Structure of the community of the Strongylidae nematodes in the dorsal colon of Equus caballus from Rio de Janeiro state Brazil

Veterinary Parasitology 112 (2003) 109 116 Structure of the community of the Strongylidae nematodes in the dorsal colon of Equus caballus from Rio de Janeiro state Brazil D.H.S. Anjos a,, M.L.A. Rodrigues b a Departamento de Parasitologia Animal, Curso de Pós graduação em Ciências Veterinárias Parasitologia Veterinária, Universidade Federal Rural do Rio de Janeiro, Br 465 Km 7, Seropédica RJ 23890-000, Brazil b Departamento de Parasitologia Animal UFRRJ, Seropédica RJ 23890-000, Brazil Received 25 June 2002; received in revised form 25 September 2002; accepted 4 December 2002 Abstract The structure of the community of Strongylidae nematodes in the dorsal colon of naturally infected horses from the metropolitan region of Rio de Janeiro State was evaluated in 33 samples. Twenty-three species were found: Cylicostephanus longibursatus, Cylicostephanus goldi, Cylicocyclus nassatus and Cyathostomum tetracanthum were the central ones; Cylicostephanus minutus, Cylicostephanus calicatus, Cylicocyclus leptostomus, Cylicodontophorus bicoronatus and Parapoteriostomum euproctus were secondary, and there were 14 satellite species. The community was considered stable, with positive associations and correlations, no significant negative associations and correlations, suggesting little competition among species. 2002 Elsevier Science B.V. All rights reserved. Keywords: Strongylidae; Brazil; Horses; Structure of the community 1. Introduction The biodiversity of parasitic intestinal nematodes in horses is ample, varying according to compartments of the large intestine: cecum, dorsal colon and ventral colon (Ogbourne, 1976; Mfitilodze and Hutchinson, 1985; Krecek et al., 1989; Gawor, 1995). There are numerous studies on prevalence, abundance and mean intensity of Strongylidae nematodes, however the different compartments were not analysed separately (Lanfredi, 1983; Silva et al., 1999). This diversity has encouraged studies about structure of the parasitic community of Strongylidae nematodes in horses. In Australia, Bucknell et al. (1996) found Corresponding author. Tel.: +55-2682-1617; fax: +55-2682-1617. E-mail addresses: danjos@ufrrj.br, lurdesar@ufrrj.br, mlazrod@uol.com.br (D.H.S. Anjos). 0304-4017/02/$ see front matter 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/s0304-4017(02)00424-7

110 D.H.S. Anjos, M.L.A. Rodrigues / Veterinary Parasitology 112 (2003) 109 116 31 species in a community that was considered stable, dominated by positive interactions, suggesting the absence of competition within the community. However, others did not observe species that were clearly divisible into core (species present in more than two-thirds of the hosts studied, with evidence of interactions among the few unfilled niches) and satellites (species present in one-third of the hosts studied, showing little evidence of mutual interaction and many empty niches) (Holmes and Price, 1986). In Brazil, the infracommunities composition of the different compartments of the large intestine of equids were studied separately for comparison purposes: cecum (Souto-Maior et al., 1999), dorsal colon (Anjos, 1998; Rodrigues et al., 2000; Rodrigues and Anjos, 2001, WAAVP) and ventral colon (Anjos, 2002). The aim of this study was to analyse the structure of the community of Strongylidae nematodes in the dorsal colon of naturally infected horses in the metropolitan region of the state of Rio de Janeiro, Brazil. 