bluuebunny/crossref_metadata_2025_split huggingface dataset:
Are codon usage patterns in unicellular organisms determined by selection‐mutation balance?
Authors: Bulmer Michael 
Published: December 2004

AbstractStrongly biased codon usage is common in unicellular organisms, particularly in highly expressed genes. The bias is most simply explained as a balance between selection and mutation, with selection favouring those codons which are more efficiently translated. In a review Ikemura (1985) has proposed four rules for predicting which codons will be preferred, based on the properties of the transfer RNAs responsible for translating messenger RNA into protein. In this paper codon usage in E. coli and yeast is re‐examined using the recent compilation of Maruyama et al. (1986). The codon adaptation index of Sharp and Li (1986a) is used as a measure of gene expression to investigate the importance of this factor. It is found that Ikemura's rules successfully predict preferred codons for yeast, but that two of them work less well for E. coli, and it is suggested that some of the apparent bias in weakly expressed genes of E. coli may be due to contextual effects on mutation rates.
Dispersal, kinship and inbreeding in an island population of the Great Tit
Authors: Van Tienderen P. H. , Van Noordwijk A. J. 
Published: December 2004

AbstractWe investigated the kinship structure of an island population of the Great Tit (Parus major). Kinship of birds could be inferred by comparing their family trees. Dispersal was also studied to explain the observed pattern of kinship.On the island of Vlieland the tits breed in several wooded areas. Both males and females preferred to breed in their natal area; males did so more strongly than females. Hence gene flow between the areas is restricted. However, within the largest wooded area females showed random dispersal, while males showed a slight tendency to breed near their natal site.The degree of kinship of neighbouring birds is a suitable control group for the relatedness of partners that takes into account the effects of dispersal. In the largest wooded area, birds were on average equally related to their partner and to their neighbours. Moreover, the mean coefficient of kinship between male and female neighbours was equal to the average kinship in this part of the population.We conclude that mating is random with respect to kinship. There is no evidence for avoidance of inbreeding. It is unlikely that kin recognition plays an important role in the process of mate choice in this population of Great Tits. We suggest that ecological factors are the main causes for the observed patterns of dispersal and mating.On the island more female than male immigrants enter the population each year. Incidental data indicate an exchange of birds between the population studied and surrounding populations. Ancestries of immigrants are not known, and indeed a first analysis of all birds, including immigrants, showed that males were more closely related than females. However, differential immigration could not fully explain the observed difference in kinship. The presence of local adaptation in males is suggested as a possible additional cause.
Genetic and maternal influences on life history plasticity in milkweed bugs (Oncopeltus): response to temperature
Authors: Groeters Francis R. , Dingle Hugh 
Published: December 2004

AbstractThis study was designed to examine life history flexibility arising from phenotypic plasticity in response to temperature and from maternal effects in response to reproductive diapause in a temperate zone population of the milkweek bug (Oncopeltus fasciatus). We employed a split‐family, first‐cousin, full‐sib design with siblings reared at different temperatures in order to quantify phenotypic plasticity, maternal effects, and variation for each. The following traits were analyzed: development time, age at first reproduction, longevity, early‐life fecundity, and wing length. We found both life history plasticity and maternal effects on life history traits which tend to enhance the colonizing ability of offspring born to mothers that have undergone reproductive diapause. We were unable to demonstrate additive genetic variation for plasticity for any of the traits, while for development time and wing length we found variation due to non‐additive genetic or common‐environmental sources. We were also unable to demonstrate additive genetic variation for maternal effects, although variation may exist at low levels that are difficult to detect using cousin‐families. The apparent lack of variation in this population would constrain evolution of life history flexibility even though considerable flexibility exists in the phenotype.
Variation in gene flow levels among predominantly self‐pollinated plants
Authors: Govindaraju Diddahally R. 
Published: December 2004

AbstractLevels of gene flow, Nm, were calculated for 34 predominantly self‐pollinated plants, using information on differentiation among populations, Gst. Gene flow levels varied from 0.01 to 6.55, and departed significantly from a uniform distribution. High, medium and low levels of gene flow were found among 15, 38, and 47 percent of the species, respectively. The average heterozygosity (H) and the Nm values showed a positively significant association. These results were compared to gene flow levels obtained with a limited number of predominantly outcrossed plants. Gene flow levels in several self‐pollinated species were comparable to those characteristic of some outcrossed species. Pollen flow, combined with long distance dispersal of propagules through various vectors may be responsible for the high levels of gene flow observed in self‐pollinated species. High gene flow may provide the genetic flexibility required for successful colonization, which is an essential feature of self‐pollinated plants.
The causes and consequences of constrained sex allocation in haplodiploid animals
Authors: Godfray H. C. J. 
Published: December 2004

