Population Structure and Habitat Selection by Anisakis ... - BioOne

Comp. Parasitol. 70(1), 2003, pp. 66–71

Population Structure and Habitat Selection by Anisakis simplex in 4 Odontocete Species from Northern Argentina F. JAVIER AZNAR,1 M. VICTORIA HERRERAS, JUAN A. BALBUENA,

AND

JUAN A. RAGA

Departamento de Biologıá Animal and Instituto Cavanilles de Biodiversidad y Biologıá Evolutiva, Universitat de Vale`ncia, P.O. Box 22085, Valencia 46071, Spain ABSTRACT: We described the population structure and habitat selection of Anisakis simplex in 46 franciscanas, Pontoporia blainvillei, 8 Burmeister’s porpoises, Phocoena spinnipinis, 2 Dusky dolphins, Lagenorhynchus obscurus, and 2 common dolphins, Delphinus delphis, caught incidentally in the coastal fisheries of northern Argentina. Prevalence ranged from 50% to 100%, but mean intensities were low (1.0–3.6), suggesting that A. simplex has low recruitment rates to coastal dolphins in this area. Adult nematodes were found exclusively in the main stomach of 64.5% of franciscanas (the first stomach of this species) and the forestomach of 50% of Burmeister’s porpoises and Dusky dolphins. Other developmental stages occurred in the first stomach but were also found in posterior digestive chambers. The median worm of the distribution among chambers was more anterior for preadults than for L4s and more anterior for L4s than for L3s. Our data are compatible with the hypothesis that individuals of A. simplex tend to select the site where digestion begins. This preference is more pronounced in adult worms. The greater restriction of adults to the first chamber could be viewed as a strategy to enhance mating opportunities. Alternatively, it might indicate that adults have stronger requirements for the resources provided by the first chamber. KEY WORDS: Nematoda, Anisakis simplex, Pontoporia blainvillei, Phocoena spinnipinis, Lagenorhynchus obscurus, Delphinus delphis, Cetacea, habitat selection, Argentina.

Anisakis simplex sensu lato has been frequently reported from many cetacean species from cold and temperate waters worldwide (Smith, 1999 and references therein). Because of sanitary and economic concerns, most of the research on A. simplex has been focused on life cycle, pathological effects, and population ecology in the intermediate and paratenic hosts (e.g., Smith and Wooten, 1978; Matiucci, 1997; Smith, 1999). Knowledge of the ecology of A. simplex in its definitive cetacean hosts is surprisingly scarce, particularly when compared with that of anisakids from pinnipeds (Desportes and McClelland, 2001 and references therein). A few studies report population structure but they are based on small host sample sizes (Oshima, 1972; Young, 1972; Smith, 1989) or present parasite data only at a component population level (Kuramochi et al., 1996). In addition, data on habitat selection are usually limited to an account of the number of worms per site surveyed (Oshima, 1972; Smith and Wootten, 1978, and references therein). There is just 1 study providing information on population structure in different habitats (Brattey and Stenson, 1995). In general, the proximate and ultimate causes of

habitat selection by A. simplex are poorly understood. In this study we describe the population structure and habitat selection of A. simplex in 4 dolphin species from northern Argentina: the franciscana, Pontoporia blainvillei; Burmeister’s porpoise, Phocoena spinnipinis; the Dusky dolphin, Lagenorhynchus obscurus; and the common dolphin, Delphinus delphis. MATERIAL AND METHODS Forty-six franciscanas, 8 Burmeister’s porpoises, 2 Dusky dolphins, and 2 common dolphins, accidentally caught in coastal gillnets off Necochea (388279S; 588509W) and Claromeco´ (388529S; 608059W) in Buenos Aires Province, Argentina, were collected from late October to early December 1988–1990 (see Corcuera et al., 1994 for details). Sampling was planned and carried out by personnel of the Estacioń Hidrobiolo´gica de Puerto Quequeń (Museo Argentino de Ciencias Naturales, Consejo Nacional de Investigaciones Cientı´ficas y Tećnicas of the Argentinean Government) as part of a research program using incidental catches of cetaceans in coastal fisheries. Dolphins were removed daily from the nets, and their digestive tracts were isolated and either examined immediately or frozen for later analysis. Contents of the forestomach, main stomach, connecting channel and pyloric stomach, duodenal ampulla (a funnel-shaped chamber at the beginning of the duodenum), and intestines proper were flushed separately through a 0.2-mm sieve. Franciscanas lack a forestomach (see Yamasaki et al., 1974; Aznar et al., 2001, for anatomical details). Worms were washed in