2. Materials and methods Thirty-three adult horses of various breeds and ages from the state of Rio de Janeiro, Brazil, were sacrificed and necropsied at the W.O. Neitz Parasitology Station, Department of Animal Parasitology of the Veterinary Institute of the Federal Rural do Rio de Janeiro University. The gastrointestinal tract of each animal was sectioned and the compartments of the large intestine were separated by double ligatures (cecum, dorsal colon and ventral colon). Each compartment of the dorsal colon was opened lengthwise and the contents placed in a graduated receptacle. The contents were homogenised and a sample of approximately 10% of the original volume was retrieved. These samples were fixed in hot alcohol formalin acetic acid (Amato et al., 1991). The nematodes collected from the samples were preserved in alcohol 70 GL, clarified in 90% phenol alcohol (Lichtenfels, 1984) and mounted temporarily on slides in Amann s lactophenol at the Helminthology Laboratory. The identification of the adult Strongylidae was done according to Lichtenfels (1975) and George (1982). The nomenclature of species of the subfamily Cyathostominae used is according to Hartwich (1986), Lichtenfels (1975) and Lichtenfels et al. (1998). The analysis was restricted to the members of Strongylidae, as these were extremely abundant. The terms used in the ecological analysis were those recomended by Bush et al. (1997). The prevalence of the species used in classifying the members of the dorsal colon infracommunities, according to Bush and Holmes (1986), was obtained from Rodrigues et al. (2000). To evaluate the association of species pairs and the correlation of their prevalence, we used the chi-square test (χ 2 ) with the correction of Yates and the Spearman correlation coefficient (r s ), both with P<0.05(Ludwig and Reynolds, 1988; Zar, 1999). These tests were applied only for the species of parasites with prevalence greater than or equal to 10%. Only those helminthes found in 10% of the host sample were examined in an attempt to eliminate accidental infections as component species, we recognised that this could also eliminate some host specific and generalist species that occur infrequently (Bush et al., 1990).

D.H.S. Anjos, M.L.A. Rodrigues / Veterinary Parasitology 112 (2003) 109 116 111 Table 1 Number of associations of species of Strongylidae nematodes by host Species/host One Two Three Four Strongylidae species (Strongylinae and Cyathostominae) Strongylus vulgaris Cylicostephanus longibursatus Cylicostephanus longibursatus and C. goldi Cylicostephanus longibursatus, C. goldi and Cylicocyclus nassatus Cylicocyclus nassatus, C. leptostomus and Cyathostomum tetracanthum Cylicostephanus longibursatus, C. goldi, Cylicocyclus nassatusand Cyathostomum tetracanthum Cylicostephanus longibursatus, C. goldi, Cyathostomum tetracanthum and Parapoteriostomum euproctus Cylicostephanus longibursatus, C. goldi, Cyathostomum tetracanthum and Coronocyclus coronatus Six Cylicostephanus longibursatus, C. goldi, Parapoteriostomum euproctus, C. labratus, Triodontophorus tenuicollis and T. minor Cylicostephanus longibursatus, C. minutus, C. nassatus, Cyathostomum tetracanthum, C. pateratum and Coronocyclus coronatus Cylicostephanus longibursatus, C. minutus, C. nassatus, C. ultrajectinus, Parapoteriostomum euproctus and Cylicodontophorus bicoronatus Eight Cylicostephanus longibursatus, C. goldi, C. calicatus, C. minutus, Cylicocyclus nassatus, C. leptostomus, Cyathostomum tetracanthum and C. labratus Cylicostephanus longibursatus, C. goldi, Cylicocyclus nassatus, C. leptostomus, Cyathostomum tetracanthum, C. bicoronatus, Gyalocephalus capitatus and Triodontophorus tenuicollis Cylicostephanus longibursatus, C. goldi, C. calicatus, C. minutus, C. leptostomus, Coronocyclus coronatus, Parapoteriostomum euproctus and Triodontophorus tenuicollis Cylicostephanus longibursatus, C. goldi, C. calicatus, C. minutus, Cylicocyclus nassatus, C. insigne, Cyathostomum tetracanthum and Parapoteriostomum euproctus Nine Cylicostephanus longibursatus, C. goldi, C. calicatus, C. minutus, Cylicocyclus nassatus, C. leptostomus, Cyathostomum tetracanthum, C. pateratum and Coronocyclus coronatus Cylicostephanus longibursatus, C. calicatus, C. minutus, Cylicocyclus