CRUSTACEAN RESEARCH，NO .26: 153-161，1997 Behavioral manipulation of the shore crab， Hemigrapsus sanguineus by the rhizocephalan ，Sacculina polygeneα

Tohru Takahashi，Aki ko Iwashige，and Shuhei Matsuura

Abstract. - Manipulation of the host's host'sbody. It is used to take nourish司 behavior by the rhizocephalan parasite， ment 仕omthe host's tissues. Theparasite Sα cculinαpolygenea，was observed in affects the host in several ways，including an aquarium with avideo camera. The areduced frequency of molting，changes brachyuran host，HemigrapBuB Bαnguin- in secondary sexual characteristics and eus，cleaned the surface of the parasite's degeneration ofthe sexual organs (Rein- externa with its chelipeds. When the hard，1956; Hartnoll，1967; Takahashi & parasite released nauplii，the host assisted Matsuura，1994). Ritchie & Hoeg (1981) the parasite by adopting the stereotypic mentioned that rhizocephalan-parasitized larval release behavior of female crabs. individuals of the porcellanid crab Petro- While releasing the nauplii，the host listhes cα brilloi provide matemal care for remained stationary on arock ，occasion- the extema. During the release of nauplii ally flexing its abdomen with awaving by the parasite，the host helped the para- action. After releasing nauplii several site by performing abehavior similar to times，the ex: terna became smaller and that associated with larval release by withered，and the host removed it with female crabs. Since then，additional its chelipeds and ate it. This behavior examples of such behavioral manipulation was displayed by both 舵玄es of the host. have been observed in three brachyuran hosts，Rhithrop αnopeus hαrrisi ，Hemi- Introduction grαpsus sα nguineus and Chαrybdis longicollis (De Vries et α1.，1989; Takahashi Rhizocephalans (Ci町 ipedia) are exclu- Matsuura 1995; Innocenti et al . 1996). sively parasitic primarily on decapod & ， ， ， Noprevious studies however have focused . Larvae of sacculinids hatch ， ， on the thorough description ofthe behav- as nauplii. Females of the subsequent ioral changes. cypris stage ect the host and p訂 tofthe 凶 In this paper，we describe the behavior parasite protrudes from the host's abdo・ of Hemigrapsus sα nguineus parasitized men and acts as asaccular reproductive bySαcculinαpolygeneαL u t z e n Taka- organ called the externa. Male cyprid & hashi 1997 S. sentαi n Takahashi larvae migrate through the mantle cavity ， (= & Matsuura 1994). This behavior includes of the externa into areceptacle where ， groom泊 g the parasite assisting in larval they metamorphose into amass of sperm ， release by the parasite and removing the cells chikawa Yanagimachi 1958 (I & ， ， extema after release. 1960; Yanagimachi，196 1a， 1961b; Lutzen， 1984; Hoeg，1982 ，1985a ，1985b ，1990). The internal root system of the rhizo- Materials and Methods cephalan parasite (the intema) branches Parasitized individuals of Hemigrap- and penetrates different parts of the sus sα nguineus were collected from the 154 T .TAKAHASHI ETAL . pebbled intertidal zone ofthe lnuki Coast cotton attached to the posterior side of the (32 0 25' N ，130 0 25' E)，in Amakusa，Kyushu ， extemae，outside the host' sfield ofvision， Japan，between December 1989 and June were removed almost completely. Figure 2 1993. Crabs were transferred to the Aitsu shows aparasitized crab missing both Marine Biological Station，Kumamoto chelipeds.Th is is arare occuπence，asthe University，and kept in the laboratory in loss of both chelipeds is expected to be runn血g seawater for at least one week. lethal for the host. The dirty externa with ln order to induce the host to groom agrowth of epiphytic algae demonstrates the parasite，the surface of the externae the e首ect of alack of grooming in nature. on three hosts (1 male and 2females) was made dirty by sticking small pieces of Host behαvwr αssisting in larvαlrele αse cotton cloth to it with waterproof glue. by thepαrasite Most of the externae of the parasites Twelve episodes of nauplii release by are filled with ovaries and developing sacculinized Hemigrαpsus sαnguineus eggs and 訂 e yellowish in color.The color (7 males and 5females) were recorded.A changes as the eggs develop. The ex- typical series offrames taken 企omrecord- ternae become brown when they contain ings of aparasitized male H .sα nguineus eyed embryos. Release of nauplii occurs is shown in Fig.3 .Normally ，the host tried wi血血a few days of this stage (Takah錨 M to hide behind or under stones (Fig. 3A). &Ma旬uura，1994).'Iも erefore，hosts wi也 As也e 鋭meof nauplii release approached， brown externae were used for the video the host began to move restlessly，occa- recordings.Afte rseveral releases ofnau- sionally stan也ngstill for several seconds， plii ，the e玄ternae shrank. and withered， and then climbed the rock (Fig.3B). but recordings were continued until the Simultaneously，a rhythmic flexing be- externae disappeared. havior of the abdomen was observed. Thevideore∞rdings were made in 也 e Following this ，the crab stopped and Aitsu Marine Biological Laboratory， g仕etched，r泊s面gi旬 bodyupon也 e second KumamotoU凶versity.Atotal of 12 epi- and出 rdp国r ofwalking legs( Fig. 3C).At sodes of nauplii release were r，田 ordedfor this stage，the crab would no longer 9hosts .During the recordings，the crabs retreat back under the rock，even if an were kept in an aquarium not provided observer approached the aquarium.Aft er with circulating seawater，24 hr lighting approximately 1min ，the crab changed and fed daily with artificial pellet food position，but continued to stretch (Fig. used for prawn culture (Higashimaru 3D).About 2min later，the extema con- Co. ，Lt d.). Host crabs carrying withered stricted and began to release nauplii (Fig. externae were given an excess of food，so 3E).The host occasionally flexed its abdo- it is not probable that alack of food men (flexing response) in synchrony with caused the observed behaviors. the constrictions .Larvae were released into water currents created by the con- Results strictions of the externa and the flexing action of the abdomen. When the externa Gr∞，mingbehαvior was empty，its color changed back from Host crabs regularly clean their body brown to yellow (Fig. 3F). During larval surfaces using their chelipeds. This release，other than flexing its abdomen， grooming behavior is also extended to the the host remained motionless (Fi g. 3E-G). externae of the parasite.Wh en dirt was ln this series of observations，the crab attached to the externae experimentally， only changed position once，and remained the hosts cleaned the surface within still for 13 min 11 s. After nauplii release about 20 min (Fig.1). Even pieces of by the parasite，the host resumed its BEHAVIOR OF SACCULINIZED HEMIGRAPSUS 155

