bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relationships between plant density, outcrossing rates and seed set in natural and experimental populations of Scabiosa columbaria
Authors: Van Treuren R. , Bijlsma R. , Ouborg N. J. , Kwak M. M. 
Published: December 2004

SummaryOutcrossing rates were estimated in both natural and experimental populations of Scabiosa columbaria, a self‐compatible, entomophilous, gynodioecious, protandrous perennial. In natural populations, estimates of the outcrossing rate in hermaphrodites were near to one and ranged from 0.84 ± 0.07 to 1.12 ± 0.11. The effect of plant density on outcrossing rates was studied in two experimental populations of 27 individuals. Contrary to expectation the estimates of the outcrossing rate in hermaphrodites were about 100% for both densities. However, in the sparse population, the fraction of developed seeds of plants used to estimate outcrossing rates was significantly lower than of plants in the dense population (0.41 ± 0.06 and 0.68 ± 0.08, respectively). Artificial pollinations of these plants in the greenhouse showed that the fraction of developed seeds was 0.60 ± 0.01 and 0.83 ± 0.05 after self‐ and cross‐pollination, respectively. The combined results suggested that the differential success of self‐ and cross‐pollination might have caused equalization of the outcrossing rates in the experimental populations, despite different plant densities. The implications of the results for conservation biology are discussed.
Mitochondrial DNA phylogeny of North American field crickets: perspectives on the evolution of life cycles, songs, and habitat associations
Authors: Harrison Richard G. , Bogdanowicz Steven M. 
Published: December 2004

AbstractNorth American field crickets (genus Gryllus) exhibit a diversity of life cycles, habitat associations, and calling songs. However, patterns of evolution for these ecological and behavioral traits remain uncertain in the absence of a robust phylogenetic framework. Analyses of morphological variation have provided few clues about species relationships in the genus Gryllus. Here we use comparisons of mitochondrial DNA restriction site maps for 29 individuals representing 11 species (including potential outgroups) to examine relationships among eastern North American field crickets. Initially chosen as likely outgroup taxa, the two European species of Gryllus do not obviously fall outside of an exclusively North American clade and (based on amount of sequence divergence) appear to have diverged from North American lineages at about the same time that major North American lineages diverged from each other. The egg‐overwintering crickets comprise a strongly supported monophyletic group, but relationships among these three closely related species cannot be resolved. The mtDNA data are consistent with a single origin of egg diapause and do not support a model of recent life cycle divergence and allochronic speciation for Gryllus pennsylvanicus and G. veletis. The two crickets are not sister species, despite remarkable similarity in morphology, habitat, and calling song. This conclusion is consistent with published data on allozyme variation in North American field crickets. The habitat associations of eastern North American field crickets have been labile, but calling songs sometimes have remained virtually unchanged across multiple speciation events.
Diverse, endemic and polyphyletic clones in mixed populations of a freshwater snail (Potamopyrgus antipodarum)
Authors: Dybdahl Mark F. , Lively Curtis M. 
Published: December 2004

AbstractUnderstanding the source and diversity of clones is necessary to resolve the complicated issues surrounding the apparent evolutionary stability of sexual reproduction. The source of clones is important because present theory is based on an “all else equal” assumption, which is predicated on the idea that clonal mutants are derived from and compete with local sexual populations. Clonal diversity is important because it reduces the advantage of sexual reproduction under either soft selection (the Tangled Bank Hypothesis) or under strict frequency‐dependent selection (the Red Queen Hypothesis). In the present study, protein electrophoresis was used to determine the source and diversity of clones in a freshwater snail (Potamopyrgus antipodarum) in four glacial lakes in which sexual and clonal females were thought to coexist. The results showed (1) that the populations were mixtures of diploid sexual and triploid asexual individuals, (2) that genotypic diversity of clonal populations is very high in all four lakes (but lower than in the sympatric sexual populations), and (3) that the clones are polyphyletically derived from their sympatric sexual populations. Consequently, repeated mutation to parthenogenetic reproduction since the Pleistocene has introduced a different and diverse set of clones in all four lakes. Such diversity may provide a challenge for the ecological theories of sex that rely on frequency‐dependent selection.
Population systematics of the snake genus Naja (Reptilia: Serpentes: Elapidae) in Indochina: Multivariate morphometrics and comparative mitochondrial DNA sequencing (cytochrome oxidase I)
Authors: Wüster W. , Thorpe R. S. , J. Cox M. , Jintakune P. , Nabhitabhata J. 
Published: December 2004

