The life cycle of Sclerocollum saudii Al-Jahdali, 2010 (Acanthocephala: Palaeacanthocephala: Rhadinorhynchidae) in amphipod and fish hosts from the Red Sea

Sclerocollum saudii Al-Jahdali, 2010 (Acanthocephala: Cavisomidae) as a sentinel for heavy-metal pollution in the Red Sea

Currently, fish helminth parasites, especially cestodes and acanthocephalans, are regarded as sentinel organisms to elucidate metal pollution in aquatic ecosystems. Here, 34 specimens of the fish Siganus rivulatus were collected in the Red Sea, from a seriously polluted, small lagoon named Sharm-Elmaya Bay, at Sharm El-Sheikh, South Sinai, Egypt; 22 (64.7%) were infected by Sclerocollum saudii (Acanthocephala: Cavisomidae). Thus, 22 natural infrapopulations (26-245 individuals) of this parasite were collected from infected fish. Samples of water and sediments from the bay, samples of muscle, intestine and liver from each fish, and samples from the parasite were taken for analysis of heavy metals (cadmium (Cd) and lead (Pb)). Both Cd and Pb concentrations in sediments were higher than those in water. The concentration of these metals were significantly higher in tissues (intestine, liver and muscle) of non-infected fish than those in infected fish, with Pb concentrations consistently higher than those of Cd, and both were drastically decreased in the order: liver > intestine > muscle. Metal concentrations in this acanthocephalan were much higher than those in its fish host. There were strong negative relationships between metal concentrations in tissues (intestine, liver and muscle) of infected fish and infrapopulation size, and between metal concentrations in the acanthocephalan and its infrapopulation size. These relationships strongly suggest competition for these metals between the fish host and its acanthocephalan parasite, and intraspecific competition among acanthocephalan individuals for available metals in the fish intestine. Bioconcentration factors were relatively high, since the mean Cd concentration in S. saudii was 239, 68 and 329 times higher than those in intestine, liver and muscle tissues, respectively, of its fish host. Also, mean Pb concentration was 55, 13 and 289 times higher than those in these tissues, respectively. The host-parasite system described here seems to be promising for biomonitoring of metal pollution in the Red Sea.

Parasite life-cycle studies: a plea to resurrect an old parasitological tradition

Many helminth taxa have complex life cycles, involving different life stages infecting different host species in a particular order to complete a single generation. Although the broad outlines of these cycles are known for any higher taxon, the details (morphology and biology of juvenile stages, specific identity of intermediate hosts) are generally unknown for particular species. In this review, we first provide quantitative evidence that although new helminth species are described annually at an increasing rate, the parallel effort to elucidate life cycles has become disproportionately smaller over time. We then review the use of morphological matching, experimental infections and genetic matching as approaches to elucidate helminth life cycles. Next we discuss the various research areas or disciplines that could benefit from a solid knowledge of particular life cycles, including integrative taxonomy, the study of parasite evolution, food-web ecology, and the management and control of parasitic diseases. Finally, we end by proposing changes to the requirements for new species descriptions and further large-scale attempts to genetically match adult and juvenile helminth stages in regional faunas, as part of a plea to parasitologists to bring parasite life-cycle studies back into mainstream research.

A review of the genus Sclerocollum Schmidt & Paperna, 1978 (Acanthocephala: Cavisomidae) from rabbitfishes (Siganidae) in the Indian and Pacific Oceans

Seven of the eleven species of Siganus Richardson (Siganidae) collected off the coasts of Australia, New Caledonia, French Polynesia and Palau were infected with species of Sclerocollum Schmidt & Paperna, 1978 (Acanthocephala: Cavisomidae). A Principal Component Analysis (PCA) and a Discriminant Analysis were performed on a morphometric dataset of specimens of Sclerocollum including borrowed type-specimens of Sc. rubrimaris Schmidt & Paperna, 1978 from the Indian Ocean and of Sc. robustum Edmonds, 1964, the only acanthocephalan species known previously from an Australian siganid. These analyses showed that the lengths of proboscis hooks were useful variables for separating specimens into groups and supported the presence of two known species (Sc. robustum and Sc. rubrimaris) and one new species (Sc. australis n. sp.) in Australian waters. We found Sc. robustum in Siganus lineatus (Valenciennes) from off Queensland and Sc. rubrimaris in S. fuscescens (Houttuyn) from off Western Australia and Queensland, S. punctatissimus Fowler & Bean from off Queensland and S. argenteus (Quoy & Gaimard), S. corallinus (Valenciennes), S. canaliculatus (Park) and S. doliatus Guérin-Méneville from off New Caledonia (all new host and locality records) which we compared with museum specimens of Sc. rubrimaris from S. rivulatus Forsskål & Niebuhr and S. argenteus [as S. rostratus (Valenciennes)] from the Red Sea. The third species, Sclerocollum australis n. sp., was found only in S. corallinus and S. doliatus from off Queensland. Sclerocollum australis n. sp. can be distinguished from its congeners by a unique combination of characters of the proboscis armature, including lengths of hooks 1-7. Specimens of Sclerocollum were also found in Zebrasoma velifer (Bloch) (Acanthuridae) from off Queensland, and Coradion altivelis McCulloch (Chaetodontidae) and Heniochus acuminatus (Linnaeus) (Chaetodontidae) from off New Caledonia. No acanthocephalans were found in siganids collected from Palau (Micronesia) or Moorea (French Polynesia) or Moreton Bay and Noosa (Queensland, Australia). We found no acanthocephalans in S. puellus (Schlegel), S. punctatus (Schneider & Forster), S. spinus (Linnaeus) or S. vulpinus (Schlegel & Müller). Evidence suggests that species of the genus Sclerocollum have travelled with S. argenteus across the Indo-Pacific with Sc. rubrimaris dispersed widely and Sc. robustum and Sc. australis n. sp. restricted to the Queensland coast, Australia.