Phylogenetic and ecological factors influencing the number and distribution of electroreceptors in elasmobranchs

Abstract

Electroreception is found throughout the animal kingdom from invertebrates to mammals and has been shown to play an important role in prey detection, facilitating social behaviours, the detection of predators and orientation to the earth's magnetic field for navigation. Electroreceptors in elasmobranchs, the ampullae of Lorenzini, detect minute electric fields and independently process these stimuli, thereby providing spatial information to the central nervous system on the location of a source, often potential prey. The ampullae of Lorenzini are individually connected to a single somatic pore on the surface of the skin, with the spatial separation of each pore directly influencing how electrical stimuli are detected and processed. Pore abundance varies across taxonomic groups resulting in unique species-specific differences. The intricate distribution patterns created by the specific positioning of somatic pores on the head are, however, consistent within families, resulting in patterns that are identifiable at higher taxonomic levels. As elasmobranchs evolved, the electrosensory system became more complex and highly specialized, which is evident by a general trend of increasing pore abundance over time. The elasmobranch electrosensory system has evolved to operate efficiently under the environmental conditions of the particular habitat in which a species lives. For example, reduced pore abundance is evident in oceanic pelagic elasmobranchs, for whom visual cues are thought to be of great importance. Pore abundance and spatial distribution may be influenced by multiple factors including head morphology, phylogeny, feeding behaviour and habitat.

Lost and found: recovery of the holotype of the ocellated angelshark, Squatina tergocellatoides Chen, 1963 (Squatinidae), with comments on western Pacific squatinids

“…The concurrent low number of dorsal pores, however, is not typically seen and may suggest that the electrosensory system may not be of relative importance to these species, compared to other sensory systems such as vision (Fouts & Nelson, 1999). The number and distribution of electrosensory pores is consistent among species of the same family, so it is therefore highly likely that other squatinids share a similar electroreceptor pattern to S. tergocellatoides (Kempster et al, 2012).…”

Microscopic aspects of electrosensory system on the partially euryhaline lesser guitarfish

“…That way, batoids little depend on vision during hunting, since most of the preys are buried (Raschi 1986). According to Kempster et al (2012), the benthic zone is a two-dimensional environment, and the majority of the species live on the bottom or very near to the substrate. Under these conditions, animals are generally slow, with limited range, often displaying cryptic camouflage.…”

“…To compensate visual inefficiency, benthic predators have become quite dependent of the electrosensory system, with a higher proportion of pores in the ventral portion of the body. Pores are more common around the mouth, position probably related to the need of orientation for animal's mouth during capture (Raschi 1986, Jordan 2008, Wueringer et al 2011, Kempster et al 2012). …”

“…All sharks and rays present an elaborate electrosensory system composed by groups of subcutaneous 32 BIANCA S. RANGEL et al electroreceptors organs, known as "ampullae of Lorenzini" (aL). The system is composed by a complex web of nerve fibers, canals and external pores ranging in size, shape and composition, related to particular needs of each species (Murray 1960, Kajiura 2001, Wueringer and Tibbetts 2008, Kajiura et al 2010, Wueringer et al 2011, 2012, Kempster et al 2012, Bedore et al 2014. The ability to detect weak bioelectric fields evolved independently in several lines of vertebrates, emphasizing the importance of this sense in a variety of behaviors (Bullock et al 1983, Collin 2010, 2012.…”

“…The distribution and density on the body surface is influenced by environment, diet composition, predatory behavior and phylogenetic position (Wueringer et al 2009, Kempster et al 2012. In batoids, the canals extend over the ventral surface to the end of the dorsal fins, with the highest density around the mouth (Jordan 2008).…”