bluuebunny/crossref_metadata_2025_split huggingface dataset:
Is there a trade‐off between egg weight and clutch size in wild Lesser Snow Geese (Anser c. caerulescens)?
Authors: Lessells C. M. , Cooke F. , Rockwell R. F. 
Published: December 2004

AbstractPrevious studies of arctic nesting geese suggest that laying is limited by the size of a female's body reserves and that larger eggs contain more nutrients. These observations imply a life‐history trade‐off between egg size and clutch size which may give rise to a negative genetic correlation between the two characters. We estimated the genetic correlation between egg weight and clutch size using measurements from mothers and their daughters in a wild population of Lesser Snow Geese Anser caerulescens caerulescens. Between 65 and 80 % of the variance in egg weight is attributable to differences between individuals, and heritability of egg weight is about 60 %. In contrast, 10–20 % of the variance in clutch size is attributable to differences between individuals, and heritability of clutch size is about 15 %. The genetic correlation coefficient between egg weight and clutch size ranges from 0.09 to 0.32 and does not differ significantly from zero. We discuss the possible reasons for the lack of the expected negative genetic correlation.
Variation in female mate preference across a grasshopper hybrid zone
Authors: Butlin R. K. , Ritchie M. G. 
Published: December 2004

AbstractA method for studying variation in female preference among populations free from the confounding effects of variation in male characters is described. This method is applied to sixteen populations in a transect across a hybrid zone in the grasshopper, Chorthippus parallelus. Significant variation in preference is revealed among populations. The pattern of this variation is analysed in the context of the reinforcement model of speciation. While the data do indicate an increased homogamic preference on one side of the zone relative to more distant populations, this pattern cannot be distinguished statistically from an abrupt transition in preference over a distance of less than 1 km. We argue that either of these patterns implies that selection operates on female preferences in the hybrid zone.
Molecular analysis of the genomic organization of the Hymenoptera Diadromus pulchellus and Eupelmus vuilleti
Authors: Bigot Yves , Hamelin Marie‐Hélène , Périquet Georges 
Published: December 2004

AbstractThe genomic organization of two parasitic wasps was analyzed by DNA reassociation. Cot curves revealed a pattern with three types of components. A highly repetitive DNA, accounting for 15 to 25% of the genome, was identified as satellite DNA. The moderately repetitive DNA corresponds to 26 to 42% of the genome in both species, and shows large variations in complexity, repetitive frequency and a number of sub‐components between males and females. These variations are seen as resulting from DNA amplification during somatic and sexual differentiation. Dot blot analyses show that such DNA amplifications concern several types of structural and regulatory genes. The presence of repeated mobile elements was studied by the Roninson method to compare the repeated sequence patterns of Diadromus pulchellus and Eupelmus vuilleti with those of Drosophila melanogaster. The occurrence and organization of mobile elements in these Hymenoptera differ from those of the neighboring order of Diptera. The repetitive and unique components define very large genomes (1 to 3 × 109 base pairs). The genomic organization in Parasitica appears to be an extreme drosophilan type. We propose that the germinal genome of these parasitic wasps is primarily composed of satellite DNA blocks and very long stretches of unique sequences, separated by a few repeated and/or variously deleted, interspersed elements of each mobile element family.
SE‐ and SW‐migrating Blackcap (Sylvia atricapilla) populations in Central Europe: Orientation of birds in the contact zone
Authors: Helbig Andreas J. 
Published: December 2004

AbstractIn the Blackcap (Aves: Sylvia atricapilla), a widespread passerine noctural migrant, a “migratory divide” between SE‐ and SW‐migrating populations exists in Central Europe at about 14° E and south of 52° N. The autumn migratory directions are known to have a genetic basis and are expressed in orientation cages in captivity. Migratory directions of birds in the contact zone between the two populations were studied by analysing ringing data and by testing three groups of hand‐raised individuals in orientation cages.Available ringing data are insufficient to establish migratory directions in the contact zone north of the Alps. Hand‐raised birds from south‐west Germany and the most eastern part of Austria oriented SW and SE, respectively, confirming directions known from ringing recoveries. A sample of birds from the contact zone near Linz (Austria) oriented SW to NW (mean = 268°) and was significantly different from both adjoining populations. This contrasts with results of a cross‐breeding experiment with mixed pairs of SW‐ and SE‐migrants bred in captivity: The F1‐offspring chose southerly directions, intermediate between both parental populations (Helbig, 1991). It is suggested, therefore, that a distinct subpopulation with a large fraction of birds wintering in the British Isles has established itself in the contact zone. Differences in directional choices between groups of siblings from this area indicate that intrapopulation genetic variability is present. This may have led to a rapid spread of the novel W‐NW migratory direction, because north of the Alps strong selection seems to be acting against mixing of SE‐ with SW‐migrating populations.
Evolutionary implications of the mode of D quadrant specification in coelomates with spiral cleavage
Authors: Freeman Gary , Lundelius Judith W. 
Published: December 2004

