Predation Protection in the Poison-Fang Blenny, Meiacanthus Atrodorsalis, and Its Mimics, Ecsenius Bicolor and Runula Laudandus (Blenniidae) 1 GEORGE S
Total Page：16
File Type：pdf, Size：1020Kb
Predation Protection in the Poison-Fang Blenny, Meiacanthus atrodorsalis, and Its Mimics, Ecsenius bicolor and Runula laudandus (Blenniidae) 1 GEORGE S. LOSEy2 ABSTRACT: The large canine teeth in Meiaeanthtts atrodorsalis impart a toxic bite which causes this animal to be rejected as a prey item by several piscivorous fishes. Two morphologically and behaviorally similar species, Rlmttla lattdandtts and Be senitts bieolor, may enjoy predator protection through Batesian mimicry and, for the former species, greater feeding efficiency through aggressive mimicry. A limited number of experiments indicate that the predator, Bpinephaltts merra, may learn to avoid Meiaeanthtts atrodorsalis and its mimics. As POINTED OUT BY WICKLER (1968), mimicry is the resemblance of a "predatory" species to a must be considered in terms of three parties. The harmless or nonpredatory form. This relation "mimic" resembles some "model" in terms of ship facilitates the mimic's "predation" through one or several characteristics such as coloration, deception of the third party, which in this case shape, odor, etc., but utmost importance must be is its "prey" organism. attached to the "third party" which is frequently Mimicry in the form of camouflage is known a predator or prey organism. Usually the third for many species of fish. Cases of Batesian, Mul party must encounter both model and mimic and lerian, and aggressive mimicry are comparatively must fail to differentiate perfectly between them. rare. Aspidonttts taeniattts Quoy & Gaimard, the For purposes of clarity, the three types of mim aggressive mimic of the cleaning wrasse, La icry discussed in this paper are defined briefly broides dimidiatlls (Cuvier & Valenciennes), is below. But it should be clear that, as with many the only well-known example of morphological biological phenomena, it is difficult to provide and behavioral mimicry in fishes (Randall, 1955, precise definitions (see Wickler, 1968). 1958; Randall and Randall, 1960; Eibl-Eibes Batesian mimicry is generally the resemblance feldt, 1955, 1959; Wickler, 1960, 1961, 1963, of a harmless or palatable species to a harmful 1965a, 1968). Rtt1l1tla azalea Jordan & Bollman or unpalatable one. This provides the mimic resembles T halassoma ltteasanttm (Gill), an with some selective advantage similar to that other cleaning wrasse, but Hobson (1969) con enjoyed by the model, usually predator protec cluded that its coloration functions primarily to tion. Mullerian mimicry involves a similar rela conceal the blenny within groups of the wrasses tionship except that both species possess some in order to facilitate the mimic's attacks on undesirable qualities. Their resemblance in larger fishes. Some other species of Rttnttla have creases the probability that the third party will at least superficial resemblance to young labrids. encounter one of their "type" and learn to avoid Starck (1969) described Besenitts midas which all others. Aggressive, or Peckhammian, mimicry joins large schools of Anthias sqttamipinnis. It is suspected that its resemblance to these nu merous anthiids serves as a protection against 1 Supported by a National Institutes of Health Post doctoral Fellowship and Atomic Energy Commission predation and allows it to exploit planktonic contract no. AT(29-2)-226. Hawaii Institute of Marine food sources. Other cases of mimicry have been Biology contribution no. 380. Manuscript received hypothesized such as baits and lures of anten 19 July 1971. nariid fishes, but there is little evidence to sup 2 University of Hawaii: Department of Zoology, Honolulu, Hawaii 96822; and Hawaii Institute of port the inclusion of these fishes as examples of Marine Biology, P.O. Box 1067, Kaneohe, Oahu, true mimicry according to the criteria suggested Hawaii 96744. by Wickler (1965a, 1968). 129 130 PACIFIC SCIENCE, Volume 26, April 1972 The large canine teeth in the lower jaw of The toxicity of the bite of Meiaeanthus atro Meiaeanthus atrodorsalis (Gunther) have an an dorsalis was assayed by force-biting the tails of terior groove which ends in a depression that two white laboratory mice and my hand. Sub is filled with glandularlike tissue (Tomiyama, sequent observations were inadvertently pro 1956; Springer, 1968). Springer mentioned a vided by bites in the more tender area of my lack of information on the possible venomosity hip. of this canine teeth and gland structure. Springer Predator reactions to Eesenius bieolor and (1971; personal communication, 1969) inde Meiaeanthus atrodorsalis were observed in a 3 pendently recognized the similarity between two m-diameter, 14-m-deep, plastic pool at the Eni species of Meiaeanthus and members of the wetok Marine Biological Laboratory. Various genus Eesenius as an indication of possible mim predators were caught in 1 to 2-m-deep water icry. Four other species of Meiaeanthus