101,012 research outputs found
Interacting cells driving the evolution of multicellular life cycles
Author summary Multicellular organisms are ubiquitous. But how did the first multicellular organisms arise? It is typically argued that this occurred due to benefits coming from interactions between cells. One example of such interactions is the division of labour. For instance, colonial cyanobacteria delegate photosynthesis and nitrogen fixation to different cells within the colony. In this way, the colony gains a growth advantage over unicellular cyanobacteria. However, not all cell interactions favour multicellular life. Cheater cells residing in a colony without any contribution will outgrow other cells. Then, the growing burden of cheaters may eventually destroy the colony. Here, we ask what kinds of interactions promote the evolution of multicellularity? We investigated all interactions captured by pairwise games and for each of them, we look for the evolutionarily optimal life cycle: How big should the colony grow and how should it split into offspring cells or colonies? We found that multicellularity can evolve with interactions far beyond cooperation or division of labour scenarios. More surprisingly, most of the life cycles found fall into either of two categories: A parent colony splits into two multicellular parts, or it splits into multiple independent cells
A Separable Model for Dynamic Networks
Models of dynamic networks --- networks that evolve over time --- have
manifold applications. We develop a discrete-time generative model for social
network evolution that inherits the richness and flexibility of the class of
exponential-family random graph models. The model --- a Separable Temporal ERGM
(STERGM) --- facilitates separable modeling of the tie duration distributions
and the structural dynamics of tie formation. We develop likelihood-based
inference for the model, and provide computational algorithms for maximum
likelihood estimation. We illustrate the interpretability of the model in
analyzing a longitudinal network of friendship ties within a school.Comment: 28 pages (including a 4-page appendix); a substantial rewrite, with
many corrections, changes in terminology, and a different analysis for the
exampl
Multi-choice opinion dynamics model based on Latane theory
In this paper Nowak--Szamrej-Latan\'e model is reconsidered. This
computerised model of opinion formation bases on Latan\'e theory of social
impact. We modify this model to allow for multi (more than two) opinions. With
computer simulations we show that in the modified model the signatures of
order/disorder phase transition are still observed. The transition may be
observed in the average fraction of actors sharing the -th opinion, its
variation and also average number of clusters of actors with the same opinion
and the average size of the largest cluster of actors sharing the same opinion.
Also an influence of model control parameters on simulation results is shortly
reviewed. For a homogeneous society with identical actors' supportiveness and
persuasiveness the critical social temperature decreases with an increase
of available opinions from () via 4.7, 4.1 to for
, 4, 5, respectively.Comment: 12 page
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