B

日g.1. The surface of an externa of Sacculinα Fig.2 .(A) A parasitized individual of Hemi- polygenea was made dirty by sticking small gnα:psus sanguineus with intact chelipeds and pieces of cotton cloth to it with waterproof glue clean externa.(B) Another individual carries (A). After 20 min，the cotton was removed by two externae (arrows indicate the mantle the host (B) . openings) and has lost both chelipeds.Epi- phytic algae remain attached to the surface of the externae.

Table 1. Immobility period of host Hemigrapsus sαnguineus and duration of nauplii release of Sα cculina polygeneα.

Host's Length Longest Duration Water carapaω of period of Inter- tempe!.a- 1 2 Host width externae ) 。f nauplii ruptions ) tureure ) No. No. Sex (mm) (mm) immobility release (times ) (" C)

唱 28.5 12.0 13' 11" 9' 58" ' 18.6 A 1 M i O 28.5 12.3 33" 8' 21" n L 1 M 17' U 17.8 q 内 24.6 14.6 21' 05" 4'43" d 15.4 o a 2 M ι a品 24.6 11. 8 24'18" 7' 09" τ 16.1 Z 2 M R 24.6 9.7 41' 22" l'12" 円 14.8 u 2 M 4 n 22.1 13.3 5'33" 0' 41" n 19.6 O 3 F L 円 16'08" 14' 21" A t 4 M 26.0 14.5 U 18.6 口 20.0 12.0 11' 17" 10'59" h 15.5 o 5 F U n 25.5 16.0 36'21" 11'04" 22.3 U 6 F 向 噌 A ，。 i U 24.5 10.9 11' 31" 8' 12" i 21. 7 噌 噌 7 M n i i 27.1 12.4 14'54" 6' 21" L 17.8 噌 8 M n 23.7 16.2 44'5 1" 12' 18" A 20. i 4 9 F U 。 Long diameter of externae before the video-recording. 2) The 戸 riod of immobi1i ty includes several periods of short interruptions . d } Themean ofthe water temperatures at the beginning and the end ofthe video-recording. 156 T .TAKAHASHI ETAL.

