Epidermal sensory organs of moles, shrew-moles, and desmans: A study of the family talpidae with comments on the function and evolution of Eimer's organ

The epidermal sensory organs of members of the family Talpidae (moles, shre w-moles, and desmans) were investigated and compared to determine the range of sensory specializations and better understand how they evolved. Small d omed mechanosensory organs called 'Eimer's organs' were present on the rhin arium of nearly all species of talpids, but not among the sister group of s hrews (Soricidae) or other insectivore families. This suggests that the com mon ancestor to the talpids possessed Eimer's organs. Two species of moles from the driest habitats did not exhibit Eimer's organs - suggesting that t heir sensory organs degenerated in response to harsh, abrasive soil conditi ons. The semi-aquatic desmans uniquely possessed tiny sensory hairs intersp ersed with their Eimer's organs; these may act to sense water currents. Som e species exhibited a subdivided, star-like, rhinarium - resembling an earl y embryonic stage of the star-nosed mole and providing clues to the evoluti on of the star. A single genera (Uropsilus) that branched off early in the evolution of the talpids had Eimer's organ-like structures but lacked some typical components. These findings fill a major gap in our knowledge of tal pid sensory biology and suggest (1) how Eimer's organs evolved, (2) how the unusual appendages of the star-nosed mole evolved, (3) that the evolution of Eimer's organ is convergent with the mechanosensory push-rod of monotrem es. The results also demonstrate the features that distinguish Eimer's orga n from similar configurations of sensory receptors in other mammalian skin surfaces. Finally, a mechanism for Eimer's organ function in detecting obje ct and prey specific surface features is proposed. Copyright (C) 2000 S. Ka rger AG, Basel.