1 Corresponding author (e-mail: francisco.aznar@ uv.es).

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AZNAR ET AL.—HABITAT SELECTION BY ANISAKIS SIMPLEX

Table 1. Prevalence and intensity of Anisakis simplex in 4 dolphin species from northern Argentina: Pontoporia blainvillei, Phocoena spinnipinis, Lagenorhynchus obscurus, and Delphinus delphis.

N Po. blainvillei Ph. spinnipinis L. obscurus D. delphis

46 8 2 2

Intensity Prevalence (%) Mean 6 SD Median 67.4 50.0 100.0 50.0

3.6 6 4.1 2.8 6 1.4 3.0 6 1.0 1.0

2.0 2.5 3.0 1.0

saline solution and preserved in 70% ethanol until examination. Worms collected from the intestine posterior to the duodenal ampulla appeared primarily in the large intestine and were partially degraded. We believe that these individuals were passed from anterior locations, and they were thus excluded from the analysis. Specimens were identified as A. simplex sensu Davey (1971). Because of field conditions, electrophoretic analyses to clarify the taxonomic status of specimens further could not be conducted. Voucher specimens are deposited in the Natural History Museum, London, U.K. (nos. 1993.5201–5205); the remaining specimens are deposited in the parasitological collection of the Marine Zoology Unit of the Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, Spain. Specimens were classified into the following developmental stages: third-stage larvae (L3), fourth-stage larvae (L4), preadult female (PF), preadult male (PM), adult female (AF), and adult male (AM). Preadults and adults were separated from the larvae by the presence of a developing or fully developed reproductive system; the AFs were distinguished from the PFs by the presence of eggs in the uterus in the AF, and the AMs from the PMs based on the presence of sperm and the mature development of papillae and spicules in the AM. To describe the population structure, we calculated the number of infected hosts and the mean, median, and range of intensities for each developmental stage. To describe the linear distribution of worms among digestive chambers, we used 2 procedures. First, we calculated the percentage of the component population and the mean percentage of the infrapopulations occurring in each chamber. Second, we calculated the median worm of the distribution for each developmental stage at the infrapopulation level, assuming a uni-

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Table 3. Infection site distribution of Anisakis simplex in 4 dolphin species from northern Argentina: Pontoporia blainvillei, Phocoena spinnipinis, Lagenorhynchus obscurus, and Delphinus delphis. Percentage of population collected from each digestive chamber at the component population level.

Po. blainvillei Ph. spinnipinis L. obscurus D. delphis

Forestomach

Main stomach

Pyloric stomach

Duodenal ampulla

63.6 66.7 0.0

91.9 9.1 33.3 0.0

5.4 18.2 0.0 100.0

2.7 9.1 0.0 0.0

form distribution within each digestive chamber (Bush and Holmes, 1986; Aznar et al., 1997, 2001).

