bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variable selection on Eurosta's gall size, III: Can an evolutionary response to selection be detected?
Authors: Weis A. E. 
Published: December 2004

AbstractStandard quantitative genetic theory predicts that when a trait is exposed to selection, the between‐generation change in the phenotypic mean, Δ&#x007a;̄i, will be equal to the product of the trait's heritability and the selection differential, h2S. By extension, this theory implies that if a number of replicate populations are exposed to varying intensities of selection, the between‐generation changes in means should covary with the selection differential applied. This relationship offers an opportunity for a statistical test to detect evolutionary change when selection is measured in replicate populations. If an evolutionary response to phenotypic selection occurs, the regression of over Si, where i indicates population, will have a positive slope. This statistical test was applied to data on the insect Eurosta solidaginis (Diptera: Tephritidae). The larvae of this fly induce galls on the stems of the host plant, Solidago altissima (Asteraceae). Previous work has shown that gall size is a heritable trait of the insect. Further, size‐dependent attack on Eurosta larvae by parasitoids selects for larger gall size (Weis and Abrahamson, 1986). Long‐term data on phenotypic selection in 16 populations across 5 generations were analyzed for selection response. Apparent upward evolutionary responses were seen in 2 of the 4 between‐generation transitions. However, no response was seen when the analysis was applied to the cumulative change in gall size. Examination of the data suggested that some of the change in mean gall size was a developmental response to spatial and temporal variation in the environment. Non‐linear developmental effects of environment, when combined with non‐linear fitness functions, can induce a spurious selection response; these non‐linear relationships can account for the apparent evolutionary change gall size found in the by‐generation analysis. Thus, there is no reliable evidence for evolutionary change in Eurosta's gall size over the generations studied. Stasis of gall size in the face of ongoing selection may be due to counterbalancing selection on the gallmaker imposed by host plant resistance.
Clonal diversity in high arctic ostracodes
Authors: Little T. J. , Hebert P. D. N. 
Published: December 2004

AbstractIt remains unclear why the majority of parthenogenetic lineages persist for only brief periods of evolutionary time. However, by characterizing their patterns of genetic variation, it is possible to gain insights regarding their evolutionary origin and potential. We examined clonal diversity patterns in high arctic populations of freshwater ostracodes with the goal of clarifying the factors promoting genotypic diversity. Allozyme electrophoresis showed that the three dominant ostracode species in high arctic ponds reproduce via apomictic parthenogenesis that two of these species (Prionocypris glacialis, Candona rectangulata) were both highly clonally diverse, and had allozyme phenotypes suggestive of polyploidy. Scanning microdensitometry confirmed that many clones of P. glacialis at Igloolik were polyploid. In contrast to most other polyploids, clones of P. glacialis seem to be autopolyploids. Although clonal variation in P. glacialis may reflect multiple transitions to parthenogenesis in an undetected sexual population, it seems likely that genomic recombination associated with polyploidy has also played a role in generating local diversity following the transition to parthenogenesis.
Mutational collapse of fitness in marginal habitats and the evolution of ecological specialisation
Authors: Kawecki T. J. , Barton N. H. , Fry J. D. 
Published: December 2004

AbstractIn spatially heterogeneous environments, natural selection for maintenance of adaptation to habitats that contribute little to the population's reproduction is weak. In this paper we model a mechanism that can result in loss of fitness in such marginal habitats, and thus lead to specialisation on the main habitat. It involves accumulation of mutations that are deleterious in the marginal habitat but neutral or nearly so in the main habitat (mutations deleterious in the main habitat and neutral in the marginal habitat have a negligible influence). If the contribution of the marginal habitat to total reproduction in the absence of the mutations is less than a threshold value, selection is too weak to counter accumulation of such mutations. A positive feedback then results in loss of fitness in the marginal habitat. This mechanism does not require antagonistic pleiotropy in adaptation to different habitats, although antagonistic pleiotropy facilitates the mutational collapse of fitness in the marginal habitat. We suggest that deleterious mutations with habitat‐specific expression may play a role in the evolution of ecological specialisation and promote evolutionary conservatism of ecological niches.
Fluctuating asymmetry in red junglefowl
Authors: Kimball R. T. , Ligon J. D. , Merola‐Zwartjes M. 
Published: December 2004

