Quantitative assessment of spicule length in Heligmosomoides spp. (Nematoda, Heligmosomidae): distinction between H. bakeri, H. polygyrus and H. glareoli

Nematode spicules play a vital role in the reproductive activity of species that possess them. Our primary objective was to compare the lengths of spicules of the laboratory mouse (Mus musculus) - maintained isolate H. bakeri - with those of H. polygyrus from naturally infected wood mice (Apodemus sylvaticus). On a more limited scale, we also included H. glareoli from bank voles (Myodes glareolus), a species reputed to possess longer spicules than either of the 2 former species. In total, we measured 1264 spicules (H. bakeri, n = 614; H. polygyrus n = 582; and H. glareoli, n = 68). There was a highly significant difference between the spicule lengths of the Nottingham-maintained H. bakeri (mean = 0.518 mm) and H. polygyrus (0.598 mm) from 11 different localities across the British Isles. A comparison of the spicules of H. bakeri maintained in 4 different laboratories in 3 continents revealed a range in the mean values from 0.518 to 0.540 mm, while those of worms from Australian wild house mice were shorter (0.480 mm). Mean values for H. polygyrus from wood mice from the British Isles ranged from 0.564 to 0.635 mm, although isolates of this species from Norway had longer spicules (0.670 mm). In agreement with the literature, the spicules of H. glareoli were considerably longer (1.098 mm). Since spicules play a vital role in the reproduction of nematode species that possess them, the difference in spicule lengths between H. bakeri and H. polygyrus adds to the growing evidence that these 2 are quite distinct species and likely reproductively isolated.