RESULTS Infection data for A. simplex in the 4 dolphin species are presented in Table 1. Percent distribution of worms among digestive chambers in 4 dolphin species is presented at the infrapopulation and component population levels in Tables 2 and 3, respectively. Prevalences ranged from 50% to 100%, but intensities were very low in all species. Most individuals of A. simplex were found in the main stomach of franciscanas and the forestomach of Burmeister’s porpoises and Dusky dolphins. The single worm collected from the common dolphin occurred in the pyloric stomach. Population structure data are presented in Table 4. Three dolphin species harbored both larvae and adult worms. In particular, 64.5% of the infected franciscanas harbored adult nematodes, and 35.5% harbored AFs. In both Burmeister’s porpoises and Dusky dolphins, the proportions of adults and AFs were both 50%. The distribution of developmental stages among digestive chambers is depicted in Figure 1. The median worm of adult worms in franciscanas, Burmeister’s porpoises, and Dusky dolphins had no variance because adult worms

Table 2. Infection site distribution of Anisakis simplex in 4 dolphin species from northern Argentina: Pontoporia blainvillei, Phocoena spinnipinis, Lagenorhynchus obscurus, and Delphinus delphis. Percentage of population (mean 6 SD) collected from each digestive chamber at the infrapopulation level.

Po. blainvillei Ph. spinnipinis L. obscurus D. delphis

Forestomach

Main stomach

Pyloric stomach

Duodenal ampulla

65.0 6 47.3 75.0 6 35.4 0.0

84.6 6 34.0 5.0 6 10.0 25.0 6 35.4 0.0

9.5 6 26.3 25.0 6 50.0 0.0 100.0

5.9 6 20.4 5.0 6 10.0 0.0 0.0

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COMPARATIVE PARASITOLOGY, 70(1), JANUARY 2003

Table 4. Infection parameters of developmental stages of Anisakis simplex in 4 dolphin species from northern Argentina: Pontoporia blainvillei, Phocoena spinnipinis, Lagenorhynchus obscurus, and Delphinus delphis.

Host

Stage*

ni†

Total number

Po. blainvillei

L3 L4 PM AM PF AF L3 L4 AM AF L4 AM AF L3

10 15 5 11 5 11 3 3 1 2 2 1 1 1

30 38 6 15 8 14 6 3 1 2 4 1 1 1

Ph. spinnipinis

L. obscurus

D. delphis

Intensity Mean 6 SD 3.0 2.5 1.2 1.4 1.6 1.3 1.7

6 2.6 6 2.8 6 0.5 6 0.8 6 1.3 6 0.7 6 0.6 1.0 — 1.0 2.0 — — —

Median

Range

2.5 1.0 2.0 1.0 1.0 1.0 2.0 1.0 — 1.0 2.0 — — —

1–9 1–2 1–12 1–3 1–4 1–3 1–2 1 — 1 2 — — —

* L3, third-stage larvae; L4, fourth-stage larvae; PM, preadult male; AM, adult male; PF, preadult female; AF, adult female. † Number of infected hosts.

were restricted to the first stomach chamber. Preadults and larvae were also found in the posterior chambers. The median worm of L3, L4, and preadult distributions occupied a more anteriad position with each successive ontogenetic stage (Fig. 1).

Figure 1. Position of the average median worm of adults (circle), preadults (triangle), fourth-stage larvae (diamond), and third-stage larvae (square) of Anisakis simplex in 4 dolphin species from northern Argentina: Pontoporia blainvillei (Pb), Phocoena spinnipinis (Ps), Lagenorhynchus obscurus (Lo), and Delphinus delphis (Dd). Bars represent 6SE. Numbers in parentheses indicate the number of hosts used to calculate the means. Values of the axis represent the forestomach (0), the main stomach (1), and the pyloric stomach (2).