日g.3. Behavior ofthe host CI油 (Hemigrapsus sanguineus) associated with the release ofnauplii by the parasite (Sacculinαpolygeneα) .Photos 企omthe video monitor: (A) H .sanguineus is αy p t i c 阻 d hides under the s旬 ne. (B) As the time ofnauplii release approaches，the host becomes restless，although sometimes it st 組 ds still for several seconds. At this time，it begins to flex its abdomen. (C) The host stretches: it stands on tip-toes (ex ，externa) .(D) The host moves.(E ) Nauplius larvae begin to be released. (F，G) The color of the externae gradually changes 企om brown to yellow.(H) Nauplii release ends. The host lowers its body and eats the nauplius larvae， picking them up with its chelipeds. BEHAVIOR OFSACCULINIZED HEMIGRAPSUS 157 normal behavior:the crab ate nauplii， picking them up with its chelipeds (Fig. 3H)，and hid under the stone within 1min of the end of nauplii release.The release oflarvae took approximately 10 min 仕om start to finish. In the other eleven cases，the duration of release varied but the behavior was similar，although it was interrupted sev- eral times in some cases (Table 1) .The hosts alternated between periods of move- ment and remaining stationary before release.Th elongest periods of immobility are shown in Table 1. The release period is included in the period of immobility. The host occasionally relaxed its stance and shifted position slightly. Mter such interruptions，the hosts soon became immobile ag出n. All interruptions observed are included in the period ofimmobility as shown in Table 1. There was no interrup- Fig. 4. Awithered externa of Sα cculinα tion during larval release.Multiple re ・ polygeneαi s removed and eaten by the host， leases by parasites on hosts No. 1and No. Hemigrαpsus sα nguineus.Photos from the 2were observed. There were two externae video monitor: (A) Thehost nips at the base of on host No. 1，both ofwhich released lar- the externa.(B) The host eats the detached externa. vae within a28 hr interval. A single externa on host No. 2released larvae three times，separated by a5 to 6day lease，female crabs remained in astretched incubation period. The length of the position on their third pair of walking externa on host No.2 decreased with each legs. They performed the stereotypic release of nauplii and the third release larval-release behavior of crabs，which was also very short，only 1min 12 s. How- includes f1 exing the abdomen. The ab- ever，there is no significant relationship dominal f1 exing was more clearly defined between the length of the externae and and more vigorous than that observed in the periods of immobility or nauplii sacculinized crabs during larval release release in the twelve replicates (r =0.30 by the parasites. However，all other 出 ld 0.4 8respectively ，P > 0.05 ，F ・ test).In aspects of the behavior of sacculinized 5ofthe 12 video-recordings，pairs ofhosts crabs were similar to those of normal bearing brown externae packed with eyed females when the eggs hatch.The three embryos were kept in the same aquarium. females remained immobile for 8min 12 s， There was no noticeable change in behav- 12 min 58 s，and 13 min 7s ，respectively. ior when another crab began to release larvae. Removαl α nd ingestion of externαby the host Compαrison with the normαll αrvαl Mter several releases of nauplii，the rele αsing behαvior of Hemigrapsus externa became pale and empty.Video re- sangUlneus cordings revealed that the externa was Three cases of larval release by females removed and eaten by the host. The host were recorded on videotape. During re ・ nipped at the stalk of the externa with its 158 T. TAKAHASHI ETAL.

chelipeds，tore it off，and ate it completely (Fig.4). Three examples of this behavior were recorded on videotape.The withered externae were removed 3，3and 6days after the final release of nauplii respec- tively. A 此er the externae were removed， stalks remained on the abdomen (Fig. 5). These stalks disappeared within afew days，leaving scars. These observations are incorporated into Fig. 6，which shows the life cycle of Fig.5 .The stalk of the externa of Sacculina the parasite.Wh en the host is uninfected， poか'geneα( a r r o w ) left on the abdomen. grooming behavior helps to defend the

