When we think about Anodontoides ferussacianus, our minds go to the post-glacial dispersal of freshwater mussels in the Interior and Great Lakes basins of North America. Everything about the biogeography of this mollusk suggests it was one of the earliest aquatic colonizers in the wake of the wasting Wisconsin glaciers.
The last round of Pleistocene glaciation (known as the Wisconsin) reached its zenith around 15,000 years ago. As the ice melted, gigantic though short-lived ice-contact lakes formed, and their discharges often breeched current drainage divides between the Great Lakes, Hudson Bay, and Mississippi basins. Since the existence (if not timing) of these glacial lakes became known to freshwater malacologists, ancient confluences have been invoked to explain mussel distributions.
Graf (1997a, 2002) argued that the ancient glacial lake card had been overplayed and that later stream captures were responsible for moving more mussel species across drainage divides. However, one mussel fauna consisting of nine species is widespread north and south of the maximum extent of Wisconsin glaciation. Those ubiquitous species (Anodontoides ferussaciacus included) probably represent the earliest mussel community in the formerly glaciated portions of North Dakota, Minnesota, Wisconsin, Michigan, and Canada.
It is interesting to note that those nine species (Anodontoides ferussacianus, Lampsilis cardium, Lampsilis siliquoidea, Lasmigona complanata, Lasmigona compressa, Ligumia recta, Pyganodon grandis, Strophitus undulatus, and Utterbackia imbecillis) are all long-term brooders. That is they are all bradytitic. Tachytictic short-term brooders arrived latter. The longer growing season for bradytictic mussels was hypothesized by Graf (1997b), in the exuberance of his youth, to be a factor in their successful northward range expansion. |
