ANIMAL BEHAVIOUR, 1999, 57, 1145–1149 Article No. anbe.1998.1075, available online at http://www.idealibrary.com on Laterality and cooperation: mosquitofish move closer to a predator when the companion is on their left side ANGELO BISAZZA*, ANDREA DE SANTI* & GIORGIO VALLORTIGARA† *Dipartimento di Psicologia Generale, Universita` di Padova †Dipartimento di Psicologia, Universita` di Trieste (Received 22 September 1998; initial acceptance 10 November 1998; final acceptance 27 December 1998; MS. number: 5998) Mirror images simulating social partners that cooperated or defected have been used as an experimental method to test the hypothesis that, while inspecting a predator, pairs of fish play a conditional strategy, Tit for Tat, in an iterated version of the Prisoner’s Dilemma game. Using this method, we found that predator inspection was more likely to occur when the mirror image was visible on the left rather than on the right side of mosquitofish, Gambusia holbrooki. The same occurred even when a videorecorded stimulus presentation was used, in which sequences of the predator were mixed with their mirror-image equivalents, thus showing that the asymmetry was not due to behavioural or morphological asymmetries of the predator itself. Moreover, irrespective of whether they were tested with a cooperative (parallel mirror) or a defecting (angled mirror) partner, mosquitofish drew closer to the predator when the mirror was on their left side. These findings suggest that the images seen on the right and left sides by a fish may evoke different types of social behaviour, probably because of differing modes of analysis of perceptual information carried out by the left and right sides of the brain; accurate control and balancing of the side of presentation of visual stimuli during behavioural experiments thus appears to be crucial. when the appearance of an otherwise familiar object is changed (Vallortigara & Andrew 1991; Vallortigara et al. 1999). In detour tests, male mosquitofish, Gambusia holbrooki, showed a right eye preference during lateral fixation of a stimulus of interest (i.e. females, predator); the preference disappeared or reversed when more neutral stimuli were used (i.e. an empty cage or an opaque barrier; see Bisazza et al. 1997a, 1998b). Are these asymmetries capable of affecting in any significant way the normal behaviour of animals? Although this has been hypothesized to be the case for birds (Andrew 1988; Workman & Andrew 1989; Vallortigara et al. 1997, 1999), direct evidence is scant. If behavioural asymmetries prove to be important in the everyday behaviour of animals, then the evolutionary pressures and genetic mechanisms maintaining these asymmetries should be of concern to evolutionary biologists. In particular, it will be crucial to establish when and why the advantages of having asymmetric brains could overcome the obvious disadvantages of displaying evident (and predictable) asymmetric behavioural patterns. To investigate this issue we took advantage of an experimental paradigm that has been widely used in recent years in the field of behavioural ecology. It is common among fish that pairs of individuals leave their shoal in order to approach and inspect a potential Hemispheric specialization of function has long been considered unique to the human species. In recent years, however, a large body of evidence has shown that in a variety of vertebrate species stimuli are processed and stored differently in the right and left sides of the brain (review in Bradshaw & Rogers 1993). Although the field of hemispheric specialization has been a domain of neurologists and neuropsychologists, there are recent signs of interest by evolutionary biologists as well (Hori 1993; Raymond et al. 1996). Apart from handedness, lateral asymmetries in humans typically manifest in pathological conditions or in highly unnatural settings (see Bradshaw & Rogers 1993). However, in species with laterally placed eyes and small binocular overlap, preferential use of the right or left eye has been shown to be associated with inspecting different stimuli or carrying out different cognitive tasks (Workman & Andrew 1986; Dharmaretnam & Andrew 1994; Cantalupo et al. 1995; Vallortigara et al. 1996; Bisazza et al. 1997a, b). For instance, chicks tend to fixate imprinting objects with the lateral field of the right eye and to shift to the left eye Correspondence: A. Bisazza, Dipartimento di Psicologia Generale, Universita` di Padova, Via Venezia 8, 35135 Padova, Italy (email: [email protected]). G. Vallortigara is at the Dipartimento di Psicologia, Universita` di Trieste, Via dell’Universita` 7, 34123 Trieste, Italy. 