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Short report on the effect of a parasitic isopod on the reproductive performance of a shrimp
Journal of Experimental Marine Biology and Ecology 321 (2005) 13 – 18 www.elsevier.com/locate/jembe
Short report on the effect of a parasitic isopod on the reproductive performance of a shrimp Ricardo Caladoa,*, Ca´tia Bartilottib, Luı´s Narcisoa a
Laborato´rio Marı´timo da Guia, Departamento de Biologia Animal, Faculdade de Cieˆncias da Universidade de Lisboa, Estrada do Guincho, 2750-642 Cascais, Portugal b Instituto Nacional de Investigac¸a˜o Agra´ria e das Pescas-IPIMAR, Av. de Brası´lia, s/n. 1449-006 Lisboa, Portugal Received 5 February 2004; received in revised form 29 November 2004; accepted 20 December 2004
Abstract The present work studied the degree of inhibition caused by the bopyrid isopod Eophryxus lysmatae (Caroli, 1930 [Caroli, E., 1930. Notizia di tre specie nuove ed una poco nota di Bopiridi addominali, parassiti di Caridei del golfo di Napoli. (Contributo alla conoscenza del genere Phrixus Rathke). Boll. Soc. Nat. Napoli 41, 258–269]), an abdominal parasite, on the reproductive performance of its host, the protandric simultaneous hermaphrodite shrimp Lysmata seticaudata (Risso, 1816). Parasitized shrimp (PS) was not able to produce embryos, although they could successfully fertilise the eggs of unparasitized shrimp (US). All US paired with PS were able to fertilise eggs when paired with other US. The average number of larvae (FS.D.) produced by US shrimp paired with US and PS (344F27 and 346F23, respectively) was not significantly different ( p=0.73). The average intermolt period duration (FS.D.) for US and PS (10F1.2 and 11F0.8 days, respectively) was not significantly different ( p=0.82), with bopyrid parasites molting synchronously with their host. No PS lost its parasite during ecdysis. Although only three parasitized shrimp were used in the present work, parasitic castration induced by E. lysmatae seems to only affect the female sexual system of the simultaneous hermaphrodite L. seticaudata, and therefore parasite-induced breproductive deathQ does not occur in this species as in other gonochoric and sequencial hermaphroditic caridean shrimp. Nutritional drain and disruption of endocrine mechanisms possibly caused by the bopyrid parasite are discussed. D 2005 Elsevier B.V. All rights reserved. Keywords: Bopyrid ispods; Eophryxus lysmatae; Hermaphroditism; Lysmata seticaudata; Parasitic castration
1. Introduction
T Corresponding author. Tel.: +351 21 4869211; fax: +351 21 4869720. E-mail address: [email protected] (R. Calado). 0022-0981/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jembe.2004.12.038
Bopyrid isopods are known to be holoparasites, with their definitive hosts being decapod crustaceans (Markham, 1986). Bopyrids are known to cause parasitic castration, which involves two associated, but according O’Brien and Van Wyk (1985) perhaps
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R. Calado et al. / J. Exp. Mar. Biol. Ecol. 321 (2005) 13–18
distinct, phenomena: gonads of female host do not mature and parasitized males are feminised. Despite the variable degree of inhibition that these two phenomena cause on host reproductive potential (Van Wyk, 1982), it always suffers a substantial reduction and generally causes the breproductive deathQ of the host. Apart the preliminary studies by Fiedler (2000), the works addressing parasitic castration in decapods have only dealt with gonochoric species. Eophryxus lysmatae (Caroli, 1930) is a member of the subfamily Hemiarthrinae, a group of bopyrids characterized by having caridean shrimp as their main host and by being abdominal parasites (Markham, 1986). This species is known to occur in the Mediterranean and only parasitizes the Monaco shrimp Lysmata seticaudata (Risso, 1816) (Caroli, 1930). Bauer and Holt (1998) and Fiedler (1998) demonstrated the existence of a unique sexual system among decapod crustaceans in the genus Lysmata, protandric simultaneous hermaphroditism. The existence of this puzzling sexual system has been recently confirmed in L. seticaudata by Udekem d’Acoz (2003), validating the idea that this may be a common feature to all members of the genus (Bauer, 2000). The objective of the present work is to study the degree of inhibition caused by parasitic castration by the bopyrid isopod E. lysmatae in the reproductive performance of its host, the protandric simultaneous hermaphrodite caridean shrimp L. seticaudata.