AbstractMales of haplodiploid species develop from unfertilized eggs. An unmated female, or a female in some other way prevented from fertilising eggs, is thus still able to produce male offspring. The presence of females constrained to produce only male progeny distorts the population sex ratio and leads to selection on unconstrained females to produce a daughter‐biased sex ratio. With panmictic mating, the response of unconstrained females maintains a population sex ratio of equality. In populations with strong local mate competition, the presence of constrained females has only a minor affect on the sex ratio of unconstrained females. If unconstrained females modulate their sex ratio in response to all‐male oviposition, there is still no penalty to the production of all‐male broods as constrained oviposition becomes more common, providing less than 50% females are so constrained. When there is local mate competition or if there is no sex ratio response by unconstrained females, there will be unequal costs and benefits to all‐male production, some of which are discussed. The paper also contains a review of the factors leading to constrained oviposition in parasitic wasps and a discussion of how the percentage constrained oviposition can be measured in natural populations.
Floral variation in Eichhornia paniculata (Spreng.) Solms (Pontederiaceae): I. Instability of stamen position in genotypes from northeast Brazil
Authors: Seburn Carolyn N. L. , Dickinson Timothy A. , Barrett Spencer C. H. 
Published: December 2004

AbstractFloral instability in the mid‐styled morph of tristylous Eichhornia paniculata (Spreng.) Solms (Pontederiaceae) was investigated in 14 genotypes from three Brazilian populations of contrasting morph structure (trimorphic, dimorphic, and monomorphic) and levels of inbreeding. Floral instability was described using uni‐ and multivariate methods, in terms of the degree and pattern of variation and covariation in 14 floral measurements from plants grown under uniform glasshouse conditions. The greatest variability was exhibited by filaments of the two lateral short‐level stamens, within and between genotypes from the dimorphic and monomorphic populations. Elongation of one of the stamens to a position adjacent to the stigma results in automatic self‐pollination of flowers. Genotypes were found to differ more in the pattern of covariation between measurements than in multivariate variability. Differences between genotypes in the correlation structure of floral traits were most pronounced in the monomorphic population, and primarily involved measurements of unmodified, rather than modified, stamens. There was no consistent relationship between multivariate variability and whether genotypes produced modified flowers. This pattern suggests that short‐stamen modification arises from changes at specific loci rather than through generalised floral instability brought about by genome‐wide homozygosity.
A phylogenetic interpretation of sexual dimorphism in body size and ornament in relation to mating system in birds
Authors: Björklund Mats 
Published: December 2004

AbstractSexual dimorphism in body size and ornament is commonly assumed to be a result of sexual selection. Therefore, a pattern among species is expected where the type of mating system correlates with the degree of sexual dimorphism. This was analysed using comparative data on birds using an autocorrelation model. Mating system did correlate with sexual dimorphism in ornament (tail), but was only weakly correlated with sexual size (tarsus) dimorphism. Polygynous species were significantly larger than monogamous species. After correcting for size, there was no difference in size dimorphism between polygynous and monogamous species. The reverse was true for tail dimorphism; polygynous species exhibited a larger degree of tail dimorphism, but there was no difference in absolute size of the tail. This pattern suggests that an evolutionary change in mating system is associated with a change in overall size, and in degree of dimorphism in secondary sexual traits.
Heterochrony of tooth root initiation in rabbits
Authors: Sych L. S. , Reade P. C. 
Published: December 2004

AbstractOne of the considerable evolutionary modifications to the dentition of rabbits and other lagomorphs has been the transition from teeth of finite growth, characterized by the presence of brachydontic roots in ancestral species, to teeth in which their generative parts operate as cell renewal systems to maintain a continuous growth of teeth in contemporary species. In contemporary lagomorphs evidence for the existence of vestigial roots in the “rootless”, continuously growing permanent cheek teeth has not been described. It was the purpose of this study to examine developing molariform teeth for evidence of such structures. The basis for the examination was serial histological sections of maxillae and mandibles of contemporary rabbits (Oryctolagus cuniculus L.) harvested from foetuses and postnatals aged from the 15th day postconception to birth and from birth to the 90th postnatal day respectively. The fossil teeth of the Miocene lagomorphs from the genus Amphilagus and Titanomys were used for direct comparisons together with evidence from the literature. It was found that of the 3 root openings which appeared during the early development of permanent molariform teeth, the two lateral ones were homologous with the 2 lateral brachydontic roots present in adult molariform teeth of ancestral lagomorphs. The time required for initiation of the root openings, counted from the day of appearance of the cap stage, was found to be 6 days for deciduous teeth and 3 to 4 days for permanent ones. Four stages in the ontogenesis and evolution of the odontogenic cell renewal system of lagomorphs have been described.
Interspecific transfer of P elements by crosses between Drosophila simulans and Drosophila mauritiana
Authors: Montchamp‐Moreau Catherine , Périquet G. , Anxolabéhère D. 
Published: December 2004

