Publications by authors named "Chiyo Kitayama"

9 Publications

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Sensitivity of turtles to anticoagulant rodenticides: Risk assessment for green sea turtles (Chelonia mydas) in the Ogasawara Islands and comparison of warfarin sensitivity among turtle species.

Aquat Toxicol 2021 Apr 25;233:105792. Epub 2021 Feb 25.

Laboratory of Toxicology, Department of Environmental Veterinary Sciences, Faculty of Veterinary Medicine, Hokkaido University, Kita 18 Nishi 9, Kita-ku, Sapporo, 060-0818, Japan. Electronic address:

Although anticoagulant rodenticides (ARs) are effectively used for the control of invasive rodents, nontarget species are also frequently exposed to ARs and secondary poisonings occur widely. However, little data is available on the effects of ARs, especially on marine organisms. To evaluate the effects of ARs on marine wildlife, we chose green sea turtles (Chelonia mydas), which are one of the most common marine organisms around the Ogasawara islands, as our primary study species. The sensitivity of these turtles to ARs was assessed using both in vivo and in vitro approaches. We administered 4 mg/kg of warfarin sodium either orally or intravenously to juvenile green sea turtles. The turtles exhibited slow pharmacokinetics, and prolongation of prothrombin time (PT) was observed only with intravenous warfarin administration. We also conducted an in vitro investigation using liver microsomes from green sea turtles, and two other turtle species (softshell turtle and red-eared slider) and rats. The cytochrome P450 metabolic activity in the liver of green sea turtles was lower than in rats. Additionally, vitamin K epoxide reductase (VKOR), which is the target enzyme of ARs, was inhibited by warfarin in the turtles at lower concentration levels than in rats. These data indicate that turtles may be more sensitive to ARs than rats. We expect that these findings will be helpful for sea turtle conservation following accidental AR-broadcast incidents.
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http://dx.doi.org/10.1016/j.aquatox.2021.105792DOI Listing
April 2021

The nasal cavity in sea turtles: adaptation to olfaction and seawater flow.

Cell Tissue Res 2021 Jan 6;383(1):347-352. Epub 2021 Jan 6.

Laboratory of Toxicology, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, 080-8555, Japan.

The nasal cavity of tetrapods has become phylogenetically adapted to the environment in terms of function, respiration, and olfaction. In addition, the nasal cavity of sea turtles plays an important role in seawater flow and water olfaction, unlike that of terrestrial species. Here, we describe the functional, morphological, and histological characteristics of the nasal cavity, and the odorant receptors encoded in the genome of sea turtles. The nasal cavity of sea turtles is well-suited to its complicated functions, and it significantly differs from those of other animals, including terrestrial and semi-aquatic turtles.
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http://dx.doi.org/10.1007/s00441-020-03353-zDOI Listing
January 2021

Investigating the effects of nest shading on the green turtle (Chelonia mydas) hatchling phenotype in the Ogasawara islands using a field-based split clutch experiment.

J Exp Zool A Ecol Integr Physiol 2020 11 7;333(9):629-636. Epub 2020 Sep 7.

Laboratory of Animal Behavior and Environmental Science, Department of Agriculture, School of Agriculture, Meiji University, Kanagawa, Japan.

The Ogasawara Islands are an important rookery for the green turtle (Chelonia mydas) in the North Pacific. Green turtles possess temperature-dependent sex determination, and warmer incubation temperatures produce more females than males. Therefore, conservation practices such as nest shading may be required for this population to mitigate the effect of global warming on their sex ratio. To consider the application of such conservation practices in the Ogasawara population, it is fundamental to understand how artificially modified nest environments will affect green turtle hatchling phenotypes that influence their fitness. Here, we investigated the effects of nest shading on green turtle hatchling phenotypes in the Ogasawara population by using a split clutch experiment equally separating the clutch, relocating each half-clutch into an outdoor hatchery area either with or without shading, and observing the subsequent hatchling phenotype. Our results showed that the shading treatment produced hatchlings with a better self-righting response and a larger carapace size. Additionally, the shading treatment mostly reduced the production of hatchlings with a nonmodal scute pattern and produced hatchlings with a smaller unabsorbed yolk sac, which may be associated with their residual yolk mass. These results suggest that conservation practices such as shading could alter not only the sex ratio but also the hatchling phenotype that influences their fitness. Hence, our results suggest that applications of such conservation strategies must be carefully considered.
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http://dx.doi.org/10.1002/jez.2411DOI Listing
November 2020

Main airway throughout the nasal cavity of green sea turtles is lined by keratinized stratified squamous epithelium.

Tissue Cell 2020 Aug 19;65:101370. Epub 2020 Apr 19.

Laboratory of Veterinary Anatomy, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555, Japan.

