Japanese Journal of Ichthyology 魚 類 学 雑 誌 Vol.24,No.31977 24巻3号1977年

Aggressive Mimicry between Juveniles of the Table 1.Comparative abundance of mimic Snapper Lutjanus bohar and Species of the and model species along selected courses at two sites at Miyake-jima,Japan. Damselfish Genus Chromis from Japan

Jack T.Moyer (Received April 1,1977)

Russell et al.(1976)briefly listed the most important papers on mimetic relationships of marine fish species.Ten new cases of mimicry were described,including apparent aggressive mimicry between juveniles of the snapper,Lutjanus bohar(Forsskal)and the model,the smallest being L.bohar juveniles damselfish Chromis ternatensis(Bleeker).A of about 20mm in total length with C.weberi similar mimetic relationship of the same lut- and C.lepidolepis of the same size.The lar- janid juvenile and four additional species of gest mimics observed were in excess of 100mm the genus Chromis has been observed annually in standard length in company with models since 1973 at Miyake-jima,Japan(34•‹05'N, of comparable size.In all cases,the model 139•‹30'E).The present paper reports these species greatly outnumbered the mimic. observations and a similar record from the Usually only a single mimic appeared in the Ryukyu Islands. Chromis aggregation under observation.The single exception was noted on Jan.2,1977, Observations when two L.bohar juveniles of greater than In the course of several hundred dives at 100mm in standard length were seen in com- Miyake-jima,I have frequently observed Lut- pany with 16 C.flavomaculata of similar size. Janus bohar juveniles seeming to mimic the Table 1 shows the comparative abundance of following Chromis species;Chromis flavom- the mimic and model species resulting from aculata Kamohara,C.weberi Fowler at Bean, a census taken over two specific courses at C.miyakeensis Moyer et Ida,and C.lepidole- Miyake-jima in November,1976. pis Bleeker.In addition,I observed a similar The possibility was considered that the relationship between L.bohar and C.weberi lutjanid might gain protection from predators in Nakagusuku Bay,Okinawa Island,in Feb- by its habit of joining heterotypic schools ruary,1976.In all observations,the mimic (Ehrlich and Ehrlich,1973).To test this aggregated in the water column near coral hypothesis,I pursued numerous aggregations, outcroppings or volcanic cliffs with the Chromis varying the intensity of the chases.When model or in heterotypic schools that included pursued rather slowly,aggregations of C. from one to three of the model species as flavomaculata quickly grouped together into well as Anthias squamipinnis(Peters)and juve- tight,compact schools.The lutjanid remain- nile Caesio spp.From a distance of 8 m or ed at the fringe of such schools,only loosely more,it was often difficult for the observer associated with them.When the intensity of to distinguish the mimic from the model, the chase increased,Lutjanus bohar individuals particularly when visibility was somewhat quickly left the Chromis aggregation to seek limited. cover solitarily.Mixed schools of Chromis Lutjanus bohar's mimetic relationship with were less likely to segregate by species when Chromis species in Miyake-jima waters was pursued than was the lutjanid. most frequently observed between the lutjanid Disscussion juvenile and Chromis flavomaculata,less often with C.weberi and C.miyakeensis,and rarely Russell et al.(1976)attribute the relation- with C.lepidolepis.In every observation the ship between Lutjanus bohar juveniles and mimic represented the same size class as the Chromis ternatensis to aggressive mimicry,

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Table 2.Similardies of Luijanu.s bohar juvenile mimics and Chromis models. not always present on model;**,30mm SL. *,

Fig.1.Top:Juvenile Lutjanu.s bohar mimic.TMBS 760905 I.Bottom:Most common model at Miyake-jima.Chromis flavomaculara.TMBS 761221-I.Bloches on body of L.bohar appear under stress condition.

