bluuebunny/crossref_metadata_2025_split huggingface dataset:
Biomimetic evolutionary analysis: testing the adaptive value of vertebrate tail stiffness in autonomous swimming robots
Authors: Long J. H. , Koob T. J. , Irving K. , Combie K. , Engel V. , Livingston N. , Lammert A. , Schumacher J. 
Published: November 2006

SUMMARYFor early vertebrates, a long-standing hypothesis is that vertebrae evolved as a locomotor adaptation, stiffening the body axis and enhancing swimming performance. While supported by biomechanical data, this hypothesis has not been tested using an evolutionary approach. We did so by extending biomimetic evolutionary analysis (BEA), which builds physical simulations of extinct systems, to include use of autonomous robots as proxies of early vertebrates competing in a forage navigation task. Modeled after free-swimming larvae of sea squirts (Chordata, Urochordata), three robotic tadpoles (`Tadros'), each with a propulsive tail bearing a biomimetic notochord of variable spring stiffness, k (N m-1), searched for, oriented to, and orbited in two dimensions around a light source. Within each of ten generations, we selected for increased swimming speed, U (m s-1) and decreased time to the light source, t (s),average distance from the source, R (m) and wobble maneuvering, W (rad s-2). In software simulation, we coded two quantitative trait loci (QTL) that determine k: bending modulus, E (Nm-2) and length, L (m). Both QTL were mutated during replication, independently assorted during meiosis and, as haploid gametes, entered into the gene pool in proportion to parental fitness. After random mating created three new diploid genotypes, we fabricated three new offspring tails. In the presence of both selection and chance events(mutation, genetic drift), the phenotypic means of this small population evolved. The classic hypothesis was supported in that k was positively correlated (r2=0.40) with navigational prowess, NP, the dimensionless ratio of U to the product of R, t and W. However, the plausible adaptive scenario, even in this simplified system, is more complex, since the remaining variance in NP was correlated with the residuals of R and U taken with respect to k, suggesting that changes in k alone are insufficient to explain the evolution of NP.
Magnetic compass in the cornea: local anaesthesia impairs orientation in a mammal
Authors: Wegner Regina E. , Begall Sabine , Burda Hynek 
Published: November 2006

SUMMARY
The mechanism of signal transduction during magnetic compass orientation is rarely evident in vertebrates and is as yet unknown in mammals. This transmission has been associated with magnetite-based receptors innervated by the ophthalmic nerve or with the involvement of the eye, particularly the retina. We provide the first behavioural support for the cornea carrying the respective primary sensors in mole-rats (Fukomys anselli) by showing that local anaesthesia disrupts their normal directional magnetic orientation. During corneal anaesthesia in normal geomagnetic conditions, mole-rats did not maintain their preferred nesting direction, but displayed a random orientation pattern. A second experiment showed that the ability of the mole-rat to discriminate between light and dark was not impeded by the same anaesthetic treatment, suggesting no retinal involvement in mole-rat magnetic orientation. Our study restricts the peripheral primary sensors in mole-rats to the ophthalmic region, probably the cornea and indicates magnetite as the responsible signal mediator.
Structure and sexual dimorphism of the electrocommunication signals of the weakly electric fish,Adontosternarchus devenanzii
Authors: Zhou Muchu , Smith G. Troy 
Published: November 2006