2. Materials and methods Monaco shrimp were collected during spring tides at Cape Raso, 30 km west of Lisbon, Portugal, in the month of May of 2001 using baited traps described by Calado and Narciso (2004). The single three specimens of L. seticaudata (out of 680 captured) carrying bopyrid isopods were isolated. Nine unparasitized shrimp with total length (TL, distance between the rostrum anterior end and the telson posterior edge) similar to that of parasitized shrimp (47F2 mm) were also isolated. The selected 12 shrimp were kept in six 30 l aquariums at 23 8C, 35x salinity and with a photoperiod of 12 h light:12 h dark. Shrimp were daily fed ad libitum minced shrimp, mussel and fish roe.
The same 12 shrimp were used sequentially in the four trials. In trial 1, each parasitized shrimp (PS) was randomly paired with an unparasitized shrimp (US), the remaining six unparasitized shrimp were randomly divided into three pairs, resulting in three PS/US and three US/US pairs. In trial 2, each PS was paired with a shrimp used in the three US/US pairs in trial 1, with the remaining US paired in three US/US pairs. In trial 3, the three US not previously paired with PS were each paired with a PS, with the remaining US paired in three US/US pairs. In trial 4, each PS was sequentially paired with each other (see Table 1). The reproductive performance of each shrimp was evaluated by counting the number of hatched larvae from the first three embryo batches produced after pairing. The molts of PS and US were collected during all trials for morphological comparison and the average intermolt period duration of each shrimp recorded. A t-test was used to compare the intermolt period duration and the number of larvae produced by shrimp paired with PS and US. The results were considered statistically significant at the 0.05 probability level (Zar, 1996). After performing the reproductive trials, parasitized shrimp were stored in ethanol for morpho-
Table 1 Random pairs of Lysmata seticaudata shrimp carrying the bopyrid isopod Eophryxus lysmatae (PS) and unparasitized shrimp (US) formed during trials to evaluate their reproductive performance Randomly formed shrimp pairs Trial 1 PS1 PS2 0 0 US1 US4 333F30 348F12 Trial 2 PS1 PS2 0 0 US3 US5 330F12 384F21 Trial 3 PS1 PS2 0 0 US2 US9 347F42 364F23 Trial 4 PS1 0 PS2 0
PS3 US5 0 386F42 US8 US6 304F5 321F14 PS3 US1 0 304(F11) US6 US7 363F19 341F24 PS3 US1 0 302F14 US7 US4 348F10 334F23 PS1 0 PS3 0
US3 US2 352F7 321F22 US7 US9 331F24 370F14 US2 US8 352F9 372F21 US9 US4 326F27 354F17 US3 US5 381F41 392F24 US6 US8 339F12 325F36 PS2 0 PS3 0
Values are averages (FS.D.) of three batches of larvae produced by each shrimp.
R. Calado et al. / J. Exp. Mar. Biol. Ecol. 321 (2005) 13–18
15
logical observation and illustration. Drawings were made with the aid of a camera lucida on a binocular Wild M8.
3. Results The infestation rate of bopyrid isopods parasitizing L. seticaudata in the present study was only 0.4% (3/680). Although in all reproductive trials PS were not able to produce any embryos, each of these specimens successfully fertilised the eggs of their unparasitized mates. Shrimp paired with PS displayed the same mating behaviour pattern described by Nouvel (1940) for L. seticaudata. All US paired with PS were able to fertilise eggs when paired with other US. The average number of larvae (FS.D.) produced by US shrimp paired with US and PS (344F27 and 346F23, respectively) was not significantly different ( p=0.73) (Table 1). The average (FS.D.) intermolt duration for US and PS (10F1.2 and 11F0.8 days, respectively) was not significantly different ( p=0.82). Bopyrid parasites had broods and molted synchronously with their host
Fig. 1. (A) Lateral view of simultaneous hermaphrodite phase Lysmata seticaudata infested with the bopyrid isopod Eophryxus lysmatae. Solid black arrow indicates the positioning of adult female Eophryxus lysmatae on host. Scale bar: 10 mm. (B) Detail of attachment area of adult Eophryxus lysmatae female infesting the abdominal region of Lysmata seticaudata. 1: Left first pleopod. 2: Left second pleopod. 3: Left third pleopod. Scale bar: 1 mm. (C) Dorsal view of adult Eophryxus lysmatae female. Shaded region represents the attachment area of male on female’s dorsal surface. Solid black arrow indicates the anterior end of adult male Eophryxus lysmatae. Scale bar: 1 mm. (D) Lateral view of adult Eophryxus lysmatae male. Scale bar: 1 mm.
Fig. 2.