AbstractWe analyze the population systematics of Asiatic cobras in Indochina, China and the Andaman Islands by means of comparative sequencing of the cytochrome oxidase subunit I gene of the mitochondrial DNA molecule and multivariate analysis of morphological characters. Canonical variate analysis and mtDNA sequence information reveal that the cobras of this region comprise four distinct species: Naja atra from China and northern Vietnam, Naja kaouthia from Burma, central Thailand, Cambodia and southern Vietnam, Naja siamensis from Thailand, Cambodia and southern Vietnam, and Naja sagittifera from the Andaman Islands. The subspecies N. kaouthia suphanensis Nutaphand 1986 shows no mtDNA sequence difference from typical N. kaouthia from central Thailand, and multivariate analysis does not reveal differences in general phenotypic profile; the subspecies is therefore synonymised with Naja kaouthia. The cytochrome oxidase subunit I gene, little used in molecular taxonomy, is shown to be well suited for studies at the species level, as it shows taxonomically useful levels of interspecific divergence but low levels of intraspecific variation; this is particularly relevant for studies of rare species, where sample size is a problem. The combination of multivariate morphometrics and molecular systematics can be particularly powerful in resolving systematic problems in such cases.
Inbreeding depression in Lychnis flos‐cuculi (Caryophyllaceae): effects of different levels of inbreeding
Authors: Hauser Thure P. , Loeschcke Volker 
Published: December 2004

AbstractIn a controlled crossing experiment on Lychnis flos‐cuculi plants in the greenhouse, outbred and selfed maternal plants were each treated with pollen from unrelated plants, siblings and selves. The seeds thus obtained had expected inbreeding coefficients of 0, 0.25 and 0.5 for the outbred maternal plants, and 0, 0.5 and 0.75 for the selfed maternal plants. Seed abortion rate, seed weight and germination rate were estimated. Seedlings were transplanted to an outdoor garden, and monitored for survival, probability of flowering, number of capsules and area of capsules next spring. Inbred seeds germinated slower and in lower proportions than those less inbred, and seedlings had lower survival, flowering, fruit set and area of capsules if inbred.Combined fitness values were estimated from the survival and fecundity components, and severe inbreeding depression was detected for these estimates (0.51 and 0.56 for one generation of selfing). The fitness function decreased linearly with the increase in inbreeding coefficient, which is as expected if the inbreeding depression is additive among loci.
Quantitative genetic analysis of cranial morphology in the cotton‐top (Saguinus oedipus) and saddle‐back (S. fuscicollis) tamarins
Authors: Cheverud J. M. 
Published: December 2004

AbstractPatterns of morphological variation play an important role in evolutionary diversification and are critical to an informed interpretation of interspecific differences. When patterns of genetic variation have not diverged substantially, it is possible to reconstruct the differences in selection which gave rise to morphological differences among extant species. Morphological variation patterns are compared between two tamarin species, the cotton‐top tamarin (Saguinus oedipus) and the saddle‐back tamarin (S. fuscicollis illigeri).Genetic, phenotypic, and environmental variance/covariance and correlation matrices were obtained for a series of 39 cranial characters in each species (cotton‐top tamarin, N = 328; saddle‐back tamarin, N = 209) and for the species combined using crania from individuals of known genealogical relationship. After accounting for the effects of estimation error on measures of matrix similarity, patterns of phenotypic, genetic, and environmental variation and correlation were found to be very similar across species and among the types of variance within species. Taking the saddle‐back tamarins as the standard, cotton‐top tamarins have been selected for an enlarged anterior temporalis attachment area and increased facial prognathism. In primates, an enlarged anterior temporalis muscle is associated with incisive food preparation, especially at wide gape.
Ecological and morphological diversification within single species and character displacement in Mandarina, endemic land snails of the Bonin Islands
Authors: Chiba S. 
Published: December 2004

AbstractThe endemic land snail species Mandarina hahajimana has undergone extensive habitat and morphological diversification within the Hahajima islands in the Bonin archipelago. This species has diversified into populations with ground, arboreal and semi‐arboreal life histories. In addition, arboreal populations and semi‐arboreal populations show diversification in preferences of species and positions of the tree on which they are found. Shell morphologies of M. hahajimana exhibit remarkable geographical variation, and they have a clear relationship with their life histories. The morphological variation of M. hahajimana results from adaptation to different lifestyles. The habitats of these populations influence the relationships with other species of Mandarina coexisting with M. hahajimana. This suggests that the morphological and ecological divergence within M. hahajimana has been induced by competitive interaction with other species of Mandarina. Character displacement may have played an important role in promoting adaptive radiation of Mandarina in the Bonin Islands.
The evolutionary consequences of niche construction: a theoretical investigation using two‐locus theory
Authors: Laland K. N. , Odling‐Smee F. J. , Feldman M. W. 
Published: December 2004