―219― 魚類学雑誌 Japan.J.Ichthyol.24(3),1977 similar to that of the serrinid genus Hypo- (Table 1),and the lutjanid mimics only as a plectrus and various Caribbean damselfishes juvenile.Hobson(1973)and others have (Randall and Randall,1960,Ehrlich,1975). shown that aggregating fishes group together Similarities between L.bohar juveniles and into compact schools at the approach of danger. the plankton-eating Chromis apparently enable The departure of L.bohar juveniles from the lutjanid to closely approach unsuspecting Chromisaggregations when vigorously pursued prey who mistake it for the harmless Chromis. negates the possibility of protective mimicry. This view is supported by the fact that the Aggressive mimicry is therefore the only type gut contents of my single specimen of L. of mimicry involved in the relationship,thus bohar,a juvenile of 55 mm in standard length, meeting criterion(g).Lutjanus bohar appears included numerous fish remains,with scales to be a facultative mimic of Chromis. of two sizes,possibly those of small glastic Russell et al.(1976)suggest the possibility juvenile apogonids that abound at the collect- that attributes of facultative mimics may, ing site. in some cases,represent"incipient"stages The relationship between Lutjanus bohar in the evolution of eventual obligative mim- juveniles and four species of Chromis in Japan icry relationships.Wickler(1965)had pre- brings to five the number of Chromis species viously theorized,that in its early stages, reported as models for the lutjanid.Lutjanus mimicry could not have evolved under the bohar is a wide-ranging species in the tropical selective pressures of mimicking,but rather Indo-West Pacific.Its similarities in body as the result of convergent similarities in depth and fin contours to several species of morphology,coloration,and behavior.With Chromis and local variation in abundance of this in mind,it is of interest to compare different Chromis in specific geographical loca- Lutjanus bohar juveniles with the five known tions throughout the vast tropical Indo-West models. Pacific suggest that the relationship between It would appear that C.miyakeensis displays L.bohar and Chromis may be a universal the most attributes of an acceptable model adaptation of the lutjanid,and that further (Table 2),but,in fact,C.flavomaculata and model species will be discovered.In addition C.weberi are more common models in Miyake- to shape and color similar to numerous jima waters,in spite of their rather super- Chromis,L.bohar juveniles display a light ficial resemblance to the mimic.Apparent spot at the base of the soft dorsal fin,resem- preference for specific models may be only bling,for example,Chromis elerae Fowler et partly due to the relative abundance of the Bean,C.hypsilepis(Gunther),C.acares various Chromis species(Table 1).As Hobson Randall et Swardloff,C.notata Temminck et (1968,1969)has noted for the aggressive Schlegel,and the known models,C.miyake- mimic blenny,Plagiotremus azaleus(Jordan ensis and C.flavomaculata(see Allen,1975). et Bollman),only a superfical resemblance Russell et al.(1976)list the criteria for fac- may serve to make the mimic inconspicuous ultative mimicry as follows:(a)the mimic to its prey as it swims in aggregations with may only superficially resemble the model, the model species.Observations at Miyake- (b)the mimic aggregates with the model,(c) lima suggest that rather than a close physical the model far outnumbers the mimic,(d)the resemblance,subtle behavioral differences may relationship is opportunistic,involving more be more important in determining the most than one species of model,(e)only juveniles ideal model.Although all of the model spe- mimic,(f)mimicry occurs during only part cies and the mimic feed in the water column, of the life history of the mimic,and(g) the lutjanid mimic and the models C. usually elements of only one type of mimicry flavomaculata and C.weberi exhibit very lim- are involved in the relationship.That L. ited home ranges,e.g.,around a specific coral bohar meets criteria(a),—(f)has been shown head or a fairly restricted section of volcanic above,i.e.,the lutjanid superficially resembles cliff.Chromis miyakeensis utilizes a somewhat the various Chromis models,it aggregates with wider home range,increasing the possibility them and is far outnumbered by the Chromis of"losing"its mimic as it strays too far for