0003–3472/99/051145+05 $30.00/0 1999 The Association for the Study of Animal Behaviour 1145 1999 The Association for the Study of Animal Behaviour 1146 ANIMAL BEHAVIOUR, 57, 5 Glass plate Parallel mirror 10 9 8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 Angled mirror 8 9 10 Plant Figure 1. Experimental apparatus showing the position of the test fish and the mirrors simulating a cooperative (parallel mirror) and defecting (angled mirror) companion. The predator is shown in the central tank. The experimental tanks were divided into 10 sectors of equal length. predator (Magurran & Pitcher 1987; Magurran & Seghers 1990). The risk of being preyed upon is shared if both fish simultaneously inspect the predator, but not if one of the fish remains at a distance. Fish are thus believed to face a classic Prisoner’s Dilemma in this situation, and predator inspection behaviour has been used as a model to analyse the evolution of mutual cooperation among unrelated individuals. In an influential paper, Milinski (1987) found that sticklebacks, Gasterosteus aculeatus, are more likely to approach a predator when a mirror is placed parallel to the tank so that the image appears to swim along with the fish (simulating a cooperative partner) than when the mirror is angled so that the image appears to swim away from the fish (simulating a defecting partner). Similar results were obtained using guppies, Poecilia reticulata (Dugatkin 1988) and mosquitofish (Stephens et al. 1997). In this study we duplicated Milinski’s original procedure. However, we checked for the effects of positioning a mirror on either the left or the right side of the fish. In the first experiment we measured the tendency of a female mosquitofish to inspect a pumpkinseed sunfish, Lepomis gibbosus, when a parallel mirror simulated a cooperating companion. To check for possible effects induced by a lateralized behaviour of the predator itself, in the second experiment we repeated the test using a manipulated video playback of the predator. The third experiment was aimed at estimating to what extent laterality could have produced artefacts in previous studies using cooperative predator inspection. METHODS Subjects In all experiments we used wild-caught female mosquitofish. They were kept in 150-litre tanks and fed dry fish food daily. Water temperature was maintained at 252C; artificial lighting was provided 16 h a day. Gambusia are live-bearing fish native to the southeastern United States and were introduced in Europe at the beginning of the 20th century for the control of mosquito larvae. Pumpkinseed sunfish, the species used as a predator stimulus, is also native to North America and was introduced in Europe in the 19th century. Both species are widely distributed in Italy and often found in the same habitats. Although L. gibbosus feed mainly on invertebrates, they occasionally capture small fish and in the laboratory readily eat adult mosquitofish. Mosquitofish and sunfish were caught at the same location (Idrovia Padova-Venezia, near Camin, northeast Italy) and released at the site of capture after the experiments. Apparatus and Procedure The apparatus used for experiments 1 and 3 (Fig. 1) consisted of three identical glass tanks (604035 cm), a central tank containing the predator and two lateral experimental tanks. Each experimental tank was divided into 10 sectors of equal length; section 1 was the closest to the predator. The two experimental tanks were divided longitudinally with a glass plate and a mirror was leant against one or other side of this plate. Fish could thus be tested with the mirror placed on their right or on their left side. A simulated plant composed of a series of elongated bars, 1 cm in size and spaced 1 cm apart, was located between sectors 8 and 9 making available to the fish a ‘safe’ starting area. The fish was dip-netted from a nearby holding tank and introduced into sectors 10 and 9. We recorded by direct observation the position of the fish every 10 s beginning when it first exited from the safe area. Each fish was tested only once. We computed the average position occupied by the fish during a 10-min testing period. In experiment 1, we placed a mirror (5830 cm) parallel to the tank either on the left or the right side. To control for possible tank effects, use of the left and right lateral tanks was counterbalanced. Four pumpkinseed BISAZZA ET AL.: LATERALITY IN PREDATOR INSPECTION 1147 Table 1. Sector position (X±SEM) of mosquitofish in the experimental apparatus in the presence of a live or recorded predator Sector position (±SEM) Experiment 1 2 3 Mirror Mirror Mirror Mirror parallel (live predator) parallel (video playback of live predator) parallel (live predator) angled away (live predator) Left Right 6.35±0.37 4.42±0.49 6.83±0.66 7.92±0.44 7.94±0.30 6.11±0.49 7.91±0.25 8.91±0.22 The experimental tank was divided into 10 sectors, with sector 1 being closest to the predator. sunfish (average length 104 mm) were alternated in the role of predator. We tested 40 mosquitofish (mean