AbstractThis paper addresses the joint evolution of environment‐altering (niche constructing) traits, and traits whose fitness depends on alterable sources of natural selection in environments. We explore the evolutionary consequences of this niche construction using a two‐locus population genetic model. The novel conclusions are that niche construction can (1) cause evolutionary inertia and momentum, (2) lead to the fixation of otherwise deleterious alleles, (3) support stable polymorphisms where none are expected, (4) eliminate what would otherwise be stable polymorphisms, and (5) influence disequilibrium. The results suggest that the changes that organisms bring about in their niche can themselves be an important source of natural selection pressures, and imply that evolution may proceed in cycles of selection and niche construction.
Laboratory evolution of longevity in the bean weevil (Acanthoscelides obtectus)
Authors: Tucić N. , Gliksman I. , Šešlija D. , Milanović D. , Mikuljanac S. , Stojković O. 
Published: December 2004

AbstractIn this study we examined the effects of long‐term selection on early and late reproduction in the bean weevil. The pure lines and the hybrids between the lines within a selection regime were compared for longevity, early and late female fecundity, male mating ability, pre‐adult developmental time and wet adult weight. Comparison of hybrid with pure lines provided some evidence for inbreeding despression in the lines from both selection regimes. We found that virgin and mated adults of both sexes from the “old” lines lived longer than “young” line beetles. Comparisons of the hybrid “young” with hybrid “old” lines revealed a trade‐off between early and late fecundity of females. For noncompetitive mating ability of males there was no difference between the lines with different rates of senescence when the males were young. But, when the males were older, beetles from the lines selected for delayed senescence expressed superior mating ability. In addition, the “old” line beetles take longer to develop and are heavier than those from “young” line beetles. Although these data suggest that shorter pre‐adult developmental time may imply more rapid senescence, there is the possibility of inadvertent selection for rapid development in the “young” lines and this complicates the interpretation of the observed trade‐off between the pre‐adult and adult performances.
Adaptive significance of environmental sex determination in an amphipod
Authors: McCabe J. , Dunn A. M. 
Published: December 2004

AbstractEnvironmental sex determination (ESD) permits adaptive sex choice under patchy environmental conditions, where the environment affects sex‐specific fitness and where offspring can predict their likely adult status by monitoring an appropriate environmental cue. For Gammarus duebeni, an amphipod with ESD, it has been proposed that this flexible sex determination system is adaptive because males gain more from large size. Under ESD, young which are born earlier in the season become mostly males and, experiencing longer to grow, are therefore larger at breeding than females which are born later in the season. In order to test the hypothesis that ESD is adaptive for this species we investigated the relationship between size and fitness for both males and females, in a population of G. duebeni known to have ESD. We measured size related pairing success and fecundity, and used these two measures to calculate the relative fitness gains achieved through an increase in size for either sex. The fitness of both males and females increased with size, but males gained more from an increase in size than did females, throughout the breeding season. The data support the adaptive explanation for the evolution and maintenance of ESD in this species.
Reaction norms of Arabidopsis. V. Flowering time controls phenotypic architecture in response to nutrient stress
Authors: Pigliucci M. , Schlichting C. D. 
Published: December 2004

AbstractThe evolutionary and environmental stability of character correlations has increasingly been the focus of ecological and quantitative genetic studies. Although the genetic stability of character correlations is a central assumption of quantitative genetic models of phenotypic evolution, theoretical considerations suggest that both the genetic and the phenotypic architecture should change in response to selection and to environmental heterogeneity. We investigate genetic (population) differences and plasticity to nutrient availability of the phenotypic architecture describing the whole‐plant phenotype of Arabidopsis thaliana (Brassicaceae). We found significant genetic differences among early and late flowering ecotypes in the relationships between several traits, when a path‐analytical model was used to estimate character correlations. Furthermore, we found significant plasticity of several path coefficients when nutrient levels were altered. A whole‐plant analysis considering all paths in the model simultaneously confirmed that populations of A. thaliana are characterized by distinct phenotypic architectures, and that these are altered in different ways by environmental changes. We discuss the implications of these findings for our understanding of selective pressure on and response by multivariate phenotypes.
The genetics of phenotypic plasticity. VII. Evolution in a spatially‐structured environment
Authors: Scheiner Samuel M. 
Published: December 2004

