bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cyclical environmental changes as a factor maintaining genetic polymorphism. 1. Two‐locus haploid selection
Authors: Kirzhner V. M. , Korol A. B. , Ronin Y. I. 
Published: December 2004

AbstractTo classify different types of cyclic selection, a measure of fitness disequilibrium was used, and a class of systems were considered where this measure has the same sign in all states (sign‐concordant environments). The necessary conditions for existence of a fixed point (considering any moment within the period as a referring one) are obtained for sign‐concordant systems. However, analytical study of such systems, in the case of selection for equal additive genes, and numerical testing of more general situations, allowed us to conclude that no polymorphism is possible. In the alternative class of sign‐concordant systems, polymorphism is possible. However, we found that global stability is an exception rather than a rule for sign‐nonconcordant systems. Massive numerical simulations of selection in a four‐state environment were made for cycle lengths in the range 8–28 and with evenly distributed selection coefficients. The proportion of polymorphic regimes ranged up to about 1.5%, and was dependent on the recombination rate between the loci. It should be stressed, that polymorphism maintenance in the haploid systems, when it is possible, can not be considered as an effect derived from constant selection, or be a result of any hidden form of heterozygous advantage. In other words, polymorphism stability is causally connected with environmental fluctuations. Equally important is that this effect of fluctuations is only possible because of recombination: in single locus systems haploid cyclical selection is unable to produce protected polymorphism.
Phenotypic variation, sexual reproduction and evolutionary population dynamics
Authors: Doebeli Michael 
Published: December 2004

AbstractI studied the effects of introducing phenotypic variation into a well‐known single species model for a population with discrete, non‐overlapping generations. The phenotypes differed in their dynamic behaviour. The analysis was made under the assumption that the population was in an evolutionary stable state. Differences in the timing of the competitive impacts of the phenotypes on each other had a strong simplifying effect on the dynamics. This result could also be applied to competition between species. The effect of sexual reproduction on the dynamics of the population was analysed by assuming the simplest genetic model of one locus with two alleles. Sexual reproduction made the system much more stable in the (mathematical) sense that the number of attractors was reduced and their basins of attraction enlarged. In a dominant system sex tended to increase the frequency of the recessive allele, and in an overdominant system it induced gene frequencies of 1/2. Whether the attractors in the dominant system tended to be simpler or more complex than the attractors in the asexual system depended on the phenotype of the recessive homozygote. The overdominant sexual system tended to have simpler dynamics than the corresponding asexual population. A 2‐locus model was used to study whether sexuals can invade an asexual population and vice versa. One locus coded for sexual and asexual reproduction, while the other coded for the dynamics. Enhanced stability through sexual reproduction seemed to be the reason why there was a clear asymmetry favouring sex in this evolutionary context.
Nucleotide Polymorphism at the rp49 region of Drosophila subobscura: Lack of geographic subdivision within chromosomal arrangements in Europe
Authors: Rozas J. , Segarra C. , Zapata C. , Alvarez G. , Aguadé M. 
Published: December 2004

AbstractRestriction‐site polymorphism at the rp49 gene region has been studied in 234 lines of Drosophila subobscura representing different gene arrangements for the O chromosome. The population surveyed (El Pedroso, Spain) was sampled four times in each of two consecutive years. The data indicate that the two chromosomal classes studied, O[ST] and O[3 + 4], are genetically differentiated in El Pedroso. Comparison of the present results with those previously obtained for two other populations further supports that, for a given chromosomal class, European populations are not genetically differentiated. This lack of differentiation at the rp49 region within O[ST] and within O[3 + 4] stands in contrast to the clear latitudinal clines found in Europe for these arrangements.
Antagonistic and reinforcing pleiotropy: a study of differences in development time in wing dimorphic insects
Authors: Roff Derek A. 
Published: December 2004

AbstractMorphological dimorphisms are found in many different taxa. Wing dimorphism in insects, in which some individuals possess wings and associated flight muscles and are thus volant while others lack a functional flight apparatus and are thus flightless, is a typical example of such types of dimorphisms. It has been extensively studied and such studies have demonstrated that the volant form, although possessing the advantage of flight capability, suffers a fitness cost in a delay in the onset of reproduction after emergence into the adult form and a reduced fecundity. Previous comparative analyses have suggested that there is no consistent trend for development time (hatching to adult) to differ between the two morphs. The present study analyses the phenotypic and genetic correlations between development time and wing morph in the cricket Gryllus firmus. It is shown that the macropterous (volant) morph develops faster than the micropterous (flightless morph). This trade‐off is manifested at both thephenotypic and genetic level. Further, a comparative analysis shows that the same phenotypic trade‐off is generally found in other Orthopteran species so far studied, but in other orders the micropterous morph develops faster. Provided that the phenotypic trade‐off is genetically based, in the Orthoptera the fitness advantage of the earlier onset of reproduction in micropterous females is offset by the extended development time (antagonistic pleiotropy). However, in other orders there is reinforcing pleiotropy in that the micropterous females develop faster and reproduce sooner than the macropterous morph. These results highlight the complexity of fitness interactions and the need to study a phenomenon across several taxa.
Intrasexual selection and phylogenetic constraints in the evolution of sexual canine dimorphism in strepsirhine primates
Authors: Kappeler P. M. 
Published: December 2004