DISCUSSION The light infections of A. simplex reported in this study suggest that the recruitment rate of the parasite to dolphins seems to be low in the inshore waters of northern Argentina. Low infections of A. simplex also have been reported in other coastal cetaceans from the southwestern Atlantic, an observation that has been related to the reduced availability of intermediate hosts in the coastal ecosystem (Beroń-Vera et al., 2001). This notion is supported by the fact that Dusky dolphin individuals captured in the offshore waters of central Patagonia harbor populations of A. simplex far greater than those observed in more coastal cetaceans from the same region (see Dans et al., 1999). It is worth noting that the intermediate and paratenic hosts of Anisakis pegreffii (the only species of the A. simplex species complex thus far reported in the southwestern Atlantic) are mainly pelagic (Mattiucci et al., 1997). There is direct evidence that individuals of A. simplex sensu lato preferentially inhabit the first stomach of odontocetes. Larvae and adults have been reported mainly, or exclusively, in this site (Kagei et al., 1967; Kikuchi et al., 1967; Oshima, 1972; Smith and Wootten, 1978; Smith, 1989; Babin et al., 1994; Brattey and Stenson, 1995). Some authors have hypothesized that the larvae of A. simplex are programmed to respond


to the conditions prevailing in the first stomach. Smith (1984) speculated that larvae might select easily digested organs within paratenic hosts to facilitate rapid release when prey digestion begins in the definitive host. Other authors (Young and Lowe, 1969; Iglesias et al., 2001) suggested that once larvae are released, the stimuli associated with the first digestion (especially high temperature and low pH) could stimulate development and behavioral responses such as attachment to the stomach wall. Evidence from our study is consistent with this hypothesis of habitat preference but with a further refinement regarding distribution of developmental stages. Individuals of A. simplex occurred more frequently and densely in the first stomach (the main stomach) of franciscanas. However, only adults were restricted to this site. The distribution of other developmental stages was ordered posteriorly according to the developmental sequence: preadults followed by L4s, with L3s the most posteriad. Although our data from sympatric dolphins were limited, they showed a similar pattern: adult worms were restricted to the forestomach, and the distribution of L4s and L3s was ordered posteriorly. Data from the only published study of population structure and distribution of A. simplex across host digestive chambers are consistent with these findings. Brattey and Stenson (1995) reported 100% of adults and L4s of A. simplex in the forestomach of harbor porpoises, Phocoena phocoena, whereas 39.3% of L3s were found in other stomach chambers. Overall, these patterns could be interpreted as a sign of greater requirement for the resources provided by the first chamber as worms develop. In this context, Gibson et al. (1998) speculated that the larvae, but especially the adults of A. simplex, feed upon the food bolus, which is produced and limited to the first stomach (Gaskin, 1978). The forestomach (or the main stomach in franciscanas) reduces whole prey to semifluid chyme through mechanical and chemical digestion; the chyme is further digested in the posterior chambers (Gaskin, 1978; Aznar et al., 2001). The greater habitat restriction of adult A. simplex also could be viewed as a strategy to enhance mating opportunities (Rohde, 1994). This hypothesis is attractive because the usual aggregation of populations of A. simplex among hosts (see references in Smith, 1999) results in most infrapopulations being composed of few individ-

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uals. Indeed, although infections were very light in the dolphins analyzed in this study, the significant number of AFs found suggests that mating was frequent among individuals of A. simplex. Two factors require additional consideration and further study. First, we have assumed that patterns of habitat selection are not significantly affected by postmortem movements of worms. Digestive chambers are large compared with parasite size, and it is unlikely that postmortem movements could significantly alter the parasite distribution among chambers (Aznar et al., 2001). Furthermore, in franciscanas the main stomach was the most important site of infection in every infected host, regardless of whether digestive tracts were analyzed fresh or after frozen storage. However, in the franciscanas examined, the pyloric stomach and the duodenal ampulla, but not the main stomach, were densely occupied by the acanthocephalan Corynosoma cetaceum (Aznar et al., 2001). The presence of C. cetaceum may influence the distribution of A. simplex. Second, the aggregation of adult A. simplex in the first stomach is not universal among cetaceans. In minke whales, Balaneoptera acutorostrata, taken from Japanese waters, A. simplex mostly occurred in the main stomach, and worms occupied the forestomach only in heavily infected hosts (Uchida et al., 1998). Uchida et al. (1998) speculated that conditions in the lumen of the forestomach and the main stomach might differ between minke whales and dolphins. This illustrates the incomplete nature of our ecological understanding of A. simplex in their definitive hosts. No quantitative study documents the relative suitability of stomach chambers, the density dependence of parasite distribution among stomach chambers, or the differences in distribution among parasite sibling species for any cetacean species infected by A. simplex. These aspects merit the attention of future studies. ACKNOWLEDGMENTS We especially thank Javier Adroher, Universidad de Granada, Spain, for sharing with us his ideas on the biology of A. simplex. Thanks are also due to David Gibson, Natural History Museum, U.K., for technical clarifications and to Toshiaki Kuramochi, National Science Museum, Japan, for providing us with unpublished infor-

