Phylogenetic distribution of electroreception within the Craniata and its evolution according to the criterion of parsimony.

<p>The phylogenetic backbone shown here follows Nelson <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036287#pone.0036287-Nelson1" target="_blank">[140]</a>, with modifications according to Gardiner et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036287#pone.0036287-Gardiner1" target="_blank">[141]</a>, Lavoué et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036287#pone.0036287-Lavou6" target="_blank">[119]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036287#pone.0036287-Lavou7" target="_blank">[142]</a>, Heimberg et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036287#pone.0036287-Heimberg1" target="_blank">[143]</a>, Kikugawa et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036287#pone.0036287-Kikugawa1" target="_blank">[144]</a>, Li et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036287#pone.0036287-Li3" target="_blank">[120]</a>, and Takezaki et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036287#pone.0036287-Takezaki1" target="_blank">[145]</a>. Approximate timeline adapted from the fossil record; data on electroreception and electroreceptors taken from Bullock et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036287#pone.0036287-Bullock1" target="_blank">[1]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036287#pone.0036287-Bullock2" target="_blank">[26]</a> and Albert and Crampton <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036287#pone.0036287-Albert1" target="_blank">[25]</a>. Colored branches indicate electroreceptive lineages possessing electroreceptors: as modified mucous glands (orange); of the ampullary sense organ type (deep blue); of both the tuberous sense organ type and the ampullary sense organ type found in teleosts (yellow). White branches signify non-electroreceptive lineages following secondary loss of electroreceptive capability; four (possibly five) such losses are indicated by white hash marks. The origins of different forms of electroreception are indicated by black hash marks. The electroreceptive conditions of the ancestors of the Craniata and of the clade (hagfishes, lampreys) are unresolved (indicated with grey and question marks) because there are several equi-parsimonious hypotheses concerning them. The end bud electroreceptor of the lampreys and the ampullary electroreceptor of the basal gnathostomes are anatomically very different, suggesting independent origins. The tree does not map atypical reports of electroreceptive gains in single species, which are in need of further study, such as tuberous electroreceptors in a blind catfish <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036287#pone.0036287-Andres1" target="_blank">[146]</a>. Recently, Czech-Damal et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036287#pone.0036287-CzechDamal1" target="_blank">[147]</a> discovered a novel sensory organ and possible electroreceptors associated with the hairless vibrissal crypts on the snout of the Guiana Dolphin (<i>Sotalia guianensis</i>), which appear to be sensitive to weak D.C. electric fields on the order of 4.6 microvolts per cm. Although their studies so far involve only one captive specimen trained to respond to the presence or absence of weak electric fields, it indeed suggests that additional research is needed on the sensory capabilities of aquatic mammals that might have independently evolved electroreception. Piranha (<i>Catoprion mento</i>) and platypus illustrations modified from images downloaded from Wikimedia Commons; paddlefish (<i>Polyodon spathula</i>) illustration modified from NOAA’s Historic Fisheries Collection Catalog of Images; other fish illustrations modified from Nelson <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036287#pone.0036287-Nelson1" target="_blank">[140]</a>; other tetrapod illustrations taken from Léo Lavoué’s coloring book.</p>