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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.,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.


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.


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

In cephalopods, sperm discharge is an important event not only for sperm transfer but also influencing sperm storage capacity of attached spermatangia (everted spermatophores). To investigate sperm discharge from spermatangia and the condition of naturally attached spermatangia in Japanese pygmy squid (Idiosepius paradoxus) we (i) investigated the morphology of spermatophores and spermatangia, and the process of spermatophore evagination and sperm discharge from spermatangia obtained in vitro; (ii) observed spermatangia that were naturally attached to female squids at 6, 12, 18, 24 and 48. h after copulation to investigate alterations in naturally attached spermatangia with time. The spermatophore of I. paradoxus is slender and cylindrical and consists of a sperm mass, a cement body and an ejaculatory apparatus, which is similar to those of loliginid squids. The spermatangium is fishhook-shaped, its distal end being open and narrow. After the spermatangium is formed, the sperm mass gradually moves to the open end of the spermatangium, from where sperm are released. Sperm discharge is a rapid process immediately after the beginning of sperm release, but within 5. min changes to an intermittent release of sperm. Although the volume of residual spermatozoa differed among spermatangia that were naturally attached to a single individual, the probability that spermatangia would be empty increased with time. Most naturally attached spermatangia discharged almost all of their spermatozoa within 24. h after copulation, and no spermatangia were attached to females 48. h after copulation. These results suggest that sperm transfer from the spermatangium to the seminal receptacle must occur within 24. h, and that the spermatangium functions as a transient sperm storage organ in pygmy squids. © 2014 Elsevier GmbH.

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