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mation about the stomach distribution of A. simplex. We greatly appreciate the technical assistance provided by Mercedes Fernańdez and Francisco Montero. The first author benefits from a postdoctoral contract from the Ministry of Science and Technology of Spain. This work was supported by projects DGES PB96-0801 (Ministry of Education and Culture) and 1FD971147 (Inter-ministry Commission of Science and Technology) of Spain, and HPMD-2000-00037 of the European Union. LITERATURE CITED Aznar, F. J., J. A. Balbuena, A. O. Bush, and J. A. Raga. 1997. Ontogenetic habitat selection by Hadwenius pontoporiae (Digenea: Campulidae) in the intestines of franciscanas (Cetacea). Journal of Parasitology 83:13–18. Aznar, F. J., A. O. Bush, J. A. Balbuena, and J. A. Raga. 2001. Corynosoma cetaceum in the stomach of franciscanas, Pontoporia blainvillei (Cetacea): an exceptional case of habitat selection by an acanthocephalan. Journal of Parasitology 87: 536–541. Babin, P., J. A. Raga, and R. Duguy. 1994. Ulce`res parasitaires gastriques chez les ce´tace´s odontoce`tes ećhoue´s sur les coˆtes de France. Le Point Veterinaire 26:77–80. Beroń-Vera, B., S. N. Pedraza, J. A. Raga, A. Gil de Pertierra, E. A. Crespo, M. K. Alonso, and R. N. P. Goodall. 2001. Gastrointestinal helminths of Commerson’s dolphins Cephalorhynchus commersonii from central Patagonia and Tierra del Fuego. Diseases of Aquatic Organisms 47:201–208. Brattey, J., and G. B. Stenson. 1995. Helminth parasites of the alimentary tract of the harbor porpoise, Phocoena phocoena (L.), from Newfoundland and Labrador. Journal of the Helminthological Society of Washington 62:209–216. Bush, A. O., and J. C. Holmes. 1986. Intestinal helminths of lesser scaup ducks: an interactive community. Canadian Journal of Zoology 64:142–152. Corcuera, J., F. Monzoń, E. A. Crespo, A. Aguilar, and J. A. Raga. 1994. Interactions between marine mammals and the coastal fisheries of Necochea and Claromeco´ (Buenos Aires Province, Argentina). Reports of the International Whaling Commission, Special Issue 15:283–290. Dans, S. L., L. M. Reyes, S. N. Pedraza, J. A. Raga, and E. A. Crespo. 1999. Gastrointestinal helminths of the Dusky dolphin, Lagenorhynchus obscurus (Gray, 1828), off Patagonia, in the southwestern Atlantic. Marine Mammal Science 15: 649–660. Davey, J. T. 1971. A revision of the genus Anisakis Dujardin, 1845 (Nematoda: Ascaridata). Journal of Helminthology 45:51–72. Desportes, G., and G. McClelland. 2001. Sealworms in the North Atlantic: Ecology and Population Dynamics. The North Atlantic Marine Mammal