(bopyrid molts being recovered from the aquariums) and none of the PS lost its parasite during ecdysis. Parasitized shrimp never showed the typical bbright green spotQ displayed by US, evidence of the presence of large vitellogenic oocytes in the ovary portion of the gonad prior to extrusion. Morphological data (not histological data) revealed that the testes, vas deferens and the terminal ampoule of PS were similar
Fig. 3.
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Fig. 4.
to those of US, but the anterior portion of the gonad where the ovarian structures are located appeared smaller than in US, and did not display vitellogenic oocytes. The observation of PS and US molts revealed the same secondary sexual characters typically present in the simultaneous hermaphrodite phase of L. seticaudata, according to Dohrn (1950) and CharniauxCotton (1959). The female isopod was always found firmly attached to its host (Fig. 1) in the base of the second left pleopod, with its dorsal surface facing the ventral face of the host and its anterior portion directed towards the posterior end of the shrimp (Fig. 2). Female parasites displayed their protruding marsupium distorted to the left in dorsal view (Fig. 3) and were always accompanied by the symmetrical dwarf male (Fig. 4), which clings to the female’s dorsal face of the left first foliaceous pleopod (see Fig. 3). The average (FS.D.) sizes of female and male parasites (from anterior to posterior end) were 10.21F0.98 mm and 0.84F0.32 mm, respectively. Due to small sample size of PS (n=3), the possible correlations between the sizes of host and parasite and female and male parasites were not investigated.
4. Discussion Shrimp collected, results presented in the present work should be regarded with caution. Nevertheless, the present trials seem to indicate that the parasitic castration induced by the bopyrid isopod E. lysmatae only affects the female sexual system of the simultaneous hermaphrodite L. seticaudata. This can explain why only US with similar TL of PS were collected incubating embryo. Parasitized shrimp retain their ability to reproduce as fully functional males, and
therefore parasite-induced breproductive deathQ does not occur in this species as in other gonochoric and sequential hermaphroditic caridean shrimp (O’Brien and Van Wyk, 1985). The preliminary study performed by Fiedler (2000) on Lysmata anchisteus (Chace, 1972), L. ternatensis (De Man, 1902) and L. trisetacea (Heller, 1861) parasitized by undescribed bopyrids of the subfamily Hemiarthrinae (abdominal parasites) also revealed that only the female function of parasitized simultaneous hermaphrodites was inhibited. The mechanisms associated with parasitic castration affecting the host are still not totally understood. Reinhard (1956) and Anderson (1977) highlighted the nutritional drain affecting PS energy flow, which could impair parasitized females of producing energy costly vitellogenic oocytes. Reinhard (1956), Baudoin (1975), Walker (1977) and Beck (1980) also discussed the possibility of endocrine mechanism disruption, by the reduction of circulating reproductive hormones (due to blood losses caused by parasites), stimulation of the gonad-inhibiting hormone (GIH) or even the secretion of GIH by bopyrids. The observations by Coutie`re (1899) on the alpheid shrimp Synalpheus biunguiculatus (Stimpson, 1860) and by Caroli (1930) on Synalpheus gambarelloides (Nardo, 1847) (=S. laevimanus) found that ovigerous shrimp simultaneously carried adult abdominal bopyrid isopods (although embryos were present in fewer numbers than normal), only highlights the complexity and lack of knowledge on this topic. Unfortunately, the works by Charniaux-Cotton (1960), Charniaux-Cotton and Touir (1973), Touir (1977a,b), Bauer and Holt (1998) and Fiedler (1998, 2000) have only partially discussed and explained the complex endocrinological processes regulating the role of the median protocerebrum, androgenic glands, ovarian and testicular portions of the gonad and the X-organ and sinus gland complex in the genus Lysmata. As stated by Noe¨l (1976), until host and parasite endocrinology is known, the understanding of parasitic castration will always be incomplete. In the present study, no parasitized male phase L. seticaudata were collected, but there is no apparent reason why bopyrid isopods would only parasitize simultaneous hermaphroditic phase shrimp. Assuming that male phase shrimp are also selected as
R. Calado et al. / J. Exp. Mar. Biol. Ecol. 321 (2005) 13–18
hosts by E. lysmatae and, for some reason, feminisation of the host is induced (cincinnuli present at the endopod of the first pair of pleopods and the appendix maculina are lost), but the testes remain functional, it can be expected that these shrimp could still act as functional males. Although the appendages mentioned above are known to play a major role in sperm transfer in decapods (Bauer, 1976, 1986; Berg and Sandifer, 1984), the studies by Zhang and Lin (2004) on simultaneous hermaphroditic Lysmata shrimp revealed that the presence of such appendages is not essential for individuals mating as males to successfully fertilize egg clutches. The present work is the first record of E. lysmatae outside the Mediterranean Sea, an area with considerably warmer water temperature than the eastern Atlantic shores of Portugal, the low infection rate recorded in the present work should be treated with caution.
