Phylogenetic Relationships of Cardiocephaloides spp. (Digenea, Diplostomoidea) and the Genetic Characterization of Cardiocephaloides physalis from Magellanic Penguin, Spheniscus magellanicus, in Chile



Cardiocephaloides is a small genus of strigeid digeneans with an essentially cosmopolitan distribution. Most members of Cardiocephaloides are found in larid birds, however, Cardiocephaloides physalis is an exception and parasitizes penguins in some coastal regions of South America and South Africa. No prior molecular phylogenetic studies have included DNA sequence data of C. physalis. Herein, we provide molecular phylogenetic analyses of Cardiocephaloides using DNA sequences from five species of these strigeids.


Adult Cardiocephaloides spp. were obtained from larid birds and penguins collected from 3 biogeographical realms (Palearctic, Nearctic and Neotropics). We have generated sequences of the complete ITS region and partial 28S gene of the nuclear ribosomal DNA, along with partial sequences of the mitochondrial CO1 gene for C. physalis, C. medioconiger and the type species of the genus, C. longicollis and used them for phylogenetic inference.


Cardiocephaloides spp. appeared as a 100% supported clade in the phylogenetic tree based on 28S sequences. The position of C. physalis varied between the phylogenetic trees based on the relatively conservative 28S gene on one hand, and variable ITS1 and COI sequences on the other. Cardiocephaloides physalis was nested within the clade of Cardiocephaloides spp. in the 28S tree and appeared as the sister group to the remaining members of the genus in the ITS1 region and COI trees. We detected 0.4–1.6% interspecific divergence in 28S, 1.9–6.9% in the ITS region and 8.7–11.8% in CO1 sequences of Cardiocephaloides spp. Our 28S sequence of C. physalis from South America and a shorter sequence from Africa available in the GenBank were identical.


Cardiocephaloides as represented in the currently available dataset is monophyletic with C. physalis parasitism in penguins likely resulting from a secondary host-switching event. Identical 28S sequences of C. physalis from South America and Africa cautiously confirm the broad distribution of this species, although comparison of faster mutating genes (e. g., CO1) is recommended for a better substantiated conclusion.

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Laboratory processing of specimens was supported by the Joe K. Neel Memorial Award and a research stipend from the Department of Biology, University of North Dakota to TJA. DGA thanks Roberto Fernández and Alejandra Silva from CONAF—Punta Arenas for their support of the studies investigation on the Magdalena Island.

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Correspondence to Vasyl V. Tkach.

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Achatz, T.J., Pulis, E.E., González-Acuña, D. et al. Phylogenetic Relationships of Cardiocephaloides spp. (Digenea, Diplostomoidea) and the Genetic Characterization of Cardiocephaloides physalis from Magellanic Penguin, Spheniscus magellanicus, in Chile. Acta Parasit. 65, 525–534 (2020).

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  • Strigeidae
  • Cardiocephaloides
  • Molecular phylogeny
  • Penguins