O American Society of Parasitologists 1997. ONTOGENETIC HABITAT ... franciscanas, Pontoporia blainvillei, a coastal South American dolphin (Aznar, 1995).
J. Parositol.. 83(1 ). 1997 p. H-18 O American Society of Parasitologists 1997
ONTOGENETIC HABITAT SELECTION BY HADWENIUS PONTOPORIAE (DIGENEA: CAMPULIDAE) IN THE INTESTINE OF FRANCISCANAS (CETACEA) F. J. Aznar, J. A. Balbuena, A.O. Bush*, and J. A. Raga Department of Animal Biology, University of Valencia, Dr. Moliner 50, 46100 Burjassot, Valencia, Spain
The linear habitat selection of 4 sequential maturity stages (I, 2, 3, and 4) of the tremat?de Ha~weniu_s pontoporiae in the intestines of 26 South American dolphins Pontoporia blainvillei was investigated. The franc1scana 1s a smtable host for H. pontoporiae because all 26 hosts were infected, the infrapopulations being composed mostly of gravid (stage 4) worms. Mo~t trematodes were found in the first third of the intestine. The niches of the maturity stages decreased from stage 1 to 4. Gravid worms favored the most anterior part of the duodenum, whereas stages l, 2, and 3 occurred more posteriorly in every host. The distributions of the maturity stages showed a narrow site fidelity and were ordered following the developmental sequence. The positions of stages 2, 3, and 4 covaried positively when the effect of inte~sity was controlled .. All this evidence s~gge.sts th~t. H. pontoporiae undergoes an anteriad ontogenetic migration from the postenor to the most antenor duodenum. At high mten~1t1es, the distribution of stages 2, 3, and 4 expanded and shifted posteriorly. According to the maturity structure of H. pontoponae at the infrapopulation level, it is proposed that there might be more developing worms at high intensities, and, therefore, the expansion and shift might result, at least partly, from the presence of more migrating worms along the fundamental niche of H. pontoporiae. Other Hadwenius species show a similar general pattern of distribution to H. pontoporiae. This raises the possibility that the habitat selection behavior of H. pontoporiae may be due to the inheritance of prior phylogenetic constraints.
ABSTRACT:
problem in the investigation of many host-parasite systems and The knowledge of the proximate and ultimate causes of habitat selection by helminths has advanced theoretically in recent we hope that this paper may also suggest some useful methyears, but many fundamental questions still remain unresolved odological approaches to obtain behavioral data of parasites ob(Su.khdeo and Su.khdeo, 1994). Logically, our current under- tained from serendipitous collections. standing of the patterns and processes of habitat selection is MATERIALS AND METHODS based upon a small set of host-parasite systems particularly well suited for experimental procedures and/or a priori sam- Data collection pling (e.g., Kennedy, 1985; Sukhdeo and Sukhdeo, 1994; Rohde, This study is based on H. ponroporiae populations from 26 francis1994; see also references therein). The investigation of other canas caught accidentally in shark fisheries off Necochea (38°27'S, models is often severely hampered by host-related problems, 58°50'W) and Claromec6 (38°52'S, 60°05'W) in Buenos Aires Provranging from the impracticality of experimentation to the un- ince, Argentina. Sampling was carried out during the austral midspring availability of appropriate natural samples. Consequently, data (late October to early December) of 1989 and 1990 (6 and 20 animals, respectively). Dolphins were removed daily from the nets, their inteson habitat selection by helminths from large, wild vertebrates, tines being immediately removed and stored in a commercial freezer for example, are usually reduced to reports from very general for later examination. The whole process could take up to 24 hr after host death. locations, i.e., organs. In this paper we provide a detailed analysis of paterns of habitat use by a digenean parasitizing a cetacean. The trematode Spatial scale Spatial patterns were analyzed using an approximation of the linear Hadwenius pontoporiae Raga, Aznar, Balbuena et Dailey, 1994 is the only helminth species found regularly in the intestine of niche axis (Bush and Holmes, 1986). Intestines were measured from the distal end of the duodenal ampulla (a transversely widened, funnelfranciscanas, Pontoporia blainvillei, a coastal South American shaped region in the proximal duodenum where H. pontoporiae ocdolphin (Aznar, 1995). We took advantage of the simplicity of curred rarely) to the anus. The mean intestinal length(~ 1 SD) was 38.4 this system to study the habitat selection of H. pontoporiae in :!: 3.9 m. From previous analyses, we knew that H. pontoporiae might its natural host. Depending on the question being asked, habitat ~xten? o~er several meters of the intestine. Therefore, we divided each selection can be dealt with at different spatial scales (Lymbery mtestme. mt~ 30 equal sections, resulting in lengths somewhat over 1 et al., 1989). In this study, we posed 2 questions at the mac- m. Cons1denng the comparatively small size of the parasite (6 x 0.6 mi;n on average) (~aga et .al., 1994), this was considered as an approrohabitat scale (sensu Sukhdeo and Sukhdeo, 1994), namely, pnate scale to obt~n me~mg.ful data, minimizing the effect of potential what was the relationship between linear position and adult postmortem helmmth migrations. The contents of each section were worm development, and what was the influence (if any) of hel- flushed through a sieve (0.2 mm mesh) and examined separately. All worms from each section were collected and counted separately. minth population size on this pattern? From a methodological viewpoint, we acknowledge at the Maturity patterns outset that the posthoc analyses employed here cannot prove ~II specimens of H. pontoporiae were allocated to 4 stages of mamechanisms. At best, the patterns observed may suggest some tunty (~m?'t~ and H_alton, 1983), using a light microscope. Fully imputative explanations that can be contrasted to those of suitable m_ature 1~d1v1d1_1als w~th no gonads were classified as stage 1, individuals host-parasite models. However, posthoc analyses are a common ~It? ~emtal ~nmord1a clearly visible, but with no vitellaria, as stage 2, md1v1duals with gonads. an~ : l, 2 = 24,333, df = 25, p < 0.0001). The prevalence, me an intensity, range, and total number of individuals of each maturity stage are shown in Table I. Stage 4 occurred in all hosts and represented the highest proportion of the total number of worms in each infrapopulation (range: 55-100%) and nearly 82% of the total population. Stages 2 and 3 showed the lowest values in prevalence and intensity. The ranked intensities of the maturity stages within each infrapopulation were highly concordant across hosts (Kendall's test, W = 0.73, n = 26, df = 3, P < 0.001). The 3 hosts with the lowest burdens (9, 23, and 32 worms) harbored only
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AZNAR ET AL-HABITAT SELECTION BY H. PONTOPORIAE
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25
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20 ~
T_AB';-£ Levins' niche breadth for realized (Br) and fundamental (Bf) d1stnbuuons, and mean position with 95% confidence intervals of the dis~butic;>n quartiles of 4. maturity stages of Hadwenius pontoporiae in the mtcsuncs of 26 franc1scanas (Pontoporia blainvillei).
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Mean quartile (95% interval)*
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15 0. cu
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10
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3
4
5
6
7
8
9
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2.40
4
(l.65) 2.42 (I.24)
9+
Intestinal section
·,, "~./~':FioURE I. Mean number (± l SE) of worms per intestinal section :
