bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationships of reproductive traits and body size with attainment of sexual maturity and age in Blanding's turtles (Emydoidea blandingi)
Authors: Congdon Justin D. , Van Loben Sels Richard C.
Published: December 2004

To place associations among body size, age at maturity, age, and reproductive traits of a long‐lived organism in the context of current life history models based on the concept of norms of reaction, we examined data from a mark‐recapture study of Blanding's turtles (Emydoidea blandingi) in southeastern Michigan during 24 of the years between 1953 and 1988. Females matured between 14 and 20 years of age. Both the smallest and largest adult females in the population were reproducing for the first time in their lives. This result suggests that a combination of differences in juvenile growth rates and ages at maturity, and not indeterminate growth, are the primary cause of variation in body size among adults. Body size variation among individuals was not related to age at sexual maturity. Females that had slower growth rates as juveniles matured later at similar mean body size compared to those with more rapid growth that matured at an earlier age. As a result, a linear model of age at sexual maturity with growth rates of primiparous females between hatching and maturity was significant and negative (R2 = 0.76). Frequency of reproduction of the largest and smallest females was not significantly different. Clutch size did not vary significantly with age among either primiparous or multiparous females. Clutch sizes of primiparous females and multiparous females were not significantly different. However, older females (>55 years minimum age) reproduced more frequently than did younger females (minimum age <36 y).
Genotypic variation for reproductive characters, and the influence of pollen‐ovule ratio on selfing rate in rape seed (Brassica napus)
Authors: Damgaard Christian , Loeschcke Volker
Published: December 2004

The variance component for genotypic effects and covariable plant vigor were estimated for pollen production, number of ovules, the weight of the flower without anther sacs and pistil, and the gender of the whole plant, in the rape seed variety Topas. There was a significant effect of the genotype for all measured characters. We did not find any trade‐off between the male and female functions. Small plants were relatively more male‐biased than large plants. The weight of the flower without anther sacs or pistil was positively correlated with pollen production. The selfing rates of the lines were positively correlated with the pollen‐ovule ratio, suggesting that the selfing rate of individual plants is positively correlated with pollen‐ovule ratio, thus supporting the “mass‐action” model. It is proposed that the observed increase in the population selfing rate during the flowering season for some species, including rape seed, can be caused by an overall decrease in male investment.
Reaction norms and the genetic basis of phenotypic plasticity in the wing pattern of the butterfly Bicyclus anynana
Authors: Windig J. J.
Published: December 2004

The genetic basis of the dry‐wet season polyphenism of wing pattern in response to temperature shown by Bicyclus anynana was studied, using a split‐family design over four temperatures. Reaction norms crossed, but were only linear in the three highest temperatures, and only when larval development time was used as the environmental axis. Significant full‐sib additive variances (VA) and heritabilities (h2) for plasticity were found using slopes of reaction norms in a bootstrap procedure. Heritabilities were lower in intermediate temperatures, mainly due to differences in the residual variances (VR). There was no clear trend in VA across temperatures, contrary to the expectation that VA would have been depleted by natural selection at the extreme temperatures and not depleted at the intermediate temperatures which occur less frequently in the field. Unpredictability in the onset of the following season at intermediate temperatures might lead to selection for diverse flresponses resulting in relatively high VRs. Theoretical models linking reaction norms to genetic parameters in separate environments were difficult to apply in this study, particularly because they are based on the assumption that VRs are constant. However the reaction norm approach combined with quantitative genetics provided a valuable insight into the evolution of the observed polyphenism.
Processes generating macroevolutionary patterns of morphological variation in birds: a simulation study
Authors: Björklund Mats
Published: December 2004

Multivariate patterns of morphological variation in birds are analysed. In general, there are strong allometric patterns among characters such that most of the variation is confined to a major “size” axis. To analyse the possible evolutionary processes behind this pattern I employed a computer simulation of cladogenesis and anagenesis based on a genetic and a random walk model (drift). All runs started with one species and speciation occurred to generate 100 species. Three levels of correlations were allowed. The results from the simulations were compared with the pattern of variation in finches (Fringillidae).