AbstractIn annelids, molluscs, echiurans and sipunculids the establishment of the dorsal‐ventral axis of the embryo is associated with D quadrant specification during embryogenesis. This specification occurs in two ways in these phyla. One mechanism specifies the D quadrant via the shunting of a set of cytoplasmic determinants located at the vegetal pole of the egg to one blastomere of the four cell stage embryo. In this case, at the first two cleavages of embryogenesis there is an unequal distribution of cytoplasm, generating one macromere which is larger than the others at the four cell stage. The D quadrant can also be specified by a contact mediated inductive interaction between one of the macromeres at the vegetal pole with micromeres at the animal pole of the embryo. This mechanism operates at a later stage of development than the cytoplasmic localization mechanism and is associated with a pattern of cleavage in which the first two cleavages are equal.An analysis of the phylogenetic relationships within these phyla indicates that the taxa which determine the D quadrant at an early cleavage stage by cytoplasmic localization tend to be derived and lack a larval stage or have larvae with adult characters. Those taxa where the D quadrant is specified by induction include the ancestral groups although some derived groups also use this mechanism.The pulmonate mollusc Lymnaea uses an inductive mechanism for specifying the D quadrant. In these embryos each of the four vegetal macromeres has the potential of becoming the D macromere; however under normal circumstances one of the two vegetal crossfurrow macromeres almost invariably becomes the D quadrant. Experiments are described here in which the size of one of the blastomeres of the four cell stage Lymnaea embryo is increased; this macromere invariably becomes the D quadrant. These experiments suggest that developmental change in relative blastomere size during the first two cleavages in spiralian embryos that normally cleave equally may have provided a route that has led to the establishment of the cytoplasmic localization mechanism of D quadrant formation.
Variation in life history and genetic traits of Hawaiian mosquitofish populations
Authors: Scribner K. T. , Wooten M. C. , Smith M. H. , Kennedy P. K. , Rhodes O. E. 
Published: December 2004

AbstractMosquitofish (Gambusia affinis) were collected from 17 reservoirs on three islands in Hawaii, USA. Genetic and life history traits for adult females from these populations were used to evaluate hypotheses concerning short‐term evolutionary divergence of populations recently established from a common ancestral source. The effects of founder events and drift on genetic variability and population differentiation were also examined. Significant differences in life history characteristics, allele frequencies, and multi‐locus heterozygosities (H) were found among fish populations collected from different reservoirs and between reservoirs classified as stable or fluctuating on the basis of temporal fluctuation in water level. Females from stable reservoirs exhibited greater standard length (35.1 vs 32.8 mm), lower fecundity (11.9 vs 15.2 embryos), lower reproductive allocation (18.2% vs 22.8%), but larger mean embryo size (1.95 vs 1.67 mg) than females from fluctuating reservoirs. Consistency in means among replicates of each reservoir class and concordance in direction and magnitude of differences reported here and results of sampling conducted from these same locations 10 years previously (Stearns, 1983a) suggest that ecological factors intrinsic to these two environments are important in determing population life history traits.Females from stable reservoirs exhibited lower heterozygosity than females from fluctuating reservoirs (0.134 vs 0.158, respectively). Levels and direction od differences in heterozygosity, the high proportion of polymorphic loci and lack of fixation of alternative alleles argue against a purely stochastic explanation for genetic and life history variation among reservoir populations. Levels of genetic variability and interpopulation differentiation were similar to those observed in mainland populations of this species. A high proportion of the genetic diversity was apportioned between populations and within populations due to differences between juveniles and adults. Significant genotypic differences between adult and juvenile age classes suggest that the genetic divergence of local populations may occur over short periods of time.
The evolutionary history of Drosophila buzzatii. XX. Positive phenotypic covariance between field adult fitness components and body size
Authors: Santos Mauro , Ruiz Alfredo , Quezada‐Díaz Jorge E. , Barbadilla Antonio , Fontdevila Antonio 
Published: December 2004

