International Journal of Ichthyology - Filer
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International Journal of Ichthyology - Filer
aqua International Journal of Ichthyology Vol. 14 (3), 10 July 2008 Aquapress ISSN 0945-9871 aqua International Journal of Ichthyology Vol. 14 (3), 10 July 2008 Contents: Gerald R. Allen, Joshua Drew and Les Kaufman: Amphiprion barberi, a new species of anemonefish (Pomacentridae) from Fiji, Tonga, and Samoa......................................................................................................... 105-114 Edward O. Murdy: Paratrypauchen, a new genus for Trypauchen microcephalus Bleeker, 1860, (Perciformes: Gobiidae: Amblyopinae) with a redescription of Ctenotrypauchen chinensis Steindachner, 1867, and a key to ‘Trypauchen’ group genera ......................................................................................................... 115-128 Gerald R. Allen, Joshua Drew and Paul Barber: Cirrhilabrus beauperryi, a new wrasse (Pisces: Labridae) from Melanesia ........................................................................................................................................................ 129-140 Kapil Mandrekar and Ronald G. Oldfield: Prior residency and social experience in contests between similar-sized juvenile black Midas cichlids, Amphilophus astorquii ........................................................................... 141-148 John E. Randall1, John L. Earle and Luiz A. Rocha: Xyrichtys pastellus, a new razorfish from the southwest Pacific, with discussion of the related X. sciistius and X. woodi ................................................................................ 149-158 Matthew T. Craig, John E. Randall and Mark Stein: The Fourspot Butterflyfish (Chaetodon quadrimaculatus) from the Philippines and the Solomon Islands, first records for the East Indies and Melanesia ............................... 159-164 Papers appearing in this journal are indexed in: Zoological Record; BioLIS – Biologische Literatur Information Senckenberg; www.aqua-aquapress.com; www.aquapress-bleher.com; www.aquageo.com; www.Joachim-Frische.com Cover photo: Amphiprion barberi, underwater photograph of subadult, about 50.0 mm SL, Namena Island, Fiji, 5 m depth. Photo by G. R. Allen. A view of the crater walls from the shore of Lake Apoyo. See page 143-150. Photo by R. G. Oldfield aqua, International Journal of Ichthyology Prior residency and social experience in contests between similar-sized juvenile black Midas cichlids, Amphilophus astorquii Kapil Mandrekar1 and Ronald G. Oldfield2 1) Department of Biology, Albion College, 611 East Porter St., Albion, MI 49224, USA. Current Address: Department of Biological Sciences, Arkansas State University, P.O. Box 599, State University, AR 72467-0599, USA 2) Museum of Zoology, University of Michigan, 1109 Geddes Ave., Ann Arbor, MI 48109, USA. Current address: Department of Biology, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106, USA. E-mail: [email protected] Received: 14 October 2007 – Accepted: 17 April 2008 Abstract The possible roles of chemical cues and a 3-D structure in eliciting a prior residency effect in juvenile black Midas cichlids, Amphilophus astorquii, were tested under laboratory conditions. The effect of recent social interaction on the outcome of contests was also tested. Fish with a clay pot in their pre-test tanks defeated opponents without such prior experience when test tanks contained an identical pot. Experience in a small group of conspecifics had no significant effect on contest outcome, although fish that held lower size ranks tended to lose contests. The subjects’ chemical cues did not result in a prior residency effect. Interestingly, juvenile Amphilophus cichlids are not typically aggressive in their natural environment. The current results demonstrate that, despite this, they are sufficiently plastic to behave aggressively when resources are made to be defensible by artificially reducing attack distance and number of competitors. In addition, the ability to modify aggressive behavior according to prior experience demonstrates a further degree of plasticity. This suggests that complex behavioral plasticity relating to aggression may generally be of such high adaptive value that it might occur in species for which it might seem to typically have little utility. Zusammenfassung Unter Laborbedingungen wurde bei jungen Schwarzen Midas-Cichliden, Amphilophus astorquii, untersucht, wieweit chemische Merkmale und räumliche Strukturen sich als frühere Wohnraum-Erfahrung auswirken. Außerdem wurde die Auswirkung