bluuebunny/crossref_metadata_2025_split huggingface dataset:
Heterochrony: Developmental mechanisms and evolutionary results
Authors: Raff Rudolf A. , Wray Gregory A. 
Published: December 2004

AbstractThe concept of heterochrony, that the relative timing of ontogenetic events can shift during evolution, has been a major paradigm for understanding the role of developmental processes in evolution. In this paper we consider heterochrony from the perspective of developmental biology. Our objective is to redefine heterochrony more broadly so that the concept becomes readily applicable to the evolution of the full range of ontogenetic processes, from embryogenesis through the adult. Throughout, we stress the importance of considering heterochrony from a hierarchical perspective. Thus, we recognize that a heterochronic change at one level of organization may be the result of non‐heterochronic events at an underlying level. As such, heterochrony must be studied using a combination of genetic, molecular, cellular, and morphological approaches.
Establishment of a tetraploid cytotype in a diploid population: Effect of relative fitness of the cytotypes
Authors: Felber François 
Published: December 2004

AbstractThe conditions for the establishment of a tetraploid in a diploid population were investigated by means of a deterministic model, on the assumption that the diploid cytotype produces some 2n gametes.If the fertility and viability of both cytotypes were the same and the initial population was diploid, then a mixed population would occur if the production of 2n gametes was below 17.16%. The tetraploid excluded the diploid above this limit. By modifying the fertility and the viability of the polyploid this threshold varied, dropping to 10% when one of the two parameters was twice that of the diploid, and falling to as low as 6% if both fertility and viability were double that of the diploid.The conditions for the establishment of a polyploid are therefore quite restrictive under the assumptions of this model. In nature, such processes would probably allow the spread of the polyploid only if the immigration of polyploids considerably enhanced the frequency of tetraploids, or if genetical or environmental changes, or chance processes in small populations caused a substantial increase in the frequency of 2n gametes produced by the diploid.
Phylogeographic histories of representative herpetofauna of the southwestern U.S.: mitochondrial DNA variation in the desert iguana (Dipsosaurus dorsalis) and the chuckwalla (Sauromalus obesus)
Authors: Lamb Trip , Jones Thomas R. , Avise John C. 
Published: December 2004

AbstractTo determine whether genetic variation in representative reptiles of the southwestern U.S. may have been similarly molded by the geologic history of the lower Colorado River, we examined restriction site polymorphisms in the mitochondrial DNA (mtDNA) of desert iguanas (Dipsosaurus dorsalis) and chuckwallas (Sauromalus obesus). Observed phylogeographic structure in these lizards was compared to that reported for the desert tortoise (Xerobates agassizi), whose mtDNA phylogeny demonstrates a striking genetic break at the Colorado River.Both the desert iguana and chuckwalla exhibit extensive mtDNA polymorphism, with respective genotypic diversities G = 0.963 and 0.983, close to the maximum possible value of 1.0. Individual mtDNA clones, as well as clonal assemblages defined by specific levels of genetic divergence, showed pronounced geographic localization. Nonetheless, for each species the distributions of certain clones and most major clonal groupings encompass both sides of the Colorado River valley, and hence are clearly incongruent with the phylogeographic pattern of the desert tortoise. Overall, available molecular evidence provides no indication that the intraspecific phylogenies of the southwestern U.S. herpetofauna have been concordantly shaped by a singular vicariant factor of overriding significance.
Disturbance, competition and the maintenance of clonal diversity in Daphnia pulex
Authors: Weider Lawrence J. 
Published: December 2004

AbstractLaboratory microcosm experiments tested the intermediate disturbance hypothesis, which states that the highest level of diversity (e.g. species diversity) will be maintained at intermediate scales of disturbance. The effects of disturbance on the maintenance of clonal diversity and on competitive interactions among clones of the obligately parthenogenetic freshwater cladoceran, Daphnia pulex were examined. No significant effect of disturbance size (i.e. dilution volume) on clonal diversity was noted. However, frequency of disturbance had a pronounced effect on clonal diversity, with the highest clonal diversity maintained at low to intermediate disturbance frequencies. Competitive hierarchies among clones were often invariant within a given experiment. Generally, one or two clones dominated, with several less abundant clones persisting throughout an experiment. Results suggest that low to intermediate disturbances could be important in the maintenance of genetic variation in natural populations (i.e. through pre‐emption of competitive exclusion between genotypes). This could have a direct bearing on the maintenance of both intra‐ and interspecific diversity.
The genetics of phenotypic plasticity. VI. Theoretical predictions for directional selection
Authors: Gavrilets Sergey , Scheiner Samuel M. 
Published: December 2004

