Scale, ecological fallacy, and the river continuum concept

Concern over scale is not new, and it is not restricted to geographers. Spatial and temporal scaling is a conceptual and methodological problem for all sciences using geographic information. This paper teases out issues of scale and ecological fallacy from the literature and discusses how these issues influence the applicability of an influential theoretical framework in stream ecology, the River Continuum Concept (RCC). Investigators are faced with decisions regarding scale during sampling location selection, field data capture, and subsequent data interpretation. A thorough understanding of the heterogeneity of stream habitats and the life histories of the organisms being studied could enable investigators to make appropriate methodological choices with regard to sampling resolution and extent. It is crucial that investigators improve their ability to understand the consequences of aggregating and extrapolating data collected point samples in order to adequately evaluate ecological hypotheses operating over relatively broad spatial and temporal scales

From Genes to Networks: The Regulatory Circuitry Controlling Candida albicans Morphogenesis

Online first chapterInternational audienceCandida albicans is a commensal yeast of most healthy individuals, but also one of the most prevalent human fungal pathogens. During adaptation to the mammalian host, C. albicans encounters different niches where it is exposed to several types of stress, including oxidative, nitrosative (e.g., immune system), osmotic (e.g., kidney and oral cavity) stresses and pH variation (e.g., gastrointestinal (GI) tract and vagina). C. albicans has developed the capacity to respond to the environmental changes by modifying its morphology, which comprises the yeast-to-hypha transition, white-opaque switching, and chlamydospore formation. The yeast-to-hypha transition has been very well characterized and was shown to be modulated by several external stimuli that mimic the host environment. For instance, temperature above 37 ℃, serum, alkaline pH, and CO2 concentration are all reported to enhance filamentation. The transition is characterized by the activation of an intricate regulatory network of signaling pathways, involving many transcription factors. The regulatory pathways that control either the stress response or morphogenesis are required for full virulence and promote survival of C. albicans in the host. Many of these transcriptional circuitries have been characterized, highlighting the complexity and the interconnections between the different pathways. Here, we present the major signaling pathways and the main transcription factors involved in the yeast-to-hypha transition. Furthermore, we describe the role of heat shock transcription factors in the morphogenetic transition, providing an edifying example of the complex cross talk between pathways involved in morphogenesis and stress response