Port of Nagoya Public Aquarium

Okazaki, Japan

Port of Nagoya Public Aquarium

Okazaki, Japan

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Sakaoka K.,Port of Nagoya Public Aquarium | Sakaoka K.,Hiroshima University | Yoshii M.,Port of Nagoya Public Aquarium | Okamoto H.,Port of Nagoya Public Aquarium | And 2 more authors.
Chelonian Conservation and Biology | Year: 2011

We investigated the effects of the order of sequential matings in captive female loggerhead turtles (Caretta caretta) on the paternity of their successive clutches. Paternity analysis revealed that only 3 of the 7 successive clutches were multiply sired, although all egg-laying females were observed to copulate with multiple males prior to egg-laying. In multiply sired, successive clutches of particular females, the relative paternal contributions of different males did not vary, although some potentially successful matings were observed during internesting intervals. Prior to nesting periods, males showed mating in response to the female reproductive cycle in which the cumulative durations of mountings observed by highly sensitive cameras peaked at 21-40 days before any individual female laid her first clutch. A regression line between cumulative duration of mountings and relative parental contributions for 21-40 days before laying the first clutch fit a predictive equation for sperm competition based on the assumptions of a fair raffle. These results suggest that sperm precedence has changed with time over the course of a prenesting period and that male turtles in this study have regulated the timing of copulations in accordance with the patterns of sperm precedence. © 2011 Chelonian Research Foundation.


Sato N.,Hokkaido University | Kasugai T.,Port of Nagoya Public Aquarium | Ikeda Y.,University of Ryukyus | Munehara H.,Hokkaido University
Journal of Zoology | Year: 2010

To examine the mechanism of sperm storage in Idiosepius paradoxus, here we describe aspects of the mating behavior of I. paradoxus and the morphology of the spermatozoa and the seminal receptacle after copulation. The seminal receptacle is located in the ventral portion of the buccal membrane surrounding the buccal mass, and opens inside the buccal membrane. It branches into approximately six sacs, similar in appearance to a bunch of bananas, and its wall consists of cuboidal ciliated epithelial cells (with oval nuclei) surrounded by a connective tissue. Multiple vacuoles are distributed in the bottom region of each sac. These histological and morphological characteristics differ from previous reports for loliginid squids and cuttlefish. In all except one receptacle observed in this study, sperm were stored near the bottom of each sac, and each sperm was facing the sac bottom. We observed spermatozoa in the entrance of the seminal receptacle in only one squid. These results suggest that spermatozoa were actively moving, and that sperm actively swam to the seminal receptacle. The volume of sperm in the seminal receptacles of the squid that had copulated eight times was the same as that in the squid that had copulated 29 times, which suggests that the seminal receptacle was filled after approximately eight copulation events. A squid that had copulated nine times retained a significant number of sperm in the seminal receptacle after spawning, suggesting that all of the sperm in the receptacle was not depleted after one spawning event. © 2010 The Authors. Journal of Zoology © 2010 The Zoological Society of London.


PubMed | Kochi University, Stanford University, National Oceanic and Atmospheric Administration, Hawaii Preparatory Academy and Port of Nagoya Public Aquarium
Type: Journal Article | Journal: Proceedings. Biological sciences | Year: 2016

Highly migratory marine species can travel long distances and across entire ocean basins to reach foraging and breeding grounds, yet gaps persist in our knowledge of oceanic dispersal and habitat use. This is especially true for sea turtles, whose complex life history and lengthy pelagic stage present unique conservation challenges. Few studies have explored how these young at-sea turtles navigate their environment, but advancements in satellite technology and numerical models have shown that active and passive movements are used in relation to open ocean features. Here, we provide the first study, to the best of our knowledge, to simultaneously combine a high-resolution physical forcing ocean circulation model with long-term multi-year tracking data of young, trans-oceanic North Pacific loggerhead sea turtles during their lost years at sea. From 2010 to 2014, we compare simulated trajectories of passive transport with empirical data of 1-3 year old turtles released off Japan (29.7-37.5 straight carapace length cm). After several years, the at-sea distribution of simulated current-driven trajectories significantly differed from that of the observed turtle tracks. These results underscore current theories on active dispersal by young oceanic-stage sea turtles and give further weight to hypotheses of juvenile foraging strategies for this species. Such information can also provide critical geographical information for spatially explicit conservation approaches to this endangered population.


