The mitochondrial genome of Unionicola foili is circular, 14,738 bp in length, and contains several notable features. The sequence and annotation revealed a unique gene order, continuing a pattern of highly rearranged mitochondrial genomes in the Trombidiformes. U. foili mitochondrial tRNA sequences predict non-canonical secondary structures for these molecules, and our annotation suggests an in-frame fusion between the nad4L and nad5 genes in this genome. The unique gene order and unusual tRNA structures could serve as idiosyncratic characters and have the potential to be phylogenetically informative.

This paper reports patterns of similarity and overlap in species presence and patterns of linear distribution of intestinal helminths in 22 avocets from 4 populations. Avocets collected from ephemeral bodies of water in Alberta and Manitoba had communities composed largely of species that are avocet specialists plus some that are host generalists. The composition of helminth communities in these hosts was similar to that reported in earlier surveys of avocet helminths. There was little evidence for competition between helminth species in these communities. In contrast, avocets collected from permanent bodies of water in Alberta had communities composed largely of species that are specialists in various duck species, particularly lesser scaup. These helminths were superimposed on the normal community, fitting into linear gaps along the intestine but also overlapping the distributions of avocet specialists. These lesser scaup specialists exhibit interactive patterns amongst themselves and, to some extent, with avocet specialists. Helminth communities in avocets from ephemeral bodies of water have vacant niches and are largely isolationist in nature. Those in avocets from permanent bodies of water are saturated and are more interactive in nature.

The mitochondrial genome of Unionicola parkeri is a 14,734 bp circular DNA molecule. The sequence and annotation revealed a unique gene order, related to but distinct from the gene order in the closely related species U. foili. Mitochondrial tRNA sequences annotated in this genome predict non-canonical secondary structures for these molecules. The continuing patterns of unique gene orders and unusual tRNA structures in the Trombidiformes in general and Unionicola in particular support the use of phylogenetic approaches that use these types of molecular features as shared, derived character states. Further progress in using these molecular character states to reconstruct phylogeny will depend on careful annotation, especially of tRNA genes.

Water mites of Unionicola spp. are common parasites of freshwater mussels as adults, living on the gills, or mantle and foot of their hosts and using these tissues as sites of oviposition. The present study addresses specialization among North American Unionicola mussel-mites using 2 measures of host specificity: (1) the number of host species used by a species of mite; and (2) a measure that considers the taxonomic distinctness of the hosts utilized by mites, weighted for their prevalence in the different hosts. Results of this study indicate the Unionicola spp. mussel-mites are highly host specific, with most species occurring in association with 1 or 2 species of hosts. If 2 or more host species are utilized, they are typically members of the same genus. These data are consistent with studies examining the dispersal abilities and host recognition behavior for members of the group. When the average values of host specificity for Unionicola subgenera were mapped on a phylogenetic tree for these taxa, a clade comprised of gill mites appeared to be more host specific than a clade consisting of mantle mites. There were, however, no apparent patterns of host specificity within each of the clades. Differences in specificity between the 2 lineages may reflect either a long evolutionary history that gill mites have had with host mussels or the intense competition among gill mites for oviposition sites within unionid mussels, leading to increased host specialization.

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