AbstractFluctuating asymmetry, the random deviation from perfect bilateral symmetry, has recently attracted considerable attention. Levels of asymmetry have been shown to correlate with measures of individual quality. We measured asymmetry in a variety of ornamental and non‐ornamental traits in red junglefowl, Gallus gallus and examined the patterns of asymmetry among different traits within an individual. All ornamental traits had significantly higher levels of fluctuating asymmetry than did non‐ornamental traits. However, inter‐trait correlations of asymmetry were low for both ornamental and non‐ornamental traits. We then correlated measures of asymmetry with several potential indicators of male quality, including comb size, body size, and body condition. We found little evidence that asymmetry in any measured trait reflected male quality. We measured asymmetry in ornamental traits at several stages of development and found no relationship between male condition and changes in asymmetry over time. Our results indicate that it is necessary to employ caution when choosing traits to be measured in studies of fluctuating asymmetry and that a relationship between asymmetry and individual quality cannot be assumed.
Assessing the nucleotide diversity of three aphid species by RAPD
Authors: Martínez‐Torres D. , Carrió R. , Latorre A. , Simon J. C. , Hermoso A. , Moya A. 
Published: December 2004

AbstractA method is presented for the estimation of nucleotide diversity and genetic structure of populations from RAPD (random amplified polymorphic DNA) data. It involves a modification of the technique developed by Lynch and Crease (1990) for the case of restriction sites as survey data. As new elements the method incorporates (i) dominance correction, (ii) values of asexual reproduction of the populations sampled, and (iii) an analytical variance of the number of nucleotide substitutions per site.Sampling was carried out at two geographic scales for three aphid species. At a macrogeographic scale, populations of Rhopalosiphum padi did not show statistical genetic differentiation. Aphis gossypii and Myzus persicae, which were sampled at a microgeographic scale, showed a higher genetic differentiation than R. padi, it being statistically significant in M. persicae. The major sources of sampling variance within‐ and between‐populations were found to be nucleotide (i.e., the number of alleles used as a function of the number of primers used) and population (i.e., sample size) sampling.Extremely low estimates of nucleotide diversity were obtained for the species studied here. This result is consistent with previous reports on genetic diversity for the same or other aphid species which were based on allozyme polymorphism, mitochondrial DNA variation and qualitative analyses of RAPDs.
Molecular phylogeny of the tribe Bovini (Mammalia: Artiodactyla): alternative placement of the Anoa
Authors: Pitra C. , Fürbass R. , Seyfert H.‐M. 
Published: December 2004

AbstractNoncoding regions from the genes encoding aromatase cytochrome P450 and lactoferrin have been sequenced in ten bovine and one cervid species for an investigation of the evolutionary relationships within the tribe Bovini. The evolutionary rate of DNA‐nucleotide alterations along the ancestral bovine lineage amounts to 0.38% per million years, as estimated from this combined 0.478‐kb‐single copy nuclear (scn) DNA sequence data set. Whereas rate homogenity is apparent within the Bovini, the relative rate test suggests that the boselaphine lineage (as represented by Boselaphus) has evolved at only about one third of the rate found within the Bovini. Consistent with other results, the scnDNA data provide evidence for (i) a monophyletic origin of the Bovini, (ii) a sister group position of the Boselaphini, and (iii) two different clades within the Bovini, the buffaloes (Bubalus and Syncerus) and the cattle (Bos/Bibos and Bison). Surprisingly, the results indicate very clearly that the enigmatic dwarf buffalo of Sulawesi Island (Anoa depressicornis) is most closely related to Boselaphus and that the divergence from the true Bovini occurred close to the base of bovine cladogenesis in the Middle Miocene (≈ 14—12 million years ago).
Dynamics of linkage disequilibrium in bacterial genomes undergoing transformation and/or conjugation
Authors: Clark A. G. , Zheng Y. 
Published: December 2004

