7,919 research outputs found
How specificity and epidemiology drive the coevolution of static trait diversity in hosts and parasites
This is the final version of the article. Available from the publisher via the DOI in this record.There is typically considerable variation in the level of infectivity of parasites and the degree of resistance of hosts within populations. This trait variation is critical not only to the evolutionary dynamics but also to the epidemiology, and potentially the control of infectious disease. However, we lack an understanding of the processes that generate and maintain this trait diversity. We examine theoretically how epidemiological feedbacks and the characteristics of the interaction between host types and parasites strains determine the coevolution of host-parasite diversity. The interactions include continuous characterizations of the key phenotypic features of classic gene-for-gene and matching allele models. We show that when there are costs to resistance in the hosts and infectivity in the parasite, epidemiological feedbacks may generate diversity but this is limited to dimorphism, often of extreme types, in a broad range of realistic infection scenarios. For trait polymorphism, there needs to be both specificity of infection between host types and parasite strains as well as incompatibility between particular strains and types. We emphasize that although the high specificity is well known to promote temporal "Red Queen" diversity, it is costs and combinations of hosts and parasites that cannot infect that will promote static trait diversity.MB was a fellow of the Wissenschaftskolleg zu Berlin 2010–2011 during
the writing of this article, and we acknowledge the support from the
Natural Environment Research Council (grant NE/K014617/1) to MB
and AB
Far-UV Emission from Elliptical Galaxies at z=0.55
The restframe UV-to-optical flux ratio, characterizing the ``UV upturn''
phenomenon, is potentially the most sensitive tracer of age in elliptical
galaxies; models predict that it may change by orders of magnitude over the
course of a few Gyr. In order to trace the evolution of the UV upturn as a
function of redshift, we have used the far-UV camera on the Space Telescope
Imaging Spectrograph to image the galaxy cluster CL0016+16 at z=0.55. Our
25''x25'' field includes four bright elliptical galaxies, spectroscopically
confirmed to be passively evolving cluster members. The weak UV emission from
the galaxies in our image demonstrates that the UV upturn is weaker at a
lookback time 5.6 Gyr earlier than our own, as compared to measurements of the
UV upturn in cluster E and S0 galaxies at z=0 and z=0.375. These images are the
first with sufficient depth to demonstrate the fading of the UV upturn expected
at moderate redshifts. We discuss these observations and the implications for
the formation history of galaxies.Comment: 4 pages, Latex. 2 figures. Uses corrected version of emulateapj.sty
and apjfonts.sty (included). Accepted for publication in ApJ Letter
Genetic analysis of safflower domestication.
BackgroundSafflower (Carthamus tinctorius L.) is an oilseed crop in the Compositae (a.k.a. Asteraceae) that is valued for its oils rich in unsaturated fatty acids. Here, we present an analysis of the genetic architecture of safflower domestication and compare our findings to those from sunflower (Helianthus annuus L.), an independently domesticated oilseed crop within the same family.We mapped quantitative trait loci (QTL) underlying 24 domestication-related traits in progeny from a cross between safflower and its wild progenitor, Carthamus palaestinus Eig. Also, we compared QTL positions in safflower against those that have been previously identified in cultivated x wild sunflower crosses to identify instances of colocalization.ResultsWe mapped 61 QTL, the vast majority of which (59) exhibited minor or moderate phenotypic effects. The two large-effect QTL corresponded to one each for flower color and leaf spininess. A total of 14 safflower QTL colocalized with previously reported sunflower QTL for the same traits. Of these, QTL for three traits (days to flower, achene length, and number of selfed seed) had cultivar alleles that conferred effects in the same direction in both species.ConclusionsAs has been observed in sunflower, and unlike many other crops, our results suggest that the genetics of safflower domestication is quite complex. Moreover, our comparative mapping results indicate that safflower and sunflower exhibit numerous instances of QTL colocalization, suggesting that parallel trait transitions during domestication may have been driven, at least in part, by parallel genotypic evolution at some of the same underlying genes
Universal reshaping of arrested colloidal gels via active doping
Colloids that interact via a short-range attraction serve as the primary
building blocks for a broad range of self-assembled materials. However, one of
the well-known drawbacks to this strategy is that these building blocks rapidly
and readily condense into a metastable colloidal gel. Using computer
simulations, we illustrate how the addition of a small fraction of purely
repulsive self-propelled colloids, a technique referred to as active doping,
can prevent the formation of this metastable gel state and drive the system
toward its thermodynamically favored crystalline target structure. The
simplicity and robust nature of this strategy offers a systematic and generic
pathway to improving the self-assembly of a large number of complex colloidal
structures. We discuss in detail the process by which this feat is accomplished
and provide quantitative metrics for exploiting it to modulate self-assembly.
We provide evidence for the generic nature of this approach by demonstrating
that it remains robust under a number of different anisotropic short-ranged
pair interactions in both two and three dimensions. In addition, we report on a
novel microphase in mixtures of passive and active colloids. For a broad range
of self-propelling velocities, it is possible to stabilize a suspension of
fairly monodisperse finite-size crystallites. Surprisingly, this microphase is
also insensitive to the underlying pair interaction between building blocks.
The active stabilization of these moderately-sized monodisperse clusters is
quite remarkable and should be of great utility in the design of hierarchical
self-assembly strategies. This work further bolsters the notion that active
forces can play a pivotal role in directing colloidal self-assembly.Comment: Supplemental Material available here:
https://aip.scitation.org/doi/suppl/10.1063/5.001651
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