bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phenotypic selection and response to selection in Lobularia maritima: importance of direct and correlational components of natural selection
Authors: GÓmez  
Published: March 2003

Abstract
By using selection differentials, gradients and structural equation modelling (SEM), I have quantified the phenotypic selection acting on Lobularia maritima (Cruciferae) flower size, display, colour and density, using data on lifetime female fitness. Furthermore, by analysing the resulting F1 generation in field and greenhouse conditions, I estimated the actual intergenerational change in the value of these traits. Both pollinators preferred plants with many and large flowers. Strong directional selection for increased flower display was found in all years of the study, regardless of the technique used. Indirect selection due to a high significant correlation with flower display occurred on flower colour and size. SEM showed that pollinators played only a minor role in this observed phenotypic selection. The analysis of the phenotypes of F1 plants showed that flower display actually increased across generations. In addition, white flowers were significantly more frequent in the offspring population than in the parental one, mostly due to the association between flower display and white coloured flowers. This suggests that both direct and indirect selection can play a role in the evolution of correlated traits in this crucifer.
Mating frequency and resource allocation to male and female function in the simultaneous hermaphrodite land snail Arianta arbustorum
Authors: Locher  , Baur  
Published: March 2003

Abstract
Sex allocation theory predicts that mating frequency and long-term sperm storage affect the relative allocation to male and female function in simultaneous hermaphrodites. We examined the effect of mating frequency on male and female reproductive output (number of sperm delivered and eggs deposited) and on the resources allocated to the male and female function (dry mass, nitrogen and carbon contents of spermatophores and eggs) in individuals of the simultaneous hermaphrodite land snail Arianta arbustorum. Similar numbers of sperm were delivered in successive copulations. Consequently, the total number of sperm transferred increased with increasing number of copulations. In contrast, the total number of eggs produced was not influenced by the number of copulations. Energy allocation to gamete production expressed as dry mass, nitrogen or carbon content was highly female-biased (&gt;95% in all estimates). With increasing number of copulations the relative nitrogen allocation to the male function increased from 1.7% (one copulation) to 4.7% (three copulations), but the overall reproductive allocation remained highly female-biased. At the individual level, we did not find any trade-off between male and female reproductive function. In contrast, there was a significant positive correlation between the resources allocated to the male and female function. Snails that delivered many sperm also produced a large number of eggs. This finding contradicts current theory of sex allocation in simultaneous hermaphrodites.
Increased body size confers greater fitness at lower experimental temperature in male Drosophila melanogaster
Authors: Reeve  , Fowler  , Partridge  
Published: March 2003

Abstract
Genetic variation of body size along latitudinal clines is found globally in Drosophila melanogaster, with larger individuals encountered at higher latitudes. Temperature has been implicated as a selective agent for these clines, because the body size of laboratory populations allowed to evolve in culture at lower temperatures is larger. In this study, we investigated the hypothesis that larger size is favoured at lower temperature through natural selection on adult males. We measured life-span and age-specific fertility of males from lines of flies artificially selected for body size at two different experimental temperatures. There was an interaction between experimental temperature and body size selection for male fitness; large-line males were fitter than controls at both temperatures, but the difference in fitness was greater at the lower experimental temperature. Smaller males did not perform significantly differently from control males at either experimental temperature. The results imply that thermal selection for larger adult males is at least in part responsible for the evolution of larger body size at lower temperatures in this species. The responsible mechanisms require further investigation.
Epistatic interactions of spontaneous mutations in haploid strains of the yeast Saccharomyces cerevisiae
Authors: Wloch D. M. , Borts R. H. , Korona R. 
Published: March 2003

Abstract
Several important biological phenomena, including genetic recombination and sexual reproduction, could have evolved to counteract genome contamination by deleterious mutations. This postulate would be especially relevant if it were shown that deleterious mutations interact in such a way that their individual negative effects are reinforced by each other. The hypothesis of synergism can be tested experimentally by crossing organisms bearing deleterious mutations and comparing the fitness of the parents and their progeny. The present study used laboratory strains of the budding yeast burdened with mutations resulting from absence of a major DNA mismatch repair function. Only in one, or possibly two, crosses out of eight did fitness of the progeny deviate from that of their parents in a direction indicating synergism. Furthermore, the distributions of progeny fitness were not skewed as would be expected if strong interactions were present. The choice of experimental material ensured that genetic recombination was extensive, all four meiotic products were available for fitness assays, and that the mutations were probably numerous. Despite this generally favourable experimental setting, synergism did not appear to be a dominating force shaping fitness of yeast containing randomly generated mutations.
Wolbachia infection in crustaceans: novel hosts and potential routes for horizontal transmission
Authors: Cordaux R. , Michel-Salzat A. , Bouchon D. 
Published: March 2003