PubMed | Kochi University, Stanford University, National Oceanic and Atmospheric Administration, Hawaii Preparatory Academy and Port of Nagoya Public Aquarium
Type: | Journal: Movement ecology | Year: 2016

The juvenile stage of loggerhead sea turtles (Results show high residency of juvenile loggerheads within the Central North Pacific and a moderate influence of the Earths magnetic field, but no real-time environmental driver to explain migratory behavior.We suggest the Central North Pacific acts as important developmental foraging grounds for young juvenile loggerhead sea turtles, rather than just a migratory corridor. We propose several hypotheses that may influence the connectivity between western and eastern juvenile loggerhead foraging grounds in the North Pacific Ocean.


PubMed | National Institute of Genetics, Port of Nagoya Public Aquarium and Nagasaki University
Type: | Journal: Evolution; international journal of organic evolution | Year: 2016

In polyandrous mating systems, sperm competition and cryptic female choice (CFC) are well recognized as postcopulatory evolutionary forces. However, it remains challenging to separate CFC from sperm competition and to estimate how much CFC influences insemination success because those processes usually occur inside the females body. The Japanese pygmy squid, Idiosepius paradoxus, is an ideal species in which to separate CFC from sperm competition because sperm transfer by the male and sperm displacement by the female can be observed directly at an external location on the females body. Here, we counted the number of spermatangia transferred to, removed from, and remaining on the female body during single copulation episodes. We measured behavioral and morphological characteristics of the male, such as duration of copulation and body size. Although males with larger body size and longer copulation time were capable of transferring larger amounts of sperm, females preferentially eliminated sperm from males with larger body size and shorter copulation time by spermatangia removal; thus, CFC could attenuate sperm precedence by larger males, whereas it reinforces sperm precedence by males with longer copulation time. Genetic paternity analysis revealed that fertilisation success for each male was correlated with remaining sperm volume that is adjusted by females after copulation.


Tomonaga M.,Kyoto University | Uwano Y.,Port of Nagoya Public Aquarium | Saito T.,Port of Nagoya Public Aquarium
Scientific Reports | Year: 2014

Bottlenose dolphins use auditory (or echoic) information to recognise their environments, and many studies have described their echolocation perception abilities. However, relatively few systematic studies have examined their visual perception. We tested dolphins on a visual-matching task using two-dimensional geometric forms including various features. Based on error patterns, we used multidimensional scaling to analyse perceptual similarities among stimuli. In addition to dolphins, we conducted comparable tests with terrestrial species: chimpanzees were tested on a computer-controlled matching task and humans were tested on a rating task. The overall perceptual similarities among stimuli in dolphins were similar to those in the two species of primates. These results clearly indicate that the visual world is perceived similarly by the three species of mammals, even though each has adapted to a different environment and has differing degrees of dependence on vision.


Sato N.,Hokkaido University | Sato N.,Nagasaki University | Kasugai T.,Port of Nagoya Public Aquarium | Munehara H.,Hokkaido University
Marine Biology | Year: 2013

In the Japanese pygmy squid Idiosepius paradoxus, females often pick up the spermatangium using their mouth (buccal mass) after copulation. To examine whether the female I. paradoxus directly transfers sperm into the seminal receptacle via this picking behaviour, or removes the spermatangium, we conducted detailed observations of picking behaviour in both virgin and copulated females and compared the sperm storage conditions in the seminal receptacle between females with and without spermatangia picking after copulation in virgin females. In all observations, elongation of the buccal mass occurred within 5 min after copulation. However, sperm volume in the seminal receptacle was not related to spermatangia picking. Observations using slow-motion video revealed that females removed the spermatangia by blowing or eating after picking. These results suggest that picking behaviour is used for sperm removal but not for sperm transfer. Moreover, the frequency of buccal mass elongation was higher in copulated females than in virgin females, consistent with the sequential mate choice theory whereby virgin females secure sperm for fertilisation, while previously copulated females are more selective about their mate. Female I. paradoxus may choose its mate cryptically through postcopulatory picking behaviour. © 2012 Springer-Verlag Berlin Heidelberg.