The simulations showed two things. First, the univariate drift model was inappropriate in terms of the level of variation; the observed level was lower than expected by drift. Univariate drift was also unable to create tight correlations among characters as observed in several taxa. Second, to create the pattern observed, either relatively strong genetic correlations (rg ≈ 0.5), or alternatively strong correlated selection, was needed. This suggests that morphological change in birds in general consists of changes in growth such that species become larger or smaller than their ancestors but retain their ancestral shape. The results stress the importance of stabilising selection in shaping the macroevolutionary patterns of morphological variation in birds.
Matching field and laboratory environments: effects of neglecting daily temperature variation on insect reaction norms
Authors: Brakefield Paul M. , Mazzotta Vincenzo
Published: December 2004

The tropical butterfly, Bicyclus anynana, exhibits seasonal polyphenism. The wet season form has large eyespots and a pale band while these characters are much less conspicuous or absent in the dry season form. This plasticity is induced in the laboratory by use of a standard series of constant temperatures in the larval stage yielding a continuous norm of reaction. Butterflies in this study were reared from hatchling larvae in seven regimes which differed with respect to thermoperiod or photoperiod. The effect of rearing treatment on the phenotypic plasticity of the adult wing pattern, on life history traits and on larval feeding rhythms was investigated. Photoperiod had little effect except that constant light produced a higher mortality and tended to produce a longer development time. Thermoperiod had a major effect on the life history traits in comparison to a constant temperature regime with the same daily mean: development time was shorter with higher growth rates. The faster development was associated with a substantial shift in the wing pattern towards the wet season form. Larvae feed mostly at night both under constant and thermoperiod (cool nights) conditions. The results are discussed with respect to the necessity of matching field and laboratory environments in studies of norms of reaction or of life history traits where the adaptive significance of the variation is important. Fluctuating conditions in nature, especially with respect to thermoperiod, must be taken into account.
Multiple morphs of sperm were required for the evolution of the Sex Ratio trait in Drosophila
Authors: Bircher U. , Jungen H. , Burch R. , Hauschteck‐Jungen E.
Published: December 2004

In Sex Ratio males of D. subobscura Y sperm degenerate. Nevertheless, Sex Ratio males can produce as many offspring as non‐Sex Ratio males. In order to find an explanation for the high number of offspring of Sex Ratio males we analysed spermatogenesis and sperm storage in females. Because D. subobscura has two morphs of sperm, short and long sperm, we studied the relationship of sperm heteromorphism to the Sex Ratio trait in this species.

Spermatids of both lengths developed simultaneously in the testes. The first mature sperm produced by a young male were nearly all short sperm. This result indicates that short cysts need less time to mature than long cysts. Thus in a given time more short cysts than long cysts can mature. In the testes of Sex Ratio males more short cysts and fewer long cysts were formed than in the tests of non‐Sex Ratio males. Thus in a unit time Sex Ratio males can produce as many or more sperm than non‐Sex Ratio males.

Females mated to Sex Ratio males had more sperm in their storage organs than those which were mated to non‐Sex Ratio males. From the transferred sperm females stored selectively more long than short sperm after mating to a Sex Ratio male than after mating to a non‐Sex Ratio male.

The effect of the high amount of sperm in Sex Ratio males is twofold: the loss of Y sperm is compensated, and probably in nature a second copulation is prevented by the complete filling of the female storage organs.

From these results we conclude that the development and persistence of the Sex Ratio trait in natural populations depends on the presence of sperm heteromorphism.
Ecological genetics of a cyclical parthenogen in temporary habitats
Authors: Gómez África , Temprano Miguel , Serra Manuel
Published: December 2004

Populations of the rotifer Brachionus plicatilis inhabiting three temporary ponds in Torreblanca Marsh (Castellón, Spain) were regularly screened for allozyme variation, sexual reproduction levels and population densities during an annual cycle. Relevant ecological parameters in the ponds were also recorded. The electrophoretic survey of the three ponds (Poza Sur, Poza Norte and Canal Central) revealed a high level of overall genetic polymorphism in four marker loci, but only 13 multilocus genotypes were found. We classified clones into three clonal groups (SS, SM, L) characterized by unique arrays of alleles in the four marker loci, and significant differences in body shape and size. Clonal group succession took place in Poza Sur; SM clones occurring in spring, SS clones from spring to fall, and L clones from fall to spring. Despite the partial overlapping of sexual periods, the absence of heterozygotes indicates that gene flow is strongly restricted between clonal groups. In the transition periods, the population was far from Hardy—Weinberg equilibrium due to hetereozygote deficiencies in all four markers. In clonal group L, the only polymorphic locus, Pgi, was in Hardy—Weinberg equilibrium. In clonal group SM, both polymorphic loci were in Hardy—Weinberg equilibrium in Poza Norte, but not in Poza Sur. Factor analysis on the limnological parameters recorded during field sampling indicates that genetically different clonal groups are also ecologically specialized. These findings suggest that the taxonomical species B. plicatilis is in fact a species complex. The complete genetic discontinuity model of rotifer population succession is supported by these data. Our results are similar to those found in cladocerans inhabiting temporary habitats.
Good genes and old age: Do old mates provide superior genes?
Authors: Hansen T. F. , Price D. K.
Published: December 2004