lengthSEM=29.20.51 mm), 20 for each treatment (in each treatment, 10 animals with the right and 10 with the left lateral tank). In experiment 2, we presented a videorecorded image of the predator on a 14-inch monitor in front of a single experimental tank, with the mirror either on the right or the left side. The behaviour of a sunfish facing a mosquitofish was videorecorded. Then, using digital techniques (Avid Videoshop for Power Macintosh), we reassembled alternating pieces of original sequences (12– 20 s in length) and their mirror-image versions, thus generating a 10-min video with no behavioural or morphological asymmetry of the predator. The monitor was placed 12 cm away from the tank; the size of the video image of the predator was increased by a factor of 2.5 in order to compensate partly for the changed retinal size consequent to the different viewing distance. We tested 24 mosquitofish (mean lengthSEM=28.40.53 mm), 12 for each left or right treatment. In experiment 3, we used the same apparatus and procedure as in experiment 1. This time, however, a mirror parallel to the tank (5830 cm) and a mirror angled 30 away and much shorter (2830 cm) were used as independent testing conditions (three sunfish alternated in the role of predator). We tested 36 mosquitofish (mean lengthSEM=29.20.64 mm), nine for each left or right treatment. RESULTS In experiment 1, predator inspection was more likely to occur when the cooperative partner was visible on the left rather than on the right side of the mosquitofish (Table 1). An ANOVA revealed a significant main effect of the side of the mirror (F1,36 =10.678, P=0.002). Tank effect and interaction were not significant (F1,36 =0.0001, P=0.99; F1,36 =0.214, P=0.65, respectively). There were no significant effects associated with the four different pumpkinseed sunfish used as the predator (F3,36 =0.59, NS). Since the trials lasted quite a long time (10 min) we also analysed the data for 2-min intervals, to check for any effect of habituation to the predator. The ANOVA revealed significant effects of duration (F4,152 =10.7, P<0.001) and side of the mirror (F1,38 =11.2, P=0.002) but no significant interaction (F4,152 =1.20, NS). In experiment 2, mosquitofish were more likely to approach the video playback of the predator when their own mirror image swam on their left rather than on their right side (F1,22 =5.79, P=0.025; Table 1). In experiment 3, the ANOVA revealed a significant main effect of the angle of the mirror (F1,32 =5.82, P=0.022) and of its right–left position (F1,32 =5.68, P=0.023). There was no significant interaction between the angle of the mirror and the right–left position (F1,32 =0.10, P=0.921). There were no significant effects associated with the three different pumpkinseed sunfish used as the predator (F2,33 =1.82, NS). The fish were more likely to approach the predator with the parallel mirror than with the angled mirror, thus duplicating Milinski’s classic findings. However, irrespective of whether they were tested with a cooperative (parallel mirror) or a defecting (angled mirror) partner, fish drew closer to the predator when the mirror was on their left side. DISCUSSION Our results show that in mosquitofish the propensity to inspect a predator depends on the side on which a social partner happens to be located, and that this effect cannot be accounted for in terms of morphological or behavioural asymmetries of the predator itself. These findings support recent claims suggesting homology of cerebral lateralization in teleosts and tetrapods: in spite of substantial differences between species in the general structure of the nervous system, there is growing evidence that the functional specializations of the two halves of the brain may be conserved throughout a wide evolutionary spectrum (Bisazza et al. 1998a; Miklosi et al. 1998; Robins et al. 1998; Vallortigara et al. 1998). The most likely explanation for the reported asymmetry is that mosquitofish tend to use the lateral parts of the right and left eyes for different purposes. When faced with a vertical-bar barrier through which a target was visible, female mosquitofish turned to the left so that they were using their right eye to look at the target when the target was a predator and vice versa when the target was conspecifics of the same sex (Bisazza et al. 1998b). Results suggest that these lateral biases arise as a consequence of preferential right- or left-eye use during 1148 ANIMAL BEHAVIOUR, 57, 5 sustained viewing of biologically relevant visual stimuli (Bisazza et al. 1997a). Considering that during the present tests mosquitofish typically swam very close to the mirror, it seems likely that positioning the mirror on the left side produced the best arrangement of monocular lateral stimulation, with the right eye fixating the predator and the left eye monitoring the