The Problem of Functional Boundaries in Prebiotic and Inter-Biological Systems

International audienceThe concept of organisational closure, interpreted as a set of internally produced and mutually dependent constraints, allows understanding organisms as functionally integrated systems capable of self-production and self-maintenance through the control exerted upon biosynthetic processes and the exchanges of matter and energy with the environment. One of the current challenges faced by this theoretical framework is to account for limit cases in which a robust functional closure cannot be realised from within. In order to achieve functional sufficiency and persist, prebiotic or biological systems may need to recruit external constraints or expand their network of control interactions to include other autonomous systems. These phenomena seem to contrast with the very idea of closure and the capability of living systems to specify their functional boundaries from within. This paper will analyse from an organisational perspective the role of environmental scaffolds and of different classes of intersystem interactions in prebiotic and su-pra-organismal biological scenarios, and show how the theoretical framework based on the notion of closure can account for these cases

Effect of Biodiversity Changes in Disease Risk: Exploring Disease Emergence in a Plant-Virus System

The effect of biodiversity on the ability of parasites to infect their host and cause disease (i.e. disease risk) is a major question in pathology, which is central to understand the emergence of infectious diseases, and to develop strategies for their management. Two hypotheses, which can be considered as extremes of a continuum, relate biodiversity to disease risk: One states that biodiversity is positively correlated with disease risk (Amplification Effect), and the second predicts a negative correlation between biodiversity and disease risk (Dilution Effect). Which of them applies better to different host-parasite systems is still a source of debate, due to limited experimental or empirical data. This is especially the case for viral diseases of plants. To address this subject, we have monitored for three years the prevalence of several viruses, and virus-associated symptoms, in populations of wild pepper (chiltepin) under different levels of human management. For each population, we also measured the habitat species diversity, host plant genetic diversity and host plant density. Results indicate that disease and infection risk increased with the level of human management, which was associated with decreased species diversity and host genetic diversity, and with increased host plant density. Importantly, species diversity of the habitat was the primary predictor of disease risk for wild chiltepin populations. This changed in managed populations where host genetic diversity was the primary predictor. Host density was generally a poorer predictor of disease and infection risk. These results support the dilution effect hypothesis, and underline the relevance of different ecological factors in determining disease/infection risk in host plant populations under different levels of anthropic influence. These results are relevant for managing plant diseases and for establishing conservation policies for endangered plant species

The problem of functional boundaries in prebiotic and inter-biological systems

The concept of organisational closure, interpreted as a set of internally pro-duced and mutually dependent constraints, allows understanding organisms as functionally integrated systems capable of self-production and self-maintenance through the control exerted upon biosynthetic processes and the exchanges of matter and energy with the environment. One of the current challenges faced by this theoretical framework is to account for limit cases in which a robust functional closure cannot be realised from within. In order to achieve functional sufficiency and persist, prebiotic or biological systems may need to recruit external constraints or expand their network of control in-teractions to include other autonomous systems. These phenomena seem to contrast with the very idea of closure and the capability of living systems to specify their functional boundaries from within. This paper will analyse from an organisational perspective the role of environmental scaffolds and of dif-ferent classes of intersystem interactions in prebiotic and supra-organismal biological scenarios, and show how the theoretical framework based on the notion of closure can account for these cases

Impact of Human Management on the Genetic Variation of Wild Pepper, Capsicum annuum var. glabriusculum

Management of wild peppers in Mexico has occurred for a long time without clear phenotypic signs of domestication. However, pre-domestication management could have implications for the population's genetic richness. To test this hypothesis we analysed 27 wild (W), let standing (LS) and cultivated (C) populations, plus 7 samples from local markets (LM), with nine polymorphic microsatellite markers. Two hundred and fifty two alleles were identified, averaging 28 per locus. Allele number was higher in W, and 15 and 40% less in LS and C populations, respectively. Genetic variation had a significant population structure. In W populations, structure was associated with ecological and geographic areas according to isolation by distance. When LM and C populations where included in the analysis, differentiation was no longer apparent. Most LM were related to distant populations from Sierra Madre Oriental, which represents their probable origin. Historical demography shows a recent decline in all W populations. Thus, pre-domestication human management is associated with a significant reduction of genetic diversity and with a loss of differentiation suggesting movement among regions by man. Measures to conserve wild and managed populations should be implemented to maintain the source and the architecture of genetic variation in this important crop relative

Robustness and autonomy in biological systems: how regulatory mechanisms enable functional integration, complexity and minimal cognition through the action of second-order control constraints