It has been suggested that female preference for older mates in species without parental care has evolved in response to an alleged higher genetic quality of older individuals. This is based on the widespread assumption that viability selection produces older individuals that are genetically superior to younger individuals. In contrast, we propose that the oldest individuals rarely are genetically superior. Quantitative genetic models of life history evolution indicate that young to intermediately aged individuals are likely to possess the highest breeding values of fitness. This conclusion is based on four arguments: 1) Viability selection on older individuals may decrease or at least not substantially increase breeding values of fitness, because there may exist negative genetic correlations between late‐age and early‐age life history parameters, 2) Fertility selection is likely to raise the fitness of gametes produced by young individuals more than those produced by old individuals, because the covariance between fertility and fitness often decreases with age, 3) The history of selection on their parents makes younger individuals more fit than older individuals, 4) Germ‐line mutations, which are generally deleterious, significantly decrease the breeding value of fitness of an individual throughout its lifespan, especially in males. Therefore, females that mate with the oldest males in a population are doing so for reasons other than to obtain offspring of high genetic quality.
Genetic evidence for natural hybridization and apparent introgression between freshwater snail species (Viviparus ater and V. contectus)
Authors: Katoh M. , Ribi G.
Published: December 2004

We examined six allozyme markers and shell morphology to study gene flow between the naturally sympatric freshwater snail species Viviparus ater and V. contectus in Lake Garda, Italy, using offspring from experimental crosses and snails collected from natural populations. Hybrid offspring obtained from experimental crosses and hybrids collected from natural populations were heterozygous at four or five out of five diagnostic loci. Shell morphology was a poor predictor of the hybrid status of individual snails. Backcrossed offspring from experimentally bred hybrids and either of the parental species morphologically resembled the parental species. There was no evidence of segregation distortion at the six loci. Linkage analysis revealed one pair of linked loci (GPI and PNP). These cross experiments indicated a Mendelian type hybrid system in which gene introgression may occur. F1 hybrids were found at four out of six sampling sites of Lake Garda, Italy. Local frequencies of F1 hybrids ranged from 0% to 1.6% (estimated average = 0.74%) of the total population including both species. Alleles typical of V. ater were found at low frequencies in V. contectus at all six sampling sites. Alleles typical of V. contectus were found at low frequencies in V. ater at three out of six sampling sites. This is consistent with the hypothesis of introgression in both directions.
A hybrid zone between two subspecies of Chorthippus parallelus. X‐chromosome variation through a contact zone
Authors: Serrano L. , García de la Vega C. , Bella J. L. , López‐Fernández C. , Hewitt G. M. , Gosálvez J.
Published: December 2004

Two grasshopper subspecies, Chorthippus parallelus parallelus (Cpp) and Chorthippus parallelus erythropus (Cpe), meet along the Pyrenees where they hybridize and produce a hybrid zone. A contact zone located in the Col de Portalet has been analyzed for the distribution of chromosome markers on the sex (X) chromosome in pure and hybrid populations. C‐banding allowed us to distinguish both pure subspecific forms and recombinant forms, and to demonstrate their different frequencies through the contact zone. Interestingly, the distal C‐band (P) on the X chromosome that characterizes Cpp individuals occurs at very high frequency through the zone and then drops sharply, close to where pure Cpe populations are found. A novel interstitial C‐band (H) has been found, probably derived from that characterizing Cpe individuals (E). This marker band is only present in hybrid populations. These data are discussed in the light of the dynamics of the hybrid zone.
Causes of covariation of phenotypic traits among populations
Authors: Armbruster W. S. , Schwaegerle K. E.
Published: December 2004

Morphological and life‐history traits often vary among populations of a species. Traits generally do not vary independently, but show patterns of covariation that can arise from genetic and environmental influences on phenotype. Covariance of traits may arise at an among‐population level when genetically influenced traits diverge among populations in a correlated manner. Genetic correlations caused by pleiotropy and/or gene linkage can cause traits to evolve together, but among‐population covariance can also arise among traits that are not genetically correlated. For example, “selective covariance” can arise when natural selection directly causes correlated change in a suite of traits. Similarly, mutation, migration, and drift may also sometimes cause correlated genetic changes among populations. Because covariation of traits among populations can arise by several different processes, the evolution of suites of traits must be interpreted with great caution. We discuss the sources of among‐population covariance and illustrate one approach to identifying the sources' using data on floral traits of Dalechampia scandens (Euphorbiaceae).
Polymorphism of the Drosophila melanogaster — sigma virus system
Authors: Fleuriet A.
Published: December 2004