Abstract
Thirty-five percent of isopods are estimated to be infected by Wolbachia, an intracellular maternally inherited α-Proteobacterium. Previous studies have indicated that horizontal transfer of Wolbachia strains may occur, although the mechanisms are unclear. The wsp gene was sequenced from 17 Wolbachia strains harboured by crustacean host species and three from their associated predators and parasites. Two major clades of Wolbachia were found in crustacean, with relatives also found in insects, the other restricted to crustaceans. Highly divergent Wolbachia strains were found in a woodlouse-eating spider and its prey, suggesting no intertaxon bacterial exchange via the predator–prey route. The phylogenetic proximity of Wolbachia from parasitoid flies or phoretic mites to those from isopods suggests that horizontal symbiont transmission may have occurred between those taxa. Two distant Wolbachia strains were detected in two intertidal amphipods; these strains were closely related to different coastal isopod symbionts, suggesting Wolbachia transmission may occur between distantly related crustacean hosts living under the same ecological conditions.
The minor transitions in hierarchical evolution and the question of a directional bias
Authors: McShea D. W. 
Published: March 2003

Abstract
The history of life shows a clear trend in hierarchical organization, revealed by the successive emergence of organisms with ever greater numbers of levels of nestedness and greater development, or ‘individuation’, of the highest level. Various arguments have been offered which suggest that the trend is the result of a directional bias, or tendency, meaning that hierarchical increases are more probable than decreases among lineages, perhaps because hierarchical increases are favoured, on average, by natural selection. Further, what little evidence exists seems to point to a bias: some major increases are known – including the origin of the eukaryotic cell from prokaryotic cells and of animals, fungi and land plants from solitary eukaryotic cells – but no major decreases (except in parasitic and commensal organisms), at least at the cellular and multicellular levels. The fact of a trend, combined with the arguments and evidence, might make a bias seem beyond doubt, but here I argue that its existence is an open empirical question. Further, I show how testing is possible.
The evolution of polyandry: an examination of the genetic incompatibility and good-sperm hypotheses
Authors: Simmons L. W. 
Published: March 2003

Abstract
I have examined the adaptive significance of polyandry using the Australian field cricket Teleogryllus oceanicus. Previous studies of polyandry have examined differences in offspring production by females mated multiply to a single male or females mated multiply to different males. Here I combine this approach with a study of parentage of offspring produced in the later group. Females mated to two different males had a higher proportion of their eggs hatching than did females mating twice with a single male. Offspring fitness parameters were not effected. There was little evidence to suggest that females elevate their hatching success via fertilizing their eggs with sperm from genetically compatible males. Although the average paternity points towards random sperm mixing, there was considerable individual variation in sperm competition success. Patterns of parentage were consistent across females mating twice or four times. Sperm competition success was not related to offspring viability or performance. Thus, the notion that competitively superior sperm produce competitively superior offspring is not supported either. The mechanism underlying increased hatching success with polyandry requires further study.
Factors influencing paternity success in Antechinus agilis: last-male sperm precedence, timing of mating and genetic compatibility
Authors: Kraaijeveld-Smit F. J. L. , Ward S. J. , Temple-Smith P. D. , Paetkau D. 
Published: March 2003

Abstract
We describe the patterns of paternity success from laboratory mating experiments conducted in Antechinus agilis, a small size dimorphic carnivorous marsupial (males are larger than females). A previous study found last-male sperm precedence in this species, but they were unable to sample complete litters, and did not take male size and relatedness into account. We tested whether last-male sperm precedence regardless of male size still holds for complete litters. We explored the relationship between male mating order, male size, timing of mating and relatedness on paternity success. Females were mated with two males of different size with either the large or the small male first, with 1 day rest between the matings. Matings continued for 6 h. In these controlled conditions male size did not have a strong effect on paternity success, but mating order did. Males mating second sired 69.5% of the offspring. Within first mated males, males that mated closer to ovulation sired more offspring. To a lesser degree, variation appeared also to be caused by differences in genetic compatibility of the female and the male, where high levels of allele-sharing resulted in lower paternity success.
Body size does not predict species richness among the metazoan phyla
Authors: Orme C. D. L. , Quicke D. L. J. , Cook J. M. , Purvis A. 
Published: March 2003

