The ultrastructure of the capsule surrounding Pomphorhynchus laevis (Acanthocephala) in its intermediate host Echinogammarus stammeri (Amphipoda).

The capsule or the membranous layer surrounding larvae of Pomphorhynchus laevis Müller, 1776 in its intermediate host, Echinogammarus stammeri S. Karaman, 1931, was studied by electron microscopy. Some observations were also made with a light microscope. Capsule components mainly show a tubular profile; capsule thickness can reach up to 8 microns. In some instances, within the hemocoel of E. stammeri, the parasite was encapsulated by amphipod hemocytes.     

Karyotypes of the Echinogammarus berilloni-group (Crustacea,Amphipoda) from Spain

The chromosome number and karyological features of Iberian populations of seven species of the Echinogammarus berilloni-group (Crustacea, Amphipoda) have been studied. For comparison, Gammarus gauthieri, belonging to the G. pulex-group was also studied. Four species of the berilloni-group share the same number n=27. Other numbers found were n=25, n=26 and n=28. The chromosomes of these species have a centromeric region surrounded by large heterochromatic blocks at late prophase. There-after, the centromere splits precociously. C. gauthieri has n=26, the same number found in the pulex-group. This species has larger chromosomes than the former but it does not show these karyological peculiarities.Cytological observations confirm both the close relationship among species of the berilloni-group and the differentiation with respect to the pulex-group. On the other hand, the existence of different numbers confirms other results that reject the older idea that speciation within Gammaridea occurred with minor changes in karyotypic characters.     

Acanthocephalus bufonis (Acanthocephala) from Bufo marinus (Bufonidae: Amphibia) in Hawaii.

During a survey of the helminth parasites of the introduced toad, Bufo marinus, on O'ahu, Hawaii, an acanthocephalan corresponding to Acanthocephalus bufonis (Shipley, 1903) was found in the intestinal tract. This is a new host and locality record for A. bufonis which has only previously been recorded from amphibians in the Orient. Possible mechanisms for the introduction of A. bufonis to Hawaii, and its transmission to the toad, are discussed. Almost 98% of toads were infected with a mean intensity of 28.6 acanthocephalans per infected toad. There was a significant negative correlation between host length and intensity of infection with subadult toads having significantly higher infection levels than adult male and female toads. Trunk length of both male and female acanthocephalans was significantly related to host length.     

Proximate factors affecting the larval life history of Acanthocephalus lucii (Acanthocephala)

The growth and eventual size of larval helminths in their intermediate hosts presumably has a variety of fitness consequences. Therefore, elucidating the proximate factors affecting parasite development within intermediate hosts should provide insight into the evolution of parasite life histories. An experimental infection that resulted in heavy intensities of an acanthocephalan (Acanthocephalus lucii) in its isopod intermediate host (Asellus aquaticus) permitted the examination of parasite developmental responses to variable levels of resource availability and intraspecific competition. Isopods were infected by exposure to egg-containing fish feces, and larval infrapopulations were monitored throughout the course of A. lucii development. The relative rate of parasite growth slowed over time, and indications of resource constraints on developing parasites, e.g., crowding effects, were only observed in late infections. Consequently, the factors likely representative of resource availability to larval parasites (host size and molting rate) primarily affected parasite size in late infections. Moreover, at this stage of infection, competitive interactions, gauged by variation in worm size, seemed to be alleviated by greater resources, i.e., larger hosts that molted more frequently. The relatively rapid, unconstrained growth of young parasites may be worse for host viability than the slower, resource-limited growth of larger parasites.     

Seasonality of recruitment and reproduction of Acanthocephalus tumescens (Acanthocephala) in fishes from Lake Moreno (Patagonia, Argentina)

The seasonality of recruitment and reproduction of Acanthocephalus tumescens at the component population level was investigated in Lake Moreno (Patagonia, Argentina). Seasonal samples of the principal fish host species were taken between spring 1999 and spring 2000. Prevalence, mean intensity, coefficient of dispersion, sex ratio, proportion of maturity stages of females, and percentages of the 2 sources of infection in the stomach of fishes were calculated. Overall prevalence, mean intensity, and coefficient of dispersion showed the same pattern of seasonal changes. The seasonal feeding patterns of fishes affect the occurrence of A. tumescens, producing 1 peak in spring and the other peak in autumn. The lower temperature in winter delay reproductive processes after the autumn period of recruitment.     