resemble where they should not have encountered M. species of the blenniid genera, Petroscirtes and atrodorsalis (see below). These predators were Runula (V. G. Springer and W. F. Smith-Vaniz, placed in a "community tank" and fed living personal communication, 1971). M. atrodorsalis, Eesenius bieolor, and Istiblen The present study was begun to investigate nius paulus, a tide pool blenny; the latter served the function of the unique canines of Meiaean as a control. I partially crippled all prey fishes thus atrodorsalis and the possibility of both just prior to their introduction by squeezing the aggressive and Batesian mimicry among M. caudal musculature. This facilitated their capture atrodorsalis, Eesenius bieolor (Day), and a third by the predators and caused the swimming blenny Rumtla laudandus Whitley. movements of I. paulus to be more similar to I thank Dr. Ralph L. Bowers and Mr. Peter that of the other species than they are in intact Rosti for their help in collecting specimens, and animals. Dr. Victor G. Springer and Mr. William F. The lack of a large number of living speci Smith-Vaniz for their discussions regarding this mens prevented a detailed investigation of the project. possible advantages gained by mimicry, so a small scale study was attempted. Four groupers MATERIALS AND METHODS (members of the "Epinephalus merra complex," 100 to 175 mm standard length) were placed Field observations on the distribution and be in individual, 1-m-diameter wire pens submerged havior of the three species were made during in a pool similar to the one mentioned above. approximately 250 hours of diving at Eniwetok All were fed once at about 0800 and again Atoll. A few hours of correlative observations at 1900 hours daily. Istiblennius paulus was were made on Meiaeanthus atrodorsalis in again used as a control food. The grouper's Guam. The number of individuals was censused feeding reaction to living Eesenius bieolor was by swimming around roughly circular areas checked both before and after they were fed (about 500 square meters) and counting all in several Meiaeanthus atrodorsalis. Two of the dividuals within the circles. Recounting of in groupers were fed intact M. atrodorsalis and two dividuals was probably minimal due to the were fed prey with their canines surgically re extreme clarity of the water. Behavioral observa moved. tions were recorded on an underwater tape re corder. Particular note was made of the feeding behavior of the fish and their response when DEPTH DISTRIBUTION approached. Specimens were speared for gut content analysis and morphological comparison. The census counts made on eight different Living specimens were captured with quinaldine reefs show that, while all three species occur in and hand nets for various laboratory studies. the same depth range, their centers of distribu Runula laudandus proved to be particularly dif tion show a slight difference (see Table 1). ficult to capture and was thus excluded from the Eesenius bieolor also differs from the other laboratory studies. species in that it is commonly found in rubble Predation Protection In the Poison-Fang Blenny and Its Mimics-LoSEY 131 TABLE 1 MEAN NUMBERS OF FISH OBSERVED ON DIFFERENT REEFS IN ENIWETOK ATOLL LAGOON Meiacanthus Ecsenius Runula NUMBER DEPTH REEF TYPE atrodorsalis bicolor laudandus OF COUNTS o to 3 m fringing reef and small coral heads 0 0 0 many 3 to 5 m large coral heads 4.75 2.25 0.5 8 5 to 7 m large coral heads and rubble piles 20.75 12.25 1.25 8 7 to 20 m lagoon pinnacles 92.8 1.7 0.6 7 > 20m lagoon pinnacles 1.2 0 0 5 NOTE: The 0-3 m depth range was not included in the statistical analyses. The center of distribution for M. atrodorJalis differs from the other species (p < 0.01, Kolmogorov-Smirnov method, Tate and Clelland, 1959) but the distribu tions of E. bicolor and R. laudal1dus do not differ from each other (p > 0.2). areas or on eroded rock faces whereas Meiacan gests that most of the yellow portion is incapable thus atrodorsalis and Runula laudandus are of significant darkening. usually found in areas of the reef covered with Runula laudandus is strikingly similar to living coral. Meiacanthus atrodorsalis. It is difficult for the The relative densities also show that Meiacan inexperienced observer to separate them at more thus atrodorsalis is the most plentiful species than about 2 m distance in the field, and I still over the entire depth range and that Runula find it difficult to differentiate between them at laudandus is the least plentiful (p < 0.005 by a distance greater than 5 m. The pigmentation Kruskal-Wallace, nonparametric analysis of vari is nearly identical (Figs. 1, 2) and the lesser ance, Tate and Clelland, 1959). body depth of Rumtla laudandus (Table 2) is visually compensated by the dorsal fin which COMPARATIVE MORPHOLOGY this species usually holds erect. It also has a fright coloration that is similar to Meiacanthus The three species have striking similarities in atrodorsalis, but it may be capable of darkening both morphology and coloration (Figs. 1, 2).