On the evolution of the solar wind between 1 and 5 AU at the time of the Cassini Jupiter flyby: Multispacecraft observations of interplanetary coronal mass ejections including the formation of a merged interaction region

The Cassini flyby of Jupiter occurred at a time near solar maximum. Consequently, the pre-Jupiter data set reveals clear and numerous transient perturbations to the Parker Spiral solar wind structure. Limited plasma data are available at Cassini for this period due to pointing restrictions imposed on the instrument. This renders the identification of the nature of such structures ambiguous, as determinations based on the magnetic field data alone are unreliable. However, a fortuitous alignment of the planets during this encounter allowed us to trace these structures back to those observed previously by the Wind spacecraft near the Earth. Of the phenomena that we are satisfactorily able to trace back to their manifestation at 1 AU, two are identified as being due to interplanetary coronal mass ejections. One event at Cassini is shown to be a merged interaction region, which is formed from the compression of a magnetic cloud by two anomalously fast solar wind streams. The flux-rope structure associated with this magnetic cloud is not as apparent at Cassini and has most likely been compressed and deformed. Confirmation of the validity of the ballistic projections used here is provided by results obtained from a one-dimensional magnetohydrodynamic projection of solar wind parameters measured upstream near the Earth. It is found that when the Earth and Cassini are within a few tens of degrees in heliospheric longitude, the results of this one-dimensional model predict the actual conditions measured at 5 AU to an impressive degree. Finally, the validity of the use of such one-dimensional projections in obtaining quasi-solar wind parameters at the outer planets is discussed.

Rational conversion of substrate and product specificity in a Salvia monoterpene synthase: structural insights into the evolution of terpene synthase function

Terpene synthases are responsible for the biosynthesis of the complex chemical defense arsenal of plants and microorganisms. How do these enzymes, which all appear to share a common terpene synthase fold, specify the many different products made almost entirely from one of only three substrates? Elucidation of the structure of 1,8-cineole synthase from Salvia fruticosa (Sf-CinS1) combined with analysis of functional and phylogenetic relationships of enzymes within Salvia species identified active-site residues responsible for product specificity. Thus, Sf-CinS1 was successfully converted to a sabinene synthase with a minimum number of rationally predicted substitutions, while identification of the Asn side chain essential for water activation introduced 1,8-cineole and alpha-terpineol activity to Salvia pomifera sabinene synthase. A major contribution to product specificity in Sf-CinS1 appears to come from a local deformation within one of the helices forming the active site. This deformation is observed in all other mono- or sesquiterpene structures available, pointing to a conserved mechanism. Moreover, a single amino acid substitution enlarged the active-site cavity enough to accommodate the larger farnesyl pyrophosphate substrate and led to the efficient synthesis of sesquiterpenes, while alternate single substitutions of this critical amino acid yielded five additional terpene synthases.

Evaluation of the model representation of the evolution of convective systems using satellite observations of outgoing longwave radiation

We introduce a technique for assessing the diurnal development of convective storm systems based on outgoing longwave radiation fields. Using the size distribution of the storms measured from a series of images, we generate an array in the lengthscale-time domain based on the standard score statistic. It demonstrates succinctly the size evolution of storms as well as the dissipation kinematics. It also provides evidence related to the temperature evolution of the cloud tops. We apply this approach to a test case comparing observations made by the Geostationary Earth Radiation Budget instrument to output from the Met Office Unified Model run at two resolutions. The 12km resolution model produces peak convective activity on all lengthscales significantly earlier in the day than shown by the observations and no evidence for storms growing in size. The 4km resolution model shows realistic timing and growth evolution although the dissipation mechanism still differs from the observed data.

A model for the evolution of pathogen-induced leaf shedding

A size-structured plant population model is developed to study the evolution of pathogen-induced leaf shedding under various environmental conditions. The evolutionary stable strategy (ESS) of the leaf shedding rate is determined for two scenarios: i) a constant leaf shedding strategy and ii) an infection load driven leaf shedding strategy. The model predicts that ESS leaf shedding rates increase with nutrient availability. No effect of plant density on the ESS leaf shedding rate is found even though disease severity increases with plant density. When auto-infection, that is increased infection due to spores produced on the plant itself, plays a key role in further disease increase on the plant, shedding leaves removes disease that would otherwise contribute to disease increase on the plant itself. Consequently leaf shedding responses to infections may evolve. When external infection, that is infection due to immigrant spores, is the key determinant, shedding a leaf does not reduce the force of infection on the leaf shedding plant. In this case leaf shedding will not evolve. Under a low external disease pressure adopting an infection driven leaf shedding strategy is more efficient than adopting a constant leaf shedding strategy, since a plant adopting an infection driven leaf shedding strategy does not shed any leaves in the absence of infection, even when leaf shedding rates are high. A plant adopting a constant leaf shedding rate sheds the same amount of leaves regardless of the presence of infection. Based on the results we develop two hypotheses that can be tested if the appropriate plant material is available.

