Reversed palatal perforation by upper incisors in ageing blind mole-rats (Spalax ehrenbergi)

Blind mole-rats (Spalax ehrenbergi) are fossorial solitary rodents that pre sent striking morphological, physiological and behavioural adaptations to t he subterranean environment in which they live. Previous studies have shown that mole-rats are specialised in tooth-digging. The rapid eruption-rate o f their incisors has evolved to compensate for their excessive wear by exca vation. Males use their incisors more than females for digging and fighting , and their rate of incisor eruption is significantly more rapid than in fe males. Since mole-rats use their incisors for digging throughout the year, we suggest that continuous mechanical pressure on their oral tissues concen trated at the apical sites of the upper incisors leads to cell and tissue f atigue. We provide evidence for 5 stages of palatal perforation by the uppe r incisors at their apical sites, with maximum perforation characterising a ged males. Interspecies comparisons with 7 other fossorial and semi-fossori al rodent species, and with beavers, which expose their incisors to enormou s mechanical pressure, revealed that this palatal perforation is unique to the male mole-rat. We suggest that while the fast eruption rate of incisors in the mole-rat compensates for the rapid wear resulting from digging, evo lutionary adaptation to continuous tooth-digging is still ongoing, since th e physical pressure of digging at the apical sites of the upper incisors le ads to tissue destruction, breakage of the palatal bone and possibly to dea th, as a result of maxillary inflammation.