AbstractWe explore the effects of linear and quadratic reaction norms on heritability and directional selection. Genetic variation for reaction norm parameters can alter the heritability of traits; the magnitude of the heritability depends upon both the environment and the correlation among the parameters. Genetic variation for reaction norm parameters can alter the response to directional selection. Selection on a trait in one environment can shift both the mean of the trait measured across environments and the plasticity of the trait; the signs and magnitudes of these responses depend on the correlations among the parameters of the reaction norm. Our model is consistent with the results of ten experiments for selection on a trait in a single environment. In all experiments, selection towards the overall mean of the population always resulted in a relatively lower plasticity than selection away from the overall mean. Our model was able to predict the results of two experiments for selection on a trait index calculated over more than one environment. Predictions were good for the direct response to selection but poorer for the correlated response to selection. Our results indicate the need for more data on the effects of environment on genetic parameters, especially correlations among reaction norm parameters.
Parental care as a game
Authors: Yamamura N. , Tsuji N. 
Published: December 2004

AbstractA new game model of parental care is presented where fitnesses of males and females depend on frequencies of care and no‐care strategies in the population, as well as strategies of individuals and those of their mates. Evolutionarily stable states (ESS) of biparental‐care (BC), female‐care (FC), male‐care (MC), and no‐care (NC) are represented as regions in a 3‐dimensional parameter space, comprising the ratio of the number of offspring raised by FC or MC to that by BC, the ratio of that by NC to that by FC or MC, and the sex ratio. ESSs are not necessarily uniquely determined: ESS regions of FC and MC overlap in parts, as well as those of BC and NC. In a region where none of the four states is ever an ESS, a polymorphism (a mixed state of care and no‐care strategies in one or both sexes) is stable. Although an asymmetry between prezygotic investment times of males and females results in the difference in sizes of the ESS regions of FC and MC, it is not responsible for determining whether FC or MC evolves from other modes of parental care as a result of slowly changing parameters. The key factor is the sex ratio of adults in the population. By a slightly modified model, it is also shown that paternity uncertainty at fertilization of eggs is highly important for evolution of FC.
Do peacock's trains advertise age?
Authors: Petrie Marion 
Published: December 2004

AbstractManning (1987 and 1989) found a positive correlation between several measured aspects of the male's upper tail coverts and male age in a sample of males measured at several different sites. Here we test whether or not the trains of individuals from the same population increase between years. There is no evidence from the data presented that variation in the degree of train elaboration amongst male peacocks is age‐dependent beyond 4 years or that peahens always prefer to mate with older males; one young male in his first year of displaying achieved high mating success and was preferred by several females over other older males present. It therefore appears unlikely that the peacock's train acts as an age‐indicator.
Transfer of a parasitic sex factor to the nuclear genome of the host: A hypothesis on the evolution of sex‐determining mechanisms in the terrestrial Isopod Armadillidium vulgare Latr.
Authors: Juchault P. , Mocquard J. P. 
Published: December 2004

AbstractIn A. vulgare sex is usually determined either by a cytoplasmic feminizing factor (F symbiotic bacteria) or by another feminizing factor (f) which behaves like a mobile element of DNA and which seems to correspond to a fragment of bacterial DNA. By inhibiting the expression of male genes carried by the Z heterochromosome, these feminizing factors induce differentiation of neo‐females [ZZ(+F) or ZZ(+f)]. Such a mechanism leads to the production of progenies whose sex ratio is highly female biased. In some populations in which F and/or f factors are present, genetic females (WZ) have disappeared and all individuals (males and females) are genetic males. However in other populations, cohabitation of ZZ(+f) neo‐females and females in all points similar to genetic females is observed. Such a situation may be unstable and is not likely to be explainable only by migrations of individuals from distinct populations.Owing to certain types of crosses, in particular those which involve an artificial neo‐male ( = female reversed into a functional male by an implant of androgenic gland) we show here that the f factor can be transmitted as a Mendelian gene. In these progenies ZfZ females may appear: like WZ females, they breed broods whose sex ratio is unbiased. The hypothesis that the “F bacteria—A. vulgare” symbiosis may have led, after a complex co‐evolutive process (F bacteria → f mobile element → insertion of f on Z heterochromosome), to the creation (from a male genotype) of a female genotype, is put forward. The consequences of such a phenomenon on the composition and the evolution of A. vulgare populations are examined.
Sex allocation variation in Daphnia pulex
Authors: Innes David J. , Dunbrack Robert L. 
Published: December 2004