5. Conclusion The complexity of the puzzling sexual system of Lysmata is once again highlighted by the parasitic castration induced by an abdominal bopyrid isopod only impairing simultaneous hermaphroditic shrimp to mate as females. Future studies should use a larger number of parasitized shrimp, address the effect of branchial bopyrid parasites infecting other Lysmata species (Fiedler, 2000) and the possible evolutionary role that parasitic castration might have had in the mating system of Lysmata and other decapod species.
Acknowledgements The authors would like to thank Fundac¸a˜o para a Cieˆncia e a Tecnologia (scholarship SFRH/BD/983/ 2000 and research project POCTI/BSE/43340/2001) and FEDER (SIGAP project 22-05-01-FDR-00013) from the Portuguese government for financial support and Milton Alfredo and Gil Penha-Lopes for their assistance in field and laboratory work. We thank G. Curt Fiedler for sharing his findings on parasitic castration affecting Lysmata species. We would also like to express our sincere gratitude to Raymond T.
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Bauer, Junda Lin and an anonymous referee for providing valuable comments on the present work. [AU]
References Anderson, G., 1977. The effects of parasitism on energy flow through laboratory shrimp populations. Mar. Biol. 42, 239 – 251. Baudoin, M., 1975. Host castration as a parasitic strategy. Evolution 29, 335 – 352. Bauer, R.T., 1976. Mating behaviour and spermatophore transfer in the shrimp Heptacarpus pictus (Decapoda: Caridea: Hippolytidae). J. Nat. Hist. 10, 415 – 440. Bauer, R.T., 1986. Phylogenetic trends in sperm transfer and storage complexity in decapod crustaceans. J. Crustac. Biol. 6 (3), 313 – 325. Bauer, R.T., 2000. Simultaneous hermaphroditism in caridean shrimps: a unique and puzzling sexual system in the decapoda. J. Crustac. Biol. 20, 116 – 128 (Special Number). Bauer, R.T., Holt, G.J., 1998. Simultaneous hermaphroditism in the marine shrimp Lysmata wurdemanni (Caridea: Hippolytiae): an undescribed sexual system in the decapod crustacea. Mar. Biol. 132, 223 – 235. Beck, J.T., 1980. The effect of an isopod castrator, Probopyrus pandalicola, on the sex characters of one of its caridean shrimp hosts, Palaemonetes paludosus. Biol. Bull. 158 (1), 1 – 15. Berg, A.-B.V., Sandifer, P.A., 1984. Mating behaviour of the grass shrimp Palaemonetes pugio Holthuis (Decapoda, Caridea). J. Crustac. Biol. 4 (3), 417 – 424. Calado, R., Narciso, L., 2004. An inexpensive baited trap for collecting cryptic decapod crustaceans. Crustaceana 77, 341 – 351. Caroli, E., 1930. Notizia di tre specie nuove ed una poco nota di Bopiridi addominali, parassiti di Caridei del golfo di Napoli. (Contributo alla conoscenza del genere Phrixus Rathke). Boll. Soc. Nat. Napoli 41, 258 – 269. Charniaux-Cotton, H., 1959. Masculinisation des femelles de la crevette a` hermaphrodisme prote´randrique Lysmata seticaudata, par greffe de glandes androge`nes. Interpre´tation de l’hermaphrodisme chez les De´capodes. Note preliminaire. Comptes Rendus Se´ances Soc. Biol. 249, 1580 – 1582. Charniaux-Cotton, H., 1960. Physiologie de l’inversion sexuelle chez la crevette a` hermaphrodisme prote´randrique fonctionnel, Lysmata seticaudata. Comptes Rendus Se´ances Soc. Biol. 250, 4046 – 4048. Charniaux-Cotton, H., Touir, A., 1973. Controˆle de la pre´vitellogene`se et de la vitellogene`se chez la crevette hermaphrodite Lysmata seticaudata Risso. C. r. Se´ances Acad. Sci. 276, 2717 – 2720. Coutie`re, H., 1899. Les bAlpheidaeQ. Morphologie externe et internes, formes larvaires, bionomie. Ann. Sci. Nat., Zool. 8 (9), 1 – 559. Dohrn, P.F.R., 1950. Studi sulla Lysmata seticaudata Risso (Hippolytidae): I. Le condizioni normali della sessualita` in natura. Pubbl. Stn. Zool. Napoli 22 (3), 257 – 272.
