bluuebunny/crossref_metadata_2025 huggingface dataset:
Small sperm, uniparental inheritance and selfish cytoplasmic elements: a comparison of two models
Authors: Randerson  , Hurst
Published: March 2003

It has previously been suggested that small sperm size may be an adaptation to achieve uniparental inheritance of organelles, and hence to prevent the spread of selfish cytoplasmic elements. Such an explanation for anisogamy implies a mechanism whereby the male gamete eliminates its own cytoplasm prior to fusion with the egg. A model has been presented demonstrating the invasion and persistence of a modifier that acts gametically to kill its own organelles. Here we show, however, that this model is far from robust; indeed, if any cost is associated with the modifier it cannot persist. We also show that despite an empirically demonstrated association between anisogamy and multicellularity, this result also applies if the analysis is applied in the multicellular case. This class of model contrasts with the majority of analyses in which the modifier kills off the incoming gamete’s organelles. We show that these models are highly robust, even if uniparental inheritance is imperfect.
The role of maternal and paternal effects in the evolution of parental quality by sexual selection
Authors: Wolf  , Brodie  , Moore
Published: March 2003

Genetic models of maternal effects and models of mate choice have focused on the evolutionary effects of variation in parental quality. There have been, however, few attempts to combine these into a single model for the evolution of sexually selected traits. We present a quantitative genetic model that considers how male and female parental quality (together or separately) affect the expression of a sexually selected offspring trait. We allow female choice of males based on this parentally affected trait and examine the evolution of mate choice, parental quality and the indicator trait. Our model reveals a number of consequences of maternal and paternal effects. (1) The force of sexual selection owing to adaptive mate choice can displace parental quality from its natural selection optimum. (2) The force of sexual selection can displace female parental quality from its natural selection optimum even when nonadaptive mate choice occurs (e.g. runaway sexual selection), because females of higher parental quality produce more attractive sons and these sons counterbalance the loss in fitness owing to over-investment in each offspring. (3) Maternal and paternal effects can provide a source of genetic variation for offspring traits, allowing evolution by sexual selection even when those traits do not show direct genetic variation (i.e. are not heritable). (4) The correlation between paternal investment and the offspring trait influenced by the parental effects can result in adaptive mate choice and lead to the elaboration of both female preference and the male sexually selected trait. When parental effects exist, sexual selection can drive the evolution of parental quality when investment increases the attractiveness of offspring, leading to the elaboration of indicator traits and higher than expected levels of parental investment.
Measuring morphological complexity of segmented animals: centipedes as model systems
Authors: Fusco  , Minelli
Published: March 2003

In segmented animals it is possible to define morphological complexity as the degree of morphological differentiation of segments. A quantitative method for measuring morphological complexity of segmental patterns was devised by McShea in 1992, who introduced three geometrical indices. Here, we introduce a new index of morphological complexity and emphasize the possible decoupling between segmentation and segment differentiation and illustrate different patterns of variation within segmental series and how these could affect morphological evolution and evolvability. Concepts are illustrated by contrasting the segmental models of two groups of centipedes (Chilopoda): the elongate Geophilomorpha and the short-bodied Lithobiomorpha. A preliminary application of the new metric provides no evidence of macroevolutionary increase in morphological complexity of centipede segmental organization.
Choice, performance and heritability of performance of specialist and generalist insect herbivores towards cacalol and seneciphylline, two allelochemicals of Adenostyles alpina (Asteraceae)
Authors: Hägele  , Rowell-Rahier
Published: March 2003

We compared the effects of a sesquiterpene (ST, cacalol) and a pyrrolizidine alkaloid (PA, seneciphylline), both occurring in Adenostyles alliariae, on food choice and performance of specialist and generalist insect herbivores which are all known to feed or live on A. alliariae. In choice experiments we investigated whether the compounds were preferred, deterrent or had no effect. All specialist species Aglaostigma discolor (Hymenoptera, Tenthredinidae), Oreina cacaliae (Coleoptera, Chrysomelidae) and O. speciosissima avoided feeding when confronted with the combination of compounds. Only larvae of A. discolor avoided the single ST treatment as well. Larvae of the generalist species Callimorpha dominula (Lepidoptera, Arctiidae), Cylindrotoma distinctissima (Diptera, Tipulidae) and Miramella alpina (Caelifera, Acrididae) generally avoided feeding from PA, ST and PAST treatments. The only exception were caterpillars of C. dominula which were indiscriminate towards PA when naive, and preferred to feed on the PA treatment when they had experienced the compound before.

Performance, measured as the growth of larvae on the different treatments in a no choice situation over a period of 10–17 days, was not different between treatments in the specialist leaf beetles O. cacaliae and O. speciosissima. Their avoidance of the combination treatment in the choice experiments had no obvious effect on growth when forced to feed from the treatment. In the generalist C. dominula only the high concentration combination treatment (PAST) reduced growth of the larvae due to decreased consumption. In C. distinctissima we found reduced growth in all treatments except one (PA3%). Poor growth performance in C. distinctissima was due to postingestive physiological effects of all treatments and additionally to consumption reduction in high-dose ST treatments.