Female cypri sinfe ctother hosts

Externa is removed o - 町 持璽与 and i ested by the host

-・喝炉

6. of condition associated with the life cycle of the rhizocephalan Sα cculinαpolygeneα. When the host is uninfected，grooming behavior prote伽 the host hminfktionbut the host shows maternal careonce it has been parasitized.Light amS indicate the internal phase of the parasite-(a)Uninfected host.(b)Modiged male host.The female host' sex 旬 rnal おrmis not altered by infection .(c) Parasitized host with newly erupted virgin externa.The e叫erna begins to grow if amale cypris larva invades the receptacles. (d) Parasitized host-carrying externa that contain eggs.(e )Releasing nauplius larvae .(f) Scarred crab.* The resumption ofmolting is based on the work ofTakahashi & Matsuura (1994). BEHAVIOR OFSACCULINIZED HEMIGRAPSUS 159 host from infection. Once parasitized， an elevated area (the top of arock) ，and in however，the host shows maternal care raising their bodies in afixed stance. (see Ritchie & Hoeg，1981). Even when apair of hosts，both of which were carrying brown extemae，were kept in an aquarium together，no noticeable Discussion behavioral change was observed in the co ・ The shore crab，Cα rcinus maenαs ， inhabiting host when the other crab when parasitized by mature Sαcculina commenced the pre・hatching behavioral cα rcini，has been reported to migrate into response. The peptide pheromones may deeper water as unparasitized females do becomet∞dilu飴d 旬 aff 田t血eco- inhabi也19 (Veillet，1945; Rasmussen，1959; Lutzen， host，although it is also possible that the 1984). Phillips & Cannon (1 978) noted parasite controls the host via the intema similar behavior in the commercial sand in conjunction with pheromones released crab，Portunus pelαgicus，parasitized by from the eggs. Sα cculinαgrαniferα. Ritchie & Hoeg Takahashi & Matsuura (1995) and (1981) first observed direct maternal Innocenti et αl. (1996) reported on the behavior by the host of arhizocephalan modified behaviors of sacculinized H. parasite in the case of aporcellanid ， sα nguineus and longicollis Petrolisthes cαbrilloi，parasitized by respectively.Innocenti et al. (1996) noted Lernαeodiscus porcellαn αe . They noted that when the portunid crab C. longicollis that the externa mimics the host's egg has externa，then the host spends more mass in both form and position .Presum- time grooming the parasite and the pres- ably，the host treats the externa as if it ence of the parasite inhibits the host 企om were its own brood. The results of the buηing in the sand，a very common activ- present study on H. sanguineus are in ity of unparasitized C. longicollis. It is agreement with their observations. likely that the behavior of C. longicollis De Vries et al. (1989) demonstrated shares many points in common with that Rhithropαnopeus hαrrisii parasit- sacculinized H. sα nguineus. ized by Loxothylαcuspαnopei showed the In arecent study，sacculinized Cα rcinus abdominal fle 垣ngresponse when exposed maenωw a sobserved 句 perform grooming to certain peptides.These peptides are and flexing behavior more often than similar to the pheromones released by the uninfected crabs.The flexing becomes crab's own eggs just before hatchlng. This more frequent as the externa mature suggests that the rhlzocephalan parasite (L批 zen，pers. comm.). Crabs with virgin also produces similar peptides prior to externa have also been observed to stand release of its larvae. De Vries et al. also on tiptoe ，and this behavior is thought to demonstrated that 出e behavioral response be advantageous for the invasion of the decreased if the externa was removed， yo田 19 extema by male cypris (see Fig. 6c). and was restored，although temporarily， Most decapod crustaceans exhibit by placing asimulated egg mass (plastic grooming behavior (Bauer，1979). The bead) on the abdomen. Thissuggests that laboratory experiment of Ritchie & Hoeg the peptides alone do not induce the fle 垣ng (1981) clearly demonstrated that groom- response，and that aphysical stimulus on ing by the porcellanid host Petrolisthes the abdomen is also necessary to induce cα brilloi plays asignificant role as afirst the response. In the present study，the defense against the invasion by the flexing