In natural populations of D. melanogaster, a minority of flies are usually infected by the sigma Rhabdovirus, which is not contagious but vertically transmitted. A few parameters have been identified that affect the evolution of the Drosophila — sigma system. Various sets of values of these parameters in males mutually adapted to one another have been established in different populations. This study analyses female characteristics that were previously reputed not to vary much between populations. The newly collected data show that these characteristics (mainly transovarial transmission here) may also be polymorphic in the wild, and may contribute to the diversity of equilibria established between the virus and its host. The observations presented here, obtained from various populations, confirm the complexity of this system of two coevolving organisms: as already noted there seem to be as many different sets of values of parameters as there are populations.
Variable selection on Eurosta's gall size, III: Can an evolutionary response to selection be detected?
Authors: Weis A. E.
Published: December 2004

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

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

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

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

A method is presented for the estimation of nucleotide diversity and genetic structure of populations from RAPD (random amplified polymorphic DNA) data. It involves a modification of the technique developed by Lynch and Crease (1990) for the case of restriction sites as survey data. As new elements the method incorporates (i) dominance correction, (ii) values of asexual reproduction of the populations sampled, and (iii) an analytical variance of the number of nucleotide substitutions per site.

Sampling was carried out at two geographic scales for three aphid species. At a macrogeographic scale, populations of Rhopalosiphum padi did not show statistical genetic differentiation. Aphis gossypii and Myzus persicae, which were sampled at a microgeographic scale, showed a higher genetic differentiation than R. padi, it being statistically significant in M. persicae. The major sources of sampling variance within‐ and between‐populations were found to be nucleotide (i.e., the number of alleles used as a function of the number of primers used) and population (i.e., sample size) sampling.

Extremely low estimates of nucleotide diversity were obtained for the species studied here. This result is consistent with previous reports on genetic diversity for the same or other aphid species which were based on allozyme polymorphism, mitochondrial DNA variation and qualitative analyses of RAPDs.
Molecular phylogeny of the tribe Bovini (Mammalia: Artiodactyla): alternative placement of the Anoa
Authors: Pitra C. , Fürbass R. , Seyfert H.‐M.
Published: December 2004

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

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

In gynodioecious species, male steriles co‐occur with hermaphrodites. Usually, the male sterile trait is maternally inherited, hence it is called Cytoplasmic Male Sterility (CMS). Nuclear loci restore male fertility in combination with their ‘own’ specific cytoplasmic types. In theory, two fitness components are important for the maintenance of this breeding system: a fitness advantage of the male steriles, and costs of restoration. The costs of restoration are alleged negative pleiotropic effects of restorer alleles.

In this study the effects of different CMS types on plant performance and the cost of restoration were assessed in two experiments with Plantago lanceolata L. Biomass production differed significantly between the CMS types studied. In order to assess the costs of restoration, hermaphrodites with or without restorer alleles for a CMS type other than its own were compared. The studied restorer alleles caused a reduction in weight per seed, but the number of seeds produced was unaffected. The estimated cost of restoration measured as reduction of seed biomass was 13% for restorer alleles for CMSI. However, in the second experiment no pleiotropic effects of restorer alleles were detected, either because the assumptions for the experimental set‐up were not valid or the costs of restoration may not always be expressed.
Selection caused by self‐fertilization
Authors: Ziehe M. , Gregorius H.‐R.
Published: December 2004

The generally held view that increased self‐fertilization should be advantageous in the absence of counteracting selective forces reducing viability or fertility is reexamined. It is pointed out that the models on which this view is based all imply a gain in male (pollen) fertility with increased selfing. Hence, the postulated advantage may equally well be due to increased fertility, a fact which reopens the discussion on the selective significance of differential selfing.

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

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

In this paper we study the evolutionary dynamics of delayed maturation in semelparous individuals. We model this in a two‐stage clonally reproducing population subject to density‐dependent fertility. The population dynamical model allows multiple — cyclic and/or chaotic — attractors, thus allowing us to illustrate how (i) evolutionary stability is primarily a property of a population dynamical system as a whole, and (ii) that the evolutionary stability of a demographic strategy by necessity derives from the evolutionary stability of the stationary population dynamical systems it can engender, i.e., its associated population dynamical attractors.

