Nematophagous fungi from the maritime antarctic: factors affecting distribution

Abstract

Soil collected from throughout the maritime Antarctic was analyzed to determine the effects of a range of abiotic and biotic soil parameters on the distribution of nematophagous fungi. Endoparasites were far more abundant than predatory fungi due to the greater efficiency of endoparasites in attracting and infecting nematodes, which resulted in a rapid completion of the infection cycle. This allowed endoparasites to colonise even the most exposed soil habitats where conditions favourable for nematode activity were restricted to only a few hours daily. 76% of all endoparasites isolated formed adhesive conidia. The success of this group of endoparasites was due to the ability of the conidia to attract nematodes. Spontaneous trap forming predators were far more abundant than nonspontaneous trap formers. The former have a clear competitive advantage over the latter, as they are able to attract nematodes to the conidia which subsequently germinate and form traps only when induced by direct chemical stimulation of nematodes. These predators are able to use internal reserves only and so rapidly respond to short periods when the soil is unfrozen and the nematodes are active. Although nematodes were utilized by all the species isolated, many were also capable of using Protozoa and Rotifera as a food source. While endoparasites were capable of infecting Rotifera, they were never observed infecting, or were isolated from soil containing, Protozoa. The distribution of endoparasites and spontaneous trap forming predators was largely independent of abiotic soil parameters. They were however significantly associated with the presence and abundance of suitable prey. These species survive solely on nematodes and therefore do not require prolonged periods of suitable soil conditions in order to produce vegetative mycelium to adsorb nutrients saprophytically from the soil, which is a significant ecological advantage over the other groups of microfungi found in the Antarctic.