früherer sozialer Interaktionen auf das Konkurrenzverhalten untersucht. Fische mit einem Tongefäß in ihrem Vortest-Aquarium besiegten Gegner ohne eine solche Erfahrung, wenn sich im Testaquarium ein entsprechendes Gefäß befand. Erfahrungen in einer kleinen Gruppe von Artgenossen hatten keine signifikante Auswirkung auf das Konkurrenzverhalten, wenn auch Fische mit einem niedrigeren Größen-Rang der Tendenz nach eher unterlagen. Die chemischen Merkmale spielten keine Rolle beim Effekt der früheren Wohnraumerfahrung. Interessant ist, dass junge Am141 philophus-Cichliden in ihrer natürlichen Umgebung nicht typischerweise aggressiv sind. Trotzdem legen die neuen Ergebnisse den Schluss nahe, dass ihr Verhalten ausreichend plastisch ist, um dann aggressiv zu werden, wenn künstliche Eingriffe die Angriffsdistanz und die Zahl der Konkurrenten verringert haben und damit eine Verteidigung nötig machen. Die Fähigkeit, das Angriffsverhalten entsprechend früheren Erfahrungen abzuwandeln, ist ein weiterer Beleg für die Plastizität des Verhaltens. Das legt den Schluss nahe, dass eine starke Plastizität beim Agressionsverhalten allgemein von so hohem Anpassungswert ist, dass sie auch bei Arten auftritt, bei denen sie anscheinend wenig Nutzen bringt. Résumé Les rôle possibles de signaux chimiques et une structure 3D pour obtenir un effet de séjour préalable chez les juvéniles d’Amphilophus astorquii ont été testés en laboratoire. L’effet d’interactions sociales récentes sur la survenue de combats a aussi été testé. Les poissons qui avaient un pot de terre cuite dans leurs bacs de prétest battaient les rivaux qui n’avaient pas connu cette situation quand les aquariums du test lui-même contenaient un pot identique. L’expérience menée sur un groupe de congénères ne montrait pas de résultat probant sur l’issue du combat, même si les poissons d’un rang hiérarchique inférieur avaient tendance à perdre. Les signaux chimiques n’avaient pas d’effet de séjour préalable chez les sujets. Chose intéressantes : les juvéniles d’Amphilophus ne sont pas spécialement agressifs dans leur environnement naturel. Les résultats les plus fréquents ont démontré que, malgré ce fait, il sont suffisamment adaptés pour un comportement agressif quand les ressources deviennent défendables par une réduction artificielle de la distance d’attaque et par le nombre de compétiteurs. En outre, la possibilité de modifier le comportement agressif en fonction d’expériences antérieures démontre un autre degré d’adaptabilité. Ceci suggère qu’une plasticité comportementale complexe, en matière d’agressivité, peut être généralement d’une valeur adaptative telle qu’elle peut apparaître chez des espèces pour lesquelles il semble que cette faculté soit typiquement peu utile. aqua vol. 14 no. 3 - 10 July 2008 Prior residency and social experience in contests between similar-sized juvenile black Midas cichlids, Amphilophus astorquii Sommario Il possibile ruolo di segnali chimici e di una struttura 3-D nell’innescare un effetto di priorità territoriale nei giovani del ciclide Mida nero, Amphilophus astorquii, sono stati saggiati in condizioni di laboratorio. è stato anche valutato l’effetto di un’interazione sociale recente sull’esito di competizioni. Pesci posti in una vasca con un vaso d’argilla prima del test respingono coloro che non hanno avuto questa esperienza quando l’esperimento è condotto in vasche contenenti un identico vaso. L’esperienza in un piccolo gruppo di conspecifici non aveva significativi effetti sull’esito della lotta, sebbene gli esemplari di taglia inferiore tendevano a perdere la contesa. Le tracce chimiche dei soggetti non comportavano un effetto di priorità territoriale. Stranamente, i ciclidi giovani di Amphilophus non sono di norma aggressivi nel loro ambiente naturale. I risultati presentati qui dimostrano che, malgrado ciò, essi sono sufficientemente plastici da comportarsi in modo aggressivo quando le risorse rappresentano un qualcosa da difendere in presenza di una distanza d’attacco artificialmente ridotta e di un certo numero di competitori. Inoltre, la capacità di modificare il comportamento aggressivo in base ad esperienze acquisite dimostra un ulteriore grado di plasticità. Ciò suggerisce che la complessa plasticità comportamentale relativa all’aggressività può essere di elevato valore adattativo è può essere bagaglio anche di specie per cui appare in genere di scarsa utilità. INTRODUCTION Aggressive behavior in animals typically occurs in defense of resources (Huntingford & Turner 1987). The outcome of aggressive contests between two animals may be influenced by asymmetries between contestants (Maynard-Smith & Parker 1976). Body size or weapons (claws, horns, teeth, etc.) can be good predictors of contest outcomes (Huntingford & Turner 1987). Prior experience with the local physical or social environment may also alter the probability that an individual will defeat an opponent. A prior-residence effect – an agonistic advantage to animals fighting in familiar locales – has been well documented in fishes (e.g., Turner 1994, Chellapa et al. 1999, Johnsson et al. 1999). Prior social experience in a subordinate role generally results in a decreased probability of attaining dominance in subsequent contests, while prior experience in a dominant role usually has little or no effect (Francis 1983). Interestingly, fishes that are not especially aggressive in their natural environments may nevertheless behave aggressively when space or number of competitors are limited (Grant 1993), as they may be under captive conditions. It is unknown whether such fishes modify aggression according to prior experiences as do some fishes that behave aggressively under natural aqua vol. 14 no. 3 - 10 July 2008 conditions. The aim of the current study was to determine if prior experience is important in influencing agonistic behavior in juveniles of a fish species in which juveniles are known not to be especially aggressive under natural conditions. The behavior of Midas cichlids, Amphilophus citrinellus (Günther, 1864), has been well-studied (Barlow 2000). Feeding territories are extremely rare in freshwater fishes (Barlow 1993, Grant 1997), and under natural conditions Amphilophus cichlids behave aggressively only while defending breeding territories (Barlow 1976). Furthermore, juvenile Amphilophus cf. citrinellus have been observed in Lake Apoyo, Nicaragua not to be attached to specific sites and performing only modest levels of aggression (Oldfield et al. 2006). However, in captivity, the enclosure limits the distance required to deliver an attack, making it easier for an individual to dominate a small number of competitors, and increased aggression is observed (Oldfield 2007). The effects of prior experience have not been tested directly in Amphilophus cichlids, but increased aggression after a period of residency has been observed in adults in the laboratory, suggesting that prior residency may provide an advantage in combat (Barlow et al. 1986). Amphilophus cichlids are capable of recognizing some conspecific chemical cues (McKaye & Barlow 1976, Barnett 1977), therefore it was hypothesized that chemical cues may be important in producing an aggressive advantage gained through prior residency. An individual’s own chemical signature may be present in its aquarium, and it was expected that subjects tested in their own aquaria would defeat opponents taken from foreign aquaria. Small juvenile Amphilophus cichlids remain close to 3-D structure (rocks) in their natural habitat (Oldfield et al. 2006); consequently, we inquired whether the presence of a possible shelter would result in a prior residence effect (Nijman & Heuts 2000, Johnsson & Forser 2002). It was also expected that increased motivation to defend a residence would decrease latency to initiate aggression and that contest asymmetries associated with prior residency would result in shorter fight durations than in contests involving equally naïve fish. The effects of prior social experience were investigated by pitting subjects that had recently been held in the presence of conspecifics against opponents recently held in isolation. Recently subordinate subjects were expected to lose more often than isolated fish, while recently dominant fish were 142 Kapil Mandrekar and Ronald G. Oldfield Table I. Body size in subjects. Mass (g) was not significantly different between winners and losers within each treatment (paired t-test). winners losers mean±SD mean±SD Treatment # n t p Control Prior residency 1 (Chemical) 2 (Clay pot) Social experience 3 (Dominant) 4 (Subordinate) 10 5.8±2.0 5.8±2.1 1.406 0.193 10 12 5.7±1.6 8.2±4.2 5.7±1.7 8.1±4.1 0.264 0.798 2.017 0.069 12 12 9.7±2.4 6.0±3.0 9.6±2.3 6.0±3.0 0.209 0.838 0.290 0.777 expected to win contests equally as often as isolates, as this pattern is commonly observed in other fish species (Francis 1983). It was expected that subordinate social experience would decrease a subject’s motivation to fight, resulting in longer latencies to initiate combat and shorter fight durations than would be expected in control contests that involved two individuals without recent social experience. MATERIALS AND METHODS Two broods of Amphilophus cichlids (Fig. 1) of a form recently described as