bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tests of sib diversification theories of outcrossing in Impatiens capensis: Effects of inbreeding and neighbour relatedness on production and infestation
Authors: Burt Austin , Bell Graham 
Published: December 2004

AbstractSeveral models of the evolution of genetic systems posit very strong frequency‐dependent selection acting on small spatial scales; in such circumstances a genetically diverse sibship outperforms a genetically uniform sibship, and genes for mixis may spread in a population. Such selection regimes may derive from resource limitation and/or parasite transmission. We describe a greenhouse experiment designed to test these ideas, using the annual herb Impatiens capensis. Plants were potted in pairs; the genetic variance within pots was manipulated by using progeny from either inbred or outcrossed parents and by using either full sibs or unrelated individuals. Treatment combinations designed to increase genetic diversity resulted in greater phenotypic variance in both morphology and production, though not in the density of spider mites or whiteflies. Despite evidence of resource limitation, there was no effect of genetic diversity on productivity, nor was there an effect on infestation. These results fail to support either the sib competition or the sib contagion theory of outcrossing.
Parasites differentially increase the degree of fluctuating asymmetry in secondary sexual characters
Authors: Møller Anders Pape 
Published: December 2004

AbstractThe degree of fluctuating asymmetry has been demonstrated to reflect the ability of individuals to cope with different kinds of environmental stress (Parsons 1990). Parasites and diseases are one kind of environmental stress which most individuals encounter during their lifetime. Parasites have also been suggested to play an important role in sexual selection and the development of ornaments, since the full expression of ornaments may reflect the ability of hosts to cope with the debilitating effects of parasites. Here I report for the first time that a parasite, the haematophagous tropical fowl mite Ornithonyssus bursa (Macronyssidae, Gamasida), directly affects the degree of fluctuating asymmetry in a secondary sexual character of its host, the elongated tail of the swallow Hirundo rustica (Aves: Hirundinidae). I experimentally manipulated the mite load of swallow nests during one season by either increasing or reducing the number of mites, or keeping nests as controls. The degree of fluctuating asymmetry was measured in the subsequent year after the swallows had grown new tail ornaments under the altered parasite regime. The degree of fluctuating asymmetry was larger at increasing levels of parasites for male tail length, but not for the length of the shortest tail feather or wing length or for tail and wing length in females. These results suggest that the degree of fluctuating asymmetry in tail ornaments, but not in other feather traits, reliably reveals the level of parasite infestation. This has important implications for the ability of conspecifics to use the size and the expression of ornaments in assessment of phenotypic quality and thus in sexual selection.
Phenotypic plasticity and selection in Drosophila life‐history evolution. I. Nutrition and the cost of reproduction
Authors: Chippindale Adam K. , Leroi Armand M. , Kim Sung B. , Rose Michael R. 
Published: December 2004

AbstractEarlier experiments have shown that the evolution of postponed senescent populations can be achieved by selection on either demographic or stress resistance characters. Both types of selection have produced results in which survival characters (stress resistance and longevity) have apparently traded‐off against early‐life fecundity.Here we present the results of a series of experiments in which an environmental variable — the level of live yeast inoculate applied to the substrate — produces a qualitatively similar phenotypic response: longevity and starvation resistance are enhanced by lower yeast levels, at the expense of fecundity. For the starvation resistance versus fecundity experiments we show a negative and linear relationship between the norms of reaction for each character across a gradient of yeast levels. This phenotypic trade‐off is stable across the 20 populations and 4 selection treatments reported on here, and its general agreement with earlier selection results suggests that the evolutionary response and the phenotypically plastic response may share a common physiological basis. However, an important discrepancy in the lifetime fecundity data between the selection response and the dietary manipulations preclude strict analogy. The results broadly conform to a simple “Y‐model” of allocation, in which a limited resource is divided between survival and reproduction; here the characters are starvation resistance and longevity versus fecundity.
Experimental heterochrony in hydractiniid hydroids: Why mechanisms matter
Authors: Blackstone Neil W. , Buss Leo W. 
Published: December 2004

AbstractAs with most clonal organisms, hydractiniid hydroids display a range of morphological variation from sheet‐like to runner‐like forms. Life history differences correlate with these morphological traits, exhibiting patterns commonly found in studies of heterochrony. Experimental studies of two hydractiniid species show that both morphological and life history heterochronies correlate with patterns of gastrovascular circulation. Similar experimental perturbations of energy metabolism, however, have opposite heterochronic effects on the two species. Treatment with 2,4‐dinitrophenol, an uncoupler of oxidative phosphorylation, produced diminished peripheral circulation and sheet‐like peramorphic morphologies in the runner‐like species, Podocoryne carnea. In contrast, similar manipulations of the sheet‐like species, Hydractinia symbiolongicarpus, produced variable peripheral circulation and more runner‐like, juvenilized morphologies. These results diverge at the level of morphological and life history pattern, but are consistent when viewed in terms of the physiology of the gastrovascular system. Interpretations of patterns of heterochrony must focus on the physiological and developmental mechanisms which mediate the expression of heterochronic traits.
Population structure and genetic diversity of metamorphic and paedomorphic populations of the tiger salamander, Ambystoma tigrinum
Authors: Routman Eric 
Published: December 2004

