐since‐fire
Authors: Quintana‐Ascencio Pedro F. , Dolan Rebecca W. , Menges Eric S. 
Published: December 2004

1 Metapopulation models predict that unoccupied, but suitable, patches will exist for species subject to extinction and colonization dynamics. We compared the demographic responses of Hypericum cumulicola, a rare herbaceous species almost entirely restricted to Florida rosemary scrub, when transplanted to occupied or unoccupied patches. 2 Seedlings were transplanted and seeds buried into Florida rosemary scrub patches differing in time since last fire, and in the presence or absence of H. cumulicola. We used a replicated, factorial design to place the transplants and seeds in the field, and monitored their performance for 18 months. 3 Neither time‐since‐fire nor prior H. cumulicola site occupancy affected survival of transplants. Only time‐since‐fire affected growth. Time‐since‐fire, H. cumulicola occupancy, and their interaction affected reproductive effort, but these effects were not consistent between years. 4 Flowering and seed production led to subsequent seedling recruitment near transplants, mainly in recently burned sites. Genetic screening of transplants and seedlings showed that transplants in occupied sites could have crossed with nearby resident plants, but that offspring in sites previously unoccupied were likely to have been parented only by nearby transplants. 5 Seeds buried, and later exhumed, germinated after 1 or 2 years of burial, demonstrating a persistent soil seed bank from which populations could recover after fire. Neither time‐since‐fire nor H. cumulicola occupancy affected seed dormancy or germination. 6 Similar demography in unoccupied and occupied patches suggests that the patchy pattern of site occupancy by H. cumulicola is probably due to limited dispersal and periodic extinction, especially associated with long fire‐free intervals. Conservation measures need to protect unoccupied patches to allow metapopulation dynamics and persistence.
Analysis of reticulate relationships within the Daphnia longispina species complex. Allozyme phenotype and morphology
Authors: Gießler S. 
Published: December 2004

AbstractA two‐step method is proposed to get reliable associations between morphology and genotype in clonal assemblages in which more than two predominantly parthenogenetic species are thought to coexist with hybrids. In dataset 1, the genetic relationships among clones of the Daphnia longispina hybrid complex from seven prealpine lakes in southern Germany were studied based on the variation at 21 enzyme loci. The spatial arrangement in the multidimensional scaling plot revealed a reticulate pattern among three presumably parental species, D. cucullata, D. galeata and D. hyalina, and three hybrid groups, D. cucullata/galeata, D. cucullata/hyalina and D. galeata/hyalina. The Got1 locus was believed to be a discriminating factor between species and hybrids (cf. Wolf and Mort, 1986). However, this locus is more variable, and 57% of the clones would have been misidentified using it. Moreover, the morphological variation within genetically defined groups is also higher than previously assumed. In dataset 2, the revision of morphological and genetic markers greatly improved the association between morphology and genotype in newly collected animals. The spatial arrangement of clones in multidimensional scaling plots and morphological asymmetries to parents suggest both, different degrees of introgression and bidirectional hybridization. Most unexpected genotypes were found in the cxh hybrid group, suggesting that F1‐hybrids are fertile.The results showed (1) that the clonal diversity was very high (2) that detailed analyses of multiple morphological and allozyme markers are necessary to resolve taxonomic relationships within clonal assemblages consisting of multiple species, hybrids and differently introgressed backcrosses, and (3) that the three original species seem to have sufficient within‐species recombination and a low enough rate of backcrossing to allow taxonomic identification. It must remain undecided if the present situation is locally restricted, if it is stable or represents a transient situation which could lead to either a consolidation of the three species by gradual elimination of the hybrids, to a taxonomic breakdown, or to hybrid speciation.
A note on the timing of tradeoffs in discrete life history models
Authors: Doebeli M. , Blarer A. 
Published: December 2004

AbstractWe discuss the timing of tradeoffs in discrete life history models. With a simple mathematical example we show that different assumptions about the temporal order of costs and benefits resulting from a reproductive effort can lead to qualitatively different predictions. We examine two models taken from the literature, in which an implicit assumption is that benefits from reproductive efforts are received before the corresponding costs are paid. We show that the reverse assumptions would have led to very different results. Since there is no biological basis for a bias towards a particular set of assumptions, we conclude that a more flexible approach should be used when studying optimality problems that are based on discrete life histories.