Genetic variability (broad sense heritability) of growth performance metabolism varied in accordance with the specialization degree of the species. O. cacaliae, the most specialized species, had no significant heritability; O. speciosissima, the less specialized specialist, had a heritability of 0.46; C. dominula, the PA adapted generalist species, had a heritability of 0.64; C. distinctissima, the generalist with no apparent adaptations, had a heritability of 0.84.
Fluctuating asymmetry of sexual and nonsexual traits in stalk-eyed flies: a poor indicator of developmental stress and genetic quality
Authors: Bjorksten  , David  , Pomiankowski  , Fowler
Published: March 2003

It has been proposed that females use fluctuating asymmetry (FA) in sexual ornaments to assess male quality. FA of sexual traits is predicted to show greater sensitivity to stress than FA of nonsexual traits, and to be heritable. We used a half-sib mating design and manipulation of larval food environment to test these predictions on stalk-eyed flies, Cyrtodiopsis dalmanni, in which females prefer males with larger eyespans. We measured size and FA of eyestalks and of two nonsexually selected characters, wing length and width. We found no evidence of an increase in FA under larval food stress in any of the individual traits, although trait size decreased under stress. We combined FA across traits into a single composite index, and found that males reared in the most benign larval environment had significantly higher composite FA than males reared on other media. There was no such effect in females. Heritability of FA was not significantly different from zero in any of the traits, in any of the environments, although trait sizes showed high heritability. We conclude that FA in sexual and nonsexual traits is a poor indicator of developmental stress and genetic quality.
The courtship song of African Drosophila melanogaster
Authors: Colegrave  , Hollocher  , Hinton  , Ritchie
Published: March 2003

For many years it was thought that Drosophila melanogaster was relatively panmictic, without differentiation in the Mate Recognition System. Recent studies have demonstrated that flies from Africa vary in pheromones and assortative mating. Strains from Zimbabwe show strong sexual isolation from others. We show that the interpulse interval (IPI) of courtship song, an important mating signal, is unusually short among African flies. Zimbabwean flies have the shortest IPI, but there is no correlation with assortative mating, suggesting little direct role in sexual isolation. Chromosome replacements show that the IPI difference is largely due to genes on chromosome III, with significant interactions involving other chromosomes. Several traits potentially influencing sexual isolation among the melanogaster group of Drosophila seem to be localized to this chromosome. A concentration of important genetic differences might mean that the interaction effects reflect secondary coadaptation of the genetic background to changes associated with chromosome III.
Variation in the frequency of the echolocation calls of Hipposideros ruber in the Gulf of Guinea: an exploration of the adaptive meaning of the constant frequency value in rhinolophoid CF bats
Authors: Guillén  , Juste B.  , Ibáñez
Published: March 2003

This study describes variation patterns in the constant frequency (CF) segment of echolocation calls of the bat Hipposideros ruber within and among populations across the region of the Gulf of Guinea. Correlations of variation in CF with variation in body size, body condition, environmental humidity and presence of ecologically similar species are studied in an attempt to identify the forces driving the evolution of CF. We found that bats may adapt the frequency to humidity, and that CF may evolve under interspecific interactions, either of ecological or of social nature. The results support an adaptive value for the high values of CF, and challenge the ‘Allotonic Frequency Hypothesis’. We found correlation between frequency and a body condition index, which may trigger social selection processes in this species sexually dimorphic in CF. Combined social and environmental selection on CF could trigger diversification of bats along ecotones separating habitats with contrasting air humidity.
Clonal integration in Ranunculus reptans: by-product or adaptation?
Authors: Van Kleunen  , Fischer  , Schmid
Published: March 2003

We studied fitness consequences of clonal integration in 27 genotypes of the stoloniferous herb Ranunculus reptans in a spatially heterogeneous light environment. We grew 216 pairs of connected ramets (eight per genotype) with mother ramets in light and daughter ramets in shade. In half of the pairs we severed the stolon connection between the two ramets at the beginning of the experiment. During the experiment, 52.7% of the ramet pairs with originally intact connection physically disintegrated. We detected significant variation among genotypes in this regard. Survival of planted ramets was 13.3% higher for originally connected pairs. Moreover, there was significant variation among genotypes in survival, in the difference in survival between plant parts developing from mother and daughter ramets, and in the effect of integration on this difference. In surviving plants connection between ramets decreased size differences between mother and daughter parts. Variation among genotypes was significant in growth and reproduction and marginally significant in the effect of physiological integration on growth and reproduction. Connected daughter ramets had longer leaves and internodes than daughters in severed pairs indicating that integration stimulated plant foraging in both the vertical and the horizontal plane. Observed effects of integration on fitness components in combination with genetic variation in maintenance and effects of connection indicate that clonal integration in R. reptans has the capability to evolve, and therefore suggest that clonal integration is adaptive. If genetic variation in integration is common, future studies on clonal integration should always use defined genetic material and many clones to allow extrapolation of results to population and wider levels.
Nonheterochronic developmental changes underlie morphological heterochrony in the evolution of the Ardeidae
Authors: Cubo  , Fouces  , González-Martín  , Pedrocchi  , Ruiz
Published: March 2003