AbstractWe present a comparative study of the relationship between body size and described taxonomic diversity in the Metazoa. We find no pattern between body size and taxonomic diversity; neither the smallest organisms nor organisms at an intermediate body size are consistently more diverse than their closest relatives. This conclusion holds for both nonphylogenetic analysis, in which phyla are treated as independent points, and analysis of independent contrasts using several recent hypotheses of metazoan phylogeny. These results appear surprising in the context of existing models of body size distributions. However, such models are built around the prevalence of right-skewed distributions and we find no evidence for such a distribution.
High resolution analysis of mating systems: inbreeding in natural populations ofPinus radiata
Authors: Vogl C. , Karhu A. , Moran G. , Savolainen O. 
Published: March 2003

AbstractPinus radiata has a history of population bottlenecks and is currently restricted to five relatively small populations, three in mainland California, and two on islands off the coast of Baja California. Using highly polymorphic microsatellite markers and a newly developed statistical approach, we were able to estimate individual inbreeding coefficients and can thus analyse the mating system with high resolution. We find a bimodal distribution of inbreeding coefficients: most individuals result from selfing whereas few (in the mainland populations) to a modest number (in the island populations) are likely selfed. In most other pine species and presumably in the ancestral P. radiata population, occurrence of mature selfed individuals would be impossible because of the high genetic load. We therefore conclude that inbreeding depression has been purged in P. radiata and that the mating system has changed as a consequence.
Genetic polymorphism in Caulerpa taxifolia (Ulvophyceae) chloroplast DNA revealed by a PCR-based assay of the invasive Mediterranean strain
Authors: . Famà P , Jousson O. , Zaninetti L. , Meinesz A. , Dini F. , Di Giuseppe G. , Millar A. J. K. , Pawlowski J. 
Published: March 2003

Abstract
An invasive, cold-tolerant strain of the tropical green alga Caulerpa taxifolia was introduced recently in the Mediterranean Sea and along the Californian coast. We screened 50 aquarium and open-sea C. taxifolia specimens for the presence/absence of an intron located in the rbcL gene of chloroplast DNA. We also reanalysed a total of 229 sequences of the Internal Transcribed Spacer (ITS) of ribosomal DNA, combining previously published sequences from different studies with 68 new sequences to complement rbcL data. The introduced Mediterranean strain was found to be characterized by the absence of the rbcL intron and by the occurrence of a particular monomorphic ITS type. A PCR assay based on rbcL gene was developed to detect new introductions of the invasive strain of C. taxifolia. This rapid and inexpensive test could be useful to assist environment managers in the preservation of coastal marine ecosystems.
Phylogeny and adaptive radiation in the Onychopoda (Crustacea, Cladocera): evidence from multiple gene sequences
Authors: Cristescu M. E. A. , Hebert P. D. N. 
Published: March 2003

Abstract
Members of the order Cladocera show remarkable morphological and ecological diversity. One of the most spectacular adaptive radiations in this group has involved species of the suborder Onychopoda, which have adopted a novel feeding strategy, predation, and have colonized habitats with a broad range of salinities. In order to evaluate the origins and systematics of this group, we derived a molecular phylogeny for its three component families including nine of 10 recognized genera based on three mitochondrial (mt) gene sequences: cytochrome c oxidase subunit I (COI), the ribosomal small and large subunits (12S and 16S) and one nuclear gene sequence: the small ribosomal subunit (18S). Maximum-parsimony, maximum-likelihood and neighbour-joining phylogenetic analyses were largely congruent, supporting the monophyly of the suborder and each of its families. Comparative analyses of data based on total evidence and the conditional combination of the ribosomal genes produced relatively congruent patterns of phylogenetic affinity. By contrast, analyses of single gene results were inconsistent in recovering the monophyletic groups identified by the multigene analyses. Based on the reconstructed phylogeny, we discriminate among the existing hypotheses regarding the evolutionary history of the onychopods. We identify a prolonged episode of speciation from the Miocene to the Pleistocene with two pulses of diversification. We discuss our results with reference to the geological history of the Ponto-Caspian basin, the region which fostered the onychopod radiation.
Ectoparasites cause increased bilateral asymmetry of naturally selected traits in a colonial bird
Authors: Brown Charles R. , Brown Mary Bomberger 
Published: March 2003