Abstract Daphnia
(Crustacea: Cladocera) reproduce by cyclical parthenogenesis in which the sex of offspring is environmentally determined. Although numerous studies have demonstrated that factors such as crowding and short‐day photoperiod stimulate male production, there is limited information on variation in allocation to male and female offspring for any species of
Daphnia
. The present study assessed the presence or absence of male production in 96 isofemale lines (clones) from each of eight populations of
Daphnia pulex
. An average of 37% (range 18–51%) of clones failed to produce males under crowded conditions in the laboratory. A subset of 14 of these non‐male‐producing clones also failed to produce males under short‐day photoperiod (8L:16D). Three male‐producing clones were within‐clone mated as well as crossed to three non‐male‐producing clones to study the inheritance of the failure to produce males. The average frequency of non‐male‐producing F
1
progeny was significantly higher (58%,
N
= 486) among the outcrossed progeny than the inbred progeny (5%,
N
= 86). In addition, when sixteen of the male‐producing outcrossed progeny were within‐clone mated, only 7% (
N
= 106) of the resulting F
2
progeny failed to produce males. These results are consistent with a genetic basis for the absence of male production. Average survival of the progeny from the nine outcrossed matings was more than twice (67%) that of the inbred progeny from the three within‐clone matings (30%), suggesting that within‐clone mating would result in significant inbreeding depression. We present a model that suggests that even low levels of inbreeding could allow non‐male‐producing females to be maintained in a population. The co‐occurrence of non‐male‐producing females and females that produce both males and females in
Daphnia pulex bears a similarity to the gynodioecious breeding system found in some plant species.
Drosophila C virus and Drosophila hosts: a good association in various environments
Authors: Gomariz‐Zilber Eliane , Thomas‐Orillard Michèle 
Published: December 2004

AbstractTo discover whether the beneficial effects observed when Drosophila C virus (DCVC) infects Drosophila larvae should be considered as a specific case or, as a general rule, the DCVC‐Drosophila association was studied in different environments (3 host‐populations, 2 temperatures, 2 viral dose). We measured pre‐adult mortality, developmental time and number of ovarioles per fly. In all experiments, and, in all contaminated populations, DCVC could be considered, either a parasite since it increased pre‐adult mortality, or a symbiont since it decreased developmental time and increased mean number of ovarioles. The viral dose necessary for the appearance of beneficial effects varied with population, temperature and life‐cycle parameters. A sufficient number of viral particles appears necessary at a specific point in the host life‐cycle for a beneficial DCVC effect on the host. DCVC does not affect the variance of any of these parameters. The observed changes in DCVC‐contaminated populations were thus not a response to the selection pressure of DCVC. Two arguments support the association as an example of the “cohabitation‐without‐struggle model” and will be discussed.
Evolution of clutch size in insects. II. A test of static optimality models using the beetle Callosobruchus maculatus (Coleoptera: Bruchidae)
Authors: Wilson Kenneth 
Published: December 2004

AbstractWilson and Lessells (1993) analysed the effect of constraint assumptions on the predictions of static optimality models for insect clutch size. They concluded that the models could be reliably distinguished between (and hence the main constraints identified) only after precise quantitative predictions had been examined. The present paper describes a series of laboratory experiments, using the bruchid beetle Callosobruchus maculatus, that allow these quantitative predictions to be made and tested. Experiments in which female encounter rate with hosts was altered gave qualitative support for 3 out of 6 basic (single oviposition) models, but the quantitative fit of them all was poor. However, when the (a priori) condition was included in these models that several other females would oviposit on the same hosts (the multiple oviposition models), the time limiting multiple oviposition model alone produced quantitative predictions that were supported by observations. In other words, the results suggest that the main constraints on bruchid oviposition behaviour are the amount of time available for laying eggs and the number of other females ovipositing. However, additional qualitative predictions indicate that the number of eggs available to the female may also constrain clutch size evolutionarily. The usefulness of static optimality models for examining clutch size decisions in insects is discussed in the context of these results.
The evolution of reaction norms: simple models for age and size at maturity
Authors: Berrigan David , Koella Jacob C. 
Published: December 2004

