Observations on relationships between infective juveniles of bovine lungworm, Dictyocaulus viviparus (Nematoda: Strongylida) and the fungi, Pilobolus kleinii and P. crystallinus (Zygomycotina: Zygomycetes)

Abstract

SUMMARYInfective 3rd-stage larvae of Dictyocaulus viviparus were filmed whilst climbing sporangiophores of the coprophilous fungus, Pilobolus and invading sporangia in numbers up to about 50, shortly before the sporangia were explosively discharged. Like the sporangiophores of Pilobolus the nematodes reacted positively towards light. Robinson (1962) demonstrated the spectacular way in which D. viviparus can be dispersed by Pilobolus, although he saw the nematodes accumulating only on top of the sporangia. Hazards including desiccation would offset the advantage of dispersal unless protection is somehow provided. Free D. viviparus larvae are susceptible to desiccation and discharged sporangia appear to dry quickly, so what protection, if any, operates? Several other nematodes that are susceptible to desiccation survive because structures surrounding them dry quickly (for example, an ensheathing cuticle, egg-shell, gelatinous ‘egg-sac’ matrix) and in doing so form barriers which limit the rate of water loss from the nematode within. Such dried sporangia of Pilobolus could aid survival of the ensheathed D. viviparus larvae inside them by retarding desiccation of the nematodes, in much the same way that within cysts of Globodera and Heterodera spp. the cyst wall, egg matrix and outer eggs protect the inner eggs by reducing the rate, if not the extent, of water loss. The sporangium wall may also protect the nematodes from harmful ultraviolet irradiation and from being washed by rain into less advantageous situations.