Commission Scientific Publications, Vol. 3, Tromsø, Norway. 171 pp. Gaskin, D. E. 1978. Form and function in the digestive tract and associated organs in Cetacea, with consideration of metabolic rates and specific energy budgets. Oceanography and Marine Biology Annual Reviews 16:313–345. Gibson, D. I., E. A. Harris, R. A. Bray, P. D. Jepson, T. Kuiken, J. R. Baker, and V. R. Simpson. 1998. A survey of the helminth parasites of cetaceans stranded on the coast of England and Wales during the period 1990–1994. Journal of Zoology, London 244:563–574. Iglesias, L., A. Valero, R. Benı´tez, and F. J. Adroher. 2001. In vitro cultivation of Anisakis simplex: pepsin increases survival and moulting from fourth larval to adult stage. Parasitology 123:285– 291. Kagei, N., T. Oshima, A. Kobayashi, M. Kumada, T. Koyama, Y. Komiya, and A. Takemura. 1967. Survey of Anisakis spp. (Anisakinae, Nematoda) in marine mammals in the coast of Japan. Japanese Journal of Parasitology 16:427–435. (In Japanese with English abstract.) Kikuchi, S., S. Hayashi, and M. Nakajima. 1967. Studies on anisakiasis in dolphins. Japanese Journal of Parasitology 16:156–166. (In Japanese with English abstract.) Kuramochi, T., M. Machida, J. Araki, A. Uchida, T. Kishiro, and K. Nagasawa. 1996. Minke whales (Balaenoptera acutorostrata) are one of the major final hosts of Anisakis simplex (Nematoda: Anisakidae) in the northwestern North Pacific Ocean. Reports of the International Whaling Commission 46:415–419. Mattiucci, S., G. Nascetti, R. Cianchi, L. Paggi, P. Arduino, L. Margolis, J. Brattey, S. Webb, S. D’Amelio, P. Orecchia, and L. Bullini. 1997. Genetic and ecological data on the Anisakis simplex complex, with evidence for a new species (Nematoda, Ascaridoidea, Anisakidae). Journal of Parasitology 83:401–416. Oshima, T. 1972. Anisakis and anisakiasis in Japan and adjacent area. Pages 305–393 in K. Morishita, Y. Komiya, and H. Matsubayashi, eds. Progress of Medical Parasitology in Japan. Vol. 4. Meguro Parasitological Museum, Tokyo. Rohde, K. 1994. Niche restriction in parasites: proximate and ultimate causes. Parasitology 109(supplement):S69–S84. Smith, J. W. 1984. The abundance of Anisakis simplex L3 in the body-cavity and flesh of marine teleosts. International Journal for Parasitology 14:491–495. Smith, J. W. 1989. Ulcers associated with larval Anisakis simplex B (Nematoda: Ascaridoidea) in the forestomach of harbour porpoises Phocoena phocoena (L.). Canadian Journal of Zoology 67: 2270–2276. Smith, J. W. 1999. Ascaridoid nematodes and pathology of the alimentary tract and its associated organs in vertebrates, including man: a literature review. Helminthological Abstracts 68:49–96. Smith, J. W., and R. Wootten. 1978. Anisakis and Anisakiasis. Advances in Parasitology 16:93–193.


Uchida, A., Y. Kawakami, S. Yuzu, S. Kishikawa, T. Kuramochi, J. Araki, M. Machida, and K. Nagasawa. 1998. Prevalence of parasites and histopathology of parasitation in minke whales (Balaenoptera acutorostrata) from the western North Pacific Ocean and the southern Sea of Okhotsk. Reports of the International Whaling Commission 48:475–479. Yamasaki, F., K. Takahasi, and T. Kamiya. 1974. Digestive tract of La Plata dolphin, Pontoporia

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blainvillei. I. Oesophagus and stomach. Okajimas Folia Anatomica Japonica 51:29–52. Young, P. C. 1972. The relationship between the presence of larval anisakinae nematodes in cod and marine mammals in British home waters. Journal of Applied Ecology 9:459–483. Young, P. C., and D. Lowe. 1969. Larval nematodes from fish of the subfamily Anisakinae and gastrointestinal lesion in mammals. Journal of Comparative Pathology 79:301–313.