AbstractThe morphological and histological features of the nasal cavity are diverse among animal species, and the nasal cavities of terrestrial and semiaquatic turtles possess 2 regions lined with each different type of sensory epithelium. Sea turtles can inhale both of volatile and water-soluble odorants with high sensitivity, but details of the architectural features and the distribution of the sensory epithelia within the sea turtle nasal cavity remain uncertain. The present study analyzed the nasal cavity of green sea turtles using morphological, computed tomographic, and histological methods. We found that the middle region of the sea turtle nasal cavity is divided into anterodorsal, anteroventral, and posterodorsal diverticula and a posteroventral excavation by connective tissue containing cartilages. The posterodorsal diverticulum was lined with a thin sensory epithelium, and the anterodorsal and anteroventral diverticula were occupied by a single thick sensory epithelium. In addition, a relatively small area on the posteroventral excavation was covered by independent sensory epithelium that differed from other 2 types of epithelia, and a single thin bundle derived from the posteroventral excavation comprised the most medial nerve that joins the anterior end of the olfactory nerve tract. These findings suggested that the posteroventral excavation identified herein transfers stimuli through an independent circuit and plays different roles when odorants arise from other nasal regions.
The morphology of the tetrapod nasal cavity has adapted to the environment in terms of olfaction and respiration. Reports indicate that the internal structure of the nasal cavity of green sea turtles is more complex than that of turtles in general, but whether or not it is similar among sea turtle species remains unknown. The present study aimed to define the internal structures of the nasal cavity of green (Chelonian mydas), loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea) sea turtles using computed tomography. The nasal cavity of green and loggerhead sea turtles contained anterodorsal, anteroventral, posterodorsal diverticula and a posteroventral excavation in the middle. In contrast, the nasal cavity of leatherback sea turtles had more complicated dorsal region comprising anterodorsal and posterodorsal diverticula, and two excavations between the nostril and anterodorsal diverticulum, but no distinct structures at the ventral region. The airway in the nasal cavity was shorter and thicker in the leatherback, than in the green and loggerhead turtles. These species differences might reflect ecological variety and different evolutionary strategies.
Sea turtles can detect airborne and waterborne odors, but whether they recognize scents from the same species and if so, how they affect their behavior remains unknown. The present study evaluated the behavioral effects of odorants on juvenile green sea turtles (Chelonia mydas). The odorants were derived from Rathke glands (external scent glands) of mature male green sea turtles, and from two types of food. The activity of the juveniles increased when exposed to food scents, and significantly decreased compared with controls when exposed to scents from Rathke glands. These findings indicated that scents from the same species affect behavior, and that chemical communication via olfaction has important outcomes for sea turtles.
Infection of boar-hunting dogs with Paragonimus westermani was
investigated in Western Japan. Blood and rectal feces were collected from 441 dogs in the
three districts (205 in Kinki, 131 in Chugoku and 105 in Shikoku District). In a screening
ELISA for serum antibody against P. westermani antigen, 195 dogs (44.2%)
showed positive reaction. In the 195 dogs, 8 dogs were found excreting P.
westermani eggs after molecular analysis of fecal eggs, and additional 7 were
identified serologically for the parasite infection because of their stronger reactivity
against P. westermani antigen than against antigens of other species of
Paragonimus. A spatial analysis showed that all of the P.
westermani infections were found in Kinki and Chugoku Districts. In this area,
dogs’ experience of being fed with raw boar meat showed high odds ratio (3.35) to the
sero-positivity in the screening ELISA, and the frequency of such experiences was
significantly higher in sero-positive dogs. While clear relationship was not obtained
between predation of boars by dogs during hunting and their sero-positivity. Therefore, it
is suggested that human activity of feeding with wild boar meat is the risk factor for
P. westermani infection in boar-hunting dogs. Considering that hunting
dogs could play as a major definitive host and maintain the present distribution of
P. westermani in Western Japan, control measures for the infection in
hunting dogs, such as prohibition of raw meat feeding and regular deworming, should be
undertaken.
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