Reduced host-specificity in a parasite infecting non-littoral Lake Tanganyika cichlids evidenced by intraspecific morphological and genetic diversity.

Nikol Kmentová,Milan Gelnar,Maarten Van Steenberge,Monika Mendlová,Maarten P M Vanhove,Stephan Koblmüller

doi:10.1038/srep39605

Abstract

Lake Tanganyika is well-known for its high species-richness and rapid radiation processes. Its assemblage of cichlid fishes recently gained momentum as a framework to study parasite ecology and evolution. It offers a rare chance to investigate the influence of a deepwater lifestyle in a freshwater fish-parasite system. Our study represents the first investigation of parasite intraspecific genetic structure related to host specificity in the lake. It focused on the monogenean flatworm Cichlidogyrus casuarinus infecting deepwater cichlids belonging to Bathybates and Hemibates. Morphological examination of C. casuarinus had previously suggested a broad host range, while the lake’s other Cichlidogyrus species are usually host specific. However, ongoing speciation or cryptic diversity could not be excluded. To distinguish between these hypotheses, we analysed intraspecific diversity of C. casuarinus. Monogeneans from nearly all representatives of the host genera were examined using morphometrics, geomorphometrics and genetics. We confirmed the low host-specificity of C. casuarinus based on morphology and nuclear DNA. Yet, intraspecific variation of sclerotized structures was observed. Nevertheless, the highly variable mitochondrial DNA indicated recent population expansion, but no ongoing parasite speciation, confirming, for the first time in freshwater, reduced parasite host specificity in the deepwater realm, probably an adaptation to low host availability.

Highlights

Host specificity is one of the basic biological factors influencing the life cycle and diversity of parasitic organisms[1]
The Cichlidogyrus host-specificity in the deepwater habitat in Lake Tanganyika is tested for all fish hosts within the presumed host range of C. casuarinus, potentially the first intermediate generalist of Cichlidogyrus reported for Lake Tanganyika, on a lake-wide geographical scale
764 Cichlidogyrus specimens were retrieved and identified from 24 fish specimens belonging to six host species, namely B. leo Poll, 1956, B. minor Boulenger, 1906, B. horni Steindachner, 1911, B. vittatus Boulenger, 1914, B. fasciatus Boulenger, 1901 and H. stenosoma (Boulenger, 1901), making use of fresh material from an expedition in 2013 and of the historical ichthyological collections of the Royal Museum for Central Africa (Tervuren, Belgium) (Fig. 1; Table 2)

Summary

Introduction

Host specificity is one of the basic biological factors influencing the life cycle and diversity of parasitic organisms[1]. Lake Tanganyika, situated in the East African Rift Valley, is the second deepest and second oldest lake in the world It is known for its remarkable species diversity characterised by rapid radiation processes in many vertebrate and invertebrate taxa[7], including parasitic flatworms that infect cichlids[8]. 24 species of Cichlidogyrus have been described from 20 different cichlid host species from Lake Tanganyika[10,11,12,13,14,15,18] Three of these have been reported from the benthopelagic and truly pelagic deepwater environment: Cichlidogyrus brunnensis, C. attenboroughi Kmentová, Gelnar, Koblmüller & Vanhove, 2016 and C. casuarinus Pariselle, Muterezi Bukinga & Vanhove, 2015. Multivariate statistic approaches of morphological characters and genetic characterisation using markers with different rates of molecular evolution were used to answer the following questions:

Objectives

Methods

Results

Conclusion