Our approach is based on numerically estimating invasion exponents or “mutant fitnesses”. The invasion exponent is defined as the theoretical long‐term average relative growth rate of a population of mutants in the stationary environment defined by a resident population system. For some combinations of resident and mutant trait values, we have to consider multi‐valued invasion exponents, which makes the evolutionary argument more complicated (and more interesting) than is usually envisaged. Multi‐valuedness occurs (i) when more than one attractor is associated with the values of the residents' demographic parameters, or (ii) when the setting of the mutant parameters makes the descendants of a single mutant reproduce exclusively either in even or in odd years, so that a mutant population is affected by either subsequence of the fluctuating resident densities only.

Non‐equilibrium population dynamics or random environmental noise selects for strategists with a non‐zero probability to delay maturation. When there is an evolutionarily attracting pair of such a strategy and a population dynamical attractor engendered by it, this delaying probability is a Continuously Stable Strategy, that is an Evolutionarily Unbeatable Strategy which is also Stable in a long term evolutionary sense. Population dynamical coexistence of delaying and non‐delaying strategists is possible with non‐equilibrium dynamics, but adding random environmental noise to the model destroys this coexistence. Adding random noise also shifts the CSS towards a higher probability of delaying maturation.
The maintenance of phenotypic and genetic variation in threshold traits by frequency‐dependent selection
Authors: Roff D. A.
Published: December 2004

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

The relationship between the number of open flowers and pollen transfer to stigmas was estimated in three insect‐pollinated species (Cynoglossum officinale, Echium vulgare and Oenothera erythrocepala) in 1995 and 1996, using fluorescent dye as a pollen analogue. Dye was applied to an equal number of flowers on a small, a medium and a large individual and its pattern of dispersal to stigmas of conspecifics in local populations was observed.

In Cynoglossum officinale and in Echium vulgare large individuals tended to receive more visits per flower. In Oenothera erythrocepala no difference in number of visits per flower was found between small and large individuals.

Geitonogamous pollination clearly occurred in all species. In Cynoglossum officinale large individuals transferred more pollen per flower within the same plant (geitonogamy) and an equal or a slightly smaller amount between plants, compared to small individuals. As a result total pollen transfer per flower increased in both years with increasing flower number. In Echium vulgare and in Oenothera erythrocepala large individuals transferred more pollen per flower within the plant (pollen discounting), but a significantly lower amount per flower to other individuals in the populations compared to small individuals. For both these species, there is no difference in total pollen transfer between small and large individuals.

In general, the male fitness curve, as estimated by pollen transfer, is a decelerating function of flower number. We discuss this in relation to optimal sex‐allocation and the pollen donation hypothesis.
Fluctuating asymmetry, body size and sexual selection in the dung fly Sepsis cynipsea — testing the good genes assumptions and predictions
Authors: Blanckenhorn W. U. , Reusch T. , Mühlhäuser C.
Published: December 2004

In the dung fly Sepsis cynipsea large and more symmetric males have been shown to enjoy a mating advantage, but we still do not know which mechanism of sexual selection is responsible. Here we test several assumptions and predictions relating to the hypothesis that either trait is indicative of ‘good genes’. We tested for good genes by regressing fitness in good and bad environments (no and high larval competition, respectively) on the family mean for size or asymmetry as expressed in the good environment, separately for both sexes. Body size (hind tibia length or head width) was positively correlated with female fecundity, growth rate of both sexes and larval survivorship for males, but only in the good environment. The corresponding evidence for asymmetry is more equivocal. Mean standardised asymmetry was weakly associated with lower survivorship in the good environment, while growth rates and female fecundity were not. As predicted by sexual selection theory, fore tibia length showed greater asymmetry than other, presumably not sexually selected traits, and asymmetry in fore tibia length was greater for males than females. However, a negative correlation between trait size and asymmetry was only evident for male seta length but not for fore tibia length, fore femur length, or any composite measure of asymmetry. Most crucially, asymmetry was heritable for some female morphological traits (hind tibia length: h2 = 0.15; fore femur length: h2 = 0.16; mean of all measured traits: h2 = 0.27), but not for any male trait. Also, asymmetry of the various traits measured was not correlated within males and only weakly so within females. The crucial assumption that asymmetry of sexually selected traits reflects overall, heritable developmental stability of an individual is thus only partly substantiated by our data. In contrast, large body size is heritable, associated with high fitness and consequently could be indicative of good genes. Fore leg asymmetry may influence male mating success by simply mechanically constraining his ability to hold on to the female.
Extra-nuclear effects on growth and development in the sand cricket Gryllus firmus
Authors: Roff D. A. , Sokolovska N.
Published: December 2004