response was not so marked as kentrogon larvae of the rhizocephalan that of R. hαrrisii. However，the crabs Lernαeodiscus porcellαnae.However ， showed remarkable behavior in moving 旬 once the parasite has circumvented this 160 T. TAKAHASHI ETAL. defense and the externa appeared，the 295. role of the grooming behavior changes to Hoeg，J. T. ，1982. The anatomy and develop- ment ofthe rhizocephalan barnacle Clisto- protect the parasite (Fig. 6) . saccuspα:guri Lillgeborg and relation to its It is not clear whether removal and host pα， .g urus bernhαrdus (L.). Journal of ingestion of the withered externae is also Experimental Marine Biology and Ecology， an example of host manipulation by the 58: 87-125. parasite or if it indicates the end of this 一一一一， 1985a. Cypris settlement，kentrogon ， formation and host invasion in the para- behavioral manipulation. Removal of the sitic barnacle Lernαeodiscus porcellanαe externae is necessary，however ，both for (Mu11er) (Crustacea: Cirripedia: Rhizo- subsequent molting of the host and for cephala).Acta Zoologica，Stockholm ，66 : the replacement of new externae by the 1-45. parasite (Takahashi & Matsuura，1994). 一一一一， 1985b.Male cypr匂 settlement in Clistosaccus pα.g uri Lillgeborg (Crustacea: This behavior may be peculiar to this Cirripedia: ).Journal of Ex- host /parasite system; replacement of perimental Marine Biology and Ecology， the externae has never been recognized 89: 221-235. as playing a significant role in other 一一一一， 1990. “Akentrogonid “host invasion sacculinid species. and an entirely new t) 予e of life cycle in the rhizocephalan parasite Clistosaccus pα.g uri (Thecostraca: Cirripedia). Journal of Crus- Acknowledgments tacean Biology，10: 37-52. Ichikawa，A.， &Yanagimachi ，R.， 1958. Studies Wewish to thank the following: Dr. T. on the sexual organization of the Rhizo- Yamaguchi，Ai tsu Marine Biological Sta- cephala. 1. The nature of the ‘testis' of tion (AMBS)，Kumamoto University，who Kruger. Annot- gave us advice and help throughout the ationes Zoologicae Japonenses，31 :82-96 . 一一一一，& 一一一一， 1960. Studies on the sexual study; Prof. R. Hirota and Mr. M .Shima- organization of the Rhizocephala. 11. The saki，AMBS ，who provided us with labo- reproductive function ofthe larval (Cypris) ratory facilities; Dr. C. Norman，Japan males of Peltogα，sterandSαcculinα. Annot- Scientific Text，for help with the English; ationes Zoologicae Japonenses，33: 42-56. Dr. J. Lutzen Department ofCell Biology Innocenti，G .，Vannini ，M. ，& Galil ，B.， 1996. ， Notes on the behaviour of the portunid 出 ld Anatomy，University ofCopenhagen， crab ChαF ツbdis longcolis Leene，parasit ・ for critically reading the manuscript; ized by the rhizocephalan Heterosαccus Messrs. M. Yoneda and K. 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shore crabs (Cα rcinus m αenαsPennant). Veillet，A. ，1945. Recherches sur le para咽 Nature，183: 479-480. sitisme de crabes et des Galathees par les Reinhard，E. G. ，1956 .Parasitic castration of Rhizocephales et les Epicarides.Annales Crustacea.Experimental Parasitology，5: de l'I nstitut Oceanographique，Monaco ，22: 79-107. 193-341. Ritchie，L. E. ，& Hoeg，J .T. ，198 1. The life Yanagimachi，R.， 1961a. Studies on the sexual his伽" y of Lernaeodiscus porcellanae (Ci汀 i- organization of the Rhizocephala. 11 1. The pedia: Rhizocephala) and co-evolution with mode of sex determination in Peltogaste- its porcellanid host.Journal of Crustacean rell α. Biological Bulletin，120: 272-283. Biology，1: 33ι347. 一一一一， 1961b. The life cycI eof Peltogαsterella Takahashi，T. ，& Matsuura ，S. ，1994. Labora- (Cirripedia: Rhizocephala). Crustaceana， tory studies on molting and growth of the 2: 183-186. shore crab，Hemigrapsus sanguineus de Haan，parasitized by arhizocephalan barnacle. Biological Bulletin，186: 300- Addresses: (TT，SM) Department of Fish- 308. eries ，Faculty of Agriculture，Kyushu Univer- 一一一一，& 一一一一， 1995. Beha吋. o ral manip叫 ation sity，Hakozaki ，Fukuoka 812，Japan; (AI) ofthe shore crab，Hemigrapsus sanguineus Nakaminami Elementary School，Oyano ， by the rhizocephalan branacle. Abstract of Kumamoto 869-36，Japan. XXIVlnternαtional Ethological Conference， E-mails:(TT)[email protected]. Honolulu，H， αwaii，123. jp; (SM) [email protected]