Evolutionary changes in developmental timing and rates (heterochrony) are a source of morphological variation. Here we explore a central issue in heterochronic analysis: are the alterations in developmental timing and rates the only factor underlying morphological heterochrony? Tarsometatarsal growth through endochondral ossification in Ardeidae evolution has been taken as a case study. Evolutionary changes in bone growth rate (morphological heterochrony) might be either (a) the result of alterations in the mitotic frequency of epiphyseal chondrocytes (process-heterochrony hypothesis), or (b) the outcome of alterations in the number of proliferating cells or in the size of hypertrophic chondrocytes (structural hypothesis). No correlation was found between tarsometatarsal growth rates and the frequency of cell division. However, bone growth rates were significantly correlated with the number of proliferating cells. These results support the structural hypothesis: morphological acceleration and deceleration are the outcome of evolutionary changes in one structural variable, the number of proliferating cells.
Intraspecific variation in sex allocation in hermaphroditic Plantago coronopus (L.)
Authors: Koelewijn  , Hunscheid
Published: March 2003

Models for sex allocation assume that increased expenditure of resources on male function decreases the resources available for female function. Under some circumstances, a negative genetic correlation between investment in stamens and investment in ovules or seeds is expected. Moreover, if fitness returns for investment in male and female function are different with respect to size, sex allocation theory predicts size-specific gender changes. We studied sex allocation and genetic variation for investment in stamens, ovules and seeds at both the flower and the plant level in a Dutch population of the wind-pollinated and predominantly outcrossing Plantago coronopus. Data on biomass of floral structures, stamens, ovules, seedset and seedweight were used to calculate the average proportion of reproductive allocation invested in male function. Genetic variation and (genetic) correlations were estimated from the greenhouse-grown progeny of maternal families, raised at two nutrient levels. The proportion of reproductive biomass invested in male function was high at flowering (0.86 at both nutrient levels) and much lower at fruiting (0.30 and 0.40 for the high and low nutrient treatment, respectively). Androecium and gynoecium mass exhibited moderately high levels of genetic variance, with broad-sense heritabilities varying from 0.35 to 0.56. For seedweight no genetic variation was detected. Significant among-family variation was also detected for the proportion of resources invested in male function at flowering, but not at fruiting. Phenotypic and broad-sense genetic correlations between androecium and gynoecium mass were positive. Even after adjusting for plant size, as a measure of resource acquisition, maternal families that invested more biomass in the androecium also invested more in the gynoecium. This is consistent with the hypothesis that genetic variation for resource acquisition may in part be responsible for the overall lack of a negative correlation between male and female function. Larger plants had a more female-biased allocation pattern, brought about by an increase in seedset and seedweight, whereas stamen biomass did not differ between small and large plants. These results are discussed in relation to size-dependent sex allocation theory (SDS). Our results indicate that the studied population harboured substantial genetic variation for reproductive characters.
Fluctuating asymmetry and fitness in Drosophila melanogaster
Authors: Bourguet
Published: March 2003

Models predict that developmental stability measured by fluctuating asymmetry should be positively correlated with fitness. Although such a correlation has often been suggested by indirect studies, there is still a lack of direct experimental evidence. In this note, I have measured the fluctuating asymmetry of sternopleural bristle counts in 32 lines of Drosophila melanogaster sharing the same genetic background but displaying all combinations of five visible mutations. Fluctuating asymmetry was heterogeneous among lines, suggesting a direct impact of the mutations on developmental stability. Two measures of fitness were made for each line: productivity (a combined measure of fecundity and egg-to-adult survivorship) and competitive male mating success. Fluctuating asymmetry was correlated with neither of these two components of fitness. This suggests that generalizations about fluctuating asymmetry must be taken with care.
Human longevity at the cost of reproductive success: evidence from global data
Authors: Thomas  , Teriokhin  , Renaud  , De Meeûs  , Guégan
Published: March 2003