AbstractIn the cactophilic species Drosphila buzzatii, it is feasible to infer the action of natural selection by simultaneously sampling different life history stages in the field. During four years of research, samples of mating and non‐mating adults and pupae were taken from a natural population. The main adult fitness components, i.e., mating success, longevity, and fecundity, were recorded in relation to body size, as measured by thorax length. The age of flies was estimated by observing the developmental stage of the reproductive system. Our data showed that larger flies can outlive and outmate small flies, and that mating success is related to age. An estimate of the fitness function showed a linear increase of mating success with increasing thorax length. There was no assortative mating for this trait. We advance the hypothesis that mating success is related to the rate of encounter and courtship time through general activity, which in turn may be related to body size. A positive phenotypic correlation between thorax length and ovariole number, which is related to fecundity, was found in females emerged from wild pupae. Neither the phenotypic nor the genetic (additive) correlations between these two traits were statistically different from zero in laboratory reared females. The genetic consequences of the observed phenotypic selection on body size are discussed.
The influence of local extinctions on the probability of fixation of chromosomal rearrangements
Authors: Michalakis Yannis , Olivieri Isabelle 
Published: December 2004

AbstractWe investigated the influence of local extinctions in a subdivided population on the probability of fixation of an initially rare allele, for different migration rates. The selective regimes considered were strict underdominance, meiotic drive, and underdominance associated with meiotic drive.We show that local extinctions can increase the probability of fixation of initially rare alleles in underdominant loci for relatively high migration rates, even when both homozygotes have the same fitness. This increase is due to drift during founder events. On the contrary, local extinctions decrease the probability of fixation of alleles favoured by meiotic drive. For a locus where both meiotic drive and underdominance act, the effect of local extinctions depends on the relative strength of the two selective regimes and the initial frequency of the rare allele. For parameter values such that the rare allele is initially selected against, local extinctions decrease the probability of fixation for low migration rates while they cause an increase for moderate migration rates. When the parameter values are such that the rare allele should always be favoured by selection, local extinctions always decrease the probability of fixation. In this latter case, we show the existence of an optimal migration rate which maximizes the probability of fixation.
Developmental stability, sexual selection and speciation
Authors: Møller Anders Pape 
Published: December 2004

AbstractFluctuating asymmetry occurs when an individual is unable to undergo identical development of an otherwise bilaterally symmetric trait on both sides of its body. Since both sides of a bilaterally symmetric trait are the result of the actions of a single genome, fluctuating asymmetry represents an epigenetic measure of the sensitivity of development to stress. Different morphological traits may show a direct relationship between their functional importance and their degree of developmental canalization. This may explain why some characters show high degrees of fluctuating asymmetry, and why these characters more often become exaggerated secondary sexual ornaments. The degree of fluctuating asymmetry is generally larger in small marginal populations living in novel environments, and this will particularly lead to relatively large degrees of asymmetry in the least developmentally canalized traits. More stringent selection against heterozygotes in marginal populations may further break down developmental stability and linkage groups which would lead to increased genetic variance. Females may prefer to mate with males having large, but relatively symmetric morphological characters, because it is more difficult to make large traits (a good genes argument), a large trait is more easily perceived (a sensory bias preference), and because symmetry signals ability to cope with stress (a good genes argument). The low degree of developmental stability and the large amount of genetic variance in secondary sexual characters in small, marginal populations could set the scene for rapid development of divergence and speciation in marginal populations.
The ontogenetic complexity of developmental constraints
Authors: Zelditch Miriam Leah , Bookstein Fred L. , Lundrigan Barbara L. 
Published: December 2004

AbstractDevelopmental constraint is a theoretically important construct bridging ontogenetic and evolutionary studies. We propose a new operationalization of this notion that exploits the unusually rich measurement structure of landmark data. We represent landmark configurations by their partial warps, a basis for morphospace that represents a set of localized features of form. A finding of developmental constraint arises from the interplay between age‐varying means and age‐specific variances in these subspaces of morphospace. Examination of variances and means in 16 ventral skull landmarks in the cotton rat S. fulviventer at ages 1, 10, 20, and 30 days yielded three types of developmental constraint: canalization (constraint to relatively constant form age by age); chreods (reduction of variance orthogonal to the mean trajectory over ages); and opposition (reduction of age‐specific variance along the mean trajectory over ages). While canalization and chreodic constraints have been noted previously, the oppositional type of constraint appears novel. Only one of our characters, relative length and orientation of the incisive foramen, appears to be canalized. Although skull growth becomes increasingly integrated through ontogeny, our characters display a remarkable spatiotemporal complexity in patterns of variance reduction. The specific assortment of constraints observed may be related to the precociality of Sigmodon. We suggest that Waddington's diagrammatic presentation of the “epigenetic landscape” may be misleading in quantitative studies of developmental regulation.
Rapid changes in pollen production in experimental outcrossing populations of wheat
Authors: David Jacques L. , Pham Jean‐Louis 
Published: December 2004