nassatus, C. leptostomus, Cyathostomum tetracanthum, C. pateratum, C. bicoronatus and Gyalocephalus capitatus. Cylicostephanus longibursatus, C. goldi, C. minutus, Cylicocyclus nassatus, C. leptostomus, Cyathostomum tetracanthum, Coronocyclus labiatus, Parapoteriostomum euproctus and Cylicodontophorus bicoronatus Cylicostephanus longibursatus, C. goldi, C. calicatus, C. minutus, Cylicocyclus nassatus, Cyathostomum tetracanthum, Parapoteriostomum euproctus, Cylicodontophorus bicoronatus and Gyalocephalus capitatus Ten Cylicostephanus longibursatus, C. goldi, C. calicatus, C. minutus, Cylicocyclus nassatus, C. leptostomus, Coronocyclus coronatus, Parapoteriostomum euproctus, Triodontophorus tenuicollis and Strongylus vulgaris Cylicostephanus longibursatus, C. goldi, C. calicatus, C. minutus, Cylicocyclus nassatus, C. leptostomus, C. insigne, Cyathostomum tetracanthum, C. pateratum and Cylicodontophorus bicoronatus Eleven Cylicostephanus longibursatus, C. goldi, C. calicatus, C. minutus, Cylicocyclus nassatus, C. insigne, Cyathostomum tetracanthum, C. pateratum, C. labiatus, C. labratus and Gyalocephalus capitatus Cylicostephanus longibursatus, C. goldi, C. calicatus, Cylicocyclus nassatus, C. leptostomus, C. insigne, Cyathostomum tetracanthum, Parapoteriostomum euproctus, Cylicodontophorus bicoronatus, Gyalocephalus capitatus and Triodontophorus tenuicollis

112 D.H.S. Anjos, M.L.A. Rodrigues / Veterinary Parasitology 112 (2003) 109 116 Table 1 (Continued ) Species/host Strongylidae species (Strongylinae and Cyathostominae) Twelve Cylicostephanus longibursatus, C. goldi, C. calicatus, C. minutus, Cylicocyclus nassatus, C. leptostomus, C. insigne, C. ultrajectinus, Coronocyclus coronatus, Parapoteriostomum euproctus, Cylicodontophorus bicoronatus and Triodontophorus tenuicollis Cylicostephanus longibursatus, C. goldi, C. calicatus, C. minutus, Cylicocyclus nassatus, C. ultrajectinus, C. brevicapsulatus, Cyathostomum tetracanthum, C. pateratum, Coronocyclus labiatus, Triodontophorus tenuicollis and T. serratus Thirteen Cylicostephanus longibursatus, C. goldi, C. calicatus, C. minutus, Cylicocyclus nassatus, C. leptostomus, C. insigne, Cyathostomum tetracanthum, C. pateratum, Coronocyclus labratus, Parapoteriostomum euproctus, Cylicodontophorus bicoronatusand Triodontophorus tenuicollis Fourteen Cylicostephanus longibursatus, C. goldi, C. calicatus, C. minutus, Cylicocyclus nassatus, C. leptostomus, C. brevicapsulatus, Cyathostomum tetracanthum, Coronocyclus coronatus, C. labratus, Parapoteriostomum euproctus, Cylicodontophorus bicoronatus, Gyalocephalus capitatus and Triodontophorus minor Cylicostephanus longibursatus, C. goldi, C. calicatus, C. minutus, Cylicocyclus nassatus, C. leptostomus, C. insigne, C. brevicapsulatus, Cyathostomum tetracanthum, C. pateratum, Coronocyclus coronatus, C. labratus, Cylicodontophorus bicoronatus and Strongylus vulgaris Table 2 Prevalence and community status of Strongylidae nematodes of the dorsal colon of naturally infected Equus caballus from the metropolitan region of Rio de Janeiro Species Prevalence (%) Community status Cylicostephanus longibursatus 90.9 C Cylicostephanus goldi 81.8 C Cylicocyclus nassatus 75.8 C Cyathostomum tetracanthum 69.7 C Cylicostephanus minutus 51.5 S Cylicostephanus calicatus 48.5 S Parapoteriostomum euproctus 45.5 S Cylicocyclus leptostomus 42.4 S Cylicodontophorus bicoronatus 33.3 S Coronocyclus coronatus 30.3 Sa Triodontophorus tenuicollis 30.3 Sa Cyathostomum pateratum 27.3 Sa Cylicocyclus insigne 24.2 Sa Coronocyclus labratus 21.2 Sa Gyalocephalus capitatus 21.2 Sa Strongylus vulgaris 12.1 Sa Cylicocyclus brevicapsulatus 12.1 Sa Coronocyclus labiatus 12.1 Sa Cylicocyclus ultrajectinus 6.1 Sa Craterostomum acudicaudatum 3.0 Sa Triodontophorus serratus 3.0 Sa Triodontophorus minor 6.1 Sa Troidontophorus ratzzi 3.0 Sa C: core specie, S: secondary specie, Sa: satellite specie.