AbstractGenetic relationships, population subdivision and genetic diversity were estimated from mtDNA and allozyme data for two subspecies of tiger salamander, one of which is obligately metamorphic and the other polymorphic for paedomorphosis (larval reproduction). Far greater genetic differentiation exists between subspecies than within subspecies, suggesting that the subspecies have evolved in allopatry. Values of Fst calculated from both mtDNA and allozymes were greater than 0.400 for each subspecies. Significant population subdivision was detected even on a microgeographic scale. This extensive population subdivision indicates that populations can respond to extremely localized selection pressures. In the case of paedomorphosis, populations in permanent water should evolve paedomorphosis as long as the appropriate genes exist. For both mtDNA and allozymes, comparisons of population structure within the polymorphic subspecies and between polymorphic and metamorphic subspecies reveal no discernible effects of paedomorphosis. However, a comparison of paedomorphic and metamorphic populations of the polymorphic subspecies showed significantly higher mtDNA diversity in paedomorphic populations. The discrepancy between the allozyme and mtDNA results may be due to the lower effective population size of mtDNA compared to autosomal genes.
The evolution of hypervariable sex and supernumerary (B) chromosomes in the relict New Zealand frog, Leiopelma hochstetteri
Authors: Green David M. , Zeyl Clifford W. , Sharbel Timothy F. 
Published: December 2004

AbstractChromosomes exhibiting elevated levels of differentiation are termed hypervariable but no proposed mechanisms are sufficient to account for such enhanced evolutionary divergence. Both hypervariable sex and supernumerary (B) chromosomes were investigated in the endemic New Zealand frog, Leiopelma hochstetteri, which is chromosomally polymorphic both within and between populations and has sufficiently elevated variation that different populations can be identified solely by their C‐banded karyotypes. This frog is further distinguished by the univalent, female‐specific W‐chromosome (0W/00 sex determination) uniquely possessed by North Island populations. This sex chromosome exhibited variation in morphology, size, and heterochromatin distribution, sufficient to resolve 11 different types, including isochromosomes. Five of the 12 populations examined also had supernumerary chromosomes that varied in number (up to 15 per individual) and morphology. Specific variations seen among the hypervariable chromosomes could have resulted from heterochromatinisation, chromosome fusions, loss‐of‐function mutations, deletions, and/or duplications. Frogs of the same species from Great Barrier Island, however, had neither supernumeraries nor the female‐specific chromosome. The 0W/00 sex chromosome system must have been derived after the isolation of Great Barrier Island from North Island populations by raised sea levels between 14 000 and 8000 years ago. Furthermore, biochemical divergence between populations is minor and therefore the chromosomal variation seen is comparatively recent in origin. The one characteristic common to all known hypervariable chromosomes is curtailment or lack of recombination. Their accelerated evolution therefore is possible via the mechanism of Muller's ratchet, either alone or in concert with other factors.
Patterns of fluctuating asymmetry in sexual ornaments predict female choice
Authors: Møller Anders Pape 
Published: December 2004

AbstractExtravagant secondary sexual characters are assumed to have arisen and be maintained by sexual selection. While traits like horns, antlers and spurs can be ascribed to intrasexual competition, other traits such as extravagant feather ornaments, displays and pheromones have to be ascribed to mate choice. A number of studies have tested whether females exert selection on the size of male ornaments, but only some of these have recorded female preferences for the most extravagantly ornamented males. Here I demonstrate that female choice can be directly predicted from the relationship between the degree of fluctuating asymmetry and the size of a secondary sexual character. Fluctuating asymmetry is an epigenetic measure of the ability of individuals to cope with stress, and it occurs when an individual is unable to undergo identical development of an otherwise bilaterally symmetric trait on both sides of its body. There is a negative relationship between the degree of fluctuating asymmetry and the absolute size of an ornament in those bird species with a female preference for the largest male sex trait, while there is a flat or U‐shaped relationship among species without a female preference. These results suggest that females prefer exaggerated secondary sexual characters if they reliably demonstrate the ability of males to cope with genetic and environmental stress. Some species may demonstrate a flat or U‐shaped relationship between the degree of fluctuating asymmetry and the absolute size of an ornament because (i) the genetic variance in viability signalled by the secondary sex trait has been depleted; (ii) the secondary sex trait is not particularly costly and therefore does not demonstrate condition dependence; or because (iii) the sex traits can be considered arbitrary traits rather than characters reflecting good genes.
Counterselection on sex chromosomes in the Mus musculus European hybrid zone
Authors: Dod Barbara , Jermiin Lars S. , Boursot Pierre , Chapman Verne H. , Nielsen J. Tönnes , Bonhomme François 
Published: December 2004

