Revealing Cryptic Parasite Diversity in a Definitive Host: Echinostomes in Muskrats

Abstract

Many trematode groups have a long history of systematic revision, which can make parasite identification a difficult task. The trematode parasites of muskrats are no exception. Here, we highlight the systematic issues associated with trematodes of muskrats (Ondatra zibethicus). Then, we demonstrate the utility of using both morphological and molecular tools to identify these parasites. Morphological examinations of specimens from muskrats (n = 63) first suggested that at least 4 genera were present including Echinostoma, Wardius, Quinqueserialis, and Notocotylus. For the latter 3 groups, the 28S region verified this assessment. For echinostomes, ND1 sequences revealed at least 5 genetic lineages. A particular lineage, Echinostoma trivolvis lineage b, predominated in both prevalence and intensity of infection. Molecular sequences provided a more accurate estimate of echinostome diversity in the muskrats and further support the idea that E. trivolvis is a species complex. Future studies will focus on whether there are differences in host specificity among the E. trivolvis lineages. In addition, this study has provided initial sequences that will help verify the life cycles of Wardius, Quinqueserialis, and especially, Notocotylus. By linking molecular, morphological, and life history information, we can better understand parasite diversity.

Tegumental ultrastructure of adult Quinqueserialis quinqueserialis (Trematoda: Notocotylidae): an intestinal parasite of muskrat (Ondatra zibethicus)

“…No information is available on the pathogenicity of this parasite. Apart from the epidemiological and molecular findings on Notocotylidae members that have already been demonstrated by other researchers (Smith 1954;Beckett and Gallicchio 1967;Beverley-Burton and Sweeny 1972;Wittrock 1976;Shuteev 1977;Radlett 1980;MacKinnon 1982;Schuster 1986;Namue and Wongsawad 1997;Seegers et al 1997;Kinsella and Tkach 2005;Flores and Brugni 2003;Kirillova and Kirillov 2009;Birmani et al 2011;Chaisiri et al 2011;Yousif et al 2011;Boyce et al 2012;Detwiler et al 2012;Iwaki et al 2012;Skála et al 2014), there is a paucity of information on the morphology of Q. quinqueserialis using light and electron microscopy (Rausch 1952;Kinsella 1971;Beverley-Burton et al 1976;Wittrock 1986). For the first time, the present SEM study provides more details of this trematode, removed from the intestine of an infected muskrat.…”

Discovery-based studies of schistosome diversity stimulate new hypotheses about parasite biology

“…Also, in addition to containing the six described genera mentioned above, this tree highlights the presence of unnamed lineages that in our view are sufficiently distinct to represent about seven provisional new genera, potentially raising the number of generic level lineages within the family to 21 [11, 28, 29, 86]. The yardstick used to support these statements is to compare the extent of genetic differentiation among the new and well-defined genera with differences in sequence known to exist between genera that are well-established based on morphological and/or host use differences [11, 13, 28, 29, 32, 33, 82, 86, 87]. …”

History of echinostomes (Trematoda)

“…The phylogenetic trees from the ND1 data helped to clarify the genetic adscriptions of all isolates and confirmed the morphological identifications. Additionally, the most recent studies have evidenced the existence of "cryptic" species within the group that highlight the need for further analyses of patterns of interspecific variation based on molecular and morphological evidence (Detwiler et al, 2010(Detwiler et al, , 2012Georgieva et al, 2013).…”