Female Pygmy Squid Cryptically Favour Small Males and Fast Copulation as Observed by Removal of Spermatangia

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

Spermatophore dimorphism in the chokka squid <i>Loligo reynaudii</i> associated with alternative mating tactics

Chokka squid (Loligo reynaudii) have characteristic alternative mating tactics: ‘consort’ males temporarily pair with and guard a female and transfer spermatophores onto her oviduct opening inside the mantle cavity, whereas ‘sneaker’ males rush towards a mating pair and transfer spermatophores onto the female’s buccal membrane near her sperm storage organ. Differences in mating behaviours and their related sperm-storage sites clearly constrain the fertilization process and can drive dimorphism between consort and sneaker males. The presence and character of male dimorphism has not yet been fully examined in this species, but consort males are commonly much larger than sneaker males. We observed clear dimorphism in spermatangia (the sperm mass ejaculated from the spermatophore), consistently associated with the two alternative sperm storage sites on the female’s body. Observations of spermatophores stored in the Needham’s sac of mature males confirmed that small males produce ‘sneaker-type’ spermatangia whereas larger males produce ‘consort-type’ spermatangia, and no individuals possessed both types. Therefore, by association, the mating tactic adopted (including the sperm deposition site used) by individual males can be determined from observation of their spermatangial type, without requiring direct behavioural observation of mating. This ability to infer information about mating tactic will improve our understanding of the reproductive system and mating dynamics in this species

Evaluation of the Effectiveness of Light Streamer Tori- Lines and Characteristics of Bait Attacks by Seabirds in the Western North Pacific

To improve the effectiveness of tori-lines it is necessary to evaluate the ability of tori-lines to mitigate seabird bycatch and determine what kind of seabird species gather during line settings, attack the bait and are incidentally caught. We conducted two experiments in the western North Pacific and examined the effectiveness for seabird mitigation of light streamer tori-lines which have no long streamers but many light (short) streamers and are mainly used in the North Pacific area. Firstly, the effectiveness of two different types of tori-line (light streamer (1 m) and long streamer (up to 7 m) tori-line) and of two different colors (yellow and red) of light streamers for seabird bycatch avoidance was evaluated using 567 sets based on data from 20 offshore surface commercial longliners. No significant difference in the bycatch number between the different tori-line types and streamer colors was found. Secondly, we investigated the characteristics of the seabird bycatch in the North Pacific and the effectiveness of three different types of streamers (light, hybrid and modified light types) by detailed observations of seabird attacks using a chartered longline vessel. Although the appearance rate of albatrosses and shearwaters were 40.9% and 27.7%, Laysan albatross was the main seabird species that followed the vessel but shearwaters seldom followed the vessel and did not aggregate during line setting. In all attacks on bait observed during line settings, 81% and 7% were by albatrosses and shearwaters, respectively. In the number of primary attacks by Laysan albatrosses which attacked most aggressively of all seabirds, there were no significant differences among the tori-line types. No individuals of shearwater were caught. The results of both experiments indicated that light streamer tori-lines were as effective as tori-lines with long streamers for mitigating seabird bycatch in the North Pacific

Male alternative reproductive tactics and associated evolution of anatomical characteristics in loliginid squid

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marian, J. E. A. R., Apostólico, L. H., Chiao, C. C., Hanlon, R. T., Hirohashi, N., Iwata, Y., Mather, J., Sato, N., & Shaw, P. W. Male alternative reproductive tactics and associated evolution of anatomical characteristics in loliginid squid. Frontiers in Physiology, 10, (2019): 1281, doi: 10.3389/fphys.2019.01281.Loliginid squids provide a unique model system to explore male alternative reproductive tactics (ARTs) and their linkage to size, behavioral decision making, and possibly age. Large individuals fight one another and the winners form temporary consortships with females, while smaller individuals do not engage in male-male agonistic bouts but use various sneaker tactics to obtain matings, each with varying mating and fertilization success. There is substantial behavioral flexibility in most species, as smaller males can facultatively switch to the alternative consort behaviors as the behavioral context changes. These forms of ARTs can involve different: mating posture; site of spermatophore deposition; fertilization success; and sperm traits. Most of the traits of male dimorphism (both anatomical and behavioral) are consistent with traditional sexual selection theory, while others have unique features that may have evolved in response to the fertilization environment faced by each temporary or permanent male morph.JM acknowledges the funding provided by FAPESP (São Paulo Research Foundation – proc. 2013/02653-1, 2014/11008-5, 2015/15447-6, 2017/16182-1, and 2018/19180-2), CNPq (National Council for Scientific and Technological Development – proc. 477233/2013–9), and CAPES (Coordination for the Improvement of Higher Education Personnel – Finance Code 001)

