Understanding the phenotypic plasticity of Mesorchis uruguayensis (Holcman-Spector & Olagüe, 1989) Cajiao-Mora & Bullard, n. comb. (Digenea: Echinochasmidae), a parasite of aquatic birds from the Americas.

Authors

A G Islas-Ortega, M T González-García, Y Aldama-Prieto, M García-Varela

Published in

Journal of helminthology. Volume 100. Pages e88. Aug 12, 2026. Epub Aug 12, 2026.

Abstract

Phenotypic plasticity allows parasites to modify their morphology in response to the ecological and physiological conditions induced by their hosts. In digeneans with complex life cycles and multiple definitive hosts, host-induced variation may complicate species delimitation and taxonomic diagnoses. In this study, we characterised intraspecific morphological variation in Mesorchis uruguayensis (Digenea: Echinochasmidae), a trematode that parasitises fish-eating birds, using an integrative morphological approach. Thirty-eight adult specimens previously collected from five definitive host species in Mexico and molecularly identified as M. uruguayensis were examined. Scanning electron microscopy (SEM) was used to assess qualitative diagnostic traits, and principal component analysis (PCA) based on 19 linear measurements was used to explore morphometric variation among host-associated groups. All specimens retained the characteristic head collar with 22 spines, 10 small spines along the anterior margin of the oral sucker, and a consistent general pattern of tegumental spines. The first two principal components explained 80.9% of the total morphometric variation. However, the host-associated group overlapped substantially, with some differences. Body size, the dimensions of reproductive organs, and the ventral sucker contributed most strongly to this variation. Because all specimens were molecularly conspecific, these differences represent intraspecific morphological variation rather than species-level divergence. Host identity constitutes a biologically plausible source of this variation through differences in intestinal physiology, resource availability, and other host-associated conditions; however, geographic origin, parasite maturity, infection intensity, and individual host condition may also contribute. Our findings emphasise the value of combining stable qualitative characters, morphometric analyses, and molecular evidence to interpret morphological variability and avoid taxonomic misidentification in digeneans.

PMID:
42581534
Bibliographic data and abstract were imported from PubMed on 12 Aug 2026.

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