AbstractThe extent to which alleles can disperse across a hybrid zone depends on the selection they are subjected to in the hybrid genetic background or, for those that are selectively neutral, on their ability to escape from the unfavourable environment by recombination. Three markers spanning a 45 cM segment in the center of the X chromosome were used to investigate the degree to which selection against X chromosome linked genes helps to maintain the barrier to gene flow in the hybrid zone between Mus musculus domesticus and M. m. musculus in Denmark. The introgression of all the sex chromosome specific markers was more limited than that of the autosomal enzymes (Idh1, Amy, Gpd1, Pgm1, Es1, Es2, Mpi, Np1, Es10, Sod1) and the mitochondrial DNA. The cline for DXPas2, which is in the center of the X chromosome, is extremely steep and shows that certain genes located in this region are strongly selected against in the hybrid background. The clines of the other two X‐linked markers, Hprt and DXPas1, and of the Y chromosome are not as abrupt and all three have similar asymmetric introgression patterns. Although the musculus variants appear to behave in much the same way as those of the autosomal genes, the domesticus variants do not introgress. The results show that X‐linked and to a lesser extent Y‐linked genes are more strongly selected against in the hybrid genome than the mitochondrial genome or the different autosomal loci. This suggests that co‐adapted gene systems involving the sex chromosomes may play an important role in the hybrid breakdown between the two subspecies.
DNA repair and the evolution of transformation IV. DNA damage increases transformation
Authors: Michod Richard E. , Wojciechowski Martin F. 
Published: December 2004

AbstractNatural genetic transformation in the bacterium Bacillus subtilis provides a model system to explore the evolutionary function of sexual recombination. In the present work, we study the response of transformation to UV irradiation using donor DNAs that differ in sequence homology to the recipient's chromosome and in the mechanism of transformation. The four donor DNAs used include homologous‐chromosomal‐DNA, two plasmids containing a fragment of B. subtilis trp+ operon DNA and a plasmid with no sequence homology to the recipient cell's DNA. Transformation frequencies for these DNA molecules increase with increasing levels of DNA damage (UV radiation) to recipient cells, only if their transformation requires homologous recombination (i.e. is recA+‐dependent). Transformation with non‐homologous DNA is independent of the recipient's recombination system and transformation frequencies for it do not respond to increases in UV radiation. The transformation frequency for a selectable marker increases in response to DNA damage more dramatically when the locus is present on small, plasmid‐borne, homologous fragments than if it is carried on high molecular weight chromosomal fragments. We also study the kinetics of transformation for the different donor DNAs. Different kinetics are observed for homologous transformation depending on whether the homologous locus is carried on a plasmid or on chromosomal fragments. Chromosomal DNA‐ and non‐homologous‐plasmid‐DNA‐mediated transformation is complete (maximal) within several minutes, while transformation with a plasmid containing homologous DNA is still occurring after an hour. The results indicate that DNA damage directly increases rates of homologous recombination and transformation in B. subtilis. The relevance of these results and recent results of other labs to the evolution of transformation are discussed.
Multiple mating, sperm competition and meiotic drive
Authors: Haig David , Bergstrom Carl T. 
Published: December 2004

AbstractMost discussions of ‘sperm competition’ have ignored the potential for competition among the different sperm genotypes present in the ejaculate of a single male. Rivalry within ejaculates may limit cooperation among the members of an ejaculate when they compete with sperm produced by other males. A gene that gains an advantage in competition within an ejaculate (a segregation distorter) may increase in frequency even if it is associated with significant costs to organismal fitness. Therefore, selection will favor genes expressed in males that suppress competition within ejaculates. This may explain why sperm function is largely controlled by the diploid genotype of the male progenitor, rather than by the genotypes of individual haploid sperm. Females who mate with multiple males reduce the relative advantage of a segregation distorter whenever the distorter impairs the competitive effectiveness of the ejaculates in which it occurs. If the distorter is associated with costs to organismal fitness, selection will favor female mating behavior that reduces the distorter's equilibrium frequency. Competition within ejaculates may thus be one reason why females choose to mate with multiple males.
Pollinators entering female dioecious figs: why commit suicide?
Authors: Patel Aviva , Anstett Marie‐Charlotte , Hossaert‐McKey Martine , Kjellberg Finn 
Published: December 2004

