Assessing the genetic diversity of the metacercariae of Posthodiplostomum minimum (Trematoda: Diplostomidae) in Middle American freshwater fishes: one species or more?

Abstract

Trematode taxonomy is mainly based on the morphological traits of adults. The identification of metacercariae is challenging because such traits are not developed in larval forms, and they even may show some level of morphological variability. Studies testing the potential correspondence between morphological differences and genetic variation of parasites are still lacking. The metacercariae of Posthodiplostomum minimum are probably the diplostomids more widely distributed in North and Middle American freshwater fish, and their intraspecific morphological variability has been attributed to the effect exerted by the host. Here, we tested the hypothesis whether they represent a single species, or a species complex by assessing the genetic divergence and phylogenetic relationships of metacercariae sampled from several host species in a wide geographical range across Middle America. The internal transcribed spacers (ITS1-5.8S-ITS2), and the mitochondrial COI gene were sequenced for 124 and 55 metacercariae, respectively. Phylogenetic analysis inferred from ITS sequences uncovered six well-supported monophyletic lineages. The six lineages show no correspondence to any Posthodiplostomum species for which sequences are available thus far in GenBank. Lineages exhibit some degree of host specificity; Lineages I, II, IV and V are primarily parasites of cyprinodontiforms of the families Poeciliidae, Goodeidae, Profundulidae and Fundulidae. In poeciliids there are at least four candidate species of Posthodiplostomum, some of them occurring in sympatry; instead, Lineages II and VI are exclusively parasites of cichlids. This study contributes to our understanding of the diversity of larval forms of diplostomids and provides an opportunity to further study their life cycles.

First integrative study of the diversity and specificity of metacercariae of Posthodiplostomum Dubois, 1936 from native and introduced fishes in the Caribbean

“…Pérez-Ponce de León et al . (2022) sequenced CO1 in metacercariae of Posthodiplostomum in a wide range of fishes across Central America and obtained results highly relevant to the present study. However, sequences of DNA from Posthodiplostomum in the study by Pérez-Ponce de León et al .…”

“…In Central America, however, the metacercariae of most lineages of Posthodiplostomum surveyed by Pérez-Ponce de León et al . (2022) were found in multiple families of fish, suggesting patterns of host specificity initially observed in temperate regions may not generalize to tropical regions. The sequences from the extensive survey of Posthodiplostomum in Central America by Pérez-Ponce de León et al .…”

“…Over the last decade, molecular studies have revealed novel species diversity and linked unknown larvae with identified adults in Posthodiplostomum (Locke et al ., 2010; Nguyen et al ., 2012; Stoyanov et al ., 2017; Boone et al ., 2018; López-Hernández et al ., 2018; Pérez-Ponce de León et al ., 2022). Several studies also demonstrated a need for revision in Posthodiplostomum and related genera (Blasco-Costa and Locke, 2017; López-Hernández et al ., 2018; Achatz et al ., 2019), culminating in the recent work of Achatz et al .…”

“…Moreover, from the relatively few sequences sampled outside the Nearctic and Palaearctic regions (238/838), most (143) originate in a single recent study by Pérez-Ponce de León et al . (2022), 1 of only 3 with data from the Neotropics. This unbalanced sampling effort is particularly noteworthy because the diversity of fish and bird hosts is higher in Neotropic and Afrotropic regions compared to regions further north (Balian et al ., 2008), which suggests that parasite diversity is also higher.…”

“…The sequences from the extensive survey of Posthodiplostomum in Central America by Pérez-Ponce de León et al . (2022) have yet to be compared with those of Achatz et al . (2021), who sequenced adults across the Americas, partly because both studies were published nearly simultaneously.…”