AbstractPrevious models of the evolution of phenotypic plasticity have, for the most part, not considered the effects of genetic architecture and spatial structure. I examine those factors with an individual‐based simulation model. With regard to genetic architecture, I considered how the presence of different types of loci would affect medium‐term evolutionary outcomes. The types of loci differed in how the environment determined phenotypic expression and included loci that were insensitive to the environment (non‐plastic loci), sensitive in a linear fashion, and sensitive in a quadratic fashion (both plastic loci). With regard to spatial structure, I investigated the affects of migration patterns. These simulations demonstrated that two general conditions are necessary for phenotypic plasticity to be selected. (1) The environment must have a strong influence on genotypic expression. (2) The between‐generation changes in the environment must be large and predictable, in the current instance because of migration in a spatially‐structured (clinal) environment. Responses to selection were not simple, however. Rarely were pure strategies — genetic specialization or phenotypic plasticity — selected for. Instead, the existence of multiple types of loci led to mixed genetic outcomes. The result of this mixed outcome were individuals with reaction norms that were less steep than the optimal reaction norm (when non‐plastic and linear‐plastic loci were present) or individuals with curved reaction norms when the optimal reaction norms was linear (when all three types of loci were present). A pure plasticity strategy had the highest global fitness because plastic individuals would match the optimal phenotype everywhere. The reason that the metapopulation did not achieve this global fitness optimum is that local selection is stronger than global selection. Each deme is driven to a local fitness peak based on the combined, locally additive effects of the non‐plastic and plastic loci. Plasticity is only selected globally, so plasticity becomes more highly favored with high migration rates. This effect was greatest in parts of the cline where the plasticity loci were not being expressed and, thus, not locally selected upon. That is, in these demes local selection was weak or absent allowing global fitness effects to predominate.
Physiological and metabolic aspects of experimental heterochrony in colonial hydroids
Authors: Blackstone N. W. 
Published: December 2004

AbstractHydractiniid hydroids display a range of morphological variation from sheet‐like to runner‐like forms, thus exemplifying the patterns of heterochrony found in many colonial animals. Experimental studies of clonal replicates of a Podocoryne carnea colony demonstrate a relationship between these heterochronic traits and physiological and metabolic factors. While colonies exposed to dilute solutions of 2, 4‐dinitrophenol (an uncoupler of oxidative phosphorylation) for 4 hours per day show a strong dose‐response relationship between within‐colony gastrovascular flow rate and the timing of morphological development, colonies exposed for 20 hours per day fail to show this relationship. Spectrofluorometric measures of redox state suggest that the degree of “loose‐coupling” of oxidative phosphorylation is proportional to the exposure time. Thus colonies exposed for 20 hours have significantly diminished ATP production relative to colonies exposed for 4 hours. Two underlying factors may be responsible for the breakdown of the dose‐response relationship between flow rate and development: (1) colonies exposed to a high dose of uncoupler for 20 hours per day allocate a larger‐than‐normal share of their total energy budget into maintaining the minimal flow rate required physiologically, and (2) colonies' redox state has a direct effect on the timing of morphological development. The latter effect is particularly intriguing, given the extensive literature relating “metabolic activity” to development. In general, these results suggest a relationship between energy allocation, metabolism, and development in these hydroids, and these interrelationships may be central to the evolutionary process of heterochrony.
Partial local mate competition and the sex ratio: A study on non‐pollinating fig wasps
Authors: West S. A. , Herre E. A. 
Published: December 2004

AbstractIn many species, mating takes place in temporary patches where only a small number of females produce offspring. In this situation Local Mate Competition (LMC) theory predicts that the optimal sex ratio (defined as proportion males) should become increasingly female biased as the number of females contributing offspring to a patch decreases. However, in a large number of these species, some mating is also likely to occur away from the natal patch (termed partial LMC). In this case the degree of LMC is reduced, and theory predicts a relatively less female biased sex ratio. We tested these two predictions with field data from 17 species of New World non‐pollinating fig wasps representing three genera. We present a model which suggests that the average number of females ovipositing in a fruit (i.e. patch) is positively correlated with the proportion of fruit of a given tree species in which that species of wasp occurs. Across species, the overall sex ratio was positively correlated with the proportion of fruit in which that species occurs. Furthermore, the males of some species are wingless, and in these species all mating must take place before females disperse from their natal fruit. In contrast, the males of other species are winged, and in these species mating may also take place away from the natal fruit. Species with winged males had less female biased sex ratios than species with wingless males that occurred in a similar proportion of fruit. Finally, the correlation between sex ratio and the proportion of fruit in which a species occurs was also observed within species when comparing between the fruit crops of different trees. This suggests that individual females facultatively adjust the sex ratio of their offspring in response to variable LMC.