AbstractBacteria may undergo recombinational exchange either by conjugation followed by crossing over, or by transformation of small segments of DNA into the cell followed by incorporation into the chromosome by gene conversion. These two forms of recombination may have very different consequences on the patterns of linkage disequilibrium seen within bacterial genomes. In this paper deterministic recursions are obtained for three linked loci in populations having these two forms of recombination. Both neutral genetic variation and the case of one selected gene are considered. It is shown that the two forms of exchange have identical consequences on two‐locus linkage disequilibria, but that three‐locus disequilibria can have different behaviors. Hitchhiking also has different consequences on the pattern of disequilibrium seen between linked neutral genes in the region of the selected locus. Inference of the relative importance of these two modes of recombination from static samples of DNA sequences will hinge on the relationship between linkage map distance and disequilibria.
Effects of CMS types and restorer alleles on plant performance in Plantago lanceolata L.: an indication for cost of restoration
Authors: De Haan A. A. , Hundscheid M. P. J. , Van Hinsberg A. 
Published: December 2004

AbstractIn gynodioecious species, male steriles co‐occur with hermaphrodites. Usually, the male sterile trait is maternally inherited, hence it is called Cytoplasmic Male Sterility (CMS). Nuclear loci restore male fertility in combination with their ‘own’ specific cytoplasmic types. In theory, two fitness components are important for the maintenance of this breeding system: a fitness advantage of the male steriles, and costs of restoration. The costs of restoration are alleged negative pleiotropic effects of restorer alleles.In this study the effects of different CMS types on plant performance and the cost of restoration were assessed in two experiments with Plantago lanceolata L. Biomass production differed significantly between the CMS types studied. In order to assess the costs of restoration, hermaphrodites with or without restorer alleles for a CMS type other than its own were compared. The studied restorer alleles caused a reduction in weight per seed, but the number of seeds produced was unaffected. The estimated cost of restoration measured as reduction of seed biomass was 13% for restorer alleles for CMSI. However, in the second experiment no pleiotropic effects of restorer alleles were detected, either because the assumptions for the experimental set‐up were not valid or the costs of restoration may not always be expressed.
Selection caused by self‐fertilization
Authors: Ziehe M. , Gregorius H.‐R. 
Published: December 2004

AbstractThe generally held view that increased self‐fertilization should be advantageous in the absence of counteracting selective forces reducing viability or fertility is reexamined. It is pointed out that the models on which this view is based all imply a gain in male (pollen) fertility with increased selfing. Hence, the postulated advantage may equally well be due to increased fertility, a fact which reopens the discussion on the selective significance of differential selfing.A new model for differential self‐fertilization is presented which avoids built‐in fertility selection by explicitly considering pollen available for self‐ and for cross‐pollination. Plant types are distinguished with respect to their amounts ri of pollen available for self‐pollination, and these types are assumed to be identical with respect to their pollen and ovule fertilities. Moreover, the efficiency of cross‐pollination is allowed to depend, for example, on population density, thus giving rise to a parameter b called “crossing potential”, while the efficiency of self‐pollination is described by a parameter a called “selfing potential”. These parameters may be conceived of as ecological parameters. Increasing ri produces a simultaneous increase in each of the four measures of self‐fertilization (introduced in Part I of the present series) irrespective of the values of the ecological parameters. It is then shown that increased selfing can be both advantageous and disadvantageous in terms of fitness, dependig on the ecological parameters as well as on the mode of self‐fertilization (i.e. where selfing occurs before or after outcrossing). The main result is, roughly, that for both selfing modes high crossing and low selfing potential favour increased cross‐fertilization, while the reverse favours increased self‐fertilization. However, the regions for a and b in which this holds true differ substantially for the two selfing modes. In the complements of these regions strange conditions for the evolution of increased selfing or outcrossing, respectively, exist. The significance of these results for explaining experimental observations is discussed.
Assessing the contributions of multiple interacting traits to plant reproductive success: environmental dependence
Authors: Lechowicz Martin J. , Blais Pierre Alain 
Published: December 2004