A trade-off between reproduction and somatic maintenance and hence survival is fundamental to life-history theory. We investigated the relationship between female fecundity and longevity in Homo sapiens using data from 153 countries located all over the world. The raw correlation between life span and fecundity was highly significant with a negative trend. After longevity and fecundity estimates were controlled for by confounding factors such as historical (i.e. human ethnic groups), religious, geographical, socio-economical and parasitological components, we still observed a negative relationship between the mean female fecundity and the mean longevity in a country. These findings support the hypothesis for the existence of a trade-off between these two key life-history traits in humans, as also reported by a recent single longitudinal study in England.
Spatial autocorrelation of allozyme and quantitative markers within a natural population of Centaurea jacea (Asteraceae)
Authors: Hardy  , Vanderhoeven  , Meerts  , Vekemans
Published: March 2003

This paper compares the fine-scale genetic structure of quantitative traits and allozyme markers within a natural population of Centaurea jacea s.l. To that end, a spatial autocorrelation approach is developed based on pairwise correlation coefficients between individuals and using sib families. Statistical properties of the proposed statistics are investigated with numerical simulations. Our results show that most quantitative traits have a significant spatial structure for their genetic component. On average, allozyme markers and the genetic component of quantitative traits have similar patterns of spatial autocorrelation that are consistent with a neutral model of isolation by distance. We also show evidence that environmental heterogeneity generates a spatial structure for the environmental component of quantitative traits. Results are discussed in terms of mechanisms generating spatial structure and are compared with those obtained on a large geographical scale.
Sponge paraphyly and the origin of Metazoa
Authors: Borchiellini C. , Manuel M. , Alivon E. , Boury-Esnault N. , Vacelet J. , Le Parco Y.
Published: March 2003

In order to allow critical evaluation of the interrelationships between the three sponge classes, and to resolve the question of mono- or paraphyly of sponges (Porifera), we used the polymerase chain reaction (PCR) to amplify almost the entire nucleic acid sequence of the 18S rDNA from several hexactinellid, demosponge and calcareous sponge species. The amplification products were cloned, sequenced and then aligned with previously reported sequences from other sponges and nonsponge metazoans and variously distant outgroups, and trees were constructed using both neighbour-joining and maximum parsimony methods. Our results suggest that sponges are paraphyletic, the Calcarea being more related to monophyletic Eumetazoa than to the siliceous sponges (Demospongiae, Hexactinellida). These results have important implications for our understanding of metazoan origins, because they suggest that the common ancestor of Metazoa was a sponge. They also have consequences for basal metazoan classification, implying that the phylum Porifera should be abandoned. Our results support the upgrading of the calcareous sponge class to the phylum level.
Changes in thermotolerance and Hsp70 expression with domestication in Drosophila melanogaster
Authors: Krebs R. A. , Roberts S. P. , Bettencourt B. R. , Feder M. E.
Published: March 2003

To examine how the duration of laboratory domestication may affect Drosophila stocks used in studies of thermotolerance, we measured expression of the inducible heat-shock protein Hsp70 and survival after heat shock in D. melanogaster strains recently collected from nature and maintained in laboratory culture for up to 50 or more generations. After an initial increase in both Hsp70 expression and thermotolerance immediately after transfer to laboratory medium, both traits remained fairly constant over time and variation among strains persisted through laboratory domestication. Furthermore, variation in heat tolerance and Hsp70 expression did not correlate with the length of time populations evolved in the laboratory. Therefore, while environmental variation likely contributed most to early shifts in strain tolerance and Hsp70 expression, other population parameters, for example genetic drift, inbreeding, and selection likely affected these traits little. As long as populations are maintained with large numbers of individuals, the culture of insects in the laboratory may have little effect on the tolerance of different strains to thermal stress.
Propagule interactions and the evolution of virulence
Authors: Lively C. M.
Published: March 2003

The evolution of parasite virulence is thought to involve a trade-off between parasite reproductive rate and the effect of increasing the number of propagules on host survivorship. Such a trade-off should lead to selection for an intermediate level of within-host reproduction (λ). Here I consider the effects of parasite propagule number on selection affecting λ when (i) the effect of each propagule is independent of propagule number, and (ii) when the effect of each propagule changes as a function of propagule number. Virulence evolves in these models as a correlated response to selection on λ. If each propagule has the same effect (s) as all previous propagules, the survivorship of infected hosts is reduced by more than 60% at equilibrium, independent of the value of s. If, instead, each propagule has a more negative effect on host survivorship than previous propagules, host survivorship at equilibrium is expected to increase as the effect becomes more pronounced. These results are directly parallel to results derived for population mean fitness at mutation-selection balance; and they suggest that high virulence should be associated with parasites for which the effect of adding propagules either remains constant or diminishes with propagule number.
Polyandry and colony genetic structure in the primitive ant Nothomyrmecia macrops
Authors: Sanetra M. , Crozier R. H.
Published: March 2003

