Graduation Year

2014

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Biology (Integrative Biology)

Major Professor

Philip J. Motta

Keywords

anatomy, elasmobranch, independent contrast, modulation, novel structure

Abstract

Cephalic lobes are unique structures derived from the anterior pectoral fins, found in select myliobatid stingrays. Many benthic batoids utilize undulatory locomotion and use their pectoral fins for both locomotion and prey capture. Pelagic myliobatids that possess cephalic lobes utilize oscillatory locomotion, using their pectoral fins to locomote and their cephalic lobes for prey capture. Despite differences in habitat usage and locomotor modes, these batoids feed on very similar benthic organisms. The purpose of this study was to 1.) compare the morphology of the cephalic lobes and anterior pectoral fins in lobed and lobeless species, looking at skeletal elements, musculature and electrosensory pore distributions; 2.) compare prey capture kinematics in lobed and lobeless species and examine the role of the cephalic lobes in prey capture modulation due to elusive/non-elusive prey; 3.) analyze multiple morphological and behavioral variables to establish any correlations to the presence of cephalic lobes. Radiography, dissections and staining techniques were employed to examine the morphology of the cephalic lobes and anterior pectoral fins in six species of batoids. High speed videography was used to film prey capture behavior in five batoid species, using elusive and non-elusive prey. Continuous morphological and behavioral variables were used to determine any correlations with the presence of the cephalic lobes, taking phylogeny into account. Results indicate that the skeletal components of the pectoral fins of oscillatory species are very different from pectoral fins of undulatory species as well as the cephalic lobes. Second moment of area (I), showed that the cephalic lobes and pectoral fins in undulatory species had greater resistance to bending in multiple directions and were also more flexible. The cephalic lobes had a novel muscle layer compared to the pectoral fin musculature. Electorsensory pores were absent from the anterior pectoral fins in oscillatory batoids, but numerous on the cephalic lobes and anterior pectoral fins in undulatory batoids. The distribution of the electrosensory pores was uniform with the exception of Rhinoptera bonasus, which possessed higher pore numbers along the edges of the cephalic lobes. Overall, the morphology of the cephalic lobes is distinct, but more similar to the pectoral fins of undulators compared to oscillators. Kinematic data showed that species with cephalic lobes localize prey capture to the cephalic region of the body. Lobed species were faster at pouncing and tenting prey, but slower during biting. The cephalic lobes were able to move more in the vertical and horizontal plane compared to the anterior pectoral fins. All species were able to modulate prey capture behavior to some degree. Species lacking lobes spent more time handling elusive prey compared to non-elusive prey. For all species, elusive prey were farther from the mouth during biting but prey escapes were rare. Lobed species were overall faster in prey capture, but did not display more modulation or feeding success than lobeless species. Phylogenetically corrected correlations showed that most morphological variables correlated to the appearance of the cephalic lobes, while kinematics variables did not. There was also a correlation among habitat, locomotion and the cephalic lobes. The cephalic lobes may have played a key role in partitioning prey capture to the head region, maintaining dexterity in the lobes while allowing the pectoral fins to shift to oscillatory locomotion and consequently a pelagic lifestyle.

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