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. 2024 May;151(6):626-633.
doi: 10.1017/S0031182024000593. Epub 2024 May 9.

Distinct evolutionary lineages of Schistocephalus parasites infecting co-occurring sculpin and stickleback fishes in Alaska

David C Heins  1 , Kristine N Moody  1   2   3 , Martin C Arostegui  4   5 , Brian S Harmon  5 , Michael J Blum  1   3 , Thomas P Quinn  5
Affiliations

Distinct evolutionary lineages of Schistocephalus parasites infecting co-occurring sculpin and stickleback fishes in Alaska

David C Heins et al. Parasitology. 2024 May.

Abstract

Sculpins (coastrange and slimy) and sticklebacks (ninespine and threespine) are widely distributed fishes cohabiting 2 south-central Alaskan lakes (Aleknagik and Iliamna), and all these species are parasitized by cryptic diphyllobothriidean cestodes in the genus Schistocephalus. The goal of this investigation was to test for host-specific parasitic relationships between sculpins and sticklebacks based upon morphological traits (segment counts) and sequence variation across the NADH1 gene. A total of 446 plerocercoids was examined. Large, significant differences in mean segment counts were found between cestodes in sculpin (mean = 112; standard deviation [s.d.] = 15) and stickleback (mean = 86; s.d. = 9) hosts within and between lakes. Nucleotide sequence divergence between parasites from sculpin and stickleback hosts was 20.5%, and Bayesian phylogenetic analysis recovered 2 well-supported clades of cestodes reflecting intermediate host family (i.e. sculpin, Cottidae vs stickleback, Gasterosteidae). Our findings point to the presence of a distinct lineage of cryptic Schistocephalus in sculpins from Aleknagik and Iliamna lakes that warrants further investigation to determine appropriate evolutionary and taxonomic recognition.

Keywords: Diphyllobothriidea; cryptic species; molecular phylogeny; parasite; sculpin; stickleback; trophic transmission.

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Conflict of interest statement

None.

Figures

None
Graphical abstract
Figure 1.
Figure 1.
Number of segments per Schistocephalus parasite by host fish species. Within panels, the lake-specific data are presented as colour-coded, overlapping distributions (lighter shade – Iliamna; darker shade – Aleknagik; intermediate shade – overlap) with their corresponding probability density functions. Coastrange sculpins with parasites were only collected at Iliamna Lake.
Figure 2.
Figure 2.
Bayesian tree (scale bar: 0.02 estimated substitutions per site) of Schistocephalus parasites sequenced with partial NADH1 gene from their respective host fish species: Cottus cognatus parasites (n = 20), light blue; Cottus aleuticus parasites (n = 33), dark blue; Gasterosteus aculeatus parasites (n = 20), dark green and Pungitius pungitius parasites (n = 4), light green. * denotes corresponding segment counts were obtained from the individual; # denotes Pusa hispida botnica host. Fishes and parasites are not drawn to scale.
See this image and copyright information in PMC

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