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Fiedler, G.C., 1998. Functional, simultaneous hermaphroditism in female-phase Lysmata amboinensis (Decapoda: Hippolytidae). Pac. Sci. 52, 161 – 169. Fiedler, G.C., 2000. Sex determination and reproductive biology of two caridean shrimp genera: Hymenocera and Lysmata. PhD Dissertation, University of Hawaii, USA. Markham, J.C., 1986. Evolution and zoogeography of the Isopoda Bopyridae, parasites of Crustacea Decapoda. In: Gore, R.H., Heck, K.L. (Eds.), Crustacean Issues 4: Crustacean Biogeography. A.A. Balkema, Rotterdam, pp. 143 – 164. NoJl, P.Y., 1976. L’e´volution des caracte´res sexuels chez Processa edulis (Risso) (De´capode, Natantia). Vie Milieu, Se´r. A Biolog. Mar. 26 (1), 65 – 104. Nouvel, L., 1940. Observations sur la biologie de Lysmata seticaudata Risso. C. R. Se´ances Acad. Sci. 210, 266 – 269. O’Brien, J., Van Wyk, P.M., 1985. Effects of crustacean parasitic castrators (epicaridean isopods and rizocephalan barnacles) on growth of crustacean hosts. In: Wenner, A.M. (Ed.), Crustacean Issues 3: Factors in Adult Growth. A.A. Balkema, Rotterdam, pp. 191–218. Reinhard, E.G., 1956. Parasitic castration of Crustacea. Exp. Parasitol. 5, 79 – 107. Touir, A., 1977a. Donne´es nouvelles concernant l’endocrinologie sexuelle des Crustace´s De´capodes Natantia hermaphrodites et
gonochoriques. Mise en e´vidence d’un controˆle neurohormonal du maintien de la´ppareil ge´nital maˆle et des glandes androge`nes exerce´ par le protoce´re´bron me´dian. C. r. Se´ances Soc. Biol. 285, 539 – 542. Touir, A., 1977b. Donne´es nouvelles concernant la endocrinologie sexuelle des crustace´s de´capodes Natantia hermaphrodites et gonochoriques: I. maintien des glandes androge`nes et role des glandes dans le controle des game´toge´ne`ses et des caracte`res sexuels externes males. Bull. Soc. Zool. Fr. 102 (4), 375 – 400. Udekem d’Acoz, C.D., 2003. Lysmata seticaudata (Risso, 1816) and L. nilita Dohrn and Holthuis, 1950 are protandrous simultaneous hermaphrodites (Decapoda, Caridea, Hippolytidae). Crustaceana 75 (9), 1149 – 1152. Van Wyk, P.M., 1982. Inhibition of the growth and reproduction of the porcellanid crab Pachycheles rudis by the bopyrid isopod, Aporobopyrus muguensis. Parasitology 85, 459 – 473. Walker, S.P., 1977. Probopyrus pandalicola: discontinuous ingestion of shrimp hemolymph. Exp. Parasitol. 41, 198 – 205. Zar, J.H., 1996. Biostatistical analysis. Prentice Hall, Upper Saddle River, New Jersey, USA. Zhang, D., Lin, J., 2004. Fertilization success without anterior pleopods in Lysmata wurdemanni (Decapoda: Caridea), a protandric simultaneous hermaphrodite. J. Crustac. Biol., 470 – 473.