companion. At present, we have no data to disentangle the roles played by right-eye use in fixation of the predator and left-eye use in fixation of the companion; in principle, either would suffice for producing the reported asymmetry, but it is probable that both contribute. The use of conditional strategies such as Tit for Tat rests on a monitoring of the cooperative or defecting behaviour of the other member of the pair and on the recognition of its identity. There is widespread evidence that among birds and mammals the neural structures in the right side of the brain have a dominant role in the recognition of individual conspecifics (review in Vallortigara & Andrew 1994a). It is unknown whether similar specializations hold for lower vertebrates such as fish but, if so, that may explain why it is the left eye (mainly feeding neural structures on the right side of the brain) that is used to monitor the behaviour of the image on the mirror. Alternative explanations for the hypothesis that fish in Milinski’s procedure are playing Tit for Tat have, however, been proposed (e.g. that they are simply schooling; Masters & Waite 1990). These different hypotheses could perhaps be tested with reference to the differential modes of analysis of perceptual information between the two halves of the brain. Whatever the final outcome of the theoretical discussion associated with the use of predator inspection responses as a way to investigate strategies of cooperation (Masters & Waite 1990; Reboreda & Kacelnik 1990; Milinski et al. 1997), it is apparent from our data that without proper control and counterbalancing of the side of presentation of visual stimuli, lateralization of response may affect the results. Our attempt to duplicate Milinski’s overall procedure showed that when the mirror was on the left, fish drew closer to the predator with either a cooperative (parallel mirror) or a defecting (angled mirror) partner (Table 1). Variation arising from left–right positioning of the mirror was equivalent to that arising from the differential cooperativeness of mirror images. This suggests that in previous studies any partner’s influence was properly assessed only when the mirror was on the same side of the fish being treated; if this was not the case, a zeroing or an artefactual increase of the phenomenon might have occurred (assuming, of course, that lateralization is there in other species of fish as well). Fish use more than their eyes when interacting with schooling partners (e.g. lateral line, olfaction). In natural situations fish will thus have a variety of sensory information that could compensate for any laterality arising solely from vision. None the less, the possibility that behavioural lateralization produces asymmetries in the organization of social structures such as fish schools deserves consideration (parallel lateralization in other sensory modalities may also be possible, see Vallortigara & Andrew 1994b for birds). Predators could exploit marked asymmetry in social behaviour during the detection of danger and schooling of prey and this therefore does not appear prima facie to be adaptive. However, the phenomenon might have arisen by some combination of the peculiar advantages of having individually asymmetric brains and the need to maintain synchronized social behaviours within the group (Rogers 1989). Obviously, direct extrapolation of our findings to real life situations is difficult. When two fish are engaged in cooperative predator inspection, the fish that has the partner to its left would be expected to approach the predator more closely; but it is unclear what the other fish (which has a partner on its right side) would do. In contrast to a mirror image, a real partner can modify its speed or its direction of movement. Fish within a small school may move continuously in order to occupy the most ‘favourable’ positions in terms of visual processing during sustained viewing, for example conspecifics on the left side, with the ‘free’ and more risky right flank monitored by the right eye. Actually, it could be that any tendency to have conspecifics on the left side is simply a by-product of preferential right use in monitoring the most potentially dangerous parts of the environment. At the level of each individual within a school, the best strategy would be having partners on both sides, but given that some individual must, eventually, occupy the more risky extreme positions, it would be advantageous to do so on the ‘right’ side. These are at present speculations, but we believe that placing the study of brain lateralization into an ecoethological framework promises to be a fruitful enterprise. Acknowledgments We thank R. J. Andrew, A. Pilastro, L. Regolin and L. J. Rogers for reading and commenting on the manuscript. The research was supported by Italian MURST 40% to