The Australian endemic ant Nothomyrmecia macrops is considered one of the most ‘primitive’ among living ants. We investigated the genetic structure of colonies to determine queen mating frequencies and nestmate relatedness. An average of 18.8 individuals from each of 32 colonies, and sperm extracted from 34 foraging queens, were genotyped using five highly variable microsatellite markers. Queens were typically singly (65%) or doubly mated (30%), but triple mating (5%) also occurred. The mean effective number of male mates for queens was 1.37. No relationship between colony size and queen mate number was found. Nestmate workers were related by b=0.61 ± 0.03, significantly above the threshold under Hamilton’s rule over which, all else being equal, altruistic behaviour persists, but queens and their mates were unrelated. In 25% of the colonies we detected a few workers that could not have been produced by the resident queen, although there was no evidence for worker reproduction. Polyandry is for the first time recorded in a species with very small mature colonies, which is inconsistent with the sperm-limitation hypothesis for the mediation of polyandry levels. Facultative polyandry is therefore not confined to the highly advanced ant genera, but may have arisen at an early stage in ant social evolution.
Evolution of floral display in Eichhornia paniculata (Pontederiaceae): genetic correlations between flower size and number
Authors: Worley A. C. , Barrett S. C. H.
Published: March 2003

The evolution of floral display is thought to be constrained by trade-offs between the size and number of flowers and inflorescences. We grew in the glasshouse 60 maternal families from each of two Brazilian populations of the annual herb, Eichhornia paniculata. We measured flower size, daily flower number, and total flower number per inflorescence, and two indices of module size, leaf area and age at flowering. We also assessed the size and number of inflorescences produced over 6 weeks. All floral traits exhibited significant heritable variation, some of which was due to genetic variation in module size. Genetic (maternal family) correlations between daily and total flower number did not differ from 1.0, indicating that display size (daily flower number) cannot evolve independently from total flower number per inflorescence. Genetic correlations between flower size and daily flower number ranged from negative to positive (r=–0.78 to +0.84), depending on population and inflorescence. Positive correlations occurred when variation in investment per inflorescence was high so that some families produced both larger and more flowers. These correlations became zero when we controlled for variation in module size. Families that flowered later produced fewer, larger inflorescences (r=–0.33, –0.85). These data support theoretical predictions regarding the combined effects of variation in resource acquisition and allocation on traits involved in trade-offs, and they emphasize the hierarchical organization of floral displays. Our results imply that patterns of resource allocation among inflorescences influence evolutionary changes in flower size and number per inflorescence.
Insularity and adaptation in coupled victim–enemy associations
Authors: Hochberg M. E. , Møller A. P.
Published: March 2003

Employing a mathematical model we show how insularity, genotypic interactions and victim life-history/demography can influence adaptation in a simple enemy–victim interaction where genotypes migrate between a large source and a smaller, initially unoccupied, isolated habitat. We find that when there are explicit costs to heightened enemy virulence and victim resistance, large/close islands resemble their immigration sources, whereas small and/or distant islands tend to be occupied only by the least defended victims and least virulent enemies. In a model with no explicit cost to genotypic identity, frequencies do not differ on average between source and island. Despite these trends in genotype frequencies, for a range of realistic conditions, both cost and cost-free genotypic interactions yield an increase in the frequency of resistant encounters as a function of isolation. Moreover, in models with explicit costs, maximal island to island variation in genotypic frequencies is found on islands of intermediate distance from the source. In contrast, the model without explicit costs produces more variable communities, attaining maximum variability in genotypic frequencies at the most isolated islands. We hypothesize that adaptive patterns in mainland–island comparisons may differ substantially from those generated by centre-periphery comparisons in continental systems.
The evolutionary significance of parasitism: do parasite-driven genetic dynamics occur ex silico?
Authors: Little T. J.
Published: March 2003

It has long been recognized that reciprocal antagonism might lock host and parasite populations into a process of constant change, adapting and reacting in open-ended coevolution. A significant body of theory supports this intuition: dynamic genetic polymorphisms are a common outcome of computer simulations of host–parasite coevolution. These in silico experiments have also shown that dynamical interactions could be responsible for high levels of genetic diversity in host populations, and even be the principle determinant of rates of genetic recombination and sexuality. The evolutionary significance of parasitism depends on the strength and prevalence of parasite-mediated selection in nature. Here I appraise whether parasitism is a pervasive agent of evolutionary change by detailing empirical evidence for selection. Although there is considerable evidence of genetic variation for resistance, and hence the potential for selection, direct observation of parasite-driven genetic change is lacking.
Evolutionary aspects of the metapopulation dynamics of Biomphalaria pfeifferi, the intermediate host of Schistosoma mansoni
Authors: Charbonnel N. , Angers B. , Rasatavonjizay R. , Bremond P. , Jarne P.
Published: March 2003