A. astorquii (Stauffer et al. 2008), notable for their solid black breeding color, were produced at the University of Michigan Museum of Zoology (free-swimming 30 October 2005, 23 November 2005) from one male and one female collected in Lake Apoyo, Nicaragua (Fig. 2). A general description of the laboratory has been provided previously (Oldfield 2005). Each brood contained approximately 175 individuals, and was housed in a single 416 l acrylic aquarium (L×W×H = [168 × 88 × 27 cm] + [47 × 46 × 11 cm]). Fish were fed once per day on commercial dry fish food, supplemented once per week with frozen brine shrimp (Artemia sp.) or frozen blood worms (Chironomus sp.). All aquaria were filled with aged tap water (26 °C, pH 7.6 ± 0.2). A single experiment, consisting of one control group and four treatments, was conducted during summer 2006. Fish were netted out and sedated in an MS-222 solution, weighed, measured, and branded with silver wire that had been cooled with dry ice (for individual identification). One brand was placed on the body of each fish, either anterior to or posterior to the dorsal fin, with care being taken not to disrupt the lateral line. Fish were paired as closely as possible to an individual of the 143 same body mass and standard length (SL). Even from a pool of 350 fish, exact matching was not possible for some pairs. However, size differences in these pairs were miniscule (mean ± SD differences between pair-members: 0.1 ± 0.1 g, 0.9 ± 0.8 mm; see Table I). Each pair-member was isolated in a standard 38 l (51 × 26 × 31 cm) glass aquarium containing 5 cm of natural gravel substrate covering an air-powered sponge filter. Standard length of subjects ranged from 40.0 to 80.0 (60.4 ± 9.1) mm. Cardboard sheets prevented visual contact between fish in adjacent aquaria. Fish were held in these pre-test aquaria for 2-3 days, except for one pair that was held for 4 days. Trials began when two fish were netted from their pre-test tanks and simultaneously introduced into a test tank, each of which was set up identically to the pre-test tanks, except as noted below. Contest start time, time at which aggressive behavior began (displays or attacks – see Baerends & Baerends van Roon 1950), and time at defeat, were recorded. Defeat occurred when one fish performed three consecutive aggressive acts without an aggressive response by its opponent. The winner was immediately netted out and identified. Each fish was tested once. The water was replaced with fresh water in pre-test and test aquaria before fish were added. In the control group all fish were held under identical pre-test conditions. With no experiential differences among combatants, fight outcomes were expected to be random and confirm that background conditions of subject selection and maintenance did not influence aggressive behavior. One member of each pair (n = 10) was randomly and nominally designated as a subject, and the other as its opponent. Both fish in each pair were netted from their pre-test tanks and simultaneously added to a third identical and novel test aquarium. Treatment 1 was designed to determine whether familiarity with a subject’s own chemical signature would result in a prior residence effect. One member of each pair (n = 10) was assigned the role of subject and the other designated as its opponent. The two fish were netted from their tanks as in the control, but instead of being transferred into a third neutral tank both fish were simultaneously released back into the tank from which the subject had been taken. Treatment 2 was performed in order to determine if familiarity with a potential shelter would result in a prior residence effect. The pre-test tank of each aqua vol. 14 no. 3 - 10 July 2008 Prior residency and social experience in contests between similar-sized juvenile black Midas cichlids, Amphilophus astorquii subject contained a terracotta pot positioned in the middle of the tank, with its opening facing the tank’s left wall, while the pre-test tank of each subject’s opponent did not possess a pot. The fish were netted out of their pre-test tanks and placed into a test tank (n = 12) that contained a pot identical to the pot in the subject’s tank. Treatments 3 and 4 were performed to determine the effects of recent social experience on contest outcome. The subject of each pair was held in a pre-test tank with five or six other fish while its opponent was held in isolation. All fish in each social group had been weighed and measured so that the relative size of each group-held subject was known. In treatment 3, each subject was the largest member of its group (n = 12). Body