Vol.4, No.6A, 46-52 (2013) Agricultural Sciences http://dx.doi.org/10.4236/as.2013.46A007 Thermal preference, tolerance and temperature-dependent respiration in the California sea hare Aplysia californica Ana Denisse Re1*, Fernando Díaz1, Alfredo Salas-Garza2, Marco Gonzalez2, Victor Cordero1, Clara E. Galindo-Sanchez3, Edna Sanchez-Castrejon4, Adolfo Sánchez Zamora5, Alexei Licea-Navarro1 1Laboratorio de Ecofisiología de Organismos Acuáticos, Departamento de Biotecnología Marina, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Ensenada Baja California, México; *Corresponding Author: [email protected] 2Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Ensenada Baja California, México 3Laboratorio de Genómica Funcional, Departamento de Biotecnología Marina, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Ensenada Baja California, México 4Laboratorio de Biología Celular y Molecular, Departamento de Biotecnología Marina, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Ensenada Baja California, México 5Unidad Multidisciplinaria de Docencia e Investigación, Facultad de Ciencias, Universidad Autónoma de México, Sisal, México Received 20 April 2013; revised 20 May 2013; accepted 10 June 2013 Copyright © 2013 Ana Denisse Re et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT temperature-dependent. Several laboratory studies of A. californica have documented these rates at different The thermoregulatory behavior of sea hare Aplysia rearing temperatures. It has been a standard hatchery californica was determined in a horizontal ther- practice to maintain a post-metamorphosis rearing tem- mal gradient; with a preferred temperature (PT) perature of 15˚C, with the objective to prevent the onset of 18.3˚C for the day cycle and 20.8˚C for the of sexual maturity before 9 months of age [1-4]. night cycle. The displacement velocity demon- Recently, environmental factors involving influence on strated an initial rate of 30 cm·h−1 and gradually −1 growth of A. californica have been studied in laboratory- the velocity diminished to 18 cm·h with several reared under controlled conditions [5]. The decision to fluctuations mainly at 02:00 am. Critical Tem- analyze Aplysia’s behavior in this particular ambiance perature Maxima (CTMax refers to the tempera- has its logic in the similar conduct Aplysia expresses in ture point where at least 50% of the experimental the field or in a regulated context. Nonetheless, there are group have a loss of attachment) was measured differences caused by the greater environmental factors at three acclimation temperatures (16˚C, 19˚C and in the field compared to laboratory environments [6]. 22˚C). At the lowest acclimation temperature Aplysia californica is found between Oregon and the (16˚C), 50% of the experimental group had an Gulf of California, and Aplysia vaccaria is extended attachment loss at CTMax 32.7˚C, and in a higher from California to the Gulf of California [7]. [8] found acclimation temperature (22˚C) CTMax was 36.2˚C. only one specimen of Aplysia californica in Las Conchas The Oxygen Consumption Rate (OCR) was closely Ecuador. [3,4,9] varied on the following factors such as correlated to acclimation temperature, and at temperature, food or stocking density in A. californica, 16˚C and 19˚C sea hare had a relatively stable maintained in laboratory conditions, while keeping the metabolic rate, with OCR increasing to 9 mg O2 others constant; these studies demonstrated that each −1 −1 h ·kg w.w. in a higher acclimation temperature. factor had a strong effect on growth rate and size at sex- ual maturity. One factor that does not appear to influence Keywords: Thermoregulatory Behavior; CTMax; growth and maturation, however, is the time of year the Oxygen Consumption; Aplysia californica life cycle begins [2,10,11]. [5] correlated that rearing temperatures would influ- 1. INTRODUCTION ence the growth rate and longevity at which A. califor- nica becomes sexually mature in the laboratory. They In the case of ectothermic organisms the growth rate is observed that A. californica lives more days in low tem- Copyright © 2013 SciRes. OPEN ACCESS A. D. Re et al. / Agricultural Sciences 4 (2013) 46-52 47 peratures than higher, but the size is larger in high tem- intimately associated with metabolic work and the en- peratures. Probably there are multiple effects in its me- ergy flow that an organism can use for homeostatic con- tabolism, unfortunately there is not enough information trol mechanisms. in order to know them or to determine which would be The aim of this study is to know in Aplysia californica, its best performance at a given temperature. the preferred temperature in which it can be correlated to Behavioral thermoregulation can be adaptive in two the optimal growth, the effect of critical temperature in complementary ways: 1) it can help an organism avoid order to know its thermal