―220― Moyer:Aggressive Mimicry between Lutjanus and Chromis the lutjanid to follow.This possibility is thanked for useful suggestions.A special further suggested by the fact that neither thanks to Katherine A.Meyer who shared Chromis albomaculata Kamohara nor C. observations,helped collect specimens,and chrysura(Bliss)have been observed in re- aided in identification of gut contents of lationship with L.bohar,although both are Lutjanus bohar,and to John W.Shepard who locally common at Miyake-jima.Both of photographed the specimens for Fig.1. these damselfishes are known to range over extremely wide areas of the reef(personal Postscript observation). At Seragaki Beach,Okinawa Island,Oct. As shown above,Lutjanus bohar juveniles 7,1977,after completion of the manuscript, share many similarities in color and shape the author observed a single juvenile Lutjanus with a variety of Chromis species,thus pre- bohar in association with a large heterotypic adapting the lutjanid for potential mimicry. aggregate consisting of approximately 200 Whether the diurnal mid-water feeding habits Pomachromis richardsoni(Snyder)and about of L.bohar were preadaptations or whether 50 Chromis flavomaculata.All members of they evolved secondarily under the selective the aggregate including the lutjanid ranged pressures of mimicking cannot be said with in size from about 80-90 mm in total length. certainty.Although substantial information The pomacentrids were actively feeding on is available on the feeding behavior of the plankton in upwelling waters along a reef Lutjanidea in general(Randall and Brock, patch.The mimic lutjanid closely resembled 1960;Hobson,1965,1974;Stark and Davis, P.richardsoni in body depth and shape,and 1966;Randall,1967),virtually nothing has by the presence of a white post-dorsal spot, been reported on the food habits of juvenile black borders to the caudal fin,and a dark lutjanids.My observations of the juveniles pectoral spot,making species distinction dif- of L.bohar,L.fulvus(Bloch et Schneider), ficult from a distance of 5-6 m in the rela- L.monostigma(Cuvier),L.sp.(see Masuda tively turbid water. et al,1975,fig.D on p.64),and L.kasmira (Forsskal)at Miyake-jima indicate that only Literature cited L.bohar and L.fulvus are primarily diurnal Allen, G. R. 1975. Damselfishes of the south feeders.All of these species except L.bohar seas. TFH Publications Inc., Neptune City, feed near the substrate as juveniles,with L. N. J., 240 pp., many figs. fulvus seeming to occupy a very limited home Ehrlich, P. R. 1975. The population biology of range,similar in area to that of L.bohar. coral reef fishes. Ann. Rev. Ecol. Syst., 6: Diurnal feeding by L.bohar and L.fulvus 211•`247, Ehrlich, P. R. and A. H. Ehrlich. 1973. Coevolu- juveniles may be relatively late evolutionary specializations(Hobson,1974:1019)with the tion: heterotypic schooling in Caribbean reef fishes. Am. Natur., 107: 157•`160, mid-water feeding habit of L.bohar juveniles Hobson, E. S. 1965. Diurnal-nocturnal activity possibly co-evolving under the selective pres- of some inshore fishes of the Gulf of California. sures of mimicking. Copeia, 1965 (3): 291•`302, 1 fig. Hobson, E. S. 1968. Predatory behavior of some Acknowledgments shore fishes of the Gulf of California. Res. Appreciation is expressed to Dr.Gerald R. Rep. 73 Bur. Sport Fish. Wildl. 1-92, figs. 1, Allen,Western Australian Museum,Dr. 26. •` Edmond S.Hobson,Tiburon Fisheries Labora- Hobson, E. S. 1969. Possible advantages to the tory,and Mr.Barry C.Russell,Macquarie blenny Runula azalea in aggregating with the University,for supplying important literature. wrasse, Thalassoma lucasanum, in the tropical Eastern Pacific. Copeia, 1969 (1): 191•`193, 1 fig. Dr.Minoru Imajima,National Science Mu- Hobson, E. S. 1973. Diel feeding migrations seum,Tokyo,kindly aided in identification in tropical reef fishes. Helgolander wiss. of the gut contents of Lutjanus bohar.Dr. Meeresunters, 24: 361•`370. Hitoshi Ida,Kitasato University,and Dr. Hobson, E. S. 1974. Feeding relationships of the Yoshiaki Tominaga,Tokyo University,are teleostean fishes on coral reefs in Kona, Hawaii.

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Fish. Bull., 72: 915-1031, figs. 1•`42. Wickler, W. 1965. Mimicry and the evolution Masuda, H., S. Araga, and T. Yoshino. 1975. of animal communication. Nature, London,

Coastal fishes of southern Japan. Tokai Univ. 208: 519•`521. Press, Tokyo, 379 pp.,11 text-figs., 143 pls.

Randall, J. E. 1962. Food habits of reef fishes (Tatsuo Tanaka Memorial Biological Station, Ako, Miyakejima, Tokyo 100-12, Japan) of the West Indies. Stud. Trop. Oceanogr.

(Miami), 5: 665•`847. Randall, J.E. and V.E. Brock. 1960. Observations ス ズ メ ダ イ属 とそ の 擬 態 種 バ ラ フ エ ダ イ幼 魚 に つ い て on the ecology of epinepheline and lutjanid Jack T.Moyer fishes of the Society Islands, with emphasis on food habits. Trans. Amer. Fish. Soc., 89 (1): 東 京 都 下 三 宅 島 及 び 沖 縄 の 潜 水 観 察 で バ ラ フ エ ダ イ Lutjanus boharの 幼 魚 が ス ズ メ ダ イ 属4種 のaggres- 9-16. siveな 擬 態 種 と し て 生 活 し て い る こ と が 明 ら か と な Randall, J. E. and H. A. Randall. 1960. Examples っ た 。 三 宅 島 で はChromis floyomaculta,C.weberi of mimicry and protective resemblance in tropi- と の 関 係 が 顕 著 で あ っ た. cal marine fishes. Bull. Mar. Sci. Gulf Caribb., 擬 態 種 で あ る バ ラ フ エ ダ イ は 多 く の 場 合1尾 で,モ 10: 444•`480, figs. 1•`15. デ ル 種 の 数 が そ れ よ り多 い こ と,擬 態 種 の 形 態 が 外 見 Russell, B. C., G. R. Allen, and H. R. Lubbock. 上 モ デ ル 種 に 似 て い る こ と,擬 態 種 が 幼 魚 で あ る こ と, 1976. New cases of mimicry in marine fishes. さ ら に 両 者 の 関 係 が 機 会 的 で あ る こ と な ど か ら, J. Zool., Lond., 180: 407•`423, figs. 1•`9. facultativeな 擬 態 と 考 え ら れ る. Stark, W. A. II and W. P. Davis. 1966. Night

habits of fishes of Alligator Reef, Florida. (100-12東 京 都 三 宅 島 阿 古 田中 達 男 記 念 生 物 研 究 Ichthyol. Aquarium J., 38: 313•`356. 所)

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