D.H.S. Anjos, M.L.A. Rodrigues / Veterinary Parasitology 112 (2003) 109 116 113 Table 3 Species pairing of Strongylidae nematodes of the dorsal colon of naturally infected Equus caballus from the metropolitan region of Rio de Janeiro, according to chi-square (χ 2 ) and correlation of Spearman coefficient (r s ) Paired species χ 2 r s Cylicostephanus longibursatus Cylicostephanus goldi 9.42 0.77 Cylicostephanus longibursatus Cylicocyclus insigne 0.10 0.46 Cylicostephanus longibursatus Triodontophorus tenuicollis 0.29 0.57 Cylicostephanus goldi Parapoteriostomum euproctus 2.96 0.46 Cylicostephanus goldi Triodontophorus tenuicollis 1.68 0.66 Cylicostephanus calicatus Cylicocyclus nassatus 6.92 0.59 Cylicostephanus calicatus Cylicocyclus leptostomus 7.94 0.47 Cylicostephanus calicatus Cylicocyclus insigne 0.01 0.42 Cylicostephanus calicatus Cyathostomum tetracanthum 2.97 0.50 Cylicostephanus calicatus Cyathostomum pateratum 3.72 0.45 Cylicostephanus calicatus Coronocyclus labratus 4.93 0.45 Cylicostephanus calicatus Coronocyclus coronatus 4.25 0.43 Cylicostephanus calicatus Parapoteriostomum euproctus 3.70 0.25 Cylicostephanus calicatus Gyalocephalus capitatus 4.93 0.32 Cylicostephanus calicatus Triodontophorus tenuicollis 5.71 0.28 Cylicostephanus minutus Cylicocyclus nassatus 8.09 0.70 Cylicostephanus minutus Cylococyclus leptostomus 5.54 0.42 Cylicostephanus minutus Cylicocyclus insigne 5.47 0.35 Cylicostephanus minutus Cyathostomum tetracanthum 3.88 0.50 Cylicostephanus minutus Cyathostomum pateratum 8.36 0.66 Cylicostephanus minutus Coronocyclus coronatus 0.42 0.52 Cylicostephanus minutus Coronocyclus labratus 4.16 0.42 Cylicostephanus minutus Coronocyclus bicoronatus 1.73 0.34 Cylicocyclus nassatus Cylicocyclus leptostomus 6.18 0.59 Cylicocyclus nassatus Cyathostomum tetracanthum 4.59 0.53 Cylicocyclus nassatus Cyathostomum pateratum 1.15 0.55 Cylicocyclus nassatus Coronocyclus labratus 0.76 0.38 Cylicocyclus nassatus Cylicodontophorus bicoronatus 3.49 0.43 Cylicocyclus leptostomus Cylicocyclus insigne 5.61 0.41 Cylicocyclus leptostomus Cyathostomum tetracanthum 3.11 0.59 Cylicocyclus leptostomus Coronocyclus labratus 3.82 0.33 Cylicocyclus leptostomus Cylicodontophorus bicoronatus 11.52 0.56 Cylicocyclus insigne Cylicocyclus brevicapsulatus 6.27 0.48 Cylicocyclus insigne Cyathostomum tetracanthum 2.06 0.35 Cylicocyclus insigne Parapoteriostomum euproctus 8.78 0.37 Cylicocyclus insigne Cylicodontophorus bicoronatus 6.81 0.54 Cylicocyclus brevicapsulatus Coronocyclus coronatus 5.23 0.37 Cylicocyclus brevicapsulatus Cylicodontophorus bicoronatus 2.94 0.40 Cyathostomum tetracanthum Cyathostomum pateratum 2.74 0.48 Cyathostomum tetracanthum Coronocyclus labratus 1.45 0.45 Cyathostomum tetracanthum Cylicodontophorus bicoronatus 0.59 0.36 Cyathostomum tetracanthum Gyalocephalus capitatus 0.01 0.42 Coronocyclus coronatus Coronocyclus labratus 3.21 0.38 Parapoteriostomum euproctus Cylicodontophorus bicoronatus 0.01 0.33 Parapoteriostomum euproctus Triodontophorus tenuicollis 11.81 0.46 Gyalocephalus capitatus Cylicodontophorus bicoronatus 1.66 0.30 Gyalocephalus capitatus Triodontophorus tenuicollis 3.03 0.34 Strongylus vulgaris Coronocyclus coronatus 2.58 0.33 Strongylus vulgaris Coronocyclus labratus 0.29 0.12 Species pairing with statistic significance to χ 2 or r s.

