The Evolution of Robust Development and Homeostasis in Artificial Organisms

During embryogenesis, multicellular animals are shaped via cell proliferation, cell rearrangement, and apoptosis. At the end of development, tissue architecture is then maintained through balanced rates of cell proliferation and loss. Here, we take an in silico approach to look for generic systems features of morphogenesis in multicellular animals that arise as a consequence of the evolution of development. Using artificial evolution, we evolved cellular automata-based digital organisms that have distinct embryonic and homeostatic phases of development. Although these evolved organisms use a variety of strategies to maintain their form over time, organisms of different types were all found to rapidly recover from environmental damage in the form of wounds. This regenerative response was most robust in an organism with a stratified tissue-like architecture. An evolutionary analysis revealed that evolution itself contributed to the ability of this organism to maintain its form in the face of genetic and environmental perturbation, confirming the results of previous studies. In addition, the exceptional robustness of this organism to surface injury was found to result from an upward flux of cells, driven in part by cell divisions with a stable niche at the tissue base. Given the general nature of the model, our results lead us to suggest that many of the robust systems properties observed in real organisms, including scar-free wound-healing in well-protected embryos and the layered tissue architecture of regenerating epithelial tissues, may be by-products of the evolution of morphogenesis, rather than the direct result of selection

Network Evolution of Body Plans

Segmentation in arthropod embryogenesis represents a well-known example of body plan diversity. Striped patterns of gene expression that lead to the future body segments appear simultaneously or sequentially in long and short germ-band development, respectively. Regulatory genes relevant for stripe formation are evolutionarily conserved among arthropods, therefore the differences in the observed traits are thought to have originated from how the genes are wired. To reveal the basic differences in the network structure, we have numerically evolved hundreds of gene regulatory networks that produce striped patterns of gene expression. By analyzing the topologies of the generated networks, we show that the characteristics of stripe formation in long and short germ-band development are determined by Feed-Forward Loops (FFLs) and negative Feed-Back Loops (FBLs) respectively. Network architectures, gene expression patterns and knockout responses exhibited by the artificially evolved networks agree with those reported in the fly Drosophila melanogaster and the beetle Tribolium castaneum. For other arthropod species, principal network architectures that remain largely unknown are predicted.Comment: 35 pages, 4 figures and 1 tabl

Hidden Costs of Modelling Post-fire Plant Community Assembly Using Cellular Automata

Cellular Automata (CA) models have been applied to different fields of knowledge, from cryptography, arts, to the modelling and simulation of complex systems. In the latter area, however, sometimes the ability to properly represent complex interacting but distinct dynamics taking place within a given area is limited by the need of calibrating models in which the number of necessary parameters grows. Hidden costs related to the identification of specific values or plausible ranges for parameters can become overwhelming. Here we model the assembly process of plant communities after fire. The number of elements of plant communities (plants of different species) and processes involved (seed dispersal, plant recruitment, competence, etc.) require a high degree of parameterization because all those processes have great relevance on the evolution of the system, for instance during post-fire recovery. The fire, aside negative effects, releases a number of resources (space, nutrients, ...) making them easily available for plants, which promptly use those resources so they are no longer available to other plants after a period of time which usually ranges from months to years. In the meantime, the plasticity of species in relation to fire and environment and the interactions among species determine the direction of changes to occur. In this work we present a novel approach to the assembly of plant communities after fire using CA. In particular we gather the preliminary results of their application and give a feasible way to optimize the parameterization of the model

A study to compare the reliability of composite finger flexion with goniometry for measurement of range of motion in the hand

OBJECTIVE: To establish the intra- and inter-rater reliability of composite finger flexion (CFF), and to compare this with goniometry. DESIGN: Fifty-one physiotherapists and occupational therapists took part in the study. The hand of a normal subject was splinted in three different positions. Using a goniometer and a ruler alternately, each therapist measured both the proximal interphalangeal joint and CFF of three digits, following a standardized protocol. This process was repeated three times.SETTING: Eighteen NHS hospital sites in the UK.RESULTS: The two measurement methods produced different ranges and standard deviations for each digit. The repeatability coefficient shows that repeated intra-rater goniometric measures fall within 4-5 degrees of each other 95% of the time. Inter-rater goniometric measures fall within 7-9 degrees. Repeated intra-rater CFF measures fall within 5-6 mm of each other, whereas inter-rater fall within 7-9 mm. The influence of occupation, experience in hand therapy, years of practice and routine use were found to have no effect on reliability. Scaling of the two methods of measurement allowed comparison between them to be made. CFF and goniometry are equally reliable when comparing inter-rater reliability, but goniometry displays less variability than composite finger flexion for intra-rater measurements. CONCLUSION: In this study involving a subject with normal joints, goniometry is more reliable than CFF when only one measurer is involved. However, CFF may be a useful alternative where multiple joint measures are required, or when goniometry is impracticable