Transcriptional plasticity of a soil arthropod across different ecological conditions TJALF E. DE BOER,* ADRIANA BIRLUTIU,† ZOLTAN BOCHDANOVITS,‡ MARTIJN J. T. N. TIMMERMANS,§ TJEERD M. H. DIJKSTRA,‡ NICO M. VAN STRAALEN,* BAUKE YLSTRA – and DICK ROELOFS* *Department of Ecological Science, VU University, de Boelelaan 1085, 1081HV, Amsterdam, the Netherlands, †Radboud University Nijmegen, Intelligent Systems, Toernooiveld 1, 6525ED, Nijmegen, the Netherlands, ‡ Department of Clinical Genetics, Section Medical Genomics, VU University Medical Center, van der Boechorststraat 7, 1081 BT, Amsterdam, the Netherlands, §Department of Ecology and Evolution, Faculty of Natural Sciences, Imperial College London, Exhibition Road, London SW7 2AZ, UK, –Department of Pathology, VU University Medical Centre, de Boelelaan 1117, 1081HV, Amsterdam, the Netherlands Abstract Ecological functional genomics, dealing with the responses of organisms to their natural environment is confronted with a complex pattern of variation and a large number of confounding environmental factors. For gene expression studies to provide meaningful information on conditions deviating from normal, a baseline or normal operating range (NOR) response needs to be established which indicates how an organism’s transcrip- tome reacts to naturally varying ecological factors. Here we determine the transcriptional plasticity of a soil arthropod, Folsomia candida, exposed to various natural environments, as part of a first attempt in establishing such a NOR. Animals were exposed to 26 different field soils after which gene expression levels were measured. The main factor found to regulate gene expression was soil-type (sand or clay). Cell homeostasis and DNA replication were affected in collembolans exposed to sandy soil, indicating general stress. Multivariate analysis identified soil fertility as the main factor influencing gene expression. Regarding land-use, only forest soils showed an expression pattern deviating from the others. No significant effect of land-use, agricultural practice or soil type on fitness was observed, but arsenic concentration was negatively correlated with reproductive output. In conclusion, transcriptional responses remained within a limited range across the different land-uses but were significantly affected by soil-type. This may be caused by the contrasting soil physicochemical properties to which F. candida strongly responds. The broad range of conditions over which this soil-living detritivore is able to survive and reproduce, indicates a strategy of high plasticity, which comes with extensive gene expression regulation. Keywords: ecophysiology, genomics, natural operating range, transcriptional plasticity Received 17 May 2010; revision received 31 October 2010; accepted 3 November 2010 Introduction Genomic and gene expression measurements are becoming commonly used techniques in ecological studies (Gibson 2002; Kammenga et al. 2007). By mea- suring gene expression, we can determine the physio- logical state of animals when exposed to different ecological conditions and determine whether some of these conditions cause adverse effects. In soil ecology one or more species of animals or plants are exposed to disturbed soils in order to determine the impact of local environmental change on soil dwelling species (Roelofs et al. 2008). To arrive at meaningful results for species functioning under stressed conditions, a reference or baseline level of functioning is needed. We dub this baseline response the normal operating range (NOR). Correspondence: Tjalf de Boer, Fax: +31 (0)205987123; E-mail: tjalf.de.boer@falw.vu.nl Ó 2011 Blackwell Publishing Ltd Molecular Ecology (2011) 20, 1144–1154 doi: 10.1111/j.1365-294X.2010.04985.x