Abstract
Parasitism has been shown to correlate with levels of bilateral symmetry in some organisms, with more asymmetric individuals often having more parasites. However, few studies have shown experimentally that parasitism directly causes increased asymmetry. By fumigating some cliff swallow (Petrochelidon pyrrhonota) colonies and leaving others untreated, we investigated experimentally whether ectoparasitism by the cimicid swallow bug led to higher levels of asymmetry in length of wings, outer tail feathers, and tarsus among juvenile and adult birds. Juveniles from fumigated colonies measured soon after fledging had significantly less asymmetry in wing and outer tail length than juveniles from nonfumigated colonies; asymmetry in tarsus length was unaffected by parasitism. Adults that had undergone one or more post-juvenal molts on the wintering grounds showed no differences in asymmetry between those reared in fumigated vs. nonfumigated colonies. These results show that ectoparasitism directly leads to increased feather asymmetry in cliff swallows, probably through parasite-induced nutritional stress. Because wing and tail asymmetry impair flight performance and reduce foraging efficiency, the increased asymmetry caused by parasites represents a fitness cost to cliff swallows. This is among the few experimental studies to show an effect of parasites on asymmetry of naturally selected characters.
Evolution of dispersal in metapopulations with local density dependence and demographic stochasticity
Authors: Parvinen K. , Dieckmann U. , Gyllenberg M. , Metz J. A. J. 
Published: March 2003

Abstract
In this paper, we predict the outcome of dispersal evolution in metapopulations based on the following assumptions: (i) population dynamics within patches are density-regulated by realistic growth functions; (ii) demographic stochasticity resulting from finite population sizes within patches is accounted for; and (iii) the transition of individuals between patches is explicitly modelled by a disperser pool. We show, first, that evolutionarily stable dispersal rates do not necessarily increase with rates for the local extinction of populations due to external disturbances in habitable patches. Second, we describe how demographic stochasticity affects the evolution of dispersal rates: evolutionarily stable dispersal rates remain high even when disturbance-related rates of local extinction are low, and a variety of qualitatively different responses of adapted dispersal rates to varied levels of disturbance become possible. This paper shows, for the first time, that evolution of dispersal rates may give rise to monotonically increasing or decreasing responses, as well as to intermediate maxima or minima.
Heritability of resistance against ectoparasitism in the Drosophila–Macrocheles system
Authors: Polak M. 
Published: March 2003

Abstract
Ectoparasites are abundant in natural communities, can have pronounced deleterious fitness consequences to their host and are important vectors of transmissible parasitic disease. Yet very few studies have estimated the magnitude of heritable genetic variation underlying resistance against ectoparasitism, which significantly limits our ability to predict the evolution of this ecologically important character. The present paper reports results of artificial selection for increased resistance in Drosophila nigrospiracula against ectoparasitic, haematophagous mites, Macrocheles subbadius. In this system, which occurs naturally in the Sonoran Desert of North America, ectoparasitism significantly damages the expression of host fitness traits, including longevity, fecundity and male mating success. In the present study, resistance, which was modelled as a threshold trait, responded significantly to selection applied on either sex. Realized heritability, calculated as a mean across four replicates, was estimated to be 0.152 ± 0.014 (SE). The heritability estimate from selection on males did not differ from that on females, but both estimates differed significantly from zero. This documented presence of additive genetic variation for resistance, coupled with knowledge of the fitness consequences of ectoparasitism, indicates that the host population possesses significant evolutionary potential. Selection was applied on the pre-attachment phase, thereby targeting behavioural forms of defence. This study therefore establishes parallels between insects and other animals in their ability to protect themselves and evolve behavioural defences against ectoparasites.
A phallus for free? Quantitative genetics of sexual trade-offs in the snail Bulinus truncatus
Authors: Ostrowski M.-F. , Jarne P. , David P. 
Published: March 2003

Abstract
Resource allocation is thought to play a key role in the coexistence of different sexual morphs within hermaphroditic species. Indeed, most models assume that sexual functions are subject to a balance between reproductive advantage and energetic cost. Various types of cost (e.g. organ construction, maintenance and utilization) and levels of trade-off (physiological and genetic) may be considered. We here examine physiological and genetic costs of phallus construction and maintenance in Bulinus truncatus, a snail species in which aphallic individuals (without phallus) coexist with regular hermaphrodites. We use a quantitative genetic design involving 37 inbred lines (four populations) known to produce different proportions of aphallics, to test for the existence of genetic and nongenetic correlations between aphally and a range of life-history traits over the totality of the life cycle. Our results show that aphallic and euphallic individuals of the same line do not show consistent differences in either growth, fecundity (including offspring survival), or longevity. Furthermore, none of these traits is genetically correlated across lines with the frequency of the aphallic morph. We conclude that the cost of the construction and maintenance of the phallus must be very low in this species. Future studies should investigate the cost associated with using the phallus (i.e. male outcrossing behaviour) to explain the maintenance of high frequencies of aphallic individuals in natural populations.