SUMMARYElectrocommunication signals of electric fish vary across species, sexes and individuals. The diversity of these signals and the relative simplicity of the neural circuits controlling them make them a model well-suited for studying the mechanisms, evolution and sexual differentiation of behavior. In most wave-type gymnotiform knifefishes, electric organ discharge (EOD)frequency and EOD modulations known as chirps are sexually dimorphic. In the most speciose gymnotiform family, the Apteronotidae, EOD frequency is higher in males than females in some species, but lower in males than females in others. Sex differences in EOD frequency and chirping, however, have been examined in only three apteronotid species in a single genus, Apteronotus. To understand the diversity of electrocommunication signals, we characterized these behaviors in another genus, Adontosternarchus. Electrocommunication signals of Adontosternarchus devenanzii differed from those of Apteronotus in several ways. Unlike in Apteronotus, EOD frequency was not sexually dimorphic in A. devenanzii. Furthermore,although A. devenanzii chirped in response to playbacks simulating conspecific EODs, the number of chirps did not vary with different stimulus frequencies. A. devenanzii chirps also differed in structure from Apteronotus chirps. Whereas Apteronotus species produce functionally distinct chirp types differing in frequency modulation (FM), A. devenanzii produced only high-frequency chirps that had either single or multiple frequency peaks. Males produced more multi-peaked chirps than females. Thus, the temporal structure of chirps, rather than the amount of FM, delineated chirp types in A. devenanzii. Our results demonstrate that the structure, function and sexual dimorphism of electrocommunication signals are evolutionary labile in apteronotids and may be useful for understanding the diversity of sexually dimorphic behavior.
Lipid remodeling in wild and selectively bred hard clams at low temperatures in relation to genetic and physiological parameters
Authors: Pernet Fabrice , Tremblay Réjean , Gionet Chantal , Landry Thomas 
Published: November 2006

SUMMARYA temperature decrease usually induces an ordering effect in membrane phospholipids, which can lead to membrane dysfunction. Poikilotherms inhabiting eurythermal environments typically counteract this temperature effect by remodeling membrane lipids as stipulated in the homeoviscous adaptation theory (HVA). Hard clams, Mercenaria mercenaria, can suffer high overwintering mortalities in the Gulf of St Lawrence, Canada. The selectively bred M. mercenaria var. notata can have higher overwintering mortalities than the wild species, thus suggesting that the two varieties have different degrees of adaptation to low temperatures. The objective of this study was to investigate the changes in lipid composition of soft tissues in wild and selected hard clams in relation to their metabolic and genetic characteristics. Clams were placed at the northern limit of their distribution from August 2003 to May 2004; they were exposed to a gradual temperature decrease and then maintained at &lt;0°C for 3.5 months. This study is the first to report a major remodeling of lipids in this species as predicted by HVA; this remodeling involved a sequential response of the phospholipid to sterol ratio as well as in levels of 22:6n-3 and non-methylene interrupted dienoic fatty acids. Hard clams showed an increase in 20:5n-3 as temperature decreased, but this was not maintained during overwintering, which suggests that 20:5n-3 may have been used for eicosanoid biosynthesis as a stress response to environmental conditions. Selectively bred hard clams were characterized by a higher metabolic demand and a deviation from Hardy-Weinberg equilibrium at several genetic loci due to a deficit in heterozygote frequency compared with wild clams, which is believed to impose additional stress and render these animals more vulnerable to overwintering mortality. Finally, an intriguing finding is that the lower metabolic requirements of wild animals coincide with a lower unsaturation index of their lipids, as predicted by Hulbert's theory of membranes as pacemakers of metabolism.
A comparison of visual and haltere-mediated feedback in the control of body saccades inDrosophila melanogaster
Authors: Bender John A. , Dickinson Michael H. 
Published: November 2006

SUMMARYThe flight trajectories of fruit flies consist of straight flight segments interspersed with rapid turns called body saccades. Although the saccades are stereotyped, it is not known whether their brief time course is due to a feed-forward (predetermined) motor program or due to feedback from sensory systems that are reflexively activated by the rapid rotation. Two sensory modalities, the visual system and the mechanosensory halteres, are likely sources of such feedback because they are sensitive to angular velocities within the range experienced during saccades. Utilizing a magnetic tether in which flies are fixed in space but free to rotate about their yaw axis, we systematically manipulated the feedback from the visual and haltere systems to test their role in determining the time course of body saccades. We found that altering visual feedback had no significant effect on the dynamics of saccades, whereas increasing and decreasing the amount of haltere-mediated feedback decreased and increased saccade amplitude, respectively. In other experiments, we altered the aerodynamic surface of the wings such that the flies had to actively modify their wing-stroke kinematics to maintain straight flight on the magnetic tether. Flies exhibit such modification, but the control is compromised in the dark, indicating that the visual system does provide feedback for flight stability at lower angular velocities, to which the haltere system is less sensitive. Cutting the wing surface disrupted the time course of the saccades, indicating that although flies employ sensory feedback to modulate saccade dynamics, it is not precise or fast enough to compensate for large changes in wing efficacy.
Sensorimotor control during isothermal tracking in Caenorhabditis elegans
Authors: Luo Linjiao , Clark Damon A. , Biron David , Mahadevan L. , Samuel Aravinthan D. T. 
Published: November 2006