Life history and population biology of adult Acanthocephalus lucii (Acanthocephala: Echinorhynchidae)

The life history and population biology of adult A. lucii in perch, Perca fluviatilis L., from the Forth and Clyde canal, Scotland, was investigated during May 1979-September 1981. There was an annual cycle in the size of the parasite population; prevalence and abundance (+/- SE) were highest during late spring and summer (70-90% and 14 +/- 4.3 to 16 +/- 5.6 worms/fish, respectively) but declined during late autumn and reached a minimum during winter (50-60% and 2.1 +/- 0.9 to 3.2 +/- 0.6 worms/fish). Parasite maturation was associated with higher water temperatures during spring and summer and most shelled acanthors were probably produced during summer and fall. There was only 1 generation of A. lucii per year, although generations tended to overlap and individuals within each generation did not develop synchronously. The sex ratio of adults was initially near unity but favoured females in the later stages of the infection. The distribution of A. lucii among perch was highly aggregated and stomach content analysis suggested that this was partly due to heterogeneity in perch feeding behaviour. The negative binomial and Poisson lognormal models fitted the data on worm distribution. Seasonal changes in the degree of parasite aggregation were detected, but no conclusive evidence of density-dependent controls on parasite population growth was obtained.     

Suckers and other bursal structures of Pomphorhynchus bulbocolli and Acanthocephalus dirus (Acanthocephala)

Accessory copulatory structures in the bursa of Pomphorhynchus bulbocolli include 2 suckers on the inner surface and bursal rays. A stylet was present in the penis of this species. Two suckers were present in the bursa of Acanthocephalus dirus, but bursal rays and a stylet in the penis were not observed. This is the first report of suckers present in the bursas of acanthocephalans. Copulatory cement caps and holes surrounded by a ring approximating the inner bursal diameter and not covered by a cap were present on the sides of some P. bulbocolli, indicating the possibility of hypodermic insemination in this species.     

Relation between habitat and antennular segmentation in Gammarus and Echinogammarus (Crustacea: Amphipoda)

In 140 species of the amphipod genera Gammarus and Echinogammarus the ratio was calculated between the number of segments of the accessory and main antennular flagellum. Minor inter-and intrapopulational variation of this ratio was found in four species of the genus Gammarus. Seasonal variation was studied in one species of this genus. For both genera a clear correlation was found between antennular composition and the occurrence in marine or freshwater habitats.     

Occurrence of Pomphorhynchus laevis Müller 1776 (Acanthocephala) in Silurus glanis (L.) from the River Po.

The sheatfish, Silurus glanis (L.), from the terminal part of River Po was examined for the presence of helminth parasites. Of 182 S. glanis specimens, 95 (52.2%) were infected with the acanthocephalan Pomphorhynchus laevis. Mid-gut followed by fore-gut appeared to be the most infected portions of host alimentary canal. In 45 sheatfish of total length < or = 40 cm, specimens of P. laevis were found encapsulated in mesenteric and peritoneal tissues. A comparison between light and electron microscopy on features and stages of testis development in both encapsulated male P. laevis and intestinal male parasites showed that the encysted acanthocephalans were immature; mature spermatozoa were rarely found within the testis of worms from the alimentary canal. Among extraintestinal P. laevis specimens, the presumable eversion of parasite praesoma was observed and described. The results of the present survey suggest that small-size individuals of S. glanis could be used as paratenic host by P. laevis during its life cycle in the study area.     

Acanthocephalus reunionensis n sp (Acanthocephala: Echinorhynchidae), a parasite of Anguilla species (Anguillidae) from Reunion Island

In a survey of 118 eels Anguilla bicolor, A. marmorata and A. mossambica, (Anguillidae) indigenous to Reunion Island in the Mascarene island group, western Indian Ocean, a new species of acanthocephalan, Acanthocepholus reunionensis n. sp., was found. With a proboscis hook formula of 19 rows of 4-5 hooks, and elongated cement glands arranged in three pairs, this species differs from all other species in the genus. This is the first record of the genus Acanthocephalus occurring in eels from the African Region.     

Isozyme differentiation among sibling species and among populations of the Echinogammarus berilloni-group (Crustacea, Amphipoda)

The sibling species of the Echinogammarus berilloni-group are endemic for the Iberian Peninsula and southern France. These species show wide morphological variability with some overlap in their dianostic characters making their distinction difficult. Reroductive isolation and enzmatic jivergence amon allopatric and sympatric populations of four species sharing the same chromosome number has been studied. The results show a clear genetic differentiation of E. longiserosus and E. calvus versus the other two species. However, E. margalefi and E. echinosetosus show no clear genetic differentiation between them, confirming their crose relationship. All four species often coexist in the same drainage system. Isozme analysis was employed to check the hypothesis Of Margalef that sympathy would occur age, long-term phenomena of speciation inside of a given basin with subsequent contact and overlap between the differentiated forms. Electrophoretic data were also used to determine whether one flow among gammarids populations exists. A model proosed by other authors according to which the heterozyosity decreases towards the headwaters foes not fit to the data we have obtained from E. calvus. Thus, populations of this species from sources and springs of the Duero basin show the hiFhest values of mean heterozygosity. The differentiation in this basin can be explained by drift. Migration between populations of different rivers is prevented by natural barriers. The lowest river stretches are without amhipods interrupting the gene flow amon populations. A correction between genetic and geographic fistances among subbasins and basins was found applying a double logarithmic model. A model of migration of E. calvus in the Duero basin is proposed on the basis of allelic frequencies and on the distribution of mean hetero-zygosities.     