size is a good indicator of dominance in Midas cichlids (Barlow 1983), so these subjects were considered to have had recent experience in a dominant social position. In treatment 4, each subject was smaller than the largest fish in its group (n = 12), and was considered to have had recent social experience in a subordinate role. No effort was made to position subjects at any particular subordinate rank. After the pre-test period, each subject and its opponent were placed simultaneously into a third aquarium identical to the pre-test tanks. For each treatment, the number of contests in which a subject defeated its opponent was analyzed for significance by considering the chance that it would occur at random by using a binomial test. Latency to begin aggression and contest duration were calculated for each trial. For each treatment, these values were compared to the control with the non-parametric multiple comparison method described by Zar (1999: 226). All statistical tests were two-tailed and alpha was set at 0.05. Residence duration did not affect outcome of contests within any of the three treatments in which it varied (2-tailed Fisher exact tests: control, p = 1.000; treatment 1, p = 0.500; treatment 4, p = 0.491), and neither did body size. There was no significant difference in mass between winners and losers in any treatment (paired t-test, Table I). RESULTS Results of all of the treatments are summarized in Table II. In the control group, six of ten trials were won by the arbitrarily designated subjects, confirming that fight outcome was random in the absence of a difference in prior experience. In treatment 1, possible chemical factors did not result in a prior residency effect. There was no difference in latency to initiate aggression or in contest duration Fig. 1. Juvenile Amphilophus astorquii. Photo by R. G. Oldfield aqua vol. 14 no. 3 - 10 July 2008 144 Kapil Mandrekar and Ronald G. Oldfield between the chemical effect trials and the controls. In treatment 2, experience with a ceramic pot caused subjects to defeat opponents held without a pot. Latency to begin aggression in test tanks containing a pot was longer than in controls. Duration of contests was not different than that observed in controls. In treatment 3, social experience as the largest member of a group did not affect the probability that an individual would win a contest. Latency to the onset of aggression was not different than in controls, and neither was contest duration. In treatment 4, the number of fish with subordinate experience that won contests was not significantly lower than expected by chance. Latency to initiate aggression was not different than that observed in control tests, and neither was duration. Each of the three of the subordinate winners had held the rank as the third largest fish in its respective group. A post hoc analysis restricted to the eight groups in which the test fish was smaller than most of its group-mates (size rank 4, 5, or 6 in a group of 6) showed that all eight subjects were defeated by isolates (binomial test: p = 0.008). DISCUSSION The current results demonstrate that recent experience can affect the outcome of aggressive contests in juvenile black Midas cichlids. Experience with a flower pot caused subjects to win contests. This is consistent with studies on other species that found 3-D structure or gravel to affect contest outcome (Johnsson et al. 2000, Nijman & Heuts 2000, Johnsson & Forser 2002). In cichlids, including Amphilophus (McKaye & Barlow 1976, Barnett 1977), parent and offspring recognition (Myberg 1975) and mate choice (Plenderleith et al. 2005) may occur through chemical signals. Therefore, it was expected that chemical signals might play a role in establishing a prior residence effect. Figler & Einhorn (1983) suggested that this occurs in convict cichlids, Amatitlania nigrofasciatus (Günther, 1867). However, the current null finding for A. astorquii is consistent with Bronstein (1985), who found that chemical cues did not influence the outcome of contests involving Betta splendens Regan, 1910. Recent social experience did not significantly affect an individual’s ability to overtake competitors, although experience as a relatively small member of a group suggested reduced dominance potential, a pattern consistent with several studies (McDonald et al. 1968, Francis 1983, Beaugrand & Zayan 1985, Beacham & Newman 1987). The ability of prior dominance relationships to affect future social Fig. 2. Male Amphilophus astorquii that was captured in Lake Apoyo, Nicaragua, and later fathered two broods of offspring that were the subjects of