AbstractInterspecific crosses were carried out between P element‐transformed strains of D. simulans and a strain of D. mauritiana, a species devoid of this transposable element family. Four lines were established from hybrid females backcrossed with D. mauritiana males for four generations, and then maintained by intra‐line mass mating. In situ hybridization of polytene chromosomes and southern blots showed that full‐length and deleted P elements were present in all of the lines after 15 generations. We conclude that at least some of the P elements observed in two lines result from their transposition into D. mauritiana genome. Gonadal sterility, induced at 29°C in D. melanogaster by P elements also occurred with these two latter lines.
The evolutionary history of Drosophila buzzatii. XVI. Fitness component analysis in an original natural population from Argentina
Authors: Hasson Esteban , Vilardi Juan C. , Naveira Horacio , Fanara Juan J. , Rodriguez Constantina , Reig Osvaldo A. , Fontdevila Antonio 
Published: December 2004

SummaryThe adaptive significance of the chromosomal polymorphism of Drosophila buzzati has been studied by means of fitness component analysis in an original population from Argentina. The results show evidence of selection acting through pupal viability, longevity (adult viability) and fecundity on the second chromosome polymorphism, and through pupal viability and virility on the fourth chromosome polymorphism.Changes in chromosomal inversion frequencies throughout the life‐cycle suggested an endocyclic pattern of directional selection, which at first seems to be the only detectable mechanism responsible for the maintenance of the polymorphism. However, slow, long‐term frequency changes cannot be ruled out. The way in which endocyclic selection acts on this population is different from that in a colonized population previously studied; that is, different fitness components are involved in the maintenance of chromosomal polymorphism. The possible factors that may explain these differences are discussed.
Allozyme analysis and phyletic relationships of two new stick‐insects from north‐west Sicily: Bacillus grandii benazzii and B. rossius‐grandii benazzii (Insecta Phasmatodea)
Authors: Mantovani Barbara , Scali Valerio , Tinti Fausto 
Published: December 2004

AbstractTwo new Sicilian stick‐insects have been discovered within the genus Bacillus. Evidence concerning the subspecific differentiation of Bacillus grandii benazzii and the hybrid constitution of B. rossius‐grandii benazzii by means of allozyme analysis is given, and is consistent with morphological and karyological data on the differentiation of these two north‐west Sicilian morphs from south‐eastern B. g. grandii and B. whitei. B. g. benazzii is more polymorphic than B. g. grandii and B. rossius‐g. benazzii embodies its genetic variability, thus differing sharply from the south‐eastern parallel hybrid B. whitei ( = B. rossius × B. g. grandii). Reproductive mechanisms also appear to be different in the two interspecific hybrids, involving parthenogenesis in the latter and hybridogenesis in the former. Finally, the phyletic relationships among all Sicilian Bacillus taxa are summarized in a revised scheme, which also takes into account new evidence that B. atticus has contributed to hybrid constitution of the triploid B. lynceorum.
Microgeographic variation in Anolis oculatus, on the island of Dominica, West Indies
Authors: Malhotra Anita , Thorpe Roger S. 
Published: December 2004

AbstractThe current study provides a quantitative description of the pattern of geographic variation in three morphological character systems of Anolis oculatus, on the ecologically diverse island of Dominica. Causal relationships were investigated by comparing observed patterns of variation to hypothesised patterns (derived from six ecological variables), using Mantel tests, partial correlations and canonical correlations. The similarity between generalised morphological and ecological matrices was highly significant. Partial correlations indicated which of the ecological factors had the most significant influence on individual characters, while canonical correlations showed that characters formed constellations which were influenced by constellations of ecological factors. This analysis also illustrates the incongruence of patterns of variation which result from ecogenetic adaptation. The conventional subspecific categories cannot adequately reflect this variation and consequently, in such cases, the use of subspecies is inappropriate.
Nestling growth in the Great Tit I. Heritability estimates under different environmental conditions
Authors: Gebhardt‐Henrich Sabine G. , Van Noordwijk Arie J. 
Published: December 2004

