A cox2 phylogeny of representative marine Peronosporomycetes (Oomycetes) Lagenidium and Haliphthoraceae
The Peronosporomycetes (Oomycetes) are a phylum of fungal-like protists included within the newly erected kingdom Stramenopila. Included among the more than 65 recognized genera are a diverse array of animal and plant pathogens responsible for significant economic damage in both aquaculture and agriculture. In an attempt to uncover the evolutionary relationships within the Peronosporomycetes, we have been generating a cox2 molecular phylogeny. This present study addresses two questions regarding the phylogeny of some of the diverse invertebrate parasitic genera. The first of these involves the genus Lagenidium (Order Lagenidiales). The ecological separation of this genus is polyphyletic with the marine representatives as members of the subclass Saprolegniomycetidae, and the terrestrial representatives as members of the subclass Peronosporomycetidae. cox2 data from 23 peronosporomycete taxa, including three marine (isolates from crabs and shrimp) and three terrestrial (isolates from soil, mosquito, and nematode) species of Lagenidium were analyzed using maximum parsimony and maximum likelihood methods. Analyses of the data set lend support for not only monophyly within the genus, but also for the placement of Lagenidium sp. within the order Pythiales and the subsequent elimination of the order Lagenidiales. The second question addresses the controversial taxonomic position of another group of marine invertebrate pathogens? the family Haliphthoraceae. This family has historically been most frequently allied with marine members of the Lagenidiales. With the demise of the Lagenidiales and the established monophyly of marine and terrestrial members of the genus Lagenidium, the phylogenetic relationship of the Haliphthoraceae becomes more obscure. We determined the cox2 sequence from four taxa within this family and analyzed the data as part of the Peronosporomycete data set. The analyses of the cox2 data from Halocrusticida (isolate from crab) and two Haliphthorus species (isolates from crab and prawn) placed these genera in a single clade basal to the separation of all other taxa into subclasses. However, Atkinsiella (isolate from abalone), another purported member of the Haliphthoraceae, was included within the subclass Saprolegniomycetidae.