this study. Photo by R. G. Oldfield 145 aqua vol. 14 no. 3 - 10 July 2008 Prior residency and social experience in contests between similar-sized juvenile black Midas cichlids, Amphilophus astorquii Table II. Numbers of trials in which the subject defeated its naïve opponent, and its significance as determined by the binomial test. Also included are summary statistics for the latencies to initiate aggression and the contest durations for each treatment. For these measures, significant differences between each experimental group and the control group were tested with a non-parametric multiple comparisons procedure (see text). NA = not applicable. Treatment # Control Prior residency 1 (Chemical) 2 (Clay pot) Social experience 3 (Dominant) 4 (Subordinate) n # won by subject p latency, min. (mean±SD) p duration, min (mean±SD) p 10 6 0.754 1.71±0.82 NA 20.59±15.80 NA 10 12 6 12 0.754 <0.001 4.05±6.27 12.98±15.81 >0.50 0.02>p>0.01 41.89±20.34 7.97±8.07 0.50 0.20>p>0.10 12 12 5 3 0.774 0.146 4.14±2.42 5.41±5.35 0.20>p>0.10 0.20>p>0.10 20.75±20.10 24.91±30.01 >0.50 >0.50 encounters may be an example of a more general ability to behave according to recent social experience. Barlow et al. (1975) observed changes in social behavior in Midas cichlids as they became more familiar with their social environment. At the begin- ning of an experiment, aggression directed toward fish that shared the color of a large dominant fish was lower than expected. By the third day the effect of color-sharing had diminished. There was extreme variability within treatments Fig. 3. A view looking into Lake Apoyo, showing its clear water, typically rocky substrate, and steep gradient. Photo by R. G. Oldfield. aqua vol. 14 no. 3 - 10 July 2008 146 Kapil Mandrekar and Ronald G. Oldfield in latency to initiate aggression and in contest duration. The only significant difference observed between the control and an experimental treatment involved the ceramic pot. In treatment 2 the increased latency may be explained by the structure blocking visual contact, which may have initially resulted in fewer opportunities for aggression (Kalleberg 1958, Bronstein 1983). Although the durations of contests involving a pot were not significantly different than in controls, the mean duration was much lower than in any other treatment, suggesting that residency might result in an asymmetry that could decrease contest duration. The increased chance of winning an aggressive contest after experience with a ceramic pot suggests that subjects may have identified an identical pot as a resource to be defended. However, the possibility remains that some other aspect of experience with the pot increased the subjects’ agonistic success. Subjects experienced with a pot might have defeated naïve fish even if tested in the absence of a pot. Also, the sudden introduction of a novel flower pot might have reduced aggression in potnaïve fish. Nevertheless, the 3-D structure seemed to provide a shelter that subjects had identified as a resource (Riechert 1979), whereas intruders did not recognize the value of the structure and were in a position in which they could not fight and evaluate it simultaneously (Johnsson et al. 1999). Experiential factors that might increase the chance of defeating an opponent include investment in reproduction, knowledge of food, knowledge of hiding places, and established territorial boundaries with neighbors (Maynard Smith & Parker 1976). The subjects used here were not reproductive, they had similar knowledge of food acquisition, and they had no neighbors, leaving knowledge of the shelter as a logical explanation for the enhanced aggressive behavior observed. In any case, the evidence demonstrates that animals that are not remarkably aggressive under natural conditions may have the ability not only to behave aggressively under certain conditions, but to modify aggression according to prior experiences, as do some animals that are typically aggressive in nature. This suggests that complex behavioral plasticity relating to aggression may generally be of such high adaptive value that it might occur in species for which it might seem to typically have little utility. 147 ACKNOWLEDGEMENTS Jeffrey McCrary and Lorenzo López Pérez helped in Nicaragua to collect the wild fish that spawned the subjects used in the current experiment. Paul Bronstein provided advice in all aspects of the project including experimental design, data analysis, and manuscript development. The manuscript was improved by comments made by Gerald Smith, Peter Esselman, and William Fink. 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