Eye reduction in subterranean mammals and eye protective behavior in Ctenomys

C. E. BORGHI; STELLA GIANNONI,; V. G. ROIG

MASTOZOOLOGíA NEOTROPICAL

Año: 2002 vol. 9 p. 123 - 134

0327-9383

ABSTRACT. The variation in eye size in subterranean mammals reflects the effect of differentselection pressures: A strong selection pressure for smaller eyes in some groups, andthe absence of factors favoring selection toward a visual system, or the net effects of thecosts of retaining large eyes versus the benefits of maintaining visual acuity in others. Thealmost complete eye reduction found in the families Spalacidae, Chrysochloridae andNotoryctidae is related to the use of the head as a wedge while digging. Species of the genusCtenomys (with eyes moderately reduced to normal) protect the eyes by keeping themclosed during the burrowing acts in which they are more exposed to damage. Hence, thedifferent degrees of eye reduction are probably the result of a complex process associatedwith the different burrowing behaviors involving eye damage, the frequency of abovegroundforaging, predation pressures, and probably other factors not considered in this analysis,such as the phylogenetic history and the metabolic cost involved in maintaining both a visualsystem and the brain tissue associated with eyes. A complete understanding of eye sizeevolution in subterranean taxa will require further studies on the phylogenetic relationshipsamong subterranean groups, and more detailed studies of the morphology, behavior andnatural history of almost all subterranean mammal species.