Living systems employ several mechanisms and behaviors to achieve robustness and maintain themselves under changing internal and external conditions. Regulation stands out from them as a specific form of higher-order control, exerted over the basic regime responsible for the production and maintenance of the organism, and provides the system with the capacity to act on its own constitutive dynamics. It consists in the capability to selectively shift between different available regimes of self-production and self-maintenance in response to specific signals and perturbations, due to the action of a dedicated subsystem which is operationally distinct from the regulated ones. The role of regulation, however, is not exhausted by its contribution to maintain a living system’s viability. While enhancing robustness, regulatory mechanisms play a fundamental role in the realization of an autonomous biological organization. Specifically, they are at the basis of the remarkable integration of biological systems, insofar as they coordinate and modulate the activity of distinct functional subsystems. Moreover, by implementing complex and hierarchically organized control architectures, they allow for an increase in structural and organizational complexity while minimizing fragility. Finally, they endow living systems, from their most basic unicellular instances, with the capability to control their own internal dynamics to adaptively respond to specific features of their interaction with the environment, thus providing the basis for the emergence of minimal forms of cognition

Complex evolutionary history of the Mexican stoneroller Campostoma ornatum Girard, 1856 (Actinopterygii: Cyprinidae)

<p>Abstract</p> <p>Background</p> <p>Studies of the phylogeography of Mexican species are steadily revealing genetic patterns shared by different species, which will help to unravel the complex biogeographic history of the region. <it>Campostoma ornatum </it>is a freshwater fish endemic to montane and semiarid regions in northwest Mexico and southern Arizona. Its wide range of distribution and the previously observed morphological differentiation between populations in different watersheds make this species a useful model to investigate the biogeographic role of the Sierra Madre Occidental and to disentangle the actions of Pliocene tecto-volcanic processes <it>vs </it>Quaternary climatic change. Our phylogeographic study was based on DNA sequences from one mitochondrial gene (<it>cytb</it>, 1110 bp, n = 285) and two nuclear gene regions (S7 and RAG1, 1822 bp in total, n = 56 and 43, respectively) obtained from 18 to 29 localities, in addition to a morphological survey covering the entire distribution area. Such a dataset allowed us to assess whether any of the populations/lineages sampled deserve to be categorised as an evolutionarily significant unit.</p> <p>Results</p> <p>We found two morphologically and genetically well-differentiated groups within <it>C. ornatum</it>. One is located in the northern river drainages (Yaqui, Mayo, Fuerte, Sonora, Casas Grandes, Santa Clara and Conchos) and another one is found in the southern drainages (Nazas, Aguanaval and Piaxtla). The split between these two lineages took place about 3.9 Mya (CI = 2.1-5.9). Within the northern lineage, there was strong and significant inter-basin genetic differentiation and also several secondary dispersal episodes whit gene homogenization between drainages. Interestingly, three divergent mitochondrial lineages were found in sympatry in two northern localities from the Yaqui river basin.</p> <p>Conclusions</p> <p>Our results indicate that there was isolation between the northern and southern phylogroups since the Pliocene, which was related to the formation of the ancient Nazas River paleosystem, where the southern group originated. Within groups, a complex reticulate biogeographic history for <it>C. ornatum </it>populations emerges, following the taxon pulse theory and mainly related with Pliocene tecto-volcanic processes. In the northern group, several events of vicariance promoted by river or drainage isolation episodes were found, but within both groups, the phylogeographic patterns suggest the occurrence of several events of river capture and fauna interchange. The Yaqui River supports the most diverse populations of <it>C. ornatum</it>, with several events of dispersal and isolation within the basin. Based on our genetic results, we defined three ESUs within <it>C. ornatum </it>as a first attempt to promote the conservation of the evolutionary processes determining the genetic diversity of this species. They will likely be revealed as a valuable tool for freshwater conservation policies in northwest Mexico, where many environmental problems concerning the use of water have rapidly arisen in recent decades.</p

Population expansions shared among coexisting bacterial lineages are revealed by genetic evidence

Comparative population studies can help elucidate the influence of historical events upon current patterns of biodiversity among taxa that coexist in a given geographic area. In particular, comparative assessments derived from population genetics and coalescent theory have been used to investigate population dynamics of bacterial pathogens in order to understand disease epidemics. In contrast, and despite the ecological relevance of non-host associated and naturally occurring bacteria, there is little understanding of the processes determining their diversity. Here we analyzed the patterns of genetic diversity in coexisting populations of three genera of bacteria (Bacillus, Exiguobacterium, and Pseudomonas) that are abundant in the aquatic systems of the Cuatro Cienegas Basin, Mexico. We tested the hypothesis that a common habitat leaves a signature upon the genetic variation present in bacterial populations, independent of phylogenetic relationships. We used multilocus markers to assess genetic diversity and (1) performed comparative phylogenetic analyses, (2) described the genetic structure of bacterial populations, (3) calculated descriptive parameters of genetic diversity, (4) performed neutrality tests, and (5) conducted coalescent-based historical reconstructions. Our results show a trend of synchronic expansions across most populations independent of both lineage and sampling site. Thus, we provide empirical evidence supporting the analysis of coexisting bacterial lineages in natural environments to advance our understanding of bacterial evolution beyond medical or health-related microbes