Organisation of the praesoma in Acanthocephalus anguillae (Acanthocephala, Palaeacanthocephala) with special reference to the muscular system

The organisation of the praesoma in the parasite Acanthocephalus anguillae was studied on the light and electron microscopic level, with emphasis on the morphology of the musculature. The study was compiled to add new data to the ground pattern of the Acanthocephala for analysis of the phylogenetic relationships within the Gnathifera. In A. anguillae the praesomal epidermis and lemnisci form a coherent syncytium, separated from the epidermis of the trunk. Hooks are seen to be derivatives of the subepidermal basal lamina and are covered by the praesomal epidermis. The praesomal circular body wall musculature forms a network of anastomosing muscle fibres that lines the proboscis; a praesomal longitudinal body wall musculature does not exist. The truncal circular and longitudinal body wall musculature rise up to the praesomal proboscis. The unpaired proboscis retractor, consisting of longitudinal circomyar fibres, forms an outer and an inner concentric tube; the latter extends through the entire praesoma and penetrates the receptacle wall. The sack-like receptacle is surrounded by a receptacle constrictor. The nervous system of the praesoma consists of a prominent cerebral ganglion, three nerves which extend anteriorly, ramify and end within the praesomal musculature, and two strong lateral posterior nerves. A. anguillae lacks an apical organ, lateral organs and a support cell. Many of the features present in the praesoma of A. anguillae can be assumed as ground-pattern characteristics of the Acanthocephala. Accepted: 22 January 2001     

Life history and population biology of larval Acanthocephalus lucii (Acanthocephala: Echinorhynchidae) in the isopod Asellus aquaticus

Hemocoels of 8,731 Asellus aquaticus collected from the Forth and Clyde canal in Glasgow, Scotland, from January 1980 to March 1981 were examined for larvae of Acanthocephalus lucii. Prevalence and mean intensity were generally low (1.5-8.3% and 1.0-1.6, respectively), but there was a slight seasonal infection pattern with fewer infected isopods during summer, reflecting the appearance of a new isopod generation. Although there were no distinct seasonal trends in the proportions of each larval stage, recruitment of larvae probably occurred mainly during summer and autumn. Some larvae reached the cystacanth stage by late summer or autumn; others overwintered as acanthors or acanthellae and completed development the following spring. The maximum life span of larvae was limited to 1 yr by annual turnover of the isopod population. The distribution of larval A. lucii among isopods was slightly aggregated. There was a peaked pattern in the relationship between isopod length and the prevalence, abundance, and degree of parasite aggregation. The rate of parasite development in laboratory-infected isopods was linearly related to temperature between 9 and 22 C; the temperature threshold was 5.7 C, and the larval parasite required 598 degree-days above threshold to complete development. Among laboratory-infected isopods, 2 mechanisms that could regulate the larval parasite population were detected: intraspecific competition and direct, parasite-induced isopod mortality. However, the intensity of infection in the natural habitat was consistently low and may have remained below the level at which these mechanisms operated.     

Virulence of Corynosoma constrictum (Acanthocephala: Polymorphidae) in Hyalella azteca (Amphipoda) throughout parasite ontogeny

Development and growth of parasites depend on resources provided by the host and the parasite's ability to use them. Identifying specific costs incurred by the host provides insight for assessment of parasite energy budgets, which differ among taxa and ontogenetic stages. Data from this study were analyzed using an accelerated failure-time model with intensity as a covariate. Results indicated significantly reduced survival of amphipods, Hyalella azteca, infected with the acanthocephalan Corynosoma constrictum compared with uninfected controls. Male and female amphipod survivorship and infection intensity did not differ; however, amphipods with high-intensity infections (> 16 larvae) died earlier compared with amphipods with low-intensity infections (< 3 larvae). The majority of infected amphipods died between 12 and 24 days postexposure, a period of rapid larval development. It is hypothesized that host death may be due either to an increase in overall larval nutritional demands or to parasite-mediated depletion of a specific host substance. Results from this study suggest that developing C. constrictum satisfies energy requirements by depriving amphipod hosts of resources normally used for somatic growth and maintenance.     

