Society of Integrative and Comparative Biology Abstract 2007

Functional Morphology of Inking Behavior in Pygmy & Dwarf Sperm Whales

Marshall, CD and Moss AL
Texas A&M University at Galveston, marshalc@tamug.edu

Pygmy & dwarf sperm whales (Kogia breviceps and K. sima) demonstrate an unusual inking behavior similar to cephalopods. Such behavior is unknown among other cetaceans. The source of ink is hypothesized to be the production of a large volume of watery stool (12-50 l). Evidence suggests that the mechanism for ink production kogiids is a derived digestive physiology in the enlarged, sac-like colon. A systematic investigation of kogiid gastrointestinal (GI) tracts has not been conducted. Therefore, this study investigated the morphology and cytology of the kogiid GI tract. Five GI tracts were collected through the SEUS Stranding Network. Standard morphometrics of the GI tract were taken (length, diameter, and volume), and samples were process for histology, and then stained with a modified Masson’s trichrome. Morphometrics of epithelia were taken and enterocytes were identified and quantified (e.g., height & width of villi, thickness of mucosa & adjacent tissue layers, and the factor of the increase in absorptive surface area). The mean length of the jejunum and colon were 23.3 m and 2.26 m, respective. External lengths of the duodenum and ileum were arbitrary due to the lack of external distinctions between adjacent segments. Mean diameter of the duodenum, jejunum, and colon, were 2.28, 1.93, and 7.84 cm, respectively. Mean volume of the duodenum, jejunum, and colon were 220, 8,693.2, & 1,398.9 ml3, respectively. Maximum colon diameter and volume was 16.5 cm & 1771.5 ml3. Plicae and villi of the jejunum and colon were remarkably limited, short and exhibited a low surface area relative to bottlenose dolphins. Mucous cells dominated both the jejunum and the colon. We hypothesize that the normal function of the colon, has been disrupted to produce large volumes of ink.

Correlations of Bite Performance with Head Morphometrics in Juvenile Loggerhead turtles (Caretta caretta): Preliminary Data

Salazar, AX, Salazar@neo.tamu.edu
Marshall, CD, Texas A&M University at Galveston

Incidental bycatch of loggerhead sea turtles from the pelagic longline fishery is a serious concern due to recent data that demonstrates a greater than predicted turtle bycatch globally. Little is known about loggerhead bite performance, but the propensity of loggerheads to bite forcefully may make them vulnerable to becoming hooked in the mouth or throat. Bite force and associated morphometric measurements were taken from juvenile captive-reared loggerheads at the NOAA turtle facility in Galveston, TX. In addition to bite force measurements, straight carapace length (SCL), straight carapace width (SCW), head width (HW), head height (HH), head length (HL) and body-mass were also recorded from individual of the 2004 (n=180) and 2005 (n=29) age classes. The mean maximum bite force was 140 N for the 2004 age class and 24 N for the 2005 age class. Mean morphometric values for the 2004 age class were 30.7 cm SCL, 25.5 cm SCW, 62.3 mm HW, 53.9 mm HH, 93.5 mm HL and mass 4032 grams. Mean values for the 2005 age class were 12.0 cm SCL, 9.7 cm SCW, 28.3 mm HW, 24.7 mm HH, 45.0 mm HL and mass was 266 grams. Maximum and mean bite force measurements are positively correlated to all body and head morphometrics (p<0.001). Head width is the best predictor of maximum (adjusted R2= 0.899; maximum bite force=3.481(HW) – 76.497) and mean bite force (adjusted R2= 0.893; mean bite force=3.215(HW) – 71.158) in these juvenile loggerheads. Investigations of loggerhead bite performance may provide data that can be used to modify longline fishing gear and diminish sea turtle bycatch.

 

Feeding Performance of Juvenile Red Snapper (Lutjanus campechanus) From Two Habitats

Case, J.E. Texas A&M University at Galveston, casejanelle@neo.tamu.edu
Marshall, C.D.

Juvenile red snapper are attracted to structure and settle onto low profile reefs, which serve as nursery grounds. Little is known about their biology during this time. Recent studies from a shell bank in the NW Gulf of Mexico have shown higher growth rates for fish located on adjacent mud habitats, perhaps due to varied prey availability and abundance. For this study juveniles were collected from a shell ridge (on ridge) and adjacent mud areas (off ridge) on Freeport Rocks, TX. Feeding morphology and kinematics were characterized and compared between the two habitats. A dynamic lever model was used to make predictions about feeding mechanics, and was validated using kinematic profiles obtained from high-speed videos of prey capture events. The model reasonably predicted kinematic profiles of jaw closure for maximum gape velocity and displacement. Model output suggested that on ridge fish have faster jaw closing velocities than off ridge fish. Off ridge fish therefore have greater mechanical advantage and longer closing durations. Analysis of prey capture events indicated that on ridge fish demonstrate greater velocities and larger displacements of the jaws than off ridge fish. Shape analysis was used to further investigate habitat effects on morphology. Off ridge fish differed from on ridge in possessing a deeper head and body. Results from model simulations, kinematic profiles, personal observations, and shape analysis all compliment the conclusion that on ridge fish exhibit suction feeding behavior, whereas fish from off ridge use biting behavior. These results suggest that habitat disparity, perhaps available prey composition, has generated variations in feeding mechanics and consequently feeding behavior. This may ultimately affect growth rate and indicate nursery quality.