Freshwater lymnaeid snails are crucial in defining transmission and epidemiology of fascioliasis. In South America, human endemic areas are related to high altitudes in Andean regions. The species
Lymnaea diaphana
has, however, been involved in low altitude areas of Chile, Argentina and Peru where human infection also occurs. Complete
nuclear ribosomal DNA 18S, internal transcribed spacer (ITS)-2 and ITS-1 and fragments of mitochondrial DNA
16S and
cytochrome c oxidase (cox)1 genes of
L. diaphana specimens from its type locality offered 1,848, 495, 520,
424 and 672 bp long sequences. Comparisons with New and Old World Galba/Fossaria, Palaearctic stagnicolines,
Nearctic stagnicolines, Old World
Radix and
Pseudosuccinea allowed to conclude that (i)
L. diaphana shows sequences
very different from all other lymnaeids, (ii) each marker allows its differentiation, except
cox1 amino acid
sequence, and (iii)
L. diaphana is not a fossarine lymnaeid, but rather an archaic relict form derived from the oldest North American stagnicoline ancestors. Phylogeny and large genetic distances support the genus
Pectinidens
as the
first stagnicoline representative in the southern hemisphere, including colonization of extreme world regions, as
most southern Patagonia, long time ago. The phylogenetic link of
L. diaphana with the stagnicoline group may give
light to the aforementioned peculiar low altitude epidemiological scenario of fascioliasis.
