CORNETT, A.D.; Florida Atlantic University: Ecomorphology of Shark Electroreceptors

Sharks are morphologically very diverse and are found in nearly every marine environment. In addition, all sharks possess an electrosensory system that enables them to detect environmental electric fields. However, how this sensory system varies among taxa and in different environments remains unexplored. I studied the ecomorphology of shark electroreception to test whether the electrosensory system is constrained by phylogeny or varies with habitat. To accomplish this, I examined representative species of i) the same taxa (family and order levels) found in different environments (pelagic, shallow coastal, deepwater) and ii) different taxa found in the same environment to determine the effect of phylogenetic constraint and evolutionary convergence on shark electroreceptors. Sharks found in a pelagic environment possess between 450�1400 electrosensory pores and the majority of these species have greater than 60% of these pores on the ventral surface of the head. Shallow coastal species possess the greatest number of pores, between 430�3000 pores, and show mixed dorsal/ventral ratios with ventral pore distribution varying between 43�66%. Species found in deepwater habitats possess the fewest electrosensory pores, between 250�1150 pores, with 48�59% distributed on the ventral surface. Members of the most speciose shark order, Carcharhiniformes, generally have an approximately even distribution of pores on the dorsal and ventral surfaces. This taxonomic group has greater pore counts overall, with a majority of species having over 1800 electrosensory pores. The results implicate evolutionary convergence as the primary factor responsible for the number of electroreceptive pores, while phylogenetic constraint is the dominant influence on pore distribution.