Sperm competition and the evolution of testes size in terrestrial mammalian carnivores

Summary Understanding the factors influencing variation in the degree of sperm competition is a key question underlying the mechanisms driving sexual conflict. Previous behavioural and comparative studies have indicated that carnivores appear to have evolved under sperm competition but an analysis of the predictors of the level of sperm competition is missing. In this study, we use phylogenetic comparative methods to investigate life-history parameters predicted to affect the degree of sperm competition in terrestrial carnivores using variation in relative testes size (RTS, after controlling for body size allometry) as a measure of the level of sperm competition. Due to a paucity of consistent data across taxa, we used three measures of RTS: testes mass (n = 40 species), testes and epididymes mass combined (n = 38), and testes volume (n = 48). We also created a derived data set (n = 79) with testes mass estimated from regression analyses on the other measures of testes size. Carnivores with shorter mating seasons had relatively larger testes, consistent with the hypothesis that sperm competition is greater when the degree of female oestrous synchrony is high. This relationship was stronger in spontaneous versus induced ovulators, suggesting higher sperm competition levels in spontaneous ovulators. This is the first comparative study to show this within mammalian taxa. Neither social mating system nor reproductive lifespan were significantly associated with variation in RTS and hence are poor predictors of sperm competition levels. None of the above relationships were found to be significant for the testes and epididymes mass combined data set, but our understanding of the role of the epididymis in sperm competition is too limited to draw any conclusions. Finally, we consistently found a significant phylogenetic signal in all analyses, indicating that phylogeny has played a significant role in the evolution of carnivore testes size and, therefore, in shaping levels of sperm competition. Our results shed new light into the factors affecting levels of sperm competition in terrestrial carnivores by showing that the degree of oestrous synchrony and ovulation type interact to predict variation in RTS.

Selfish genetic elements favor the evolution of a distinction between soma and germline

Many multicellular organisms have evolved a dedicated germline. This can benefit the whole organism, but its advantages to genetic parasites have not been explored. Here I model the evolutionary success of a selfish element, such as a transposable element or endosymbiont, which is capable of creating or strengthening a germline-soma distinction in a primitively multicellular host, and find that it will always benefit the element to do so. Genes causing germline sequestration can therefore spread in a population even if germline sequestration is maladaptive for the host organism. Costly selfish elements are expected to survive only in sexual populations, so sexual species may experience an additional push toward germline-soma distinction, and hence toward cell differentiation and multicellularity.

Population genetic models can be used to study the evolution of the interacting behaviours of parents and their progeny

An example of the evolution of the interacting behaviours of parents and progeny is studied using iterative equations linking the frequencies of the gametes produced by the progeny to the frequencies of the gametes in the parental generation. This population genetics approach shows that a model in which both behaviours are determined by a single locus can lead to a stable equilibrium in which the two behaviours continue to segregate. A model in which the behaviours are determined by genes at two separate loci leads eventually to fixation of the alleles at both loci but this can take many generations of selection. Models of the type described in this paper will be needed to understand the evolution of complex behaviour when genomic or experimental information is available about the genetic determinants of behaviour and the selective values of different genomes. (c) 2007 Elsevier Inc. All rights reserved.

The evolution of mobile DNAs: when will transposons create phylogenies that look as if there is a master gene?

Some families of mammalian interspersed repetitive DNA, such as the Alu SINE sequence, appear to have evolved by the serial replacement of one active sequence with another, consistent with there being a single source of transposition: the "master gene." Alternative models, in which multiple source sequences are simultaneously active, have been called "transposon models." Transposon models differ in the proportion of elements that are active and in whether inactivation occurs at the moment of transposition or later. Here we examine the predictions of various types of transposon model regarding the patterns of sequence variation expected at an equilibrium between transposition, inactivation, and deletion. Under the master gene model, all bifurcations in the true tree of elements occur in a single lineage. We show that this property will also hold approximately for transposon models in which most elements are inactive and where at least some of the inactivation events occur after transposition. Such tree shapes are therefore not conclusive evidence for a single source of transposition.

The evolution of sensory placodes

The vertebrate cranial sensory placodes are ectodermal embryonic patches that give rise to sensory receptor cells of the peripheral paired sense organs and to neurons in the cranial sensory ganglia. Their differentiation and the genetic pathways that underlay their development are now well understood. Their evolutionary history, however, has remained obscure. Recent molecular work, performed on close relatives of the vertebrates, demonstrated that some sensory placodes (namely the adenohypophysis, the olfactory, and accoustico-lateralis placodes) first evolved at the base of the chordate lineage, while others might be specific to vertebrates. Combined with morphological and cellular fate data, these results also suggest that the sensory placodes of the ancestor of all chordates differentiated into a wide range of structures, most likely to fit the lifestyle and environment of each species.