Darwin noted that “organs of extreme perfection and complication” were one of the chief challenges facing his theory of evolution by natural selection. He acknowledged that it defies common sense to imagine that the human eye – with all of its intricate adaptations – was shaped by the gradual and imperfect process of natural selection. If only Darwin had the chance to see some of the Lampsilis mussels which are in the arb! For the reader new to aquatic critters, all freshwater Mussels belong to the class Bivalvia (meaning, “two shells”) which includes animals such as clams, oysters, and scallops.
All Lampsilis release larva which attach to the gills of fish. These larva stay on the gills of fish for weeks or even months before falling off as juvenile mussels. To deposit these larva, female Lampsilis employ an ornate fish shaped lure fashioned out of their marsupial pouch and mantle. These mantle flaps pulse rhythmically, simulating the motion of fish, attracting unwitting predatory fish to “pounce” – and scoop up a set of Lampsilis larva.
This lure is so well “designed” that, much like the human eye, it can be difficult to imagine that it could be shaped by natural selection. To the paleontologist Stephen Jay Gould, the lure of the Lampsilis is the most awe-inspiring adaptation in nature.
Two species of Lampsilis can be found in the arb: the pocketbook (Lampsilis cardium) and the fatmucket (Lampsilis siliquoidea). Mussels play a pivotal role in the Cannon ecosystem : they serve as “ecosystem engineers” and significantly improve water quality. Unfortunately, more than half of mussels found in the midwest are endangered and dams in the river prevent fish from spreading Lampsilis larva as far as the once did. To learn more about the mussels of the Cannon River please visit the Arboretum website.