SUMMARY
In order to purposefully navigate their environments, animals rely on precise coordination between their sensory and motor systems. The integrated performance of circuits for sensorimotor control may be analyzed by quantifying an animal's motile behavior in defined sensory environments. Here,we analyze the ability of the nematode C. elegans to crawl isothermally in spatial thermal gradients by quantifying the trajectories of individual worms responding to defined spatiotemporal thermal gradients. We show that sensorimotor control during isothermal tracking may be summarized as a strategy in which the worm changes the curvature of its propulsive undulations in response to temperature changes measured at its head. We show that a concise mathematical model for this strategy for sensorimotor control is consistent with the exquisite stability of the worm's isothermal alignment in spatial thermal gradients as well as its more complex trajectories in spatiotemporal thermal gradients.
Association Genetics in Pinus taeda L. I. Wood Property Traits
Authors: González-Martínez Santiago C , Wheeler Nicholas C , Ersoz Elhan , Nelson C Dana , Neale David B 
Published: November 2006

Abstract
Genetic association is a powerful method for dissecting complex adaptive traits due to (i) fine-scale mapping resulting from historical recombination, (ii) wide coverage of phenotypic and genotypic variation within a single experiment, and (iii) the simultaneous discovery of loci and alleles. In this article, genetic association among single nucleotide polymorphisms (58 SNPs) from 20 wood- and drought-related candidate genes and an array of wood property traits with evolutionary and commercial importance, namely, earlywood and latewood specific gravity, percentage of latewood, earlywood microfibril angle, and wood chemistry (lignin and cellulose content), was tested using mixed linear models (MLMs) that account for relatedness among individuals by using a pairwise kinship matrix. Population structure, a common systematic bias in association studies, was assessed using 22 nuclear microsatellites. Different phenotype:genotype associations were found, some of them confirming previous evidence from collocation of QTL and genes in linkage maps (for example, 4cl and percentage of latewood) and two that involve nonsynonymous polymorphisms (cad SNP M28 with earlywood specific gravity and 4cl SNP M7 with percentage of latewood). The strongest genetic association found in this study was between allelic variation in α-tubulin, a gene involved in the formation of cortical microtubules, and earlywood microfibril angle. Intragenic LD decays rapidly in conifers; thus SNPs showing genetic association are likely to be located in close proximity to the causative polymorphisms. This first multigene association genetic study in forest trees has shown the feasibility of candidate gene strategies for dissecting complex adaptive traits, provided that genes belonging to key pathways and appropriate statistical tools are used. This approach is of particular utility in species such as conifers, where genomewide strategies are limited by their large genomes.
Multilevel Selection 1: Quantitative Genetics of Inheritance and Response to Selection
Authors: Bijma Piter , Muir William M , Van Arendonk Johan A M 
Published: November 2006

AbstractInteraction among individuals is universal, both in animals and in plants, and substantially affects evolution of natural populations and responses to artificial selection in agriculture. Although quantitative genetics has successfully been applied to many traits, it does not provide a general theory accounting for interaction among individuals and selection acting on multiple levels. Consequently, current quantitative genetic theory fails to explain why some traits do not respond to selection among individuals, but respond greatly to selection among groups. Understanding the full impacts of heritable interactions on the outcomes of selection requires a quantitative genetic framework including all levels of selection and relatedness. Here we present such a framework and provide expressions for the response to selection. Results show that interaction among individuals may create substantial heritable variation, which is hidden to classical analyses. Selection acting on higher levels of organization captures this hidden variation and therefore always yields positive response, whereas individual selection may yield response in the opposite direction. Our work provides testable predictions of response to multilevel selection and reduces to classical theory in the absence of interaction. Statistical methodology provided elsewhere enables empirical application of our work to both natural and domestic populations.
Multilevel Selection 2: Estimating the Genetic Parameters Determining Inheritance and Response to Selection
Authors: Bijma Piter , Muir William M , Ellen Esther D , Wolf Jason B , Van Arendonk Johan A M 
Published: November 2006

