Aterglαtis Floridus (Linnaeus) - Advantages of Possessing To玄ins?
Total Page：16
File Type：pdf, Size：1020Kb
CRUSTACEAN RESEARCH，NO. 24: 137-145，1995 Limb loss in the poisonous crab Aterglαtis floridus (Linnaeus) - advantages of possessing to玄ins? Christopher P. Norman Abstract. - To determine the effec. 1969; Konosu et α1 . ，1969; Yasumura et tiveness of possessing to玄ins as adefense α1 . ，1986). In Japan，three species，all mechanism in crabs，the level of limb loss xanthids [Atergαtis βoridus (Linnaeus， was examined in a poisonous crab 1767)，Zosimus aeneus (Linnaeus，1758) Atergatis floridus. Crabs were col1 ected and P1αtypodiαgrαnu10sα( R u p p e l l ， individua11yusing SCUBAbetween June 1830)] are reported as highly toxic 1990 and December 1992. The sex ratio (Hashimoto et α1 . ，1967; Konosu et α1 . ， approximated 1: 1. Significant levels of 1969). Thedistribution of Z. aeneus and limb loss were observed in both males P.grα，nu10sαi s largely restricted to coral and females，but limb loss 仕equency d品 habitats，however A. βoridus，a rock reef fered between se玄es. Higher 仕equencies dwelling species，is broadly distributed in of limb loss were found in males (4 1. 3% Japan along the southern (temperate) with limb loss) than females (18.4%). Site coastline of Honshu and Shikoku and of loss also differed between sexes，with Kyushu (Sakai，1976). Atergatis floridus males having ahigher loss of the walking also has abroad geographical range legs 1，3and 4than the chelipeds and leg throughout the Indo-Pacific 企omJapan 2(P<O.OI). Females have amore random and the Red Sea to northern Australia pattern of limb loss. In conclusion，A and 仕omTahiti 田 ld Hawaii to the South flo 吋dus was found to have asimilar de. African coast (Saisho & Ushio ，1969; gree of limb loss to other reported crab Sakai，1976; Llewellyn & Endean，1991). studies. ln situ observations of the Studies in Japan of the to垣city levels behaviour of A floridus and predator in. of A. βoridus indicate that the severity of teractions suggest the ecological benefit toxic material varies between different from the possession of toxins as apri. geographic localities and also variations mary anti.predation strategy maybe less 血 severity occur between individuals at effective than initia11ysuspected. the same locality，suggesting that the tox- ins，or at least the source of the toxic ma- terial ，is exogenous in ori民n (Konosu et Introduction α1 . ，1969; Noguchi et α1 . ，1983a; 1986). Poisonous crabs are rare (Holthius， The principal toxic material has also been 1968; Hashimoto et a1 .，1969). Only arela- shown to vary between geographically tively few tropical species have been re- separate specimens of A. βoridus，e.g. ， ported to have toxins，and these are gonyautoxins (GTXs)，Kominato ，Chiba largely restricted to coral areas of the Prefecture (Shiomi et α1 . ，1982); saxitoxin Indo・Pacific (Halstead，1992). However， and neosaxitoxin (STXs)，Ishigaki ， m 出 ly of the species that possess toxins， Ryukyu Islands (Noguchi et α1 . ，1983a); possess extremely strong toxic material and tetrodotoxin (TTX)，Miura Peninsula， and sporadic poisonings，sometimes fatal ， Kanagawa Prefecture (Noguchi et α1 . ， have been recorded 企omconsumption of 1983b). Vibrio sp. isolated for the 思I t ofA. these species (Hashimoto et α1 . ，1967 ， floridus has been found to be able to con- 138 C.P.NORMAN vert GTXs into STXs (Kotaki et αl. ，1985) can autotomize alimb at apredetermined 出 ld further investigation found asimilar break point，the basi-ischium. While the mechanism responsible for the production predator has the limb，the crab has an op- of the more toxic ，TTX (Noguchi et αl. ， portunity to escape (McVean，1976 ，1982). 1986; Sugita et αl. ，1987). The initial For decapods with 10 limbs，this may be source of the gonyautoxins in the diet has seen as having 10 chances to escape，how- been suggested as the red calcareous al- ever the loss of alimb(s) affects the future gae，JIα niαs p . (Kotaki et αl. ，1985). feeding ability ，particularly the loss of The role of the paralytic shellfish poi- chelipeds (Smith & Hines，1991) ，the sons，GTXs 出 ldSτ玄s，in the marine envi- probability of escape from any future ronment has been extensively examined predatory aggression (i. e. the crab's de- due the occuπence of toxic dinoflagellate gree ofmobility)，mating success in males blooms and their economic impact from (Sekkelsten，1988) ，female brood size fish kills and the accumulation of toxins (Norman & Jones，1993) and subsequent in mollusks (White ，1981; Hall，1988). growth (Smith，1990; Norman & Jones， Tτ 宝， initiaJl ythought to be only found in 1991). Therefore，although limb loss c田 1 pufferfish，has subsequently been found be seen as an effective anti-(absolute)pr・e- in abroad variety of fauna: fish ，amphib- dation strategy，limb loss places the indi- ians，mollusks ，echinoderms and crusta- vidual at