![]() ![]() Equally old as the “Fish hook”distributions, the southern route includes the western Great Plains, Rio Grande River and northern Mexico through southern Arizona to southern California. The most classic is the Pliocene and Miocene “Fish hook” distribution between Bonneville Basin and Snake River and the western Great Basin and Pacific Coast drainages. This study examines the geological processes to understand more ancient distributions as applied to mollusks and fish. ![]() Each regional section discusses the regions geology, the geological effects on aquatic fauna, and the geological effects on the leech distributions. The leeches, as fish, illustrate similar colonization of these same post-glacial habitats. The recession of the last continental glacier (10 – 15 Ka) revealed colonization from the southern Mississippi River to the mouth of the Mackenzie River and from the Columbia River and the Mackenzie River to British Columbia coastal drainages. Western North America fish species have been extensively studied to determine aquatic connectivity among these dispersed habitats. ![]() The leech distributions today may also reflect habitats some 10 Ma (million years) ago, with different drainages, climate, and topography, lacking precise geological events for leech barrier crossings, and correlated with other aquatic fauna distributions. The western North America leech distributions was studied to assess this aquatic fauna diversity in widely dispersed and arid habitats during the last 10 Ka (thousand years). We also find preliminary evidence for the presence of cryptic and undescribed diversity within the genus. We discuss the evolutionary implications of several internal relationships that are robustly resolved by all three optimality criteria, paying particular attention to the apparent fluidity of morphological characters exhibited by members of Placobdella. We conclude that Placobdella is a monophyletic group that places as the sister group to a clade formed by the genera Haementeria and Helobdella. Finally, we assess genetic variation at the COI locus to validate initial specimen identifications and estimate how COI variation may reflect species boundaries. We also examine the isolated COI phylogeny for the genus using an expanded dataset encompassing three additional species not included in the concatenated dataset. Here, we conduct a phylogenetic analysis of 55 individuals representing 20 of the 24 currently recognized nominal taxa using COI, ND1, 12S rDNA and ITS sequences under parsimony, maximum likelihood and Bayesian inference. Historically, species of Placobdella have posed difficulty for systematists owing to a lack of informative morphological characters and the preponderance of inadequate or incomplete species descriptions. Placobdella is a genus of blood-feeding leeches in the family Glossiphoniidae. A recent range expansion following the last ice age and/or host-mediated dispersal are discussed as potential explanations for this unexpected phylogeographic pattern. Although we find preliminary evidence for a barrier to gene flow between eastern and western collecting localities, our vastly expanded dataset largely corroborates prior studies, showing minimal phylogeographic signal among the sequences and negligible levels of genetic isolation by distance. rugosa using COI sequences from specimens collected across Canada and the United States. In the present study, we investigate the relationship between geographic distance and genetic diversity in P. Given the lack of any obvious mechanism by which this species could disperse between distant habitats, it was expected that widespread populations would be genetically isolated from each other. ![]() Recent molecular analyses revealed a surprising lack of genetic variation among morphologically disparate, geographically widespread specimens of P. Its extreme morphological variability and similarity to some congeneric species has confounded classification for over a century. Placobdella rugosa has long presented challenges to leech biologists. ![]()
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