114 D.H.S. Anjos, M.L.A. Rodrigues / Veterinary Parasitology 112 (2003) 109 116 3. Results Of the 33 samples examined, from the dorsal colon, 23 species were observed, distributed in 11 genera belonging to the Strongylidae family. The infection rate per host varied from two species for Strongylinae to 14 for Cyathostominae (Table 1). Based on the prevalence of species, the community in the dorsal colon was composed of four central species (17.39%) (Cylicostephanus longibursatus, Cylicostephanus goldi, Cylicocyclus nassatus and Cyathostomum tetracanthum), five secondary species (21.73%) (Cylicostephanus minutus, Cylicostephanus calicatus, Cylicocyclus leptostomus, Cylicodontophorus bicoronatus and Parapoteriostomum euproctus) and 14 satellite species (60.86%) (Table 2). Of the 263 pairs of Strongylidae nematode species, only four (1.52%) showed both significant positive association and correlation (χ 2 and r s ), while 21 (7.98%) and 24 (9.13%) pairs, respectively, presented significant positive association (χ 2 ) or positive correlation (r s ) alone. We did not observe any species with significant negative association and correlation in both tests used (Table 3). 4. Discussion The parasite community in the equine gastrointestinal tract can be interactive when composed of a rich variety of parasites and many central species (species present in more than two-thirds of the hosts studied), with evidence of interactions among them and few unfilled niches. Or, they may be isolationist when they have a low level of richness and few central species (species present in one-third of the hosts studied), showing little evidence of mutual interaction and many empty niches (Holmes and Price, 1986). In this study, the community of strongylidae nematodes was characterized by a few central species, moderate parasitic richness and few species with significant positive association and correlation, indicating that these species are independent and that the abundance among them varies in the same direction. The absence of negative association and correlation shows that the species are not competing for the available space, but instead coexist in distinct ecological niches. This community does not fit in the classification of Holmes and Price (1986); suggesting an intermediate classification between interactive and isolationist. However, this community can be considered to be intermediate in a continuum. The number of core species in the parasitic community may determine its position along the continuum from non-interative or isolationist communities to highly interative communities (Holmes and Price, 1986; Esch et al., 1990). Although species interactions may be important in species-poor and uneven communities, evenness could be a rough index of how likely coexisting parasite species are to co-occur and interact with one another. The present study agrees with that of Bucknell et al. (1996), who found a stable community consisting of central species (6.5%) C. longibursatus and C. tetracanthum, according to the classification of Holmes and Price (1986). To check this similarity, prevalence of species data found by Bucknell et al. (1996) were used. The parasitic richness observed in the dorsal colon of horses of this study, however, differed from the results of Bucknell et al.