AbstractThe goals of this study were to analyze the origin and function of sex differences in the size of canine teeth among Malagasy lemurs and other strepsirhine primates. These analyses allowed me to illuminate interactions between different mechanisms of sexual selection and to elucidate constraints on this sexually‐selected trait. In contrast to central predictions of sexual selection theory, polygynous lemurs lack both sexual dimorphism in body size and male social dominance, but the degree of sexual dimorphism in the size of their canines is not known. A comparison of male and female canine size in 31 species of lemurs and lorises revealed significant male‐biased canine dimorphism in only 6 of 13 polygynous lemur species. This result is in contrast to predictions of a hypothesis that would explain the lack of size dimorphism in lemurs as a result of high viability costs because canine teeth presumably have low maintenance costs and because they are used as weapons in male‐male combat. Moreover, because females had significantly larger maxillary canines than males in only one lemur species, female dominance is not generally based on female physical superiority and selective forces favoring female dominance do not constrain sexual canine dimorphism in the sense of a pleiotropic effect. Contrary to predictions of sexual selection theory, species differences in canine dimorphism across strepsirhines were neither associated with differences in mating system, nor with the potential frequency of aggression. Variation in canine dimorphism was also unrelated to differences in body size, but there were significant differences among families, pointing to strong phylogenetic constraints. This study demonstrated that polygynous lemurs are at most subject to weak intrasexual selection on dental traits used in male combat and that traits thought to be under intense sexual selection are strongly influenced by phylogenetic factors.
Geographic variation in allozymes of populations of Salamandra salamandra (Amphibia: Urodela) exhibiting distinct reproductive modes
Authors: Alcobendas M. , Dopazo H. , Alberch P. 
Published: December 2004

AbstractThe populations of the urodele Salamandra salamandra in the Northern Iberian Peninsula exhibit very different coloration patterns and a remarkable range in reproductive modes (from giving birth to a large number of aquatic larvae to a parturition event of just a few fully metamorphosed, i.e. terrestrial, offspring). Electrophoretic study of geographic variation in allozymes shows that this extraordinary diversity, particularly in reproductive modes, is not accompanied by a genetic differentiation of similar magnitude. All the populations sampled along a transect crossing the Northern part of the Iberian Peninsula and encompassing the various reproductive strategies, as previously described, can be ascribed to a single species, because of small interpopulational genetic distances (ranging DNei from 0.05 to 0.199) and absence of fixed (diagnostic) alleles. A variety of phenetic and cladistic methods were used to elucidate the relationship among populations, based on allozyme data. These methods defined two well corroborated clusters: the first contains populations of salamanders with a blotched dorsal coloration pattern and characterized by parturition of aquatic larvae; the second group is composed of populations exhibiting a striped dorsal coloration pattern, smaller adult body size, and giving birth to fully metamorphosed terrestrial offspring. The latter group also encompasses some populations where mixed parturition events, which include both larvae and metamorphosed offspring, which have been recorded (Dopazo and Alberch, 1994). The absence of a correlation between genetic and geographic distance suggests that the mode of differentiation of the species is based on at least two successive events of isolation, radiation, and secondary contact between populations. Furthermore, the validity of the described “subspecies” is questioned by our data, which point out the need for a detailed systematic study of Salamandra from a global perspective. “Viviparity”, here meaning giving birth to fully metamorphosed offspring, originated once and occurs as intraspecific, and even as intrapopulational variation. Thus, we confirm a system where a major evolutionary innovation ‐the acquisition of independence from the aquatic media in the primitive amphibian complex life cycle‐, can be studied at the microevolutionary, i.e., intra‐ and inter‐populational level.
Evolution of sexual mimicry in sperm‐dependent all‐female forms of Poeciliopsis (Pisces: Poeciliidae)
Authors: Lima N. R. W. , Kobak C. J. , Vrijenhoek R. C. 
Published: December 2004