adisadvantage. This brings us ceans (Maruyama & Noguchi，1984). Ex- to the question of what is the ecological amination of the sensitivity of marine or- benefit to acrab in possessing toxins? The ganisms to these toxins ，generally shows physiological adaptations required to ac- organisms to have ahigh sensitivity， cumulate and store toxic material pre・ death occurring rapidly 仕omthe blockage sumably have ecological advantages for of the excitable membrane sodium chan- the crab. The highest concentrations of nels (Davis & Stuart，1988). Poisoned toxin have been found in the walking ap- crabs 田 ld fish essentially show the same pendages of all 3toxic Japanese species S戸nptoms as in man- paralysis，suspen- examined，with concentrations in the sion of respiration and death (Hashimoto muscle of the walking legs of A. floridus et αl. ，1967 ，1969; Koyama et αl. ，1983; being approximately 10 times that of Hwang et al. ，1990). Atergatis floridus cepthalothoracic muscle (Konosu et αl. ， and other toxic species ，such as the 1969; Saisho & Ushio，1969). Atergatis pufferfish T αkifugu rubripes and T. floridus by concentrating toxins in its niphobles，have amuch higher resistance limbs，the part ofthe body most accessible to both the ingestion and interperitoneal to attack，may: (1) minimize limb loss ， injection of Gτ 玄， SτXandTτ宝 (Koyama and therefore species with toxins may be et αl. ，1983; Saito et al. ，1984 ，1985). Le- expected to have less limb loss than non- thal doses of GTX，STX and TTX to A. toxic species; (2) be used as awarning floridus being in the order of 1，000-5，000 sign，that after asingle limb has been re- 討mes higher than 5sympatric crab spe- moved，further predation (absolute or cies which showed minimal resistance to partial) on that individual will only lead these toxins; death occurring rapidly to prey which is highly toxic. As 白 1 initial (Koy.田 naetαl. ，1983). test of whether the possession of toxins Predatory pressure on crabs can be ei- reduces limb loss ，1 have examined the ther (1) absolute，i.e. ，the crab is killed 仕equency of limb loss of A. βoridus in a outright and eaten ，or (2) partial ，i. e. ， wild population. Atergαtis floridus has a where limbs are consumed but the indi- high level of limb loss which is compa- vidual survives. When acrab is attacked， rable to other non司 toxic crabs. The eco 鞠 or perceives the threat of attack，the crab logical advantages to crabs of possessing LIMB LOSS IN ATERGATIS FLORIDUS 139 toxins as adefense mechanism are dis- ischium prior to the regeneration of the cussed. limb，was measured and staged using the developmental stages，G 1 (仕 esh break，no Materials and Methods bud) to G7 (fully pigmented and differen- Over a2 .5year period (June 1990 - tiated limb bud)，of Ary et al. (1985).For December 1992) A. βoridus were sampled ovigerous females，egg and ovarian devel- from approximately 0-8 m via SCUBA opmental stages were determined follow- from rock reefs adjacent to the Banda ing the criteria used by Norman &Jones Marine LaboratoIγ，Tokyo University of (1993). Fisheries (34 0 58'3"N，139 0 46'5"E). This survey was carried out concurrently with Results observations on juvenile spiny lobster Thesex ratio (92M:98F) did not signifi- Pα nulirus jα:ponicus ，and amap of the cantlyvary 企omaratio of 1:1 (χ2 =0.189 ， sampling location，details of seasonal df=1，P>0 .5) . The maximum sizes S出 npling frequency，dive duration，habi- sampled were，male 57.2 and female 52.4 tats examined etc. are given in Norman et mmCW; minimum sizes 12.2 and 10.55 α1. (1994).Over atotal of 330 dives，A. mmCW ，respectively. No obvious peaks βoridus were only in 企equently observed in the size distribution pattem relating to and a total of 190 specimens were year classes were observed in either sex sampled. Atergαtis floridus were sampled (Fig. 1). Small juveniles (10-20 mmCW) during the day，being found under boul- were first observed in AugustlSeptember ders and in holes on the rock surface. In- of each year sampled. In both sexes the dividuals were captured by hand，taking mode was the size class 40-45mm CW care not to damage (remove limbs) the (Fig. 1) .Ovigerous females (n =9) were crab.Crabs were placed，individually in observed from June (2 4/6/90) to Septem- self sealing plastic bags in situ to avoid ber (6/9/90). Minimum size of ovigerous any limb loss post-capture. females was 35.4 mmCW; maximum 52.4 In the laboratory，crabs were exam- mmCW (Fig. 1). Dissection of ovigerous ined 品r sex，c訂 apace width (CW)，molt females revealed 5specimens all with late stage and limb loss pattem. Sex was de- staged，eyed eggs (stages 3or 4) with ova- termined from the external abdominal ries in the maturing or ripe condition. morphology，and for specimens <15 mm This suggests that as ovarian develop- CWfrom the pleopod structure via bin- ment is proceeding whilst the females are ocular microscope.