Although largely ignored until recently, parental effects on the phenotypes of their offspring are both ubiquitous in nature and of a potentially great importance to evolution. Our study examines the presence of extra-nuclear (maternal and paternal) effects in growth traits, development time and adult size in the sand cricket Gryllus firmus using a diallel cross of inbred lines. Sex linkage was shown to be nonsignificant for development time but the other traits could not be tested. We assume that they are nonsignificant but use the term ‘reciprocal’ effects to include this effect. We show that reciprocal effects are present in the growth traits and development time, where they account for 10–30% of the phenotypic variance. They are not present in adult size as indexed by head width. We demonstrate that reciprocal effects are due, at least in part, to maternal effects by an analysis of the positive correlation between egg size, a maternal trait, and the growth traits. The growth rate traits show no significant decline with age either with respect to extra-nuclear contributions to variance or difference between phenotypic means of reciprocal pairs. This study demonstrates that extra-nuclear effects are important contributors to the phenotypic variation in life history traits of G. firmus.
Disruption of structural and functional integrity of α2‐macroglobulin by cathepsin E
Authors: Shibata Mitsue , Sakai Hideaki , Sakai Eiko , Okamoto Kuniaki , Nishishita Kazuhisa , Yasuda Yoshiyuki , Kato Yuzo , Yamamoto Kenji
Published: December 2004

α2‐Macroglobulin (α2M) is an abundant glycoprotein with the intrinsic capacity for capturing diverse proteins for rapid delivery into cells. After internalization by the receptor‐ mediated endocytosis, α2M‐protein complexes were rapidly degraded in the endolysosome system. Although this is an important pathway for clearance of both α2M and biological targets, little is known about the nature of α2M degradation in the endolysosome system. To investigate the possible involvement of intracellular aspartic proteinases in the disruption of structural and functional integrity of α2M in the endolysosome system, we examined the capacity of α2M for interacting with cathepsin E and cathepsin D under acidic conditions and the nature of its degradation. α2M was efficiently associated with cathepsin E under acidic conditions to form noncovalent complexes and rapidly degraded through the generation of three major proteins with apparent molecular masses of 90, 85 and 30 kDa. Parallel with this reaction, α2M resulted in the rapid loss of its antiproteolytic activity. Analysis of the N‐terminal amino‐acid sequences of these proteins revealed that α2M was selectively cleaved at the Phe811‐Leu812 bond in about 100mer downstream of the bait region. In contrast, little change was observed for α2M treated by cathepsin D under the same conditions. Together, the synthetic SPAFLA peptide corresponding to the Ser808–Ala813 sequence of human α2M, which contains the cathepsin E‐cleavage site, was selectively cleaved by cathepsin E, but not cathepsin D. These results suggest the possible involvement of cathepsin E in disruption of the structural and functional integrity of α2M in the endolysosome system.
The thermodynamic analysis of protein stabilization by sucrose and glycerol against pressure‐induced unfolding
Authors: Ruan Kangcheng , Xu Chunhe , Li Tingting , Li Jiong , Lange Reinhard , Balny Claude
Published: December 2004

We have studied the reaction native ⇆ denatured for the 33‐kDa protein isolated from photosystem II. Sucrose and glycerol have profound effects on pressure‐induced unfolding. The additives shift the equilibrium to the left; they also cause a significant decrease in the standard volume change (ΔV). The change in ΔV was related to the sucrose and glycerol concentrations. The decrease in ΔV varied with the additive: sucrose caused the largest effect, glycerol the smallest. The theoretical shift of the half‐unfolding pressure (P1/2) calculated from the net increase in free energy by addition of sucrose and glycerol was lower than that obtained from experimental mea‐ surements. This indicates that the free energy change caused by preferential hydration of the protein is not the unique factor involved in the protein stabilization. The reduction in ΔV showed a large contribution to the theoretical P1/2 shift, suggesting that the ΔV change, caused by the sucrose or glycerol was associated with the protein stabilization. The origin of the ΔV change is discussed. The rate of pressure‐induced unfolding in the presence of sucrose or glycerol was slower than the refolding rate although both were significantly slower than that observed without any stabilizers.