Comparative morphology of stingray lateral line canal and electrosensory systems

Abstract

Elasmobranchs (sharks, skates, and rays) possess a variety of sensory systems including the mechanosensory lateral line and electrosensory systems, which are particularly complex with high levels of interspecific variation in batoids (skates and rays). Rays have dorsoventrally compressed, laterally expanded bodies that prevent them from seeing their mouths and more often than not, their prey. This study uses quantitative image analysis techniques to identify, quantify, and compare structural differences that may have functional consequences in the detection capabilities of three Eastern Pacific stingray species. The benthic round stingray, Urobatis halleri, pelagic stingray, Pteroplatytrygon (Dasyatis) violacea, and benthopelagic bat ray, Myliobatis californica, show significant differences in sensory morphology. Ventral lateral line canals correlate with feeding ecology and differ primarily in the proportion of pored and nonpored canals and the degree of branching complexity. Urobatis halleri shows a high proportion of nonpored canals, while P. violacea has an intermediate proportion of pored and nonpored canals with almost no secondary branching of pored canals. In contrast, M. californica has extensive and highly branched pored ventral lateral line canals that extended laterally toward the wing tips on the anterior edge of the pectoral fins. Electrosensory morphology correlates with feeding habitat and prey mobility; benthic feeders U. halleri and M. californica, have greater electrosensory pore numbers and densities than P. violacea. The percentage of the wing surface covered by these sensory systems appears to be inversely related to swimming style. These methods can be applied to a broader range of species to enable further discussion of the relationship of phylogeny, ecology, and morphology, while the results provide testable predictions of detection capabilities.

Distribution of ampullary pores on three catshark species (Apristurus spp.) suggest a vertical-ambush predatory behaviour

“…Intra-specific variation in total pore count was high (>10%) for all target species, as found in other studies (Jordan 2008, Bedore et al 2014, but is unlikely due to observer error owing to the marking methodology employed. Future research should aim to understand to what extent, if any, such variation has on electrosensory capability.…”

“…However, the increase in TL with age necessarily results in a decrease in pore density as pore number remains constant. High pore densities are correlated with less mobile prey (like epifaunal and infaunal crustaceans) whereas lower pore densities are correlated with more mobile prey (like cephalopods and teleosts), due to a reduction in resolution as pore density decreases (with age-related growth), leaving the animal less able to detect immobile prey items (Jordan 2008, Bedore et al 2014. It is therefore likely that the ontogenetic diet shift as described by Mauchline & Gordon (1983) is driven by both a reduced ability to detect more immobile prey and an increase in mouth gape size that allows it to target larger prey items.…”

Functional consequences of structural differences in stingray sensory systems. Part II: electrosensory system

“…Ventral electrosensory pore numbers range from 1200±27 and 1425±41 in Urobatis halleri and Myliobatis californica, respectively, to just 553±26 in Pteroplatytrygon violacea (Jordan, 2008). The density of pores within the ventral pore field in the two benthically feeding species is more than three times that of the pelagic stingray P. violacea (Jordan, 2008).…”

“…Like the lateral line canal system, the electrosensory system is highly modified in batoid fishes. In stingrays the canals extend over the ventral body surface and out toward the wing tips with increased density surrounding the mouth (Chu and Wen, 1979;Raschi, 1986;Jordan, 2008). Electric signals have a short range relative to visual and olfactory signals and provide directional information for locating buried prey and directing the mouth strike to ingest prey.…”

“…Carcharhinid and sphyrnid sharks with similar pore densities yet different pore numbers showed similar behavioralresponse thresholds to dipole electric fields (Kajiura and Holland, 2002). Benthic-feeding elasmobranchs typically have high electrosensory pore numbers and densities whereas pelagic species have a lower pore number and density with more similar dorsoventral distributions (Raschi, 1986;Kajiura, 2001;Raschi et al, 2001;Cornett, 2006;Jordan, 2008).…”