Sato N.,Nagasaki University | Sato N.,Aberystwyth University | Takeshita F.,Nagasaki University | Fujiwara E.,Documentary Channel | Kasugai T.,Port of Nagoya Public Aquarium
Marine Biology | Year: 2016

Inking is one of the defensive tactics in cephalopods. By observing the predatory behaviours of Japanese pygmy squid (Idiosepius paradoxus) towards three crustacean prey species (Neomysis intermedia, Latreutes acicularis, and Palaemon serrifer), we found that ink is also used for predation. Inking behaviour during predation was observed 17 times in 322 trials. Squid successfully attacked prey after inking in 13 cases (8 trials with L. acicularis and 5 trials with P. serrifer). Ink was never used to attack N. intermedia despite the fact that this was the most commonly captured prey. Ink use during attacks can be divided into two types: (1) squid release ink between themselves and the prey and then attack through the ink cloud, and (2) squid release ink away from the prey and then attack from another direction. The success rate of ink attacks differed significantly between the two prey species on which ink attacks were made. © 2016, Springer-Verlag Berlin Heidelberg.


Sato N.,Nagasaki University | Sato N.,Hokkaido University | Kasugai T.,Port of Nagoya Public Aquarium | Munehara H.,Hokkaido University
Evolutionary Biology | Year: 2014

Females can express mate (or fertilisation) preferences after copulation. In the Japanese pygmy squid, Idiosepius paradoxus, in which males do not show any conspicuous pre-copulatory displays, the females remove the spermatangia attached to their bodies after copulation. In this study, we observed pre- and post-copulatory behaviours and analysed which variables associated with copulation were correlated with spermatangia removal. When females mated with larger males or copulation lasted longer female squid elongated their buccal mass after copulation and removed more spermatangia. We also investigated the effects of spermatangia removal on the retained spermatangia to predict whether cryptic female choice (CFC) influenced fertilisation success. Spermatangia removal by females had a stronger effect on the number of spermatangia retained than did the number of spermatangia ejaculated by males. These results suggest that spermatangia removal after copulation by buccal mass elongation works as a CFC in Japanese pygmy squid, and females cryptically favoured small males and fast copulation. © 2013 Springer Science+Business Media New York.


PubMed | Tohoku Gakuin University, Tokai University, Port of Nagoya Public Aquarium and Tokyo University of Marine Science and Technology
Type: | Journal: Zoological letters | Year: 2015

Species with fission-fusion social systems tend to exchange individualized contact calls to maintain group cohesion. Signature whistles by bottlenose dolphins are unique compared to the contact calls of other non-human animals in that they include identity information independent of voice cues. Further, dolphins copy the signatures of conspecifics and use them to label specific individuals. Increasing our knowledge of the contact calls of other cetaceans that have a fluid social structure may thus help us better understand the evolutionary and adaptive significance of all forms of individually distinctive calls. It was recently reported that one type of broadband pulsed sounds (PS1), rather than whistles, may function as individualized contact calls in captive belugas. The objective of this study was to assess the function and individual distinctiveness of PS1 calls in an isolation context. Recordings were made from five captive belugas, including both sexes and various ages.PS1 was the predominant call type (38% in total) out of five broader sound categories. One sub-adult and three adults had individually distinctive and stereotyped pulse repetition pattern in PS1; one calf showed no clear stereotyped pulse repetition pattern. While visual inspection of the PS1 power spectra uncovered no apparent individual specificity, statistical analyses revealed that both temporal and spectral parameters had inter-individual differences and that there was greater inter-individual than intra-individual variability. Discriminant function analysis based on five temporal and spectral parameters classified PS1 calls into individuals with an overall correct classification rate of 80.5%, and the most informative parameter was the average Inter-pulse interval, followed by peak frequency.These results suggest that belugas use individually distinctive contact calls in an isolation context. If belugas encode signature information in PS1 calls, as seen in bottlenose dolphins, the pulse repetition pattern may be the carrier, as it is individually stereotyped and appears to require vocal development. This idea is supported by the finding that the average inter-pulse interval is the most powerful discriminator in discriminant analysis. Playback experiments will elucidate which parameters are perceived as individual characteristics, and whether one of the parameters functions as a signature.

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