FUNGI WITH HETEROXENOUS LIFE-HISTORIES

Heteroxenous (multiple host) life histories are characteristic of many groups of parasitic protista and animals, including Zoomastigina, Api complexa, Mesozoa, Platyhelminthes, Nematoda, Acanthocephala, Pentasto mida, and Arthropoda. Parasitic fungi, including the Chytridiomycota a nd the Dikaryomycota (ascomycetes and basidiomycetes), may also have h eteroxenous life histories and have many features in common with paras ites from other groups. In spite of many conceptual similarities, the study of parasitic fungi has occurred in isolation, resulting in the c reation of a separate vocabulary and literature. Many of the concepts developed by zoologists are useful to mycologists and allow examinatio n of parasitic fungi from new perspectives. These new perspectives rev eal that heteroxenous fungi are not only similar to heteroxenous proti stans and animals but that they also have unique characteristics of th eir own. Chief among these is a high level of endocyclic asexual repro duction, a phenomenon promoting exponential increases of infections in definitive host populations. Heteroxeny appears to have a number of b enefits including (i) increased lifetime reproductive success, (ii) in creased transmission efficiency (iii) enhanced effectiveness in coloni zing ephemeral or periodically appearing hosts and hosts occurring in low population densities, (iv) maintenance or enhancement of overdispe rsed frequency distributions in host populations, and (v) enhancement of genetic exchange through multiple dispersal events.