Short report on the effect of a parasitic isopod on the reproductive performance of a shrimp Ricardo Caladoa,*, Ca´tia Bartilottib, Luı´s Narcisoa a
Laborato´rio Marı´timo da Guia, Departamento de Biologia Animal, Faculdade de Cieˆncias da Universidade de Lisboa, Estrada do Guincho, 2750-642 Cascais, Portugal b Instituto Nacional de Investigac¸a˜o Agra´ria e das Pescas-IPIMAR, Av. de Brası´lia, s/n. 1449-006 Lisboa, Portugal Received 5 February 2004; received in revised form 29 November 2004; accepted 20 December 2004
Abstract The present work studied the degree of inhibition caused by the bopyrid isopod Eophryxus lysmatae (Caroli, 1930 [Caroli, E., 1930. Notizia di tre specie nuove ed una poco nota di Bopiridi addominali, parassiti di Caridei del golfo di Napoli. (Contributo alla conoscenza del genere Phrixus Rathke). Boll. Soc. Nat. Napoli 41, 258–269]), an abdominal parasite, on the reproductive performance of its host, the protandric simultaneous hermaphrodite shrimp Lysmata seticaudata (Risso, 1816). Parasitized shrimp (PS) was not able to produce embryos, although they could successfully fertilise the eggs of unparasitized shrimp (US). All US paired with PS were able to fertilise eggs when paired with other US. The average number of larvae (FS.D.) produced by US shrimp paired with US and PS (344F27 and 346F23, respectively) was not significantly different ( p=0.73). The average intermolt period duration (FS.D.) for US and PS (10F1.2 and 11F0.8 days, respectively) was not significantly different ( p=0.82), with bopyrid parasites molting synchronously with their host. No PS lost its parasite during ecdysis. Although only three parasitized shrimp were used in the present work, parasitic castration induced by E. lysmatae seems to only affect the female sexual system of the simultaneous hermaphrodite L. seticaudata, and therefore parasite-induced breproductive deathQ does not occur in this species as in other gonochoric and sequencial hermaphroditic caridean shrimp. Nutritional drain and disruption of endocrine mechanisms possibly caused by the bopyrid parasite are discussed. D 2005 Elsevier B.V. All rights reserved. Keywords: Bopyrid ispods; Eophryxus lysmatae; Hermaphroditism; Lysmata seticaudata; Parasitic castration
1. Introduction
T Corresponding author. Tel.: +351 21 4869211; fax: +351 21 4869720. E-mail address: [email protected] (R. Calado). 0022-0981/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jembe.2004.12.038
Bopyrid isopods are known to be holoparasites, with their definitive hosts being decapod crustaceans (Markham, 1986). Bopyrids are known to cause parasitic castration, which involves two associated, but according O’Brien and Van Wyk (1985) perhaps
14
R. Calado et al. / J. Exp. Mar. Biol. Ecol. 321 (2005) 13–18
distinct, phenomena: gonads of female host do not mature and parasitized males are feminised. Despite the variable degree of inhibition that these two phenomena cause on host reproductive potential (Van Wyk, 1982), it always suffers a substantial reduction and generally causes the breproductive deathQ of the host. Apart the preliminary studies by Fiedler (2000), the works addressing parasitic castration in decapods have only dealt with gonochoric species. Eophryxus lysmatae (Caroli, 1930) is a member of the subfamily Hemiarthrinae, a group of bopyrids characterized by having caridean shrimp as their main host and by being abdominal parasites (Markham, 1986). This species is known to occur in the Mediterranean and only parasitizes the Monaco shrimp Lysmata seticaudata (Risso, 1816) (Caroli, 1930). Bauer and Holt (1998) and Fiedler (1998) demonstrated the existence of a unique sexual system among decapod crustaceans in the genus Lysmata, protandric simultaneous hermaphroditism. The existence of this puzzling sexual system has been recently confirmed in L. seticaudata by Udekem d’Acoz (2003), validating the idea that this may be a common feature to all members of the genus (Bauer, 2000). The objective of the present work is to study the degree of inhibition caused by parasitic castration by the bopyrid isopod E. lysmatae in the reproductive performance of its host, the protandric simultaneous hermaphrodite caridean shrimp L. seticaudata.
2. Materials and methods Monaco shrimp were collected during spring tides at Cape Raso, 30 km west of Lisbon, Portugal, in the month of May of 2001 using baited traps described by Calado and Narciso (2004). The single three specimens of L. seticaudata (out of 680 captured) carrying bopyrid isopods were isolated. Nine unparasitized shrimp with total length (TL, distance between the rostrum anterior end and the telson posterior edge) similar to that of parasitized shrimp (47F2 mm) were also isolated. The selected 12 shrimp were kept in six 30 l aquariums at 23 8C, 35x salinity and with a photoperiod of 12 h light:12 h dark. Shrimp were daily fed ad libitum minced shrimp, mussel and fish roe.
