Revisiting the diversity of freshwater fish trematode metacercariae in cenotes (sinkholes) of Yucatán: molecular characterisation and comments on their phylogenetic interrelationships

Abstract

Abstract The limestone soil of the Yucatán Peninsula is highly permeable, allowing fluvial waters to filter into the aquifer, resulting in the absence of rivers on the surface and the formation of underground reservoirs that, on some occasions, open to the surface, forming the so-called cenotes (or sinkholes). Information about the freshwater fish parasite diversity of cenotes in the Yucatán Peninsula is scarce. Only 50 cenotes of the approximately 9,000 occurring in the peninsula have been sampled to assess the fish parasite fauna. Available information predates the molecular era and is based on morphological assessments solely. Here, specimens of 7 fish species were sampled in 15 localities distributed along an area known as the ‘Ring of Cenotes’, a depression associated with the Chicxulub crater formed by the impact of a meteorite. Trematode metacercariae were collected, sorted by morphotype, and sequenced for the partial 28S rRNA and/or COI mtDNA genes. Twelve trematode metacercariae were identified, seven to species level and five to genus or family level, since they did not match any known sequenced species available in the BLAST search. Metacercariae corresponded to three families; Diplostomidae was the most diverse with eight taxa. The cichlid Mayaheros urophthalmus harboured the greatest number of taxa, with nine. Three species of Clinostomum were identified molecularly in what previous findings considered a single species on morphological grounds. The importance of continually expanding the genetic library of larval trematodes and establishing links between adults and larval forms to fully assess and understand trematode diversity is discussed.