Morphological and Molecular Phylogenetic Characterization of Sp. Nov. and Other Novel, Closely Related Spp. Infecting Small Mammals and Colubrid Snakes in Asia

We investigated the morphology and phylogenetic relationships of novel and previously recognized spp. infecting small mammals and colubrid snakes in Asia. The nuclear and mitochondrial of sp.1 from mangrove snakes () in Thailand and sp.2 from a ricefield rat () in Sumatra were partially sequenced. Sporocysts of sp.1 induced development of sarcocysts in experimentally infected rats, which showed a unique ultrastructure that was observed previously by S.P. Kan in rats from Malaysia; therefore, we describe this species as sp. nov. Its integration into the phylogeny of spp. cycling between small mammals and colubrid snakes helped clarify relationships among the so-called . -complex of molecularly cryptic species: sp. nov., . sp.2, . , . , and . were all included in this clade. Tree topology was resolved into dichotomies congruent with the morphological disparities between the taxa. However, gene sequencing (including newly sequenced . and . ) revealed that , . , and . were identical suggesting a recent, common ancestry. To identify other distinctive features, lineage-specific molecular patterns within both genes were examined revealing that all sequences of the . - complex possess a unique, 7-nt long motif in helix 38 of domain V7 that was different in . which branched off basally from the complex. Three-dimensional homology modelling of COX1 protein structure identified amino acid substitutions within the barcode area specific for the -complex and substantial divergence in structurally important amino acids between species of snakes as definitive hosts and other lineages of the Sarcocystidae. We discuss the utility of selected genes for species delimitation of the spp. under investigation, which probably evolved during recent radiations of their intermediate and definitive hosts.