Integrated taxonomic studies highlight the virus vector family Trichodoridae as a source of many unknown cryptic species in Spain

Abstract

The polyphagous root ectoparasitic family Trichodoridae occurs worldwide. Its major pest status is as vector of Tobraviruses, especially in the didelphic genera Paratrichodorus and Nanidorus, with 27% and 28.6% of vector species, respectively. Current study focused on the biodiversity of Paratrichodorus from southern Spain. Identification of Paratrichodorus species is hampered even more than in Trichodorus, by their largely conserved morphology and restricted number of diagnostic morphological features, overlap of morphometrics, difficulty to fix specimens properly and co-occurrence of at least two species in the same soil sample, often with a restricted number of specimens. Molecular analyses based on nuclear ribosomal RNA genes (D2-D3 expansion segments of 28S and partial 18S gene) clearly directs the comparative morphological study while the morphology and morphometrics helps the molecular research to interpret the results when dealing with co-occurrence of several species. Surveys for trichodorids were carried out in cultivated and natural habitats in southern Spain. The integrative taxonomic approach revealed several new species belonging to two main clades: (1) a P. hispanus related group, characterized in male by large sperm cells with sausage-shaped nucleus and spicules with undulating outline of anterior blade part, and (2) a P. allius related group with small sperm and nucleus and about straight spicules with finely striated blade. The first group is common within the Iberian Peninsula, while the second group of species occurs in general in warmer (Mediterranean) to subtropical climates. This study strengthens the need for integrative taxonomy in this group of nematodes because of their high molecular biodiversity and similar morphology and morphometrics with examples of cryptic diversity.