Combining genetic and demographic data is a powerful approach to study adaptation process and evolutionary forces acting in natural populations. We focus on the freshwater snail Biomphalaria pfeifferi, the intermediate host of Schistosoma mansoni. Twenty-one populations sampled in the south of Madagascar were genotyped at six microsatellite loci. Demographic parameters and parasitic prevalence were estimated monthly over the year preceding the genetic sampling. Our results indicate that populations experience recurrent bottlenecks and size fluctuations, which strongly depresses the genetic diversity within population. The recolonization of depleted sites involves genetically differentiated immigrants. We detected frequent migration events along rivers and rare migration events between watersheds. This explains the high level of differentiation observed among populations. The negative regression observed between the prevalence of S. mansoni and the genetic diversity of B. pfeifferi populations indicates that host consanguinity may affect prevalence through the genetic mechanisms involved in resistance. Coevolutionary outcomes are also influenced by the relative migration rates of snails and flukes, but the parasite local adaptation may be prevented by rare long distance dispersal in snails and the phylogeographical patterns of colonization of both hosts and snails.
Local adaptation, evolutionary potential and host–parasite coevolution: interactions between migration, mutation, population size and generation time
Authors: Gandon S. , Michalakis Y.
Published: March 2003

Local adaptation of parasites to their sympatric hosts has been investigated on different biological systems through reciprocal transplant experiments. Most of these studies revealed a local adaptation of the parasite. In several cases, however, parasites were found to be locally maladapted or neither adapted nor maladapted. In the present paper, we try to determine the causes of such variability in these results. We analyse a host–parasite metapopulation model and study the effect of several factors on the emergence of local adaptation: population sizes, mutation rates and migration rates for both the host and the parasite, and parasite generation time. We show that all these factors may act on local adaptation through their effects on the evolutionary potential of each species. In particular, we find that higher numbers of mutants or migrants do, in general, promote local adaptation. Interestingly, shorter parasite generation time does not always favour parasite local adaptation. When genetic variability is limiting, shorter generation time, via an increase of the strength of selection, decreases the capacity of the parasite to adapt to an evolving host.
Reverse evolution of fitness in Drosophila melanogaster
Authors: Teotónio H. , Matos M. , Rose M. R.
Published: March 2003

The evolution of fitness is central to evolutionary theory, yet few experimental systems allow us to track its evolution in genetically and environmentally relevant contexts. Reverse evolution experiments allow the study of the evolutionary return to ancestral phenotypic states, including fitness. This in turn permits well-defined tests for the dependence of adaptation on evolutionary history and environmental conditions. In the experiments described here, 20 populations of heterogeneous evolutionary histories were returned to their common ancestral environment for 50 generations, and were then compared with both their immediate differentiated ancestors and populations which had remained in the ancestral environment. One measure of fitness returned to ancestral levels to a greater extent than other characters did. The phenotypic effects of reverse evolution were also contingent on previous selective history. Moreover, convergence to the ancestral state was highly sensitive to environmental conditions. The phenotypic plasticity of fecundity, a character directly selected for, evolved during the experimental time frame. Reverse evolution appears to force multiple, diverged populations to converge on a common fitness state through different life-history and genetic changes.
Longevity and resistance to cold stress in cold-stress selected lines and their controls in Drosophila melanogaster
Authors: Norry F. M. , Loeschcke V. R.
Published: March 2003

Thermal environments can influence many fitness-related traits including life span. Here, we assess whether longevity in Drosophila melanogaster can experimentally evolve as a correlated response to cold-stress selection, and whether genotype-by-temperature and sex-by-temperature interactions are significant components of variation in life span. Three replicated S lines were cold-stress selected and compared with their respective unselected controls (Clines) in the 16th generation of thermal selection. Cold-stress resistance exhibited a substantial direct response to selection, and also showed a significant interaction between sex and type of line. Mean longevity exhibited a significant interaction between adult test temperature (14 and 25 °C) and line (with suggestive evidence for increased longevity of S lines when tested at 14 °C), but there was no evidence for increased longevity in S lines at normal temperatures (i.e. 25 °C). Another temperature-dependent effect was sex-specific, with males being the longer lived sex at 25 °C but the less long-lived sex at 14 °C. Additionally, we tested in an exploratory way the relationship between longevity and cold-stress resistance by also measuring resistance to a prefreezing temperature before and after one generation of longevity selection at 14 °C (selection intensity, i = 1.47 for S lines, and 1.42 for C lines). In this longevity selection, we found that cold-stress resistance increased by about 6% in S lines and 18% in C lines. However, taken together, the results indicate no simple relationship between longevity and cold-stress resistance, with genotype-by-sex interactions in both traits. Temperature dependent interaction in longevity is apparent between S and C lines, and sex-specific variation in mean longevity also depends on temperature.
Confidence of paternity and paternal care: covariation revealed through the experimental manipulation of the mating system in the beetle Onthophagus taurus
Authors: Hunt J. , Simmons L. W.
Published: March 2003

