Behavioral thermoregulation and critical thermal limits of giant keyhole limpet Megathura crenulata (Sowerby 1825) (Mollusca; Vetigastropoda) $ Fernando Díaz a,n , Ana Denisse Re a , Alfredo Salas b , Clara E. Galindo-Sanchez c , Marco A. Gonzalez b , Adolfo Sanchez d , Carlos Rosas d a Laboratorio de Ecofisiología de Organismos Acuáticos, Departamento de Biotecnología Marina, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Carretera Ensenada–Tijuana # 3918, Ensenada, Baja California, México b Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Kilometro 103 Carretera Tijuana–Ensenada, Ensenada, Baja California, México c Laboratorio de Genómica Funcional, Departamento de Biotecnología Marina, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Carretera Ensenada–Tijuana # 3918, Ensenada, Baja California, México d Unidad Multidisciplinaria de Docencia e Investigación, Facultad de Ciencias, Universidad Nacional Autónoma de México, Puerto de abrigo s/n, Sisal, Yucatán, México article info Keywords: Preferred temperature Critical thermal maxima Gastropod abstract The thermoregulatory behavior of the giant keyhole limpet Megathura crenulata was determined in a horizontal thermal gradient during the day at 18.9 1C and 18.3 1C for the night. The final preferendum determined for giant keyhole limpets was of 18.6 71.2 1C. Limpets' displacement velocity was 10.0 73.9 cm h −1 during the light phase and 8.4 71.6 cm h −1 during the dark phase. The thermotolerance (measured as CTMax at 50%) was determined in a keyhole limpet in three acclimation temperatures 17, 20, and 23 1C. Limpets were subjected to water increasing temperatures at a rate of 1 1C every 30 min, until they detached from the substrate. The critical thermal maximum at 50% was 27.2, 27.9 and 28.3 1C respectively. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Temperature is one of the principal abiotic factors influencing aquatic organisms. Marine ectotherms are especially affected by this variable, it exerts its effect at different levels of organization, for instance molecular, biochemical, physiological and behavioral (Stillman and Somero, 2000; Mora and Ospina, 2001). Thermal stress leads to changes in energy allocation for organisms' activ- ities such as growth, reproduction and foraging, with conse- quences in their performance and fitness (Pörtner et al., 2008). The intertidal ectotherms body temperature can vary drasti- cally in low tides, making the intertidal zone of wave-washed rocky shores one of the most thermally stressful habitats; causing interspecific differences in thermal environment tolerance, which have been implicated in establishing the vertical zonation characteristics of intertidal zones (Harley, 2008; Miller et al., 2009; Tepler et al., 2011). Organisms living in greater vertical shore heights, evolved specific adaptations that allow them to cope with environmental stress due to exposure to terrestrial conditions; this characteristic makes intertidal organisms great models for ecology, evolution stress and physiology studies (Stillman, 2002). Many ectotherms are able to buffer the effects of space–time heterogeneity in thermal stress, these occurring in the intertidal zone in relation to diel and tidal cycles. More specifically, survival is warranted by adjustment of their body temperatures through a range of physiological, behavioral, and morphological adaptations (Somero, 2002; Lee and Lim, 2009). The tolerance window for each species is described as a favorable range of temperature or performance breadth. It includes an optimal and suboptimal zone, above or below that range, performance is negatively affected and the species cannot survive unless it is for a limited period of time (Madeira et al., 2012). Nonetheless, all species do not exhibit the same thermoregulatory ability. Specifically, tropical species inhabit stable and nonseasonal environments and have physiological acclimation abilities to thermal stress, as their thermal windows are narrower than those of temperate species (Compton et al., 2007; Chapperon and Seuront, 2011). Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jtherbio Journal of Thermal Biology 0306-4565/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jtherbio.2013.05.007 ☆ This article belongs to the Special Issue dedicated to Prof. Ken Bowler for on- going, long-term contributions to thermal biology; WHAT SETS THE LIMIT? HOW THERMAL LIMITS, PERFORMANCE AND PREFERENCE IN ECTOTHERMS ARE INFLU- ENCED BY WATER AND ENERGY BALANCE n Correspondence to: Departamento de Biotecnología Marina (CICESE), P.O. Box 430222, San Diego, CA 92143-0222, USA. Fax +1 52 646 175 05 69. E-mail address: fdiaz@cicese.mx (F. Díaz). Please cite this article as: Díaz, F., et al., Behavioral thermoregulation and critical thermal limits of giant keyhole limpet Megathura crenulata (Sowerby 1825) (Mollusca; Vetigastropoda). J. Thermal Biol. (2013), http://dx.doi.org/10.1016/j.jtherbio.2013.05.007i Journal of Thermal Biology ∎ (∎∎∎∎) ∎∎∎–∎∎∎