AbstractInteractions among individuals are universal, both in animals and in plants and in natural as well as domestic populations. Understanding the consequences of these interactions for the evolution of populations by either natural or artificial selection requires knowledge of the heritable components underlying them. Here we present statistical methodology to estimate the genetic parameters determining response to multilevel selection of traits affected by interactions among individuals in general populations. We apply these methods to obtain estimates of genetic parameters for survival days in a population of layer chickens with high mortality due to pecking behavior. We find that heritable variation is threefold greater than that obtained from classical analyses, meaning that two-thirds of the full heritable variation is hidden to classical analysis due to social interactions. As a consequence, predicted responses to multilevel selection applied to this population are threefold greater than classical predictions. This work, combined with the quantitative genetic theory for response to multilevel selection presented in an accompanying article in this issue, enables the design of selection programs to effectively reduce competitive interactions in livestock and plants and the prediction of the effects of social interactions on evolution in natural populations undergoing multilevel selection.
Fine Mapping Reveals Sex Bias in Quantitative Trait Loci Affecting Growth, Skeletal Size and Obesity-Related Traits on Mouse Chromosomes 2 and 11
Authors: Farber Charles R , Medrano Juan F 
Published: November 2006

AbstractPrevious speed congenic analysis has suggested that the expression of growth and obesity quantitative trait loci (QTL) on distal mouse chromosomes (MMU) 2 and 11, segregating between the CAST/EiJ (CAST) and C57BL/6J-hg/hg (HG) strains, is dependent on sex. To confirm, fine map, and further evaluate QTL × sex interactions, we constructed congenic by recipient F2 crosses for the HG.CAST-(D2Mit329-D2Mit457)N(6) (HG2D) and HG.CAST-(D11Mit260-D11Mit255)N(6) (HG11) congenic strains. Over 700 F2 mice were densely genotyped and phenotyped for a panel of 40 body and organ weight, skeletal length, and obesity-related traits at 9 weeks of age. Linkage analysis revealed 20 QTL affecting a representative subset of phenotypes in HG2DF2 and HG11F2 mice. The effect of sex was quantified by comparing two linear models: the first model included sex as an additive covariate and the second incorporated sex as an additive and an interactive covariate. Of the 20 QTL, 8 were sex biased, sex specific, or sex antagonistic. Most traits were regulated by single QTL; however, two closely linked loci were identified for five traits in HG2DF2 mice. Additionally, the confidence intervals for most QTL were significantly reduced relative to the original mapping results, setting the stage for quantitative trait gene (QTG) discovery. These results highlight the importance of assessing the contribution of sex in complex trait analyses.
Controlling the False-Positive Rate in Multilocus Genome Scans for Selection
Authors: Thornton Kevin R , Jensen Jeffrey D 
Published: November 2006

AbstractRapid typing of genetic variation at many regions of the genome is an efficient way to survey variability in natural populations in an effort to identify segments of the genome that have experienced recent natural selection. Following such a genome scan, individual regions may be chosen for further sequencing and a more detailed analysis of patterns of variability, often to perform a parametric test for selection and to estimate the strength of a recent selective sweep. We show here that not accounting for the ascertainment of loci in such analyses leads to false inference of natural selection when the true model is selective neutrality, because the procedure of choosing unusual loci (in comparison to the rest of the genome-scan data) selects regions of the genome with genealogies similar to those expected under models of recent directional selection. We describe a simple and efficient correction for this ascertainment bias, which restores the false-positive rate to near-nominal levels. For the parameters considered here, we find that obtaining a test with the expected distribution of P-values depends on accurately accounting both for ascertainment of regions and for demography. Finally, we use simulations to explore the utility of relying on outlier loci to detect recent selective sweeps. We find that measures of diversity and of population differentiation are more effective than summaries of the site-frequency spectrum and that sequencing larger regions (2.5 kbp) in genome-scan studies leads to more power to detect recent selective sweeps.
Ecological Zones Rather Than Molecular Forms Predict Genetic Differentiation in the Malaria VectorAnopheles gambiaes.s. in Ghana
Authors: Yawson Alexander E , Weetman David , Wilson Michael D , Donnelly Martin J 
Published: November 2006

