Biology of acanthocephalan Acanthocephalus anguillae in subterranean habitats

Benko, Grega (author), Kostanjšek, Rok (mentor)

The trophically transmitted acanthocephalan Acanthocephalus anguillae typically cycles between waterlice (Asellus aquaticus) and freshwater fishes. Its presence in the Postojna–Planina Cave System (PPCS), where it infests cave-dwelling waterlice and the olm (Proteus anguinus), provides an exceptional opportunity to explore the ecological flexibility of this parasite while simultaneously raising important conservation considerations. This thesis applied an integrative approach combining parasitological examination of olm collection specimens, assessment of parasite gravidity, molecular analyses, behavioural experiments, and histological examinations. Systematic examination of olms collected between 1968 and 2022 revealed A. anguillae only in PPCS, with records beginning in 1994. The survey also provided the first confirmation of Pomphorhynchus sp. in olms, which predominated prior to the emergence of A. anguillae. Gravidity assessment revealed contrasting evidence of host suitability: while many parasites were extraintestinal and degraded, gravid females were found in recent specimens, indicating that the olm is a partially compatible host capable of supporting parasite reproduction. Genetic analyses showed substantial gene flow between cave and nearby surface populations of A. anguillae, supporting ongoing connectivity rather than long-term isolation. Behavioural experiments detected no novel manipulation of waterlice by A. anguillae adapted to subterranean conditions, as the reduction in photophobia persisted. Histological analyses revealed typical acanthocephalan-induced intestinal lesions in olms, although their impact on host health remains uncertain. Overall, A. anguillae represents a new population in PPCS sustained by surface influx. It appears to have recently gained the ability to reproduce in a cave definitive host, while its manipulation strategies in the intermediate host remain unadapted to subterranean conditions. Severe inflammatory responses and potential sublethal effects highlight the need for continued health monitoring of olm populations and their parasites.

• Language: English
• Keywords: parasite infestation, olm, subterranean environment, waterlice, ecological flexibility, behavioural manipulation, helminths, conservation biology
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: BF - Biotechnical Faculty
• Publisher: [G. Benko]
• Year: 2025
• PID: 20.500.12556/RUL-178243
• UDC: 595.151:551.44(043.3)
• COBISS.SI-ID: 266027267
• Publication date in RUL: 22.01.2026

Secondary language

• Language: Slovenian
• Title: Biologija ježerilca Acanthocephalus anguillae v podzemnih habitatih

Abstract

Ježerilec vrste Acanthocephalus anguillae običajno kroži med vodnimi oslički (Asellus aquaticus) in sladkovodnimi ribami. Njegova prisotnost v Postojnsko-planinskem jamskem sistemu (PPJS), kjer parazitira jamsko populacijo vodnih osličkov in močerila (Proteus anguinus), predstavlja edinstveno priložnost za preučevanje ekološke prilagodljivosti parazita in odpira pomembna naravovarstvena vprašanja. V doktorski nalogi je bil uporabljen celovit pristop, ki je združeval parazitološki pregled arhivske zbirke močerilov, oceno gravidnosti parazitov, molekularne analize parazita, vedenjske eksperimente in histopatološko analizo črevesa. Sistematični pregled močerilov zbranih med letoma 1968 in 2022, je prisotnost A. anguillae potrdil le v PPJS s prvimi zaznanimi pojavnostmi iz leta 1994. Pred tem je prevladovala okužba z ježerilcem iz rodu Pomphorhynchus, katerega prisotnost je bila v tej nalogi prvič potrjena. Ocena gravidnosti je potrdila prisotnost gravidnih samic A. anguillae v močerilih, kar kljub degradiranim primerkom izven črevesja kaže na primernost močerila kot končnega gostitelja. Genetske analize so pokazale znaten genetski pretok med jamsko in okoliškimi površinskimi populacijami A. anguillae, kar potrjuje povezanost in izključuje dolgotrajno izolacijo v podzemlju. Vedenjski poskusi niso pokazali novih ali okoljsko prilagojenih strategij manipulacije vmesnega gostitelja. Zmanjšanje fotofobije, kot ključne strategije manipulacije v površinskih vodah, se je namreč ohranilo tudi v jamskem okolju. Histopatološke spremembe črevesnega tkiva močerilov s pritjenimi paraziti so pokazale tipične lezije značilne za okužbe z ježerilci, medtem ko njihov vpliv na splošno stanje gostitelja ostaja negotov. A. anguillae predstavlja novo populacijo v PPJS, ki jo vzdržuje dotok jajčec s površja. Rezultati doktorske naloge kažejo, da je vrsta pridobila sposobnost spolnega razmnoževanja v jamskem gostitelju šele nedavno, medtem ko njene manipulacijske strategije v vmesnem gostitelju ostajajo neprilagojene podzemnemu okolju. Izrazit vnetni odziv in možni subletalni učinki poudarjajo potrebo po nadaljnjem spremljanju stanja populacij močerilov in njihovih parazitov.

• Keywords: parazitske okužbe, močeril, vodni osliček, podzemno okolje, ekološke prilagoditve, manipulacije vedenja, helminti, varstvena biologija