The same 12 shrimp were used sequentially in the four trials. In trial 1, each parasitized shrimp (PS) was randomly paired with an unparasitized shrimp (US), the remaining six unparasitized shrimp were randomly divided into three pairs, resulting in three PS/US and three US/US pairs. In trial 2, each PS was paired with a shrimp used in the three US/US pairs in trial 1, with the remaining US paired in three US/US pairs. In trial 3, the three US not previously paired with PS were each paired with a PS, with the remaining US paired in three US/US pairs. In trial 4, each PS was sequentially paired with each other (see Table 1). The reproductive performance of each shrimp was evaluated by counting the number of hatched larvae from the first three embryo batches produced after pairing. The molts of PS and US were collected during all trials for morphological comparison and the average intermolt period duration of each shrimp recorded. A t-test was used to compare the intermolt period duration and the number of larvae produced by shrimp paired with PS and US. The results were considered statistically significant at the 0.05 probability level (Zar, 1996). After performing the reproductive trials, parasitized shrimp were stored in ethanol for morpho-
Table 1 Random pairs of Lysmata seticaudata shrimp carrying the bopyrid isopod Eophryxus lysmatae (PS) and unparasitized shrimp (US) formed during trials to evaluate their reproductive performance Randomly formed shrimp pairs Trial 1 PS1 PS2 0 0 US1 US4 333F30 348F12 Trial 2 PS1 PS2 0 0 US3 US5 330F12 384F21 Trial 3 PS1 PS2 0 0 US2 US9 347F42 364F23 Trial 4 PS1 0 PS2 0
PS3 US5 0 386F42 US8 US6 304F5 321F14 PS3 US1 0 304(F11) US6 US7 363F19 341F24 PS3 US1 0 302F14 US7 US4 348F10 334F23 PS1 0 PS3 0
US3 US2 352F7 321F22 US7 US9 331F24 370F14 US2 US8 352F9 372F21 US9 US4 326F27 354F17 US3 US5 381F41 392F24 US6 US8 339F12 325F36 PS2 0 PS3 0
Values are averages (FS.D.) of three batches of larvae produced by each shrimp.
R. Calado et al. / J. Exp. Mar. Biol. Ecol. 321 (2005) 13–18
15
logical observation and illustration. Drawings were made with the aid of a camera lucida on a binocular Wild M8.
3. Results The infestation rate of bopyrid isopods parasitizing L. seticaudata in the present study was only 0.4% (3/680). Although in all reproductive trials PS were not able to produce any embryos, each of these specimens successfully fertilised the eggs of their unparasitized mates. Shrimp paired with PS displayed the same mating behaviour pattern described by Nouvel (1940) for L. seticaudata. All US paired with PS were able to fertilise eggs when paired with other US. The average number of larvae (FS.D.) produced by US shrimp paired with US and PS (344F27 and 346F23, respectively) was not significantly different ( p=0.73) (Table 1). The average (FS.D.) intermolt duration for US and PS (10F1.2 and 11F0.8 days, respectively) was not significantly different ( p=0.82). Bopyrid parasites had broods and molted synchronously with their host
Fig. 1. (A) Lateral view of simultaneous hermaphrodite phase Lysmata seticaudata infested with the bopyrid isopod Eophryxus lysmatae. Solid black arrow indicates the positioning of adult female Eophryxus lysmatae on host. Scale bar: 10 mm. (B) Detail of attachment area of adult Eophryxus lysmatae female infesting the abdominal region of Lysmata seticaudata. 1: Left first pleopod. 2: Left second pleopod. 3: Left third pleopod. Scale bar: 1 mm. (C) Dorsal view of adult Eophryxus lysmatae female. Shaded region represents the attachment area of male on female’s dorsal surface. Solid black arrow indicates the anterior end of adult male Eophryxus lysmatae. Scale bar: 1 mm. (D) Lateral view of adult Eophryxus lysmatae male. Scale bar: 1 mm.
Fig. 2.
(bopyrid molts being recovered from the aquariums) and none of the PS lost its parasite during ecdysis. Parasitized shrimp never showed the typical bbright green spotQ displayed by US, evidence of the presence of large vitellogenic oocytes in the ovary portion of the gonad prior to extrusion. Morphological data (not histological data) revealed that the testes, vas deferens and the terminal ampoule of PS were similar
Fig. 3.
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Fig. 4.
to those of US, but the anterior portion of the gonad where the ovarian structures are located appeared smaller than in US, and did not display vitellogenic oocytes. The observation of PS and US molts revealed the same secondary sexual characters typically present in the simultaneous hermaphrodite phase of L. seticaudata, according to Dohrn (1950) and CharniauxCotton (1959). The female isopod was always found firmly attached to its host (Fig. 1) in the base of the second left pleopod, with its dorsal surface facing the ventral face of the host and its anterior portion directed towards the posterior end of the shrimp (Fig. 2). Female parasites displayed their protruding marsupium distorted to the left in dorsal view (Fig. 3) and were always accompanied by the symmetrical dwarf male (Fig. 4), which clings to the female’s dorsal face of the left first foliaceous pleopod (see Fig. 3). The average (FS.D.) sizes of female and male parasites (from anterior to posterior end) were 10.21F0.98 mm and 0.84F0.32 mm, respectively. Due to small sample size of PS (n=3), the possible correlations between the sizes of host and parasite and female and male parasites were not investigated.