D.H.S. Anjos, M.L.A. Rodrigues / Veterinary Parasitology 112 (2003) 109 116 115 (1996) by the absence of Strongylus edentatus, S. equinus, Triodontophorus brevicauda, Petrovinema poculatum, Cylicocyclus ashworthi, Cylicocyclus elongatus, Cylicocyclus auriculatus, Cylicocyclus radiatus, Poteriostomum imparidentatum, and Parapoteriostomum mettami. This can be attributed to the number, origin of the hosts and the methodology applied (e.g. in this study we analysed 10% of the total contents of the dorsal colon (200 of 7000 worms). The Bucknell s study examined at least 40 worms in each sample. The species C. longibursatus, C. goldi, C. nassatus and C. tetracanthum were classified as central for the dorsal colon of horses in Rio de Janeiro, whereas C. goldi and C. nassatus were secondary species in the community of the large intestine of horses in Australia. This difference may be related to the methodology used by Bucknell et al. (1996). An analysis of samples taken from the total content of the large intestine can have a make up different from the entire community of strongylidae nematodes, since each compartment has a distinct fauna and consequently a characteristic structure. The community structure of these nematodes was considered to be dominated by a species grouping phenomenon by Kennedy and Bush (1992), mainly due to the coexistence of species. In this grouping, it was observed that single infections were more frequent (60%) and that the percentage of hosts with multiple infections decrease as the parasitic richness increased. In the present study and that of Bucknell et al. (1996), the most frequent type of infection was multiple, indicating similarity between the communities of Strongylidae nematodes in horses in Rio de Janeiro and Australia. Both studies differ from that of Kennedy and Bush (1992) by their finding of various species of the genus Equus and the greater prevalence of Cyathostominae. The frequency distribution for the two subfamilies differed markedly in our study. The majority of animals were free of Strongylinae infection, or when infected, only by one species. This distribution was observed in the present study and that of Bucknell et al. (1996). For Cyathostominae, the greatest frequencies were observed in animals afflicted by four, eight and nine species in the present study, while in Bucknell et al. (1996), the highest frequencies were five and six species per host. However, in both studies, Cylicocyclus and Cylicostephanus were the only genera that had more than three species present despite a different distribution pattern Cylicocyclus had the highest frequency of double infection. Cylicostephanus, with a maximum frequency of four species had a pattern similar to that observed by Bucknell et al. (1996). References Amato, J.F.R., Boeger, W.A., Amato, S.B., 1991. Protocolos para laboratório, coleta e processamento de parasitos de pescado. 1 Edição. Imprensa Universitária, Universidade Federal Rural do Rio de Janeiro. Anjos, D.H.S., 1998. Estrutura das infracomunidades de estrongilídeos (Nematoda: Strongylidae) do cólon dorsal de Equus caballus naturalmente infectados, proveniente da Região Metropolitana do Rio de Janeiro. Dissertação de Mestrado, Universidade Federal Rural do Rio de Janeiro, 62 pp. Anjos, D.H.S., 2002. Estrutura da comunidade dos nematóides estrongilídeos (Nematoda: Strongylidae) do cólon ventral de Equus caballus naturalmente infectados, proveniente da Região Metropolitana do Rio de Janeiro. Tese de Doutorado. Universidade Federal Rural do Rio de Janeiro, 60 pp. Bucknell, D., Hoste, H., Gasser, R.B., Beveridge, I., 1996. The structure of the community of strongyloid nematodes of domestic equids. J. Helminthol. 70, 185 192.

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