AbstractThe reproductive success of sibling cocklebur plants (Compositae: Xanthium strumarium) was monitored after growth at different levels of availability of water and nutrient resources. Variation in reproductive success among individual plants was related to physiological, structural, and phenological characteristics. Reproductive success increased with increased availability of resources, but the relative contribution of particular traits to reproductive success varied with resource availability. Allocation of biomass to different vegetative tissues, time to seedling emergence, degree of branching, transpiration rates, water use efficiency, the rate of decline in height growth after seedling emergence and final plant size all varied significantly with resource availability. However, the changes in each of these phenotypic traits across three garden environments did not always correlate with reproductive success. The shifts across environments in the apparent importance of somatic traits for reproductive success were attributed to plastic changes in the traits but also to changes in the phenotypic correlations of the traits with reproductive success.
Delayed maturation in temporally structured populations with non‐equilibrium dynamics
Authors: Van Dooren T. J. M. , Metz J. A. J. 
Published: December 2004

AbstractIn this paper we study the evolutionary dynamics of delayed maturation in semelparous individuals. We model this in a two‐stage clonally reproducing population subject to density‐dependent fertility. The population dynamical model allows multiple — cyclic and/or chaotic — attractors, thus allowing us to illustrate how (i) evolutionary stability is primarily a property of a population dynamical system as a whole, and (ii) that the evolutionary stability of a demographic strategy by necessity derives from the evolutionary stability of the stationary population dynamical systems it can engender, i.e., its associated population dynamical attractors.Our approach is based on numerically estimating invasion exponents or “mutant fitnesses”. The invasion exponent is defined as the theoretical long‐term average relative growth rate of a population of mutants in the stationary environment defined by a resident population system. For some combinations of resident and mutant trait values, we have to consider multi‐valued invasion exponents, which makes the evolutionary argument more complicated (and more interesting) than is usually envisaged. Multi‐valuedness occurs (i) when more than one attractor is associated with the values of the residents' demographic parameters, or (ii) when the setting of the mutant parameters makes the descendants of a single mutant reproduce exclusively either in even or in odd years, so that a mutant population is affected by either subsequence of the fluctuating resident densities only.Non‐equilibrium population dynamics or random environmental noise selects for strategists with a non‐zero probability to delay maturation. When there is an evolutionarily attracting pair of such a strategy and a population dynamical attractor engendered by it, this delaying probability is a Continuously Stable Strategy, that is an Evolutionarily Unbeatable Strategy which is also Stable in a long term evolutionary sense. Population dynamical coexistence of delaying and non‐delaying strategists is possible with non‐equilibrium dynamics, but adding random environmental noise to the model destroys this coexistence. Adding random noise also shifts the CSS towards a higher probability of delaying maturation.
The maintenance of phenotypic and genetic variation in threshold traits by frequency‐dependent selection
Authors: Roff D. A. 
Published: December 2004