AbstractThe twofold advantage of all‐female reproduction is limited in many asexual lineages because females are sperm‐dependent. Males of a related sexual‐host species typically prefer conspecific females as mates. According to the “sexual mimicry” hypothesis, an all‐female lineage that closely resembles females of the sexual‐host species should have enhanced mating success. Examination of mating success in all‐female fish of the genus Poeciliopsis supported this hypothesis. The excellent sexual mimicry of some all‐female strains could have evolved through mutations within clonal lineages subsequent to their origins as interspecific hybrids. Alternatively, this mimicry may have been “frozen” from variation in the sexual gene pool when new unisexual lineages first arose. To test the latter hypothesis, we examined laboratory synthesized strains of the hybridogenetic fish P. monacha‐lucida. The frozen variation hypothesis was supported by the present results.
Genetic covariances within and between species: indirect selection for hybrid inviability
Authors: Johnson N. A. , Wade M. J. 
Published: December 2004

AbstractGenotype‐environment interactions and natural selection can result in local specialization when different genotypes are favored in different environments. Restricted gene flow or genetic subdivision enhances local genetic diversification across a species when natural selection acts on such variation. The indirect evolution of reproductive isolation and the restriction of gene flow between species in statu nascendi may provide a central role for genotype‐environment interactions in speciation genetics. We derive the expected genetic covariance between heterospecific and conspecific viability fitness under several different models of selection, dominance, and breeding structure. Standard quantitative genetic methods can be used to estimate these covariances in experimental studies. These genetic covariances permit us to evaluate in a formal way the indirect effects of selection within a species on the evolution of hybrid inviability between species. We find that, for autosomal loci and random mating, the genetic covariance across species is equal to the product of three quantities: (1) the viability of the best hybrid genotype; (2) the viability effect of an allele in hybrids; and, (3) the change in allele frequency due to selection in the conspecific population. Inbreeding within the conspecific population, expressed as Wright's coefficient, F, increases the genetic covariance by a factor (1 + F). In all cases, a negative genetic covariance across species is evidence for hybrid inviability evolving as an indirect effect of selection within species for adaptive (as opposed to neutral) genetic change.“It is an irony of evolutionary genetics, that although it is a fusion of Mendelism and Darwinism, it has made no direct contribution to what Darwin obviously saw as the fundamental problem: the origin of species…. While it is a question of elementary population genetics to state how many generations will be required for the frequency of an allele to change from q1 to q2, we do not know how to incorporate such a statement into speciation theory, in large part because we know virtually nothing about the genetic changes that occur in species formation.”(Lewontin 1974, p. 159)
Measuring spatial variation in natural selection using randomly‐sown seeds of Arabidopsis thaliana
Authors: Stratton D. A. , Bennington C. C. 
Published: December 2004

AbstractWe describe a simple method of measuring spatial variation in fitness using randomly sown seeds. Given a random initial distribution of seeds, any spatial variation in the final distribution of genotypes must be the result of spatial variation in natural selection. Departures from spatial randomness are tested using a modification of join‐count statistics, based on the probability that two randomly chosen plants separated by a given distance carry the same genetic marker. Monte Carlo simulations showed that for the randomly sown seeds design the join‐count test had higher power to detect spatial variation in fitness than analysis of variance. The power was relatively independent of the number of genotypes used or the number of microsites sampled. The method was tested in the field using three standard lines of Arabidopsis thaliana. At the end of the life cycle, adjacent plants were significantly more likely to be the same line than randomly chosen pairs and the spatial dependence extended to distances of nearly 50 cm. Simple experiments like this may be especially useful for “comparative ecological genetics”, allowing systematic studies of natural selection among many species or habitats.
Sympatric and allopatric combinations of hen fleas and great tits: a test of the local adaptation hypothesis
Authors: Dufva R. 
Published: December 2004

AbstractTo test whether allopatric nest parasites differ from sympatric ones in their effect on various life history traits of their avian host, I designed a cross‐transfer experiment in which hen fleas (Ceratophyllus gallinae) were exchanged between great tit (Parus major) nests in two geographically widely separated areas. In neither of the areas did allopatric fleas influence body mass, tarsus length, wing length, duration of nestling period or mortality in great tit nestlings more severely than did sympatric fleas. Duration of incubation was also similar among females independent of experimental treatment. This lack of difference between allopatric and sympatric fleas is hypothesized to reflect the comparative harmlessness of hen fleas for their hosts.
Population structure and interdemic selection in the cooperative spider Anelosimus eximius
Authors: Smith D. R. , Hagen R. H. 
Published: December 2004

