Uneven distribution of cryptic diversity among higher taxa of parasitic worms

Abstract

Cryptic species cause problems for estimates of biodiversity. In the case of parasites, cryptic species also plague efforts to detect potential zoonotic diseases or invasive pathogens. It is crucial to determine whether the likelihood of finding cryptic species differs among higher parasite taxa, to better calibrate estimates of diversity and monitor diseases. Using published reports of cryptic species of helminth parasites identified using molecular tools, I show that the number of species found is strongly related to the number of parasite individuals sequenced, weakly influenced by the number of host species from which parasites were obtained, and unaffected by the genetic markers used. After correction for these factors, more cryptic species of trematodes are found than in other helminth taxa. Although several features distinguish trematodes from other helminths, it is probable that our inability to discriminate among sibling species of trematodes results from their lack of structures serving as species-specific morphological markers. The available data suggest that current estimates of helminth diversity may need to be doubled (tripled for trematodes) to better reflect extant diversity.

An updated look at the uneven distribution of cryptic diversity among parasitic helminths

“…This suggests an uneven distribution of cryptic diversity among higher taxa. A few years ago, Poulin (2011) reported a similar uneven distribution among higher groups of parasitic helminths. Specifically, after correcting for sampling effort (i.e.…”

“…A few years ago, Poulin (2011) reported that more cryptic species were uncovered among trematodes than other helminth groups when controlling for the number of DNA sequences obtained per study. Here, using a much larger dataset, we generally confirmed this earlier finding.…”

“…Also, the number of markers, the number of sequences and the number of base pairs generally correlate positively with each other across studies, for both mitochondrial and nuclear genes (see Poulin & Pérez-Ponce de León, 2017). Therefore, we use only the number of sequences to control for study effort in subsequent analyses, since the number of cryptic species found tends to increase with the level of effort put into their search (Poulin, 2011).…”

“…Here, we re-visit Poulin's (2011) observation that cryptic species are more common among trematodes than other helminths, using an expanded dataset including almost three times more studies than the 33 that were available for Poulin's (2011) analysis. Our results confirm that, all else being equal, more cryptic species tend to be found per study effort among trematodes than other groups of parasitic helminths, an intriguing pattern for which we propose some explanations.…”

Diversity, specificity and speciation in larval Diplostomidae (Platyhelminthes: Digenea) in the eyes of freshwater fish, as revealed by DNA barcodes

“…Unrecognised diversity is routinely encountered in molecular surveys of digeneans (Poulin, 2011) and some lag can be expected between the genetic detection and identification, description or characterisation of putative species with other methods. Furthermore, provisional species delineations can be valuable.…”