AbstractMany traits are phenotypically dimorphic but determined by the action of many loci, the phenotype being a result of a threshold of sensitivity. Quantitative genetic analysis has shown that generally there is considerable additive genetic variation for the trait, the average heritability being 0.52. In numerous cases threshold traits have been shown, or are assumed, to be under frequency‐dependent selection; examples include satellite‐territorial behaviour, sex‐determination, wing dimorphism and trophic dimorphism. In this paper I investigate the potential for frequency‐dependent selection to maintain both phenotypic and additive genetic variation in threshold traits. The qualitative results are robust to the particular form of the frequency‐dependent selection function. The equilibrium proportion is more or less independent of population size but the heritability increases with population size, typically approaching its maximal value at a population size of 5000, when the mutation rate is 10−4. A tenfold decrease in the mutation rate requires an approximate doubling of the population size before an asymptotic value is approached. Thus frequency‐dependent selection can account for both the existence of two morphs in a population and the observed levels of heritability. It is also shown, both via simulation and theory, that the quantitative genetic model and a simple phenotypic analysis predict the same equilibrium morph proportion.
Effects of flower number on estimated pollen transfer in natural populations of three hermaphroditic species: an experiment with fluorescent dye
Authors: Rademaker M. C. J. , De Jong T. J. 
Published: December 2004

AbstractThe relationship between the number of open flowers and pollen transfer to stigmas was estimated in three insect‐pollinated species (Cynoglossum officinale, Echium vulgare and Oenothera erythrocepala) in 1995 and 1996, using fluorescent dye as a pollen analogue. Dye was applied to an equal number of flowers on a small, a medium and a large individual and its pattern of dispersal to stigmas of conspecifics in local populations was observed.In Cynoglossum officinale and in Echium vulgare large individuals tended to receive more visits per flower. In Oenothera erythrocepala no difference in number of visits per flower was found between small and large individuals.Geitonogamous pollination clearly occurred in all species. In Cynoglossum officinale large individuals transferred more pollen per flower within the same plant (geitonogamy) and an equal or a slightly smaller amount between plants, compared to small individuals. As a result total pollen transfer per flower increased in both years with increasing flower number. In Echium vulgare and in Oenothera erythrocepala large individuals transferred more pollen per flower within the plant (pollen discounting), but a significantly lower amount per flower to other individuals in the populations compared to small individuals. For both these species, there is no difference in total pollen transfer between small and large individuals.In general, the male fitness curve, as estimated by pollen transfer, is a decelerating function of flower number. We discuss this in relation to optimal sex‐allocation and the pollen donation hypothesis.
Fluctuating asymmetry, body size and sexual selection in the dung fly Sepsis cynipsea — testing the good genes assumptions and predictions
Authors: Blanckenhorn W. U. , Reusch T. , Mühlhäuser C. 
Published: December 2004

AbstractIn the dung fly Sepsis cynipsea large and more symmetric males have been shown to enjoy a mating advantage, but we still do not know which mechanism of sexual selection is responsible. Here we test several assumptions and predictions relating to the hypothesis that either trait is indicative of ‘good genes’. We tested for good genes by regressing fitness in good and bad environments (no and high larval competition, respectively) on the family mean for size or asymmetry as expressed in the good environment, separately for both sexes. Body size (hind tibia length or head width) was positively correlated with female fecundity, growth rate of both sexes and larval survivorship for males, but only in the good environment. The corresponding evidence for asymmetry is more equivocal. Mean standardised asymmetry was weakly associated with lower survivorship in the good environment, while growth rates and female fecundity were not. As predicted by sexual selection theory, fore tibia length showed greater asymmetry than other, presumably not sexually selected traits, and asymmetry in fore tibia length was greater for males than females. However, a negative correlation between trait size and asymmetry was only evident for male seta length but not for fore tibia length, fore femur length, or any composite measure of asymmetry. Most crucially, asymmetry was heritable for some female morphological traits (hind tibia length: h2 = 0.15; fore femur length: h2 = 0.16; mean of all measured traits: h2 = 0.27), but not for any male trait. Also, asymmetry of the various traits measured was not correlated within males and only weakly so within females. The crucial assumption that asymmetry of sexually selected traits reflects overall, heritable developmental stability of an individual is thus only partly substantiated by our data. In contrast, large body size is heritable, associated with high fitness and consequently could be indicative of good genes. Fore leg asymmetry may influence male mating success by simply mechanically constraining his ability to hold on to the female.