tolerance, and in which tem- extreme heat or cold that could be damaging or lethal perature it has its best metabolic response. [12]; 2) it can increase the time an animal spending at optimal physiological temperatures [13]. The thermal 2. MATERIALS AND METHODS preference of a species corresponds closely with a tem- perature that maximizes growth, and other physiological Sea Hare and Experimental Design processes [14,15]. The temperature intervals in which the Adult Aplysia californica were collected in nets in the organism congregates or spends time are defined opera- intertidal zone in the area of Punta Morro Baja California, tionally as preferred temperature or thermal preference México (32.25˚ Lat N 116.983 Long W). The organisms [16]. In order to determine these two processes two were kept for thirty days in reservoirs of 2000 L, 35‰ methods are utilized, acute and gravitational by bipartite salinity and 16˚C ± 1˚C as the same conditions measure definition [17]. As for the gravitational method it takes in the moment of capture in a flow-through water system. 24 hours and the preferendum to determine organisms The photoperiod was maintained at 12 - 12 h light-dark gravitates freely towards their preferred temperature [18, with a 30 minute transition periods in between. 19]. We used 90 organisms acclimated to 16˚C, 19˚C and [20] mentions that critical thermal limits are typically 22˚C ± 1˚C experimental condition. The Aplysia califor- determined experimentally within a controlled laboratory nica was kept for 21 days in acclimated time. Afterwards, environment and are often based on dynamic non-lethal a group of 6 organisms was introduced to the horizontal or static lethal methods. The Critical Thermal Method thermal gradient described by [30]. A Neslab thermo- involves a dynamic changing temperature at a constant regulator (HX model 150) was connected at one end to rate until a Critical Thermal End Point (predefined sub- cool the water gradient. A 1000 watts heater was placed lethal endpoint), is reached. In order to measure thermal at the opposite end connected to a temperature controller tolerance in marine environment, where organisms are (Moeller CI-K3-125-M), generating a steady gradient of often exposed to relatively high temperatures, the CTMax 10˚C to 30˚C, (y = 6.20 + 1.60x, r2 = 0.98 where x = gra- previously mentioned is likely to be one of the principal dient segments, and each segment = temperature gradi- methods in terms of ecological significance [21]. ent). Twenty aeration stones were placed along the gra- Thermal stress in aquatic organisms is likely to in- dient to maintain a dissolved oxygen concentration of 5.8 crease with the effect of global climate change. CTE is a - 7.2 mg·L−1 and thus eliminate the effect of stratification behavioral stress response and is defined as the arithme- of the water column. The depth of the water column in tic mean of collecting thermal points at which mobile the gradient was 9 cm and to maintain good water quality activity becomes disorganized to the point that organisms turnover rate was 10.0 - 12.0 L·h−1. Every organism was lose their ability to escape conditions that will lead to tagged with a nylon tread, a circular plastic tag allowed death [22]. The analogous behavioral stress response of us to identify the experimental organism behavior; now aquatic macroinvertebrates varies amongst taxa but gen- we could determine the preferred temperature gravita- erally includes inability to remain attached to a substrate tional method as applied and described by [18]. or increased movement, followed by immobility with a Six tagged Aplysia were introduced to the gradient in lack of response when stimulated [23]. the segment where the water temperature was the same In the intertidal zone, organisms can spend part of as that of the experimental acclimation temperatures. their lives immersed in stable and benign seawater and They were exposed at day to a light intensity of 0.55 × the remaining time in extreme conditions during emer- 1015 quanta·sec−1·cm−2 and at night to a light intensity of sion. Therefore, the relationship between temperature 0.09 × 1015 quanta·sec−1·cm−2. For each temperature and metabolism of animals living in the intertidal zone there were four trials performed (N = 60). Nudibranches can provide a suitable model to clarify their physiologi- were not fed 24 h before the trial period to avoid inter- cal adaptation to temperature fluctuation [24]. Among ference from the diet [31,32]. the physiological parameters that correlate with envi- The velocity displacement of the sea hare in the gra- ronmental changes such as temperature, the measurement dient was determined by observing the tagged organism of the metabolic rate allows us to determine the energetic in each segment of the trough every hour during the 24 h cost that combinations have on an organism [25-27].