SHORT COMMUNICATION Optocardiographic recording of heart rate in Talitrus saltator (Amphipoda: Talitridae) PIERO CALOSI, GUIDO CHELAZZI and ALBERTO UGOLINI Dipartimento di Biologia Animale e Genetica Universita` di Firenze, Firenze, Italy Abstract. An optocardiographic non-invasive technique was used to monitor heart activity in small arthropods. Heart rate was recorded in adult individuals of the supralittoral amphipod Talitrus saltator after 3 h of immersion in marine artificial water (0, 11 and 33‰, t ¼ 15  1  C). Mean heart rate ( SE) ranged from 210  26 beats min 1 (at 33‰) to 276  15 beats min 1 (at 0‰) and, despite the small increase in temperature (0.5  C) due to the infrared beam, the heart frequency remained constant for several hours. Neither the glue used to apply the sensor to the animal nor the beating of the pleopods affected heart rate. This technique could be a useful tool for the investigation of ecophysiological aspects in T. saltator, which is already well known for its ecology and behaviour. Key words. Heart rate, recording technique, sandhoppers, Talitrus saltator. Introduction Metabolic activity in invertebrates usually is evaluated by means of oxygen consumption, and several studies of the relationship between metabolism and abiotic environmental factors in amphipods have been based on this parameter (Opalinski & Jaz˘dz˘ewski, 1978; Opalinski, 1980; Venables, 1980; Williams, 1981). Heart rate in Crustacea has rarely been proposed as a parameter of metabolism (McMahon, 1998). In sandhoppers, studies on the use of heart rate as indicator of metabolism are absent. Due to their small size, the application of invasive heart detection techniques is not possible, although some studies have used various visual observation techniques. In the amphipod Hyale camptonyx, Dubuisson (1928) demonstrated the dependence of pleopo- dal respiration movements on cardiac pulsations, Kinne (1961) studied the heart beat of Gammarus zaddachi in different environmental conditions and Opalinski (1979) investigated the dependence of heart rate on temperature and body weight in the Antarctic amphipod Parathemisto gaudichaudi. More recently, Spicer & Morritt (1996) studied the ontogenic changes in cardiac function in Gammarus duebeni and other crustaceans. Few other techniques to monitor heart activity are non- invasive. Among them are a technique introduced by Coelho & Amaya (2000) used on the spider Aphonopelma hentzi and an infrared (IR)-based technique introduced by Depledge & Andersen (1990). The optocardiographic tech- nique developed by Depledge (Depledge & Andersen, 1990) and later modified by Santini et al. (1999) has been used to monitor heart beat activity in response to various environ- mental factors in several rocky shore gastropods and deca- pods (Bamberg & Depledge, 1997; Chelazzi et al., 1999; DePirro et al., 1999a,b; Santini et al., 1999; Rovero et al., 2000; DePirro et al., 2001). This technique is based on an IR light-emitting diode coupled axially with a phototransistor. Because it is non-invasive, it has led to a considerable increase in heart rate studies under experimental laboratory conditions, and has also made it possible to carry out record- ings easily in the field (Chelazzi et al., 1999; Santini et al., 1999). The supralittoral amphipod Talitrus saltator (Montagu) is well known for its behavioural and physiological adapta- tion to sandy beach ecosystems (Pardi & Ercolini, 1986; Morritt, 1988; Ugolini, 1996; Morritt & Spicer, 1998; Ugolini, 2003). Indeed sandhoppers are important elements of the sandy beach food chain on account of their detri- vorous habits (Griffiths et al., 1983; Wildish, 1988). The aim of this study was to evaluate the use of the IR-based optocardiographic technique in the Mediterranean sandhopper, T. saltator, and to record its heart rate under standard conditions. The heart rate of talitrids could be a useful tool for the monitoring of environmental stress factors. Correspondence: Dr A. Ugolini, Dipartimento di Biologia Animale e Genetica, Universita` di Firenze, Via Romana 17, I-50125 Firenze, Italy. E-mail: ugolini_alb@dbag.unifi.it Physiological Entomology (2003) 28, 344–348 344 # 2003 The Royal Entomological Society