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"Worthy, Graham A. J."

Worthy, Graham A. J.: SEE ALSO Courbis & Worthy, 2003; Dierauf, L. A., 1990; Ortiz & Worthy, 2004; Ortiz et al., 1998, 1999. (detail)
Worthy, Graham A. J.; Hickie, John P. (detail)
Relative brain size in marine mammals.
Amer. Naturalist 128(4): 445-459.
Ortiz, Rudy M.; Worthy, Graham A. J.; MacKenzie, Duncan S. (detail)
Osmoregulation in wild and captive West Indian manatees (Trichechus manatus).
Physiol. Zool. 71(4): 449-457. 4 tabs. 2 figs. July/Aug. 1998.
–Experiments manipulating water salinity and animals' access to fresh water were conducted on captive and wild-caught T. m. latirostris and T. m. manatus in Florida, Brazil, Colombia, and Puerto Rico. High aldosterone levels in wild freshwater animals may indicate a need to conserve sodium or to have access to marine habitats; captinve animals in fresh water may be susceptible to salt deficiency. High vasopressin levels in wild brackish-water manatees suggest use of an antidiuretic state to conserve water. Concludes that manatees are good osmoregulators regardless of the environment.
Ortiz, Rudy M.; Worthy, Graham A. J.; Byers, Floyd M. (detail)
Estimation of water turnover rates of captive West Indian manatees (Trichechus manatus) held in fresh and salt water.
Jour. Exper. Biol. 202(1): 33-38. 2 tabs. Jan. 1999.
–Reports that animals held in fresh water had the highest water turnover rates (145ñ12 ml/kg/day); animals acutely exposed to salt water decreased their turnover rate significantly, then increased it upon re-entry into fresh water. Manatees chronically exposed to salt water and fed seagrass had very low turnover rates compared with ones held in salt water but fed lettuce, which is consistent with a lack of drinking of seawater. Manatees in fresh water drank large volumes of water, which may make them susceptible to hyponatremia if a source of sodium (such as access to marine environments) is not provided.
Courbis, S. S.; Worthy, Graham A. J. (detail)
Opportunistic carnivory by Florida manatees (Trichechus manatus latirostris).
Aquatic Mammals 29(1): 104-107.
–Feeding on tunicates.
Ortiz, Rudy M.; Worthy, Graham A. J. (detail)
Could lower body fat mass contribute to cold-water susceptibility in calves of the West Indian manatee (Trichechus manatus)?
Mar. Mamm. Sci. 20(1): 176-183. 2 tabs. 2 figs. Jan. 13, 2004.
–Estimation of body components by isotopic dilution in 8 Florida and 5 Brazilian captive manatees showed correlation between fat mass and age. Manatees appear to reach adult levels of body fat between 1 and 2.5 years of age, prior to which their relatively lower fat mass may indeed increase their cold susceptibility.
Fertl, Dagmar; Schiro, A. J.; Regan, G. T.; Beck, Cathy A.; Adimey, Nicole M.; Price-May, L.; Amos, A.; Worthy, Graham A. J.; Crossland, R. (detail)
Manatee occurrence in the northern Gulf of Mexico, west of Florida.
Gulf & Caribbean Research 17: 69-94. 1 fig. 2 appendices.
Reich, K. J.; Worthy, Graham A. J. (detail)
An isotopic assessment of the feeding habits of free-ranging manatees.
Mar. Ecol. Progress Series 322: 303-309.
Alves-Stanley, C. D.; Worthy, Graham A. J. (detail)
Carbon and nitrogen stable isotope turnover rates and diet-tissue discrimination in Florida manatees (Trichechus manatus latirostris).
Jour. Exper. Biol. 212(15): 2349-2355.
Alves-Stanley, C. D.; Worthy, Graham A. J.; Bonde, Robert K. (detail)
Feeding preferences of West Indian manatees in Florida, Belize, and Puerto Rico as indicated by stable isotope analysis.
Marine Ecology Progress Series 402: 255-267.
Worthy, Graham A. J.; Worthy, Tamara A. M. (detail)
Digestive efficiencies of ex situ and in situ West Indian manatees (Trichechus manatus latirostris).
Physiological & Biochemical Zoology 87(1): 77-91. May 1, 2014.
–ABSTRACT: Digestive efficiencies (Dm) of ex situ and in situ manatees (Trichechus manatus latirostris) were, for the first time, assessed using manganese (Mn(2+)) as a naturally occurring marker. The Dm of ex situ manatees determined using [Mn(2+)] did not differ significantly from the Dm assessed using lignin, supporting the efficacy of the manganese approach. Gastrointestinal tract samples, obtained from recently dead animals, showed [Mn(2+)] concentrations were lowest in the stomach and remained low in the duodenum and small intestine but increased in the cecum, colon, and rectum, consistent with colonic digestion and absorption. In situ manatees consuming marine vegetation had significantly lower Dm (mean ± SE, 46.9% ± 1.8%; n=8) than did in situ manatees consuming freshwater vegetation (77.8% ± 2.6%; n=7), which in turn had significantly lower values than did ex situ manatees consuming lettuce (84.0% ± 0.7%; n=37). In situ manatees eating seagrasses had significantly higher Dm than did long-term ex situ animals consuming seagrass for short periods of time (46.9% ± 1.8% vs. 36.2% ± 1.2%, respectively), suggesting potential modification of gut flora over time. One significant ramification of our results is that manatees consuming seagrasses would require a greater standing biomass to support their needs than would be required if they were eating freshwater vegetation. This reinforces the critical need to implement habitat conservation and protection before considering downlisting or delisting manatees as an endangered species.

Daryl P. Domning, Research Associate, Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, and Laboratory of Evolutionary Biology, Department of Anatomy, College of Medicine, Howard University, Washington, D.C. 20059.
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