AbstractThe degree of relatedness among interacting individuals helps determine the fitness consequences of particular behaviors, whereas the partitioning (and amount) of genetic variation among and within groups controls the level at which selection will act most effectively. Three criteria are considered necessary for selection to act at the group or interdemic level: high rate of group initiation/extinction; differential survival and reproduction among groups; and highly subdivided population structure. The first two criteria have been demonstrated by earlier studies of Anelosimus eximius colonies. This study employs hierarchical analysis of allozyme polymorphisms to demonstrate the third criterion, subdivided population structure. Anelosimus eximius
were collected from Suriname, Panama, Ecuador, Peru and Trinidad. Seven of 40 scorable enzyme loci revealed variation; 4 of these were polymorphic within colonies or regions. Expected heterozygosities were low, ranging from 0 (Ecuador, Peru) to ∼0.03 (Suriname). For each polymorphic locus, hierarchical
F
‐statistics were used to partition overall genetic variation into among‐region (or among‐population;
F
rt
), among‐colony (
F
sr
), and within‐colony (
F
is
) components. Samples from Suriname (43 colonies, 4 local populations) were the most informative; lack of scorable variation limited the inferences that could be drawn from other regions.
A. eximius
colonies are highly inbred: negative estimates of
F
is
imply very small effective colony sizes (∼6.5 for Suriname samples). By contrast, estimates of
F
sr
were very high: the mean for Suriname samples was 0.890, indicating neglibible gene flow among established colonies. Inbreeding within colonies, and genetic differentiation among colonies are consistent with demographic and behavioral observations of
A. eximius .We suggest that interdemic selection is probable in this species and other cooperative spiders with this type of social system, and that mutual tolerance and absence of nest‐mate recognition, as well as female‐biased sex ratios, may have arisen by interdemic selection.
Parent‐offspring regression suggests heritable susceptibility to ectoparasites in a natural population of kittiwake Rissa tridactyla
Authors: Boulinier T. , Sorci G. , Monnat J.‐Y. , Danchin E. 
Published: December 2004

AbstractLittle information is available on the genetic variability of host susceptibility to parasites in natural populations despite its importance for the understanding of the evolution of host‐parasite interactions. A long‐term demographic and epidemiologic survey of a seabird population allowed us to investigate the potential correlation between parent and offspring ectoparasite load, while controlling for various environmental factors. In particular, parasite loads were measured for all individuals (i.e., parents and offspring) when they were nestlings and the effect of the year and breeding cliff were taken into account. The positive correlation found between parent and offspring parasite loads suggests a heritable susceptibility to ectoparasitism by ticks in this host population and that this character has the potential to respond to natural selection.
A genetic analysis of some components of reproductive isolation between two closely related species, Spodoptera latifascia (Walker) and S. descoinsi (Lalanne‐Cassou and Silvain) (Lepidoptera: Noctuidae)
Authors: Monti L. , Génermont J. , Malosse C. , Lalanne‐Cassou B. 
Published: December 2004

AbstractThe two closely related noctuid moths Spodoptera latifascia and S. descoinsi have been found in sympatry in some parts of French Guiana. They differ by i) ecological preferences, ii) some anatomical features of the genital tract, iii) the relative amounts of the two main components of the female pheromonal blend, and iv) the temporal pattern of sexual behaviour. Viable and fertile interspecific hybrids can be obtained in the laboratory, thus permitting a genetic study of some of these traits.The anatomical differences cause perturbations in mating efficiency. Experimental results show that these differences are hereditarily transmitted, but their exact mode of inheritance remains unknown. The timing of initiation of female calling activity is very likely to be under polygenic control. Conclusive evidence showed that a pair of major autosomal alleles determined the pheromone composition. Moreover, some of the data suggest that the descoinsi allele would become lethal in certain mosaic latifascia/descoinsi genomic environments.The ecological factor is likely to be the major component of reproductive isolation between the two species in natural conditions. However in contact zones, the differences in pheromone composition and in timing of sexual activity are probably involved in preventing interspecific hybridization.Two speciation scenarios are proposed, both sympatric. In one of them, the primary event would be a fragmentation of the tropical forest followed by disruptive selection associated with habitat diversification. In the other, the speciation process might have been initiated by the occurrence of mutations acting on the pheromone mediated mate recognition system.
Variation in growth in the blue tit (Parus caeruleus)
Authors: Björklund M. 
Published: December 2004

AbstractThe pattern and amount of phenotypic and genetic variation in growth was analysed using the infinite‐dimensional model in natural populations of the blue tit (Parus caeruleus). A size‐index was used to analyse patterns of variation and covariation across ages (2, 5, 8, 11 and 14 days). Genetic variation was analysed using mother‐, father‐, and midparent‐offspring regressions in the blue tit. Phenotypic variation in growth was limited to a few dimensions only, while heritabilities were close to zero at all ages except at 2 days when a significant mother‐offspring relation was found. The phenotypic variance‐covariance matrix over ages was found to be singular, which suggests that there are trajectories for which there is no phenotypic variation, and which therefore they cannot evolve. The phenotypic growth trajectory associated with the largest amount of variation basically showed a high to moderately high covariation across ages. These results have macroevolutionary implications in terms of the outcome of selection which generally will be in terms of overall size changes but with a slow rate of change due to low heritabilities; an outcome consistent with macro‐evolutionary patterns of morphological variation in birds. A simulation study supported the conclusion that high covariances among traits and ages can impose considerable constraint on a microevolutionary scale.