Phylogenetic evidence for an ancestral coevolution between a major clade of coccidian parasites and elasmobranch hosts
Cartilaginous fishes are the oldest jawed vertebrates and are also reported to be the hosts of some of the most basal lineages of Cestoda and Aporocotylidae (Digenea) parasites. Recently a phylogenetic analysis of the coccidia (Apicomplexa) infecting marine vertebrates revealed that the lesser spotted dogfish harbours parasite lineages basal to Eimeria Schneider, 1875 and the group formed by Schellackia Reichenow, 1919, Lankesterella Ames, 1923, Caryospora Leger, 1904 and Isospora Schneider, 1881. In the present study we have found additional lineages of coccidian parasites infecting the cownose ray Rhinoptera bonasus Mitchill and the blue shark Prionace glauca Linnaeus. These lineages were also found as basal to species from the genera Lankesterella, Schellackia, Caryospora and Isospora infecting higher vertebrates. These results confirm previous phylogenetic assessments and suggest that these parasitic lineages first evolved in basal vertebrate hosts (i.e. Chondrichthyes), and that the more derived lineages infect higher vertebrates (e.g. birds and mammals) conforming to the evolution of their hosts. We hypothesise that elasmobranchs might host further ancestral parasite lineages harbouring unknown links of parasite evolution.
The authors would like to thanks David J. Harris for useful comments on the manuscript, and Jan R. McDowell for sharing cownose ray tissue samples.
This work was funded by FEDER funds through the Operational Programme for Competitiveness Factors - COMPETE and by National Funds through FCT - Foundation for Science and Technology under the project PTDC/MAR-BIO/0902/2014, PTDC/MAR-BIO/4458/2012 and POCI-01-0145-FEDER-016550, and partially funded by the Norte Portugal Regional Operational Programme (NORTE 2020) under the PORTUGAL 2020 Partnership Agreement under project MarInfo. RX and AV are supported by FCT under the Programa Operacional Potencial Humano - Quadro de Referência Estratégico Nacional from the European Social Fund and Portuguese Ministério da Educação e Ciência (RX: IF/00359/2015; AV post-doctoral Grant SFRH/BPD/77487/2011).
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Conflicts of interest
The authors declare that they have no conflict of interest.
All applicable institutional, national and international guidelines for the care and use of animals were followed.
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