Ecology of Gordian knots in natural conditions

AbstractThe ecology of “Gordian knots” – aggregates of entwined reproductive individuals of nematomorphs, or hair worms – remains poorly understood. We studied the ecology of Gordian knots in a wild population of the hair worm Paragordius tricuspidatus sampled from a stream near Montpellier, France, in 2005 and 2006. At our study site, knots were composed entirely of males. The number of adults per knot varied throughout the summer, most likely due to the seasonal decrease in stream water level and the appearance of females later in the season. The average length of individual worms in each knot did not change significantly over time, but it became significantly more variable. We also showed that knots within these streams were more likely to be attached to floating rather than immobile substrates. Because the water levels in our sampling stream decrease as the season progresses, males in knots attached to floating substrates could be in a better position to cope with decreasing water levels, as they always remain immersed. An important avenue of future study would be to explore the effects of varying water level and the presence of females on the size and maintenance of knots in laboratory conditions.