Spermatangium formation and sperm discharge in the Japanese pygmy squid Idiosepius paradoxus

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

Sperm transfer or spermatangia removal: postcopulatory behaviour of picking up spermatangium by female Japanese pygmy squid

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

Seasonal occurrence and sexual maturation of Japanese pygmy squid (Idiosepius paradoxus) at the northern limits of their distribution

The distribution of aquatic animals is severely limited by water temperature. However, little is known about migration pattern, over-wintering and reproduction at the northern limits of their distribution. To investigate the sexual maturation of the Japanese pygmy squid (Idiosepius paradoxus) and its ability to survive during winter at the northern limits of its distribution, we conducted monthly collections at Usujiri in northern Japan and carried out low temperature tolerance experiments. Squids were collected only during four months in autumn and early winter. In autumn, all squids were large and sexually mature, and many egg masses were found on the surface of seagrass, whereas in early winter, only small immature squids were collected. A warm northward-flowing current reached near Usujiri in autumn. These results suggest that squids were transported by the current and some small squids were recruits that hatched at Usujiri. Field data and low temperature tolerance experiments showed that I. paradoxus can not survive in the low seawater temperature that occurs at Usujiri in winter. The migration pattern in I. paradoxus may differ from the major pattern where young fish are passively transported and never reproduce at the northern limits

The effect of predation risk on post-copulatory sexual selection in the Japanese pygmy squid

Abstract: Conspicuous male sexual traits (e.g. weapons for male?male competition and displays for courting females) may attract predators. Under conditions of high predation risk, females typically become less choosy with respect to mates to reduce the time spent on mate selection. However, post-copulatory sexual traits, such as sperm ejaculation for sperm competition and sperm removal for cryptic female choice (CFC), may increase with predation risk because they are more inconspicuous to predators. To examine this hypothesis, we observed the reproductive behaviour in the Japanese pygmy squid, Idiosepius paradoxus, in which the male attaches ejaculated spermatangia to the female’s body and the female removes the spermatangia after copulation. Squid from two populations (Ohmura and Oki), with low and high predation levels, respectively, were copulated in tanks under controlled presence/absence of predator conditions. Among the Ohmura individuals, spermatangia removal was suppressed in the presence of a predator. Females may not be able to remove spermatangia effectively when facing a predator because they feel threatened by the predator; as a result, more spermatangia were retained during trials in which they were exposed to predators. In contrast, squid from the Oki (high predation) population, which is exposed to a higher predation risk, were not strongly affected by the predator presence. While the males ejaculated more spermatangia, the females removed more of them. The effect of sexual conflict may be greater than that of the predation risk in the pygmy squid. This suggests adaptive differences in post-copulatory sexual selection traits linked to predation. Significance statement: In general, the strength of pre-copulatory sexual selection decreases with increasing predation risk because the sexual traits attract predators. However, post-copulatory sexual traits which are often inconspicuous may not be influenced by predation risk. Post-copulatory behaviour of Japanese pygmy squid collected from two populations experiencing different predation levels were investigated under experimental predator presence/absence conditions. Among low predations, individual sperm rejection by females (a post-copulatory trait) was suppressed in the presence of a predator. In contrast, individuals from the high predation population reported no change in sperm rejection. As with pre-copulatory sexual selection, post-copulatory female choice was suppressed by predator presence among individuals from a low predation. However, post-copulatory female choice was not affected by predator presence among individuals from the high-predation population. This may indicate predation-driven adaptive differences and plastic responses in post-copulatory traits