Acanthocephalus saurius n. sp. (Acanthocephala: Echinorhynchidae) and other helminths from the lizard Norops limifrons (Sauria: Polychrotidae) from Costa Rica

Acanthocephalus saurius n. sp. from the small intestine of Norops limifrons collected in Costa Rica is described and illustrated. Acanthocephalus saurius n. sp. represents the third acanthocephalan species in which gravid individuals have been found in lizard hosts. In addition to A. saurius; 1 species of Trematoda, Mesocoelium monas; 3 species of Nematoda, Piratuba digiticauda, Strongyluris panamaensis, and Acuariidae gen. sp. (larvae in cysts) were found.     

Acanthocephalus tahlequahensis sp. n. (Acanthocephala: Echinorhynchidae) from the the stippled darter, Etheostoma punctulatum (Agassiz), in northeastern Oklahoma.

Acanthocephalus tahlequahensis sp. n. was recovered from the intestines of 4 species of freshwater fishes, Etheostoma punctulatum, E. spectabile, Nocomis asper, and Notropis pilsbryi, collected in northeastern Oklahoma. The new species is distinguished from all other species of Acanthocephalus, except A. japonicus (Fukui and Morisita 1936) Petrochenko 1956, and A. fluviatilus Paperna 1964, by having smaller proboscis hooks. The length of the proboscis hooks for males is 27 to 38 (33) mum and for females 35 to 46 (42) mum. A. tahlequahensis is smaller than either A. japonicus or A. fluviatilis, and has about half the number of longitudinal rows of proboscis hooks of A. japonicus and half the number of proboscis hooks in each longitudinal row of A. fluviatilus. In addition to having smaller hooks. A. tahlequahensis differs from other species of Acanthocephalus parasitizing North American fishes by its smaller, spindle-shaped trunk and more hooks in each longitudinal row.     

Occurrence of the ectoparasite Isocyamus deltobranchium (Amphipoda: Cyamidae) on cetaceans from Atlantic waters

The cyamids collected from a True's beaked whale (Mesoplodon mirus), a common dolphin (Delphinus delphis), and a harbour porpoise (Phocoena phocoena) stranded in Galicia (NW Spain) were identified as Isocyamus deltobranchium, extending the range of this species to the Atlantic Ocean. The three cetacean species examined are new hosts for this parasite. The microscopic examination of female specimens reveals that certain important taxonomic characters can be present or absent depending on the maturation stage, an aspect which should be considered in future studies describing cyamid species.     

Effects of Acanthocephalus lucii (Acanthocephala) on intermediate host survival and growth: implications for exploitation strategies

Intermediate host exploitation by parasites is presumably constrained by the need to maintain host viability until transmission occurs. The relationship between parasitism and host survival, though, likely varies as the energetic requirements of parasites change during ontogeny. An experimental infection of an acanthocephalan (Acanthocephalus lucii) in its isopod intermediate host (Asellus aquaticus) was conducted to investigate host survival and growth throughout the course of parasite development. Individual isopods were infected by exposure to fish feces containing parasite eggs. Isopods exposed to A. lucii had reduced survival, but only early in the infection. Mean infection intensity was high relative to natural levels, but host mortality was not intensity dependent. Similarly, a group of naturally infected isopods harboring multiple cystacanths did not have lower survival than singly infected isopods. Isopods that were not exposed to the parasite exhibited sexual differences in survival and molting, but these patterns were reversed or absent in exposed isopods, possibly as a consequence of castration. Further, exposed isopods seemed to have accelerated molting relative to unexposed controls. Infection had no apparent effect on isopod growth. The effects of A. lucii on isopod survival and growth undermine common assumptions concerning parasite-induced host mortality and the resource constraints experienced by developing parasites.     

The dynamics of a declining population of the acanthocephalan Acanthocephalus clavula in eels Anguilla anguilla in a small river

Changes in the size and composition of a population of the acanthocephalan Acanthocephalus clavula in eels, Anguilla anguilla , and flounders, Platichthys flesus , its definitive hosts, in a small river are described over a period of 4.5 years in the course of which the population underwent a steady and continuous decline. Parasite prevalence and abundance declined more rapidly initially and then more gradually, and during the period the frequency distribution changed from overdispersed to being close to random on most occasions. Throughout the whole period newly recruited parasites were found in eels, and adult females continued to mature and produce acanthors. Data on the distribution and occurrence of the intermediate host Asellus meridianus in the river suggested that in the latter part of the decline it was no longer possible for the parasite to complete its life cycle in some parts of the river, and the cause of the parasite population decline is believed to be the decrease in abundance of the intermediate host as a result of interspecific competition with a congeneric species. During this latter period, immigration of infected eels from another river in the catchment may have contributed to the maintenance of the parasites in the locality, but it is considered that the decline in the river was representative of what was happening in other parts of the catchment and that the whole parasite population in the catchment was declining for the same reason.