AbstractIn the dioecious fig/pollinator mutualism, the female wasps that pollinate figs on female trees die without reproducing, whereas wasps that pollinate figs on male trees produce offspring. Selection should strongly favour wasps that avoid female figs and enter only male figs. Consequently, fig trees would not be pollinated and fig seed production would ultimately cease, leading to extinction of both wasp and fig. We experimentally presented pollinators in the wild (southern India) with a choice between male and female figs of a dioecious fig species, Ficus hispida L. Our results show that wasps do not systematically discriminate between sexes of F. hispida. We propose four hypotheses to explain why wasp choice has not evolved, and how a mutualism is thus maintained in which all wasps that pollinate female figs have zero fitness.
The evolutionary history of Drosophila buzzatti. XXVI. Macrogeographic patterns of inversion polymorphism in New World populations
Authors: Hasson Esteban , Rodríguez Constantina , Fanara Juan J. , Naveira Horacio , Reig Osvaldo A. , Fontdevila Antonio 
Published: December 2004

AbstractInversion polymorphisms in the second and fourth chromosomes of the cactophilic Drosophila buzzatti in the native distribution range of the species are described. Over 5,000 flies from 26 localities were scored revealing interesting geographic structuring of arrangement frequencies. Multiple regression and partial correlation approaches showed that the frequencies of second and fourth chromosome arrangements vary clinically along latitudinal and altitudinal gradients and to a lesser extent with longitude. Although many non selective explanations can account for this pattern, its resemblance to the clinal pattern described in recently established Australian populations of Drosophila buzzatii, strongly suggests a selective explanation. Additionally, the correlated variation observed between the frequencies of arrangements 2St on the second chromosome and 4St on the fourth suggests a pattern of interchromosomal association, which, when considering the vast area surveyed, might be explained as the result of epistatic interactions. The analysis of population structure revealed a significant regional pattern, concordant with previously described phytogeographic regions. F‐statistics showed that the patterns of variation were different not only between the second and fourth chromosomes, but also between second chromosome arrangements, suggesting that selective differentiation might have contributed to population structure.Since D. buzzatii breeds and feeds on the decaying tissues of diverse cactus species present in different phytogeographic regions, it is difficult to distinguish the underlying causes of the geographic patterns observed. However, inversion heterozygosity is not correlated with the diversity of potential cactus hosts.The evidence presented suggests that differential selection may be the main cause for the population structure. It is also possible to conclude that the inversion polymorphism of D. buzzatti is flexible rather than rigid.
The differential genetic and environmental canalization of fitness components in Drosophila melanogaster
Authors: Stearns Stephen C. , Kaiser Marcel , Kawecki Tadeusz J. 
Published: December 2004

AbstractCanalization describes the process by which phenotypic variation is reduced by developmental mechanisms. A trait can be canalized against environmental or genetic perturbations. Stabilizing selelction should favor improved canalization, and the degree of a trait's canalization should be positively correlated with its impact on fitness. Here we report, for Drosophila melanogaster, measurements of environmental canalization for five fitness components. We compare them with measurements of genetic canalization, and we discuss the impact of inbreeding on both. In three experiments we measured the variation of fitness components within lines nested within temperature, treatment, and experiment. Lines differed in the position of a P element insert or in genetic background. Within lines flies were genetically nearly identical. We designated trait variation within lines as environmental canalization. The canalization of the traits increased with their impact on fitness, and the pattern was similar to that found for the canalization of fitness components against genetic differences, measured as the variation among lines nested within temperature, treatment, and experiment. This suggests that developmental mechanisms buffer the phenotype against both genetic and environmental disturbance. The results also suggest, less strongly, that inbreeding weakens canalization.
Assessing population genetic structure and variability with RAPD data: Application to Vaccinium macrocarpon (American Cranberry)
Authors: Stewart C. N. , Excoffier L. 
Published: December 2004

AbstractA method for estimating and comparing population genetic variation using random amplified polymorphic DNA (RAPD) profiling is presented. An analysis of molecular variance (AMOVA) is extended to accomodate phenotypic molecular data in diploid populations in Hardy‐Weinberg equilibrium or with an assumed degree of selfing. We present a two step strategy: 1) Estimate RAPD site frequencies without preliminary assumptions on the unknown population structure, then perform significance testing for population substructuring. 2) If population structure is evident from the first step, use this data to calculate better estimates for RAPD site frequencies and sub‐population variance components. A nonparametric test for the homogeneity of molecular variance (HOMOVA) is also presented. This test was designed to statistically test for differences in intrapopulational molecular variances (heteroscedasticity among populations). These theoretical developments are applied to a RAPD data set in Vaccinium macrocarpon (American cranberry) using small sample sizes, where a gradient of molecular diversity is found between central and marginal populations. The AMOVA and HOMOVA methods provide flexible population analysis tools when using data from RAPD or other DNA methods that provide many polymorphic markers with or without direct allelic data.