Theoretical models of paternal care predict that facultative reductions in male care may occur under certain conditions. One important parameter that has been shown to influence the outcome of these models is a male's confidence of paternity. In this study, we tested whether the amount of care provided by horned males in the dimorphic beetle, Onthophagus taurus, varied with his confidence of paternity. Male care results in an increased weight of dung provided in the brood masses produced by the pair. Using the sterile male technique we showed that a horned male's paternity declined with the number of sneak males in the population. The relationship was nonlinear, with paternity declining most rapidly between a frequency of one and three sneaks, and stabilizing thereafter at about 50%. A horned male's paternity was directly related to the number of copulations with the female, relative to the number of copulations achieved by sneaks. Horned males were shown to reduce their care in relation to their declining paternity. Video analysis demonstrated that reductions in male care occurred through a combination of male desertion and a trade-off between caring and paternity assurance behaviours. The number of fights with sneak males was negatively related to the amount of care provided by a horned male. These results suggest that by gauging his expected paternity through the number of fights with sneaks, a horned male is able to assess his paternity and reduce his investment accordingly. Our data thus provide strong empirical support for the proposed link between paternity and paternal care.
Contrasting effects of Wolbachia on cytoplasmic incompatibility and fecundity in the haplodiploid mite Tetranychus urticae
Authors: Perrot-Minnot M.-J. , Cheval B. , Migeon A. , Navajas M.
Published: March 2003

Recent studies on Wolbachia-induced incompatibility in haplodiploid insects and mites have revealed a diversity of cytoplasmic incompatibility (CI) patterns among host species. Here, we report intraspecific diversity in CI expression among four strains of the arrhenotokous mite Tetranychus urticae and in T. turkestani. Variability of CI expression within T. urticae ranged from no CI to complete CI, and included either female embryonic mortality or male conversion types of CI. A fecundity cost attributed to the infection with the high-CI Wolbachia strain was the highest ever recorded for Wolbachia (−80 to −100% decrease). Sequence polymorphism at a 550-bp-portion of Wolbachia wsp gene revealed two clusters distant by 21%, one of which included three Wolbachia strains infecting mite populations sampled from the same host-plant species, but showing distinct CI patterns. These data are discussed in the light of theoretical predictions on the evolutionary pathways followed in this symbiotic interaction.
The origin of a ‘true’ worker caste in termites: phylogenetic evidence is not decisive
Authors: Grandcolas P. , D'Haese C.
Published: March 2003

The phylogenetic study of the origin of a ‘true’ worker caste in termites by Thompson et al. [J. Evol. Biol. 13 (2000) 869] did not take into account all possibilities of character coding and character optimization on the phylogenetic tree. Actually, contrary to the authors' statements, the phylogenetic evidence presented does not permit to answer decisively most of the questions asked concerning the origin and evolution of worker castes in termites. Particular attention was paid to assumptions implied by the coding of the characters of interest, namely concerning the homology between pseudergates and a ‘true’ worker caste and the kind of the cockroach life type.
Evolution of the capacity to evolve
Authors: Carroll R. L.
Published: March 2003

During the past two decades, the fields of molecular biology and genetics have enabled study of far broader and more detailed aspects of evolutionary change than were possible when the evolutionary synthesis was elaborated in the mid-twentieth century. The capacity for complete sequencing of both genes and proteins of all groups of organisms provide, simultaneously, the means to determine both the patterns and processes of evolution throughout the history of life. Increased knowledge of the genome documents the changing nature of its composition, mode of transmission, and the nature of the units of selection. Advances in evolutionary developmental biology demonstrate the conservation of genetic elements throughout multicellular organisms, and explain how control of the timing, position and nature of their expression has produced the extraordinary diversity of living plants and animals. The next generation of evolutionary biologists will benefit greatly from the increased integration of these new fields of research with those that are currently emphasized in the standard textbooks and journals.
Detecting genetic variation in developmental instability by artificial selection on fluctuating asymmetry
Authors: Fuller R. C. , Houle D.
Published: March 2003

Fluctuating asymmetry (FA) is frequently used as a measure of developmental instability (DI). Assuming a genetic basis to DI, many have argued that FA may be a good indicator of genetic quality to potential mates and to human managers of populations. Unfortunately FA is a poor indicator of DI, making it very difficult to verify this assertion. A recent review of the literature suggests that previous studies of the inheritance of FA and DI using half-sib covariances and parent–offspring regression have been unable to put meaningful limits on the heritability of FA and DI because of the extremely low power of the experiments performed. In this study, we consider the power of artificial selection on FA as an alternative approach to studying the inheritance of FA and DI. Using simulations, we investigate the efficacy of selection for both increased and decreased FA for detecting genetic variation. We find that selection for increased FA has much more power to detect the presence of genetic variation than does selection for decreased FA. These results hold when realistic sample sizes are employed. Artificial selection for increased FA is currently the most powerful approach for the detection of genetic variation in DI.
Spatially structured genetic variation in a broadcast spawning bivalve: quantitative vs. molecular traits
Authors: Luttikhuizen P. C. , Drent J. , Van Delden W. , Piersma T.
Published: March 2003

