Inviability of Interspecific Hybrids in the Coelomomyces dodgei Complex

Abstract

Studies of experimentally produced hybrids of Coelomomyces dodgei and C. punctatus demonstrate that all stages of the F1 sporophytic phase are functional but that the F1 gametophyte is inviable. Hybrid zygotes formed in reciprocal crosses of gametes of these species are infective for mosquito larvae within which they form viable sporophytes and resting sporangia. The surface structure of these sporangia, as well as the cleavage and dehiscence patterns, are similar to those of the parental species. Additionally, meiospores produced by hybrid sporangia appear normal in that they are highly motile and capable of recognizing and encysting upon the alternate copepod host, Cyclops vernalis. However, in contrast to parental species, encystment does not result in production of a functional gametophyte. These results provide substantial evidence that C. dodgei and C. punctatus, though closely related, are reproductively isolated and, therefore, are distinct and valid species. The possible use of experimental hybrids to study the systematics of other species and varieties of the genus Coelomomyces is discussed.