87,155 research outputs found
Natural selection. II. Developmental variability and evolutionary rate
In classical evolutionary theory, genetic variation provides the source of
heritable phenotypic variation on which natural selection acts. Against this
classical view, several theories have emphasized that developmental variability
and learning enhance nonheritable phenotypic variation, which in turn can
accelerate evolutionary response. In this paper, I show how developmental
variability alters evolutionary dynamics by smoothing the landscape that
relates genotype to fitness. In a fitness landscape with multiple peaks and
valleys, developmental variability can smooth the landscape to provide a
directly increasing path of fitness to the highest peak. Developmental
variability also allows initial survival of a genotype in response to novel or
extreme environmental challenge, providing an opportunity for subsequent
adaptation. This initial survival advantage arises from the way in which
developmental variability smooths and broadens the fitness landscape.
Ultimately, the synergism between developmental processes and genetic variation
sets evolutionary rate
Phenotypic mixing and hiding may contribute to memory in viral quasispecies
Background. In a number of recent experiments with food-and-mouth disease
virus, a deleterious mutant, was found to avoid extinction and remain in the
population for long periods of time. This observation was called quasispecies
memory. The origin of quasispecies memory is not fully understood.
Results. We propose and analyze a simple model of complementation between the
wild type virus and a mutant that has an impaired ability of cell entry. The
mutant will go extinct unless it is recreated from the wild type through
mutations. However, under phenotypic mixing-and-hiding as a mechanism of
complementation, the time to extinction in the absence of mutations increases
with increasing multiplicity of infection (m.o.i.). The mutant's frequency at
equilibrium under selection-mutation balance also increases with increasing
m.o.i. At high m.o.i., a large fraction of mutant genomes are encapsidated with
wild-type protein, which enables them to infect cells as efficiently as the
wild type virions, and thus increases their fitness to the wild-type level.
Moreover, even at low m.o.i. the equilibrium frequency of the mutant is higher
than predicted by the standard quasispecies model, because a fraction of mutant
virions generated from wild-type parents will also be encapsidated by wild-type
protein.
Conclusions. Our model predicts that phenotypic hiding will strongly
influence the population dynamics of viruses, particularly at high m.o.i., and
will also have important effects on the mutation--selection balance at low
m.o.i. The delay in mutant extinction and increase in mutant frequencies at
equilibrium may, at least in part, explain memory in quasispecies populations.Comment: 10 pages pdf, as published by BM
Transgressivity in Key Functional Traits Rather Than Phenotypic Plasticity Promotes Stress Tolerance in A Hybrid Cordgrass
Hybridization might promote offspring fitness via a greater tolerance to environmental stressors due to heterosis and higher levels of phenotypic plasticity. Thus, analyzing the phenotypic expression of hybrids provides an opportunity to elucidate further plant responses to environmental stress. In the case of coastal salt marshes, sea level rise subjects hybrids, and their parents, to longer tidal submergence and higher salinity. We analyzed the phenotypic expression patterns in the hybrid Spartina densiflora x foliosa relative to its parental species, native S. foliosa, and invasive S. densiflora, from the San Francisco Estuary when exposed to contrasting salinities and inundations in a mesocosm experiment. 37% of the recorded traits displayed no variability among parents and hybrids, 3% showed an additive inheritance, 37% showed mid-parent heterosis, 18% showed best-parent heterosis, and 5% presented worst-parent heterosis. Transgressivity, rather than phenotypic plasticity, in key functional traits of the hybrid, such as tiller height, conveyed greater stress tolerance to the hybrid when compared to the tolerance of its parents. As parental trait variability increased, phenotypic transgressivity of the hybrid increased and it was more important in response to inundation than salinity. Increases in salinity and inundation associated with sea level rise will amplify the superiority of the hybrid over its parental species. These results provide evidence of transgressive traits as an underlying source of adaptive variation that can facilitate plant invasions. The adaptive evolutionary process of hybridization is thought to support an increased invasiveness of plant species and their rapid evolution
Population–reaction model and microbial experimental ecosystems for understanding hierarchical dynamics of ecosystems
Understanding ecosystem dynamics is crucial as contemporary human societies face ecosystem degradation. One of the challenges that needs to be recognized is the complex hierarchical dynamics. Conventional dynamic models in ecology often represent only the population level and have yet to include the dynamics of the sub-organism level, which makes an ecosystem a complex adaptive system that shows characteristic behaviors such as resilience and regime shifts. The neglect of the sub-organism level in the conventional dynamic models would be because integrating multiple hierarchical levels makes the models unnecessarily complex unless supporting experimental data are present. Now that large amounts of molecular and ecological data are increasingly accessible in microbial experimental ecosystems, it is worthwhile to tackle the questions of their complex hierarchical dynamics. Here, we propose an approach that combines microbial experimental ecosystems and a hierarchical dynamic model named population–reaction model. We present a simple microbial experimental ecosystem as an example and show how the system can be analyzed by a population–reaction model. We also show that population–reaction models can be applied to various ecological concepts, such as predator–prey interactions, climate change, evolution, and stability of diversity. Our approach will reveal a path to the general understanding of various ecosystems and organisms
The case for absolute ligand discrimination : modeling information processing and decision by immune T cells
Some cells have to take decision based on the quality of surroundings
ligands, almost irrespective of their quantity, a problem we name "absolute
discrimination". An example of absolute discrimination is recognition of
not-self by immune T Cells. We show how the problem of absolute discrimination
can be solved by a process called "adaptive sorting". We review several
implementations of adaptive sorting, as well as its generic properties such as
antagonism. We show how kinetic proofreading with negative feedback implements
an approximate version of adaptive sorting in the immune context. Finally, we
revisit the decision problem at the cell population level, showing how
phenotypic variability and feedbacks between population and single cells are
crucial for proper decision
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