Narwhale´s tusk ser­ves as a sen­so­ry organ

The remar­kab­le and uni­que tusk of the nar­wha­le ser­ves as a sen­si­ble sen­so­ry organ which enables the ani­mals to sen­se chan­ges in their envi­ron­ment. Sci­en­tists were now able to con­firm this assump­ti­on.

Nar­wha­les are, tog­e­ther with white wha­les (belugas), part of the Mon­odon­ti­dae fami­ly. They live in the Arc­tic Oce­an, espe­ci­al­ly west and east of Green­land, around Spits­ber­gen and north of the Sibe­ri­an coast.

The main cha­rac­te­ristic of the nar­wha­le is it´s up to 2,60m long tusk. It usual­ly grows from the males left cani­ne tooth, brea­king through the upper lip in a spi­ral rota­ti­on. In sin­gle cases a second tusk can grow from the right cani­ne tooth. It is also pos­si­ble that fema­le indi­vi­du­als have one or two tusks but this is rather uncom­mon.

In histo­ry the­re were many dif­fe­ring theo­ries try­ing to explain the func­tion of the narwhale´s tusk. Today the­re are two com­mon expl­ana­ti­ons: They ser­ve as a distin­gu­is­hing attri­bu­te for males, to main­tain hier­ar­chies and as a sen­so­ry organ.

Dr. Mar­tin Nweeia from the Har­vard School of Den­tal Medi­ci­ne (HSDM) is part of an inter­na­tio­nal group of sci­en­tists who stu­dy the func­tion of the narwhale´s tusk. They were now able to con­firm their assump­ti­on that the tusk ser­ves as a sen­si­ble sen­so­ry organ. In pre­vious stu­dies the­re was poin­ted out that the narwhale´s tusk, dif­fe­ring from other mammal tee­th, is not cover­ed by an ena­mel which pro­tects the tooth against exter­nal influen­ces. Now the sci­en­tists could reve­al that the outer lay­er of the tusk, the cementum, is porous and that the inner lay­ers con­tain micro­sco­pic tubes lea­ding to the cen­ter of the tooth. So the mate­ri­al of the tooth is rigid but per­meable. In the inner core of the tusk, in the pulp, the sci­en­tists could find ner­ve endings con­nec­ted to the whale´s brain. With this struc­tu­re the tusk is sen­si­ble for chan­ges in the exter­nal envi­ron­ment such as chan­ges in tem­pe­ra­tu­re, salt level in the water or other che­mi­cal para­me­ters. Expe­ri­ments could show that the whale´s heart rate chan­ged when the tusk was expo­sed to dif­fe­rent salt levels in the water.

It is sug­gested that the abili­ty of the tusk ser­ves the male indi­vi­du­als to find food or to find fema­les and to eva­lua­te their wil­ling­ness to mate.

The sci­en­tists are now inte­res­ted in the ques­ti­on if the nar­wha­les uni­que abili­ty to use a tooth as a sen­so­ry organ is an evo­lu­tio­na­ry advance­ment or an abili­ty which is left from a for­mer stage of deve­lo­p­ment.

Source: BBC Natu­re News

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