Structural and histological features of the nasal cavity of sea turtles are largely different from those of other Testudines species. The sea turtle nasal cavity is a pair of tubular structures with three diverticula and an excavation in the center, and three types of sensory epithelium are present in these four significant structures. To more clarify the adaptation of the nasal cavity to marine life style in sea turtles, non-sensory epithelium in the nasal cavity of green sea turtles (Chelonia mydas) were histologically determined from nostril to choanae in this study. Unlike many other animals including terrestrial turtles, the vestibular area and nasopharyngeal duct were all lined by keratinized stratified squamous epithelium. In the main nasal cavity, the margins of each sensory epithelium turned into respiratory epithelium with goblet cells, followed by keratinized stratified squamous epithelium. Keratinized epithelium appears more appropriate in sea turtle upper airway to protect against osmotic pressure when they release seawater through the nostrils, and thus this histological feature of upper airway might reflect adaptation to marine life style.
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http://dx.doi.org/10.1016/j.tice.2020.101370DOI Listing
August 2020

Behavioral effects of scents from male mature Rathke glands on juvenile green sea turtles (Chelonia mydas).

J Vet Med Sci 2020 Sep 13;82(9):1312-1315. Epub 2020 Jul 13.

Laboratory of Veterinary Anatomy, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555, Japan.

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.
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http://dx.doi.org/10.1292/jvms.20-0058DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7538326PMC
September 2020

Computed tomographic analysis of internal structures within the nasal cavities of green, loggerhead and leatherback sea turtles.

Anat Rec (Hoboken) 2021 03 24;304(3):584-590. Epub 2020 Jun 24.

Laboratory of Veterinary Anatomy, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Japan.

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.
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http://dx.doi.org/10.1002/ar.24469DOI Listing
March 2021

Infection by and Molecular Features of (Digenea: Schistosomatoidea) in Green Sea Turtles () on the Ogasawara Islands, Japan.

J Parasitol 2019 08;105(4):533-538

3   Laboratory of Veterinary Parasitology, Faculty of Agriculture, Iwate University, 3-18-8 Ueda, Morioka 020-8550, Japan.

Price, 1934 , is a blood fluke found in sea turtles, and the adult fluke parasitizes the cardiovascular system of the host. In this study we surveyed 46 green sea turtles, , on the Ogasawara Islands, Japan, and blood flukes were detected in the heart and blood vessels of 26 turtles. The flukes were identified as based on a detailed morphological description. In addition, molecular identification and characterization of the parasite were performed. The nucleotide sequences of nuclear internal transcribed spacer 2 () regions were almost identical to those of reported previously, but not to those of spp., which is the closest related genus. The nucleotide sequences of the ribosomal DNA region formed a single clade with those of the reference in the phylogenetic tree, but not with those of spp. Therefore, the nucleotide sequences of and are robust markers for distinguishing from other species. The nucleotide sequences of the mitochondrial cytochrome oxidase subunit 1 () region were analyzed to evaluate the genetic variations in . The haplotypes revealed the extremely high genetic diversity of the species as well as the host turtles on the Ogasawara Islands. The haplotype frequency in the mitochondrial DNA of the green sea turtles on the Ogasawara Islands is known to be significantly different from those in other Pacific rookeries. Although the number of analyzed flukes is small in this study, no haplotype was close to that in other areas; on the basis of the data, we hypothesized that differentiated along with the host turtles on the Ogasawara Islands.
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August 2019

Nasal Cavity of Green Sea Turtles Contains 3 Independent Sensory Epithelia.

Chem Senses 2019 09;44(7):427-434

Everlasting Nature of Asia (ELNA), Ogasawara Marine Center, Chichi-Jima Byobudani, Ogasawara, Tokyo, Japan.

The 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.
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http://dx.doi.org/10.1093/chemse/bjz033DOI Listing
September 2019

Structure and functions of the placenta in common minke (Balaenoptera acutorostrata), Bryde's (B. brydei) and sei (B. borealis) whales.

J Reprod Dev 2015 20;61(5):415-21. Epub 2015 Jun 20.

Laboratory of Veterinary Anatomy, Department of Basic Veterinary Medicine, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan.

The structure and functions of placentas were examined in 3 species of rorqual whales, common minke (Balaenoptera acutorostrata), Bryde's (B. brydei) and sei (B. borealis) whales, with the aim of confirming the structural characteristics of the chorion, including the presence of the areolar part, and clarifying steroidogenic activities and fetomaternal interactions in the placentas of these whales. Placentas were collected from the second phase of the Japanese Whale Research Program under Special Permit in the North Pacific (JARPN II). Histological and ultrastructural examinations revealed that these whale placentas were epitheliochorial placentas with the interdigitation of chorionic villi lined by monolayer uninucleate cells (trophoblast cells) and endometrial crypts as well as folded placentation by fold-like chorionic villi. Moreover, well-developed pouch-like areolae were observed in the placentas, and active absorption was suggested in the chorionic epithelial cells of the areolar part (areolar trophoblast cells). Berlin blue staining showed the presence of ferric ions (Fe(3+)) in the uterine glandular epithelial cells and within the stroma of chorionic villi in the areolar part. An immunohistochemical examination revealed tartrate-resistant acid phosphatase (TRAP; known as uteroferrin in uteri) in the cytoplasm of glandular cells and areolar trophoblast cells. This result suggested that, in cetaceans, uteroferrin is used to supply iron to the fetus. Furthermore, immunoreactivity for P450scc and P450arom was detected in trophoblast cells, but not in areolar trophoblast cells, suggesting that trophoblast cells synthesize estrogen in whale placentas. Therefore, we herein immunohistochemically revealed the localization of aromatase and uteroferrin in cetacean placentas during pregnancy for the first time.
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http://dx.doi.org/10.1262/jrd.2015-005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4623147PMC
August 2016