AbstractThe malaria mosquito Anopheles gambiae s.s. is rapidly becoming a model for studies on the evolution of reproductive isolation. Debate has centered on the taxonomic status of two forms (denoted M and S) within the nominal taxon identified by point mutations in the X-linked rDNA region. Evidence is accumulating that there are significant barriers to gene flow between these forms, but that the barriers are not complete throughout the entire range of their distribution. We sampled populations from across Ghana and southern Burkina Faso, West Africa, from areas where the molecular forms occurred in both sympatry and allopatry. Neither Bayesian clustering methods nor FST-based analysis of microsatellite data found differentiation between the M and S molecular forms, but revealed strong differentiation among different ecological zones, irrespective of M/S status and with no detectable effect of geographical distance. Although no M/S hybrids were found in the samples, admixture analysis detected evidence of contemporary interform gene flow, arguably most pronounced in southern Ghana where forms occur sympatrically. Thus, in the sampled area of West Africa, lack of differentiation between M and S forms likely reflects substantial introgression, and ecological barriers appear to be of greater importance in restricting gene flow.
Drosophila melanogasterMale Somatic Cells Feminized Solely by TraF Can Collaborate With Female Germ Cells to Make Functional Eggs
Authors: Evans Daniel S , Cline Thomas W 
Published: November 2006

AbstractFemale differentiation of Drosophila germ cells is induced by cell-nonautonomous signals generated in the gonadal soma that work with germ-cell-autonomous signals determined by germ-cell X chromosome dose. Generation of the nonautonomous feminizing signals was known to involve female-specific protein encoded by the master sex-determination gene Sex-lethal (Sxl) acting on its switch-gene target transformer (tra) to produce TraF protein. However, it was not known whether Sxl's action on tra alone would suffice to trigger a fully feminizing nonautonomous signal. We developed a constitutively feminizing tra transgene that allowed us to answer this question. In gynanders (XX//XO mosaics) feminized by this TraF transgene, functionally Sxl− haplo-X (chromosomally male) somatic cells collaborated successfully with diplo-X (chromosomally female) germ cells to make functional eggs. The fertility of such gynanders shows not only that TraF is sufficient to elicit a fully feminizing nonautonomous signal, but also that haplo-X somatic cells can execute all other somatic functions required for oogenesis, despite the fact that their genome is not expected to be dosage compensated for such diplo-X-specific functions. The unexpected observation that some TraF-feminized gynanders failed to lay their eggs showed there to be diplo-X cells outside the gonad for which TraF-feminized haplo-X cells cannot substitute.
SSP2 and OSW1, Two Sporulation-Specific Genes Involved in Spore Morphogenesis in Saccharomyces cerevisiae
Authors: Li Jing , Agarwal Seema , Roeder G Shirleen 
Published: November 2006

Abstract
Spore formation in Saccharomyces cerevisiae requires the synthesis of prospore membranes (PSMs) followed by the assembly of spore walls (SWs). We have characterized extensively the phenotypes of mutants in the sporulation-specific genes, SSP2 and OSW1, which are required for spore formation. A striking feature of the osw1 phenotype is asynchrony of spore development, with some spores displaying defects in PSM formation and others spores in the same ascus blocked at various stages in SW development. The Osw1 protein localizes to spindle pole bodies (SPBs) during meiotic nuclear division and subsequently to PSMs/SWs. We propose that Osw1 performs a regulatory function required to coordinate the different stages of spore morphogenesis. In the ssp2 mutant, nuclei are surrounded by PSMs and SWs; however, PSMs and SWs often also encapsulate anucleate bodies both inside and outside of spores. In addition, the SW is not as thick as in wild type. The ssp2 mutant defect is partially suppressed by overproduction of either Spo14 or Sso1, both of which promote the fusion of vesicles at the outer plaque of the SPB early in PSM formation. We propose that Ssp2 plays a role in vesicle fusion during PSM formation.