AbstractThis paper presents a simple model for the evolution of reaction norms for age and size at maturity that predicts reaction norms with a variety of shapes. Using realistic parameter values the model predicts reaction norms close to those observed in Drosophila. The major assumptions of the model are: 1) that net reproductive rate is maximized, 2) that growth is determinate, and 3) that mortality rates are independent of age and size at maturity. If, additionally, juvenile mortality is uncorrelated with a growth coefficient, k, the model predicts that selection favors maturation later at a smaller size when k is reduced by environmental factors and that decreased juvenile mortality leads to delayed maturity. These two predictions conform with those found by previous models using other measures of fitness. Correlations between k and juvenile mortality can change the shape of the predicted reaction norm. Depending on the precise form of the correlation, the model can predict done‐ or bowl‐shaped reaction norms and can predict delayed or earlier maturity as k decreases. These shapes are qualitatively different from those predicted by previous models that used different fitness measures. Systematic estimates of the parameter values for this and for related models are required to determine the appropriate fitness measure for models of reaction norms.
Selection on the genetical and environmental components of tarsal growth in juvenile willow tits (Parus montanus)
Authors: Thessing A. , Ekman J. 
Published: December 2004

AbstractWe studied selection on tarsus length among first year willow tits Parus montanus in relation to environmental and genetical influences on growth. The main environmental influence on growth was a cohort effect. We also found a substantial heritable component of phenotypic variation for tarsus length (h2 = 0.61), and crossfostering in one year showed no shared environment effect which could account for parent/offspring resemblance. The deteriorating conditions for growth later in the season did not confound our heritability estimates as the time of laying was not correlated to parent size, and no maternal effects operating through egg size were found. We tested for selection during the summer dispersal phase by comparing tarsus length among fullgrown pulli (age 14 days, controlled by repeated measurements of the same individuals later during breeding and the ensuing winter) and the tarsus length of the first year cohort in autumn composed of a mixture of locally born birds remaining within our study area after the dispersal phase and immigrants born outside the study site. Following a season with poor nestling growth, birds with short tarsi were selected against when underweight, suggesting that growth condition is the target of selection. Such selection on those individuals which show the strongest environmental influence on phenotypic variation will reduce the potential for an evolutionary response to selection.
Metapopulations: an arena for local speciation
Authors: Levin Donald A. 
Published: December 2004

AbstractSpeciation in many groups of plants and animals is thought to occur in single, isolated populations. Recent investigations of metapopulation longevity and genetic structure indicate that metapopulations have demographic and genetic properties which may be more conducive for local speciation than properties of single populations. It is argued that metapopulations may persist longer than single populations, that the former may retain genetic variation more readily, and that the former offers more opportunity for genomic reorganization.
The effects of relatedness on progeny sex ratio in spider mites
Authors: Roeder C. , Harmsen R. , Mouldey S. 
Published: December 2004

AbstractTheory predicts that optimal sex allocation in subdivided populations is dependent on the genetic relatedness among competing offspring such that when relatedness is high, progeny sex allocation should be more biased than when relatedness is low. In the laboratory we compared the progeny sex ratio of four groups of five ovipositing females of various presumed degrees of relatedness (sisters of inbred laboratory population, sisters of outbred field population, non‐sisters of the same field population and non‐sisters each from a different, geographically distant field population). We found a greater female bias in the progeny of inbred sisters than for sisters from the field population; the progeny sex ratio was also more strongly female biased for sisters than for non‐sisters from the field population. These differences in sex ratio are in line with theoretical predictions. Our results indicate that spider mites are capable of some method of discrimination between kin and non‐kin.
Placental hormones, genomic imprinting, and maternal—fetal communication
Authors: Haig D. 
Published: December 2004

AbstractPlacental hormones are produced by one genetic individual (the fetus) to act on the receptors of another genetic individual (the mother). Mothers are probably able to extract some information from placental hormones, but this information may be limited to a crude measure of fetal vigor. Placental hormones are most easily interpreted as fetal attempts to manipulate maternal metabolism for fetal benefit. An evolutionary model is presented for a hypothetical hormone that increases the nutrient content of maternal blood. The model predicts that, at an evolutionary equilibrium, the hormone will be produced solely by the mother or solely by the placenta, but not by both. If the gene for the hormone is subject to genomic imprinting, the paternally‐derived allele will be active and the maternally‐derived allele will be silent. Hormone production benefits the members of the mother's current litter at some cost to future litters. Therefore, paternity changes between litters increase the level of hormone production. On the other hand, offspring that produce less of the hormone than litter‐mates share the benefits but have lower costs. Therefore, multiple paternity within litters reduces the level of hormone production.