AbstractFor evolutionary reasons, pollen production is expected to be modified when changes occur in plant mating systems. In this study, outcrossing was enforced through male‐sterility in usually autogamous populations of winter wheat. The correlated changes in pollen production were studied after a 6‐year period of natural evolution. Both the disappearance of individuals with the lowest pollen production and the increase in the production of fertile pollen per spike were observed in male‐fertile plants. The results are interpreted as a selection on male function. Some morphological differences also appeared in evolved populations between male‐fertile and male‐sterile plants. These differentiations are discussed in light of resource allocation theory.
Estimating the minimum rate of genetic transformation in bacteria
Authors: Smith J. Maynard 
Published: December 2004

AbstractExtensive data from multilocus electrophoresis are available for many bacterial populations. In some cases, for example Neisseria gonorrhoeae, these data are consistent with the population being in linkage equilibrium. This raises the following question. What frequency of transformation, or other means of genetic recombination, is needed, relative to mutation, to produce apparent panmixis? Simulation of a finite‐population model suggests that, if transformation is at least twenty times as frequent as mutation, the population structure will be indistinguishable from a panmictic one, using the best available data sets. That is, relatively infrequent transformation is sufficient to produce approximate linkage equilibrium.
Opposing fitness consequences of colour pattern in male and female snakes
Authors: Forsman Anders 
Published: December 2004

AbstractLocal populations of the adder, Vipera berus, are polymorphic for dorsal colour pattern, containing both melanistic (black) and zig‐zag patterned individuals. Colour patterns in snakes influence crypsis and thermoregulatory capacity and therefore may be subjected to natural selection. To find an explanation for the maintenance of this polymorphism I examined temporal and spatial variation in morph frequency, and tested for differential selection among morphs using data from a six year capture‐mark‐recapture study. The data derive from six groups of islands in the Baltic Sea off the Swedish east coast, two mainland localities near the coast, and one inland locality.Morph frequency did not change over time within a population but varied among populations: melanistic individuals were not found at the inland locality, but comprised from 17 to 62% of the coastal and island populations. Adders frequently moved between islands within a group, but the tendency to disperse was independent of morph. These results suggest that the polymorphism is stable and maintained by a deterministic process. Scar frequency was twice as high among melanistic as among zig‐zag snakes, and melanistic individuals were easier to capture, indicating that predation may be higher on the melanistic morph. Colour morphs did not differ in body size, but analysis of recapture data shows evidence for differential survival among morphs. Zig‐zag males survived better than melanistic males, but the relative survival rates of morphs were reversed in females. This difference was consistent through time and may be due to sexual differences in behaviour, with melanism increasing predation intensity when associated with male but not with female behaviour. Opposing fitness consequences of colour pattern in the two sexes may help maintain colour polymorphism within populations of Vipera berus.
Origin of clonal diversity in triploid parthenogenetic Trichoniscus pusillus pusillus (Isopoda, Crustacea) based upon allozyme and nucleotide sequence data
Authors: Friis Theisen Bent , Christensen Bent , Arctander Peter 
Published: December 2004

AbstractVariation in PGM (phosphoglucomutase) and MDH (malate dehydrogenase) allozymes and in mitochondrial and nuclear (ribosomal) DNA gives evidence of at least three independent origins of triploid Trichoniscus pusillus pusillus. Much of the genetic variation found may reflect variation within the parental diploid population(s), but it is argued that some of the variation in PGM allozymes have accumulated within the parthenogenetic lines. Based upon the variation at this locus, 15 genetically distinct clones are distinguished.
Thermal evolution of rate of larval development in Drosophila melanogaster in laboratory and field populations
Authors: James Avis C. , Partridge Linda 
Published: December 2004

AbstractThe duration of Drosophila melanogaster larval and pupal periods was measured in laboratory thermal lines and in populations collected along a latitudinal transect in eastern Australia. In replicated laboratory lines kept for 9 years at 16.5° C or 25° C the duration of larval development had continued to diverge compared with 4 and 5 years previously, with more rapid larval development, and hence reduced total duration of pre‐adult development, in the low temperature lines at both experimental temperatures. After 4 years of separate evolution, lines derived from the 25° C lines and subsequently cultured at 29° C showed no evidence of significant divergence in the duration of any part of the pre‐adult period. The geographic populations showed a decrease in the duration of larval development, and hence of the total pre‐adult period, with increasing latitude. In both laboratory and field populations, evolution at lower temperature was associated with more rapid larval development to a larger adult body size, the opposite genetic correlation between these traits to that found within a single temperature. The indications are that lower temperatures may be permissive of more efficient growth in D. melanogaster. It will be important to discover if evolution in response to temperature induces similar correlations in other ectotherms.