Contrasting Physiological Responses of Two Populations of the Razor Clam Tagelus dombeii with Different Histories of Exposure to Paralytic Shellfish Poisoning (PSP) Jorge M. Navarro 1 *, Katerina Gonza ´ lez 2 , Barbara Cisternas 1 , Jorge A. Lo ´ pez 1 , Oscar R. Chaparro 1 , Cristian J. Segura 1 , Marco Co ´ rdova 3 , Benjamı´n Sua ´ rez-Isla 3 , Marı´a J. Fernandez-Reiriz 4 , Uxio Labarta 4 1 Instituto de Ciencias Marinas y Limnolo ´ gicas, Universidad Austral de Chile, Valdivia, Chile, 2 Escuela de Acuicultura, Universidad Cato ´ lica de Temuco, Temuco, Chile, 3 Laboratorio de Toxinas Marinas, Facultad de Medicina, Universidad de Chile, Santiago, Chile, 4 Instituto de Investigaciones Marinas, Consejo Superior de Investigaciones Cientı ´ficas, Vigo, Espan ˜a Abstract This study describes the physiological performance of two populations of the razor clam Tagelus dombeii from two geographic areas with different histories of exposure to paralytic shellfish poisoning (PSP) linked to the toxic dinoflagellate Alexandrium catenella. Clams from Melinka-Ayse ´n, which are frequently exposed to PSP, were not affected by the presence of toxins in the diet. However, clams from Corral-Valdivia, which have never been exposed to PSP, exhibited significantly reduced filtration activity and absorption, affecting the energy allocated to scope for growth (SFG). Ammonia excretion and oxygen uptake were not affected significantly by the presence of A. catenella in the diet. Measurements of energy acquisition and expenditure were performed during a 12-day intoxication period. According to three-way repeated measure ANOVAs, the origin of the clams had a highly significant effect on all physiological variables, and the interaction between diet and origin was significant for the clearance and absorption rates and for the scope for growth. The scope for growth index showed similar positive values for both the toxic and non-toxic individuals from the Melinka-Ayse ´ n population. However, it was significantly reduced in individuals from Corral-Valdivia when exposed to the diet containing A. catenella. The absence of differences between the physiological response of the toxic and non-toxic clams from Melinka-Ayse ´n may be related to the frequent presence of A. catenella in the environment, indicating that this bivalve does not suffer negative consequences from PSP. By contrast, A. catenella has a negative effect on the physiological performance, primarily on the energy gained from the environment, on T. dombeii from Corral-Valdivia. This study supports the hypothesis that the history of PSP exposure plays an important role in the physiological performance and fitness of filter feeding bivalves. Citation: Navarro JM, Gonza ´lez K, Cisternas B, Lo ´ pez JA, Chaparro OR, et al. (2014) Contrasting Physiological Responses of Two Populations of the Razor Clam Tagelus dombeii with Different Histories of Exposure to Paralytic Shellfish Poisoning (PSP). PLoS ONE 9(8): e105794. doi:10.1371/journal.pone.0105794 Editor: Hans G. Dam, University of Connecticut, United States of America Received March 21, 2014; Accepted July 24, 2014; Published August 25, 2014 Copyright: ß 2014 Navarro et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are within the paper and its Supporting Information files. Funding: This study was funded by the Comisio ´ n Nacional de Investigacio ´ n Cientı ´fica y Tecnolo ´ gica de Chile (CONICYT-CHILE), by research grants to JMN (FONDECYT 1080127 and FONDECYT 1120470). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * Email: jnavarro@uach.cl Introduction Harmful algae blooms (HABs) are cosmopolitan phenomena that cause serious public health problems. HABs are also detrimental to aquatic organisms, with negative effects on their physiological functions and also on aquaculture activities. During recent decades, HABs producing paralytic shellfish poisoning (PSP) have increased worldwide [1,2], and dinoflagellates of the genus Alexandrium are the primary producer of the paralytic toxin. This toxin may accumulate in different taxa of the marine food chain, including bivalves, zooplankton, crustaceans, and gastropods [3]. Several physiological and behavioral effects have been described in marine copepods and bivalves exposed to diets containing PSP, such as reductions in ingestion, metabolism and growth rates [4,5,6,7,8] and changes in the burial patterns of infaunal bivalves [9]. However, the responses to PSP may be influenced by the history of exposure to the toxin [9]. The evolution of grazer adaptation to toxic algae, in both the ocean and freshwater, has been well established [8]. Populations of the copepod Acartia hudsonica historically exposed to PSP produced by bloom of dinoflagellates of the genus Alexandrium spp., exhibit enhanced feeding and growth rate, as well as fecundity [10,7], compared to populations never exposed to PSP. Hairston et al. [11] showed that the freshwater grazing cladoceran Daphnia galeata evolved a selection response to increased abundance of toxic cyanobacteria in its environment. Mya arenaria clams from areas frequently exposed to toxic dinoflagellate blooms are less affected by PSP than specimens from areas that have not been previously exposed to PSP [9]. According these authors, the PLOS ONE | www.plosone.org 1 August 2014 | Volume 9 | Issue 8 | e105794