A.B. References Andrew, R. J. 1988. The development of visual lateralization in the domestic chick. Behavioural Brain Research, 29, 201–209. Bisazza, A., Pignatti, R. & Vallortigara, G. 1997a. Detour tests reveal task- and stimulus-specific behavioural lateralization in mosquitofish (Gambusia holbrooki ). Behavioural Brain Research, 89, 237–242. Bisazza, A., Pignatti, R. & Vallortigara, G. 1997b. Laterality in detour behaviour: interspecific variation in poeciliid fishes. Animal Behaviour, 54, 1273–1281. Bisazza, A., Rogers, L. J. & Vallortigara, G. 1998a. The origins of cerebral asymmetry: a review of evidence of behavioural and brain lateralization in fishes, amphibians, and reptiles. Neuroscience and Biobehavioral Reviews, 22, 411–426. Bisazza, A., Facchin, L., Pignatti, R. & Vallortigara, G. 1998b. Lateralization of detour behaviour in Poeciliid fishes: the effect of species, gender and sexual motivation. Behavioural Brain Research, 91, 157–164. Bradshaw, J. L. & Rogers, L. J. 1993. The Evolution of Lateral Asymmetries, Language, Tool Use and Intellect. San Diego: Academic Press. BISAZZA ET AL.: LATERALITY IN PREDATOR INSPECTION 1149 Cantalupo, C., Bisazza, A. & Vallortigara, G. 1995. Lateralization of predator-evasion response in a teleost fish. Neuropsychologia, 33, 1637–1646. Dharmaretnam, M. & Andrew, R. J. 1994. Age- and stimulusspecific use of right and left eyes by the domestic chick. Animal Behaviour, 48, 1395–1406. Dugatkin, L. A. 1988. Do guppies play tit for tat during predator inspection visits? Behavioral Ecology and Sociobiology, 23, 395– 399. Hori, M. 1993. Frequency-dependent natural selection in the handedness of scale-eating cichlid fish. Science, 260, 216–219. Magurran, A. E. & Pitcher, T. J. 1987. Provenance, shoal size and the sociobiology of predator-evasion behaviour in minnow shoals. Proceedings of the Royal Society of London, Series B, 229, 439–465. Magurran, A. E. & Seghers, B. H. 1990. Population differences in predator recognition and attack cone avoidance in the guppy, Poecilia reticulata. Animal Behaviour, 40, 443–452. Masters, W. & Waite, T. 1990. Tit-for-tat during predator inspection, or shoaling? Animal Behaviour, 39, 603–604. Miklo`si, A., Andrew, R. J. & Savage, H. 1998. Behavioural lateralization of the tetrapod type in the zebrafish (Brachydanio rerio). Physiology and Behavior, 63, 127–135. Milinski, M. 1987. TIT FOR TAT in sticklebacks and the evolution of cooperation. Nature, 325, 433–435. Milinski, M., Lu ¨ thi, J. H., Eggler, R. & Parker, G. A. 1997. Cooperation under predation risk: experiments on costs and benefits. Proceedings of the Royal Society of London, Series B, 264, 831–837. Raymond, M., Pontier, D., Dufour, A. & Møller, A. P. 1996. Frequency-dependent maintenance of left-handedness in humans. Proceedings of the Royal Society of London, Series B, 263, 1627–1633. Reboreda, J. & Kacelnik, A. 1990. On cooperation, tit-for-tat and mirrors. Animal Behaviour, 40, 1188–1189. Robins, A., Lippolis, G., Bisazza, A., Vallortigara, G. & Rogers, L. J. 1998. Lateralized agonistic responses and hindlimb use in toads. Animal Behaviour, 56, 875–881. Rogers, L. J. 1989. Laterality in animals. International Journal of Comparative Psychology, 3, 5–25. Stephens, D. W., Anderson, J. P. & Benson, K. E. 1997. On the spurious occurrence of Tit for tat in pairs of predator-approaching fish. Animal Behaviour, 53, 113–131. Vallortigara, G. & Andrew, R. J. 1991. Lateralization of response to change in a model partner by chicks. Animal Behaviour, 41, 187–194. Vallortigara, G. & Andrew, R. J. 1994a. Differential involvement of right and left hemisphere in individual recognition in the domestic chick. Behavioural Processes, 33, 41–58. Vallortigara, G. & Andrew, R. J. 1994b. Olfactory lateralization in the chick. Neuropsychologia, 32, 417–423. Vallortigara, G., Regolin, L., Bortolomiol, G. & Tommasi, L. 1996. Lateral asymmetries due to preferences in eye use during visual discrimination learning in chicks. Behavioural Brain Research, 74, 135–143. Vallortigara, G., Andrew, R. J., Sertori, L. & Regolin, L. 1997. Sharply timed behavioural changes during the first 5 weeks of life in the domestic chick (Gallus gallus). Bird Behavior, 12, 29–40. Vallortigara, G., Rogers, L. J., Bisazza, A., Lippolis, G. & Robins, A. 1998. Complementary right and left hemifield use for predatory and agonistic behaviour in toads. NeuroReport, 9, 3341–3344. Vallortigara, G., Regolin, L. & Pagni, P. 1999. Detour behaviour, imprinting and visual lateralization in chicks. Cognitive Brain Research, 7, 307–320. Workman, L. & Andrew, R. J. 1986. Asymmetries of eye use in birds. Animal Behaviour, 34, 1582–1584. Workman, L. & Andrew, R. J. 1989. Simultaneous changes in behaviour and in lateralization during the development of male and female domestic chicks. Animal Behaviour, 38, 596–605.
© Copyright 2024