AbstractEvolutionary change requires natural selection in the presence of heritable variation for the trait(s) under selection. Since heritabilities and selection pressures are known to vary with environmental conditions, it is crucial to know how much genetic variation is expressed under which conditions. This study addresses the question of how the expression of genetic variation for fledgling body size of Great Tits varies with the environment. Different environmental conditions were created experimentally by manipulating brood sizes. The treatment affected body size, measured as either fledging weight or tarsus length, and interacted with natural temporal variation in food availability. Both measurements show stabilizing selection.A cross‐fostering design was carried out to separate genetic and environmental causes of variation. Heritabilities as measured from offspring‐midparent regressions and from full‐sib analyses were substantial for both traits, except that no heritability was found for weight under poor conditions. Instead, fledging weights were significantly correlated with the weights of their unrelated guardians' ( = fosterparents') weight under poor conditions.We propose that under poor conditions, when selection on fledging weights is expected to be directional and strong, only little genetic variance is expressed. Any evolutionary response to this selection on fledging weight might therefore be slow, if the increase in selection pressure is not greater than the decrease in heritability.
Genetic prenatal maternal effects on organ size in mice and their potential contribution to evolution
Authors: Cowley David E. 
Published: December 2004

AbstractTwo embryo transfer experiments were carried out in order to estimate the magnitude of prenatal maternal effects, independent of postnatal maternal factors, on the growth of internal organs and fat pads in mice. Reciprocal embryo transfers between the inbred mouse strains C3HeB/FeJ and SWR/J yielded three significant findings. First, all traits were not equally influenced by prenatal maternal factors. Genetic prenatal maternal factors, stemming from the genotype of the uterine mother, had a significant effect on testis weight, subcutaneous fat pad weight and epididymal fat pad weight in 21 day old progeny, but they had no effect on cranial capacity, an index of brain size, kidney weight, or liver weight. Prenatal litter size, defined as the sum of live and dead pups at birth, had a significant negative relationship with 21 day testis weight and kidney weight, and a significant positive association with subcutaneous and epididymal fat pad weights. Cranial capacity and liver weight at 21 days postnatally were not influenced by prenatal litter size. Second, the experiments demonstrated that there was ontogenetic variability in the strength of prenatal maternal effects. At 70 days of age, only subcutaneous fat pad weight was significantly influenced by genetic prenatal effects, and prenatal litter size had a significant negative relationship only with subcutaneous fat pad weight and body weight. Third, genetic prenatal effects had a significant influence on the among‐trait covariances at 21 days postnatally, but not at 70 days. Because multivariate evolution involves covariances among characters, the latter results suggest that prenatal effects due to the mother's genotype can affect phenotypic evolution of mammals, especially for selection imposed early in life.
Colony‐level sex ratio selection in the eusocial Hymenoptera
Authors: Boomsma J. J. , Grafen A. 
Published: December 2004

AbstractWe present an inclusive fitness model on worker‐controlled sex investments in eusocial Hymenoptera which expands the existing theory for random mating populations as formulated by Trivers and Hare (1976) and Benford (1978). We assume that relatedness asymmetry is variable among colonies — owing to multiple mating, worker reproduction and polygyny — and that workers are able to assess the relatedness asymmetry in their own colony. A simple marginal value argument shows that “assessing” workers maximize their inclusive fitness by specializing on the production of the sex to which they are relatively more related than the average worker in the population is related to that sex. The model confirms our earlier verbal argument on this matter (Boomsma and Grafen, 1990) and gives further quantitative predictions of the optimal sex ratio of relatedness‐asymmetry classes for both infinite and finite, random mating populations.It is shown that in large populations all but one of the relatedness‐asymmetry classes should specialize on the production of one sex only. The remaining, balancing class is selected to compensate any bias induced by the other class(es) such that the population sex ratio reflects the relatedness asymmetry of that balancing class. In the absence of worker‐reproduction, the sex ratio compensation by the balancing‐class is generally close to 100%, unless the population is very small.In the Discussion we address explicitly the likelihood of our relatedness‐assessment hypothesis and other assumptions made in the model. The relationship of our model with previous theory on sex allocation in eusocial Hymenoptera is worked out in the Appendix.
Parental effects in Lychnis flos‐cuculi. I: Seed size, germination and seedling performance in a controlled environment
Authors: Biere A. 
Published: December 2004

AbstractSelection responses in natural plant populations depend on how the phenotypic variation of traits is composed. The contributions of nuclear genetic, maternal, paternal, environmental and inbreeding effects to variation in time to germination, germination percentage, and seed‐ and seedling size were studied in a population of Lychnis flos‐cuculi.It was found that: (1) Maternal effects predominated in the determination of progeny seed size and germination characteristics; (2) Maternal environment during seed development was less important than maternal genotype; (3) Small but significant variation within maternal families could be observed among individuals sired by different fathers; (4) Additive genetic variance was significant for seedling size 4 weeks after germination. In conclusion, selection shortly after emergence will mainly favour particular maternal genotypes, while selection later in the life cycle may act upon zygotic genotypes. Inbreeding depression was significant, especially for vegetative growth.Consistent differences were found among maternal genotypes in the degree of variation in the time to germination, suggesting that selection could operate to favour polymorphic or uniform germination behaviour.