4. Discussion Shrimp collected, results presented in the present work should be regarded with caution. Nevertheless, the present trials seem to indicate that the parasitic castration induced by the bopyrid isopod E. lysmatae only affects the female sexual system of the simultaneous hermaphrodite L. seticaudata. This can explain why only US with similar TL of PS were collected incubating embryo. Parasitized shrimp retain their ability to reproduce as fully functional males, and
therefore parasite-induced breproductive deathQ does not occur in this species as in other gonochoric and sequential hermaphroditic caridean shrimp (O’Brien and Van Wyk, 1985). The preliminary study performed by Fiedler (2000) on Lysmata anchisteus (Chace, 1972), L. ternatensis (De Man, 1902) and L. trisetacea (Heller, 1861) parasitized by undescribed bopyrids of the subfamily Hemiarthrinae (abdominal parasites) also revealed that only the female function of parasitized simultaneous hermaphrodites was inhibited. The mechanisms associated with parasitic castration affecting the host are still not totally understood. Reinhard (1956) and Anderson (1977) highlighted the nutritional drain affecting PS energy flow, which could impair parasitized females of producing energy costly vitellogenic oocytes. Reinhard (1956), Baudoin (1975), Walker (1977) and Beck (1980) also discussed the possibility of endocrine mechanism disruption, by the reduction of circulating reproductive hormones (due to blood losses caused by parasites), stimulation of the gonad-inhibiting hormone (GIH) or even the secretion of GIH by bopyrids. The observations by Coutie`re (1899) on the alpheid shrimp Synalpheus biunguiculatus (Stimpson, 1860) and by Caroli (1930) on Synalpheus gambarelloides (Nardo, 1847) (=S. laevimanus) found that ovigerous shrimp simultaneously carried adult abdominal bopyrid isopods (although embryos were present in fewer numbers than normal), only highlights the complexity and lack of knowledge on this topic. Unfortunately, the works by Charniaux-Cotton (1960), Charniaux-Cotton and Touir (1973), Touir (1977a,b), Bauer and Holt (1998) and Fiedler (1998, 2000) have only partially discussed and explained the complex endocrinological processes regulating the role of the median protocerebrum, androgenic glands, ovarian and testicular portions of the gonad and the X-organ and sinus gland complex in the genus Lysmata. As stated by Noe¨l (1976), until host and parasite endocrinology is known, the understanding of parasitic castration will always be incomplete. In the present study, no parasitized male phase L. seticaudata were collected, but there is no apparent reason why bopyrid isopods would only parasitize simultaneous hermaphroditic phase shrimp. Assuming that male phase shrimp are also selected as
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hosts by E. lysmatae and, for some reason, feminisation of the host is induced (cincinnuli present at the endopod of the first pair of pleopods and the appendix maculina are lost), but the testes remain functional, it can be expected that these shrimp could still act as functional males. Although the appendages mentioned above are known to play a major role in sperm transfer in decapods (Bauer, 1976, 1986; Berg and Sandifer, 1984), the studies by Zhang and Lin (2004) on simultaneous hermaphroditic Lysmata shrimp revealed that the presence of such appendages is not essential for individuals mating as males to successfully fertilize egg clutches. The present work is the first record of E. lysmatae outside the Mediterranean Sea, an area with considerably warmer water temperature than the eastern Atlantic shores of Portugal, the low infection rate recorded in the present work should be treated with caution.
5. Conclusion The complexity of the puzzling sexual system of Lysmata is once again highlighted by the parasitic castration induced by an abdominal bopyrid isopod only impairing simultaneous hermaphroditic shrimp to mate as females. Future studies should use a larger number of parasitized shrimp, address the effect of branchial bopyrid parasites infecting other Lysmata species (Fiedler, 2000) and the possible evolutionary role that parasitic castration might have had in the mating system of Lysmata and other decapod species.
Acknowledgements The authors would like to thank Fundac¸a˜o para a Cieˆncia e a Tecnologia (scholarship SFRH/BD/983/ 2000 and research project POCTI/BSE/43340/2001) and FEDER (SIGAP project 22-05-01-FDR-00013) from the Portuguese government for financial support and Milton Alfredo and Gil Penha-Lopes for their assistance in field and laboratory work. We thank G. Curt Fiedler for sharing his findings on parasitic castration affecting Lysmata species. We would also like to express our sincere gratitude to Raymond T.
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Bauer, Junda Lin and an anonymous referee for providing valuable comments on the present work. [AU]
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