Understanding the origin, maintenance and significance of phenotypic variation is one of the central issues in evolutionary biology. An ongoing discussion focuses on the relative roles of isolation and selection as being at the heart of genetically based spatial variation. We address this issue in a representative of a taxon group in which isolation is unlikely: a marine broadcast spawning invertebrate. During the free-swimming larval phase, dispersal is potentially very large. For such taxa, small-scale population genetic structuring in neutral molecular markers tends to be limited, conform expectations. Small-scale differentiation of selective traits is expected to be hindered by the putatively high gene flow. We determined the geographical distribution of molecular markers and of variation in a shell shape measure, globosity, for the bivalve Macoma balthica (L.) in the western Dutch Wadden Sea and adjacent North Sea in three subsequent years, and found that shells of this clam are more globose in the Wadden Sea. By rearing clams in a common garden in the laboratory starting from the gamete phase, we show that the ecotypes are genetically different; heritability is estimated at 23%. The proportion of total genetic variation that is between sites is much larger for the morphological additive genetic variation (QST = 0.416) than for allozyme (FST = 0.000–0.022) and mitochondrial DNA cytochrome-c-oxidase-1 sequence variation (ΦST = 0.017). Divergent selection must be involved and intraspecific spatial genetic differentiation in marine broadcast spawners is apparently not constrained by low levels of isolation.
Cerebral and peripheral near‐infrared spectroscopy: an alternative transfusion trigger?
Authors: Torella F. , Haynes S. L. , McCollum C. N.
Published: March 2003

Background and Objectives To develop a transfusion trigger based on tissue oxygenation, near‐infrared spectroscopy (NIRS) was evaluated in a model of compensated haemorrhage.

Patients and Methods Regional haemoglobin oxygen saturation from the cerebral cortex (CsO2) and the gastrocnemius muscle (PsO2) was monitored (using an INVOS 4100 near‐infrared oximeter) in 30 patients during acute normovolaemic haemodilution to a target haemoglobin of 11 g/dl. Arterial oxygen saturation, end‐tidal carbon dioxide tension, mean arterial pressure and haemoglobin concentration were also measured.

Results During blood collection, CsO2 and PsO2 fell by a mean (95% CI) of 8 (5·3–10·7)% (P < 0·001) and 5·5 (3·2–7·8)% (P < 0·001), respectively. Arterial pressure and oxygen saturation did not change, whilst the end‐tidal carbon dioxide tension fell by 2·3 (0·8–3·8) mmHg (P = 0·004). Haemoglobin concentration correlated with CsO2 (R = 0·76, P < 0·001) and PsO2 (R = 0·63, P < 0·001), as did the volume of blood removed.

Conclusions CsO2 and PsO2 fell predictably during compensated blood loss. With further research, NIRS may be developed into a transfusion trigger.
Validation of flow cytometry to quantify the potency of anti‐D immunoglobulin preparations
Authors: Schäffner G. , Kayser T. , Tönjes A. , Volkers P.
Published: March 2003

Background and Objectives Flow cytometry has been recommended as an alternative to that of autoanalyser methodology for estimation of anti‐D potency. This investigation was performed to validate the flow cytometry method based on a quality assurance system.

Materials and Methods A flow cytometry method based on indirect labelling of Rh(D)‐positive red blood cells was validated using the parameters precision and accuracy and was compared to the autoanalyser data of manufacturers of anti‐D immunoglobulin preparations.

Results The experiment first investigated the possible differences between assays from single donors compared with a pooled assay. Red blood cells of four individual donors and their pooled red blood cells were interchangeable. There was no significant difference between donors, on one hand, and between the use of a single donation and the pooled red blood cells, on the other hand (P = 0·695). The two‐sided 95% confidence intervals (CIs) of the difference between single donors and the pool ranged from −4·6% to 4·7%. The intermediate variability was determined by standard deviation (SD) = 48·4 IU/ml [coefficient of variation (CV) = 3·8%]; the repeatability was SD = 34·3 IU/ml (CV = 2·7%). Using a spiking experiment, the second part of the experiment investigated recovery of a known anti‐D potency. The recovery of samples spiked with defined amounts of reference preparation was 97·7–101%, with a mean bias of −1·3 (95% CI: −4·1 to 1·6). The results of the flow cytometry assay, as compared to those of the autoanalyser performed by the manufacturers of anti‐D immunoglobulin preparations for those manufacturers who have their method validated in‐house, ranged from 87 to 129%, indicating good correlation.

Conclusions Flow cytometry is a suitable quality control method for polyclonal anti‐D immunoglobulins, which can be standardized in a quality control laboratory using a quality assurance system.