Idiosepius paradoxus

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Idiosepius paradoxus
Idiosepius paradoxus himeika03 1.jpg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Idiosepida
Family: Idiosepiidae
Genus: Idiosepius
Species:
I. paradoxus
Binomial name
Idiosepius paradoxus
(Ortmann, 1888)
Synonyms
  • Microteuthis paradoxus
    Ortmann, 1888
  • Idiosepius pygmaeus paradoxus
    (Ortmann, 1888)

Idiosepius paradoxus, also known as the northern pygmy squid, is a species of pygmy squid native to the western Pacific Ocean. This species can be found inhabiting shallow, inshore waters around central China, South Korea, and Japan. [2] [3]

Contents

Appearance

This species is part of the smallest known squid genus, growing only to 16 mm (0.63 in) in mantle length. [3] [4] Females tend to be larger than males, and the presence of nidamental glands for secretion of egg jelly differentiates them from males. [5] Males can be identified by the presence of a singular white testis found posteriorly in the body. [4] Both sexes have a unique organ found on their dorsal mantle for binding themselves to a substrate, such as seagrass. [6] The type specimen was collected off Kadsiyama in Tokyo Bay and is conserved at the Musee Zoologique in Strasbourg. [7]

Distribution and habitat

I. paradoxus is found farthest North of all the species in genus Idiosepius. [2] The distribution of this species includes the waters off South Korea and northern Australia, as well as the Japanese islands of Honshu, Kyushu, and southern Hokkaido. In these locations, this squid can be found in the demersal zone of the ocean in subtropical climates. It resides in algae, seagrass, and seaweed. [3] Based on season within its distribution, there are two recorded life histories. Small type squid hatch between March and July and spawn between June and September, while large type squid hatch in the summer and spawn during the next spring, and have longer reproductive seasons. [8] [9]

Diet

This species feeds mainly on small fish, shrimp, and other organisms. They can prey on larger fish, but may not be able to fully digest all of the flesh. [10] Just as they utilize external fertilization, these squid can externally digest their food as well. Anatomically, they possess both a beak and a buccal mass. The buccal mass is used to break through hard exoskeletons, secrete digestive fluids, and then remove the softened flesh of prey. [10] With small prey, the beak is not needed for biting or severing any body parts. [10] There is also evidence of a sex-specific cognitive bias in I. paradoxus, such that females more often than males overestimate the size of prey they will be able to successfully attack. [11]

Reproduction and sexual selection

Copulation and spawning

I. paradoxus mates through a polyandrous system, in which females copulate with numerous males. [6] The focus of existing research seems to be on female promiscuity, with little information on how many partners are acquired per male. Males do not exhibit precopulatory behaviors, such as male-male competition, so a male and female will mate upon finding one another. [6] The male grasps the female in a head-to-head position using his right hectocotylus, which he also uses to point towards her arm crown externally. He then uses his left hectocotylus to grasp spermatophores containing sperm from his funnel, post ejaculation. [4] The spermatophores become spermatangia through an eversion reaction involving the ejaculatory apparatus and cement body, and are then placed on the female's body directed by the groove on the right hectocotylus. [4] [12] The sperm become activated by seawater, and will swim to the seminal receptacle around the female's buccal mass on the ventral mantle, where they will be stored until spawning and fertilization. [12] [13] In this species, sperm form swarms when swimming from spermatangia to the seminal receptacle. [14] The receptacle does not become full until about 8 copulations, after which no more sperm can be held until spawning has occurred. [13]

The female can mate with multiple males and retain sperm from each before adhering to a substrate such as seagrass to spawn. [5] Once ready, the female releases egg jelly from her nidamental gland, out her funnel, and into her arms, followed by a single egg that she attaches to the substrate. [5] During attachment, she covers the egg with her buccal membrane so that sperm can be passed from the seminal receptacle to the egg through individualized external fertilization. [5] This process is repeated for multiple rows of eggs. [5] Each egg is wrapped in 8–10 gelatinous layers, and these may function in protection against small microorganisms. [15] Females may spawn several times in this fashion from a full seminal receptacle. [13]

Cryptic female choice

I. paradoxus has been used in the study of cryptic female choice due to male sperm transfer to an external location on the female's body, making this process more easily observable than in other species. [6] Once the female has mated, either with one male or several, she can use her buccal mass to pull spermatangia off her body individually to get rid of as many as she chooses. [16] By removing spermatangia, she is choosing which male(s) will have greater opportunity to sire her offspring. In this way, postcopulatory mechanisms in this species can act as sexual selection for certain traits in males. [6]

There is evidence from multiple studies that smaller males are preferred by females, meaning females remove more spermatangia from larger males. [6] [17] However, whether females prefer longer or shorter copulations is debated. Some evidence points towards preference for longer copulating males, while other evidence shows preference for decreased copulation times. [6] [17] It has been observed that sperm transfer to the seminal receptacle from the spermatangium must occur within 24 hours, as almost all spermatangia in the species discharged their spermatozoa within 24 hours. In the beginning, rapid sperm discharge is observed, but after 5 minutes it becomes intermittent. [18] A possible explanation for female preference of small and fast copulating males could be that predation risk is decreased with shorter time spent in copula and less attention drawn with smaller body size. [17] Predation could actually act as a selection pressure for increased postcopulatory versus precopulatory behaviors in I. paradoxus, as postcopulatory behaviors like cryptic female choice may draw less attention and be easier to exhibit when also under threat of predation. [19] In addition, there is evidence that cryptic female choice could be adaptive when comparing populations experiencing high versus low predation: the population more often exposed to predation may be able to carry out cryptic female choice as usual without decreasing the behavior, unlike in populations which are not used to predation. [19]

While females are able to exhibit choice, males engage in behaviors to give their sperm the best chance of making it to the female's seminal receptacle. During copulation, males have been observed directing their spermatangia by the right hectocotylus to different locations on the female's body (such as different arm crown bases) per spermatophore ejaculation. [4] This is thought to reduce the number of spermatangia removed by the female from a particular male, as their spermatangia are spread to multiple locations that the female may be unaware of. [4]

Related Research Articles

<span class="mw-page-title-main">Sexual selection</span> Mode of natural selection involving the choosing of and competition for mates

Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with, and compete with members of the same sex for access to members of the opposite sex. These two forms of selection mean that some individuals have greater reproductive success than others within a population, for example because they are more attractive or prefer more attractive partners to produce offspring. Successful males benefit from frequent mating and monopolizing access to one or more fertile females. Females can maximise the return on the energy they invest in reproduction by selecting and mating with the best males.

<span class="mw-page-title-main">Cephalopod</span> Class of mollusks

A cephalopod is any member of the molluscan class Cephalopoda such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.

<i>Idiosepius</i> Genus of molluscs

Idiosepius is a genus of squids in the family Idiosepiidae. They are small, reaching mantle lengths of no more than about 21 mm (0.8 in); members of this genus represent no interest to commercial fisheries. They occur in tropical and temperate waters throughout the Indo-Pacific, primarily in association with seagrass and mangrove roots.

<span class="mw-page-title-main">Sperm competition</span> Reproductive process

Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction. Competition can occur when females have multiple potential mating partners. Greater choice and variety of mates increases a female's chance to produce more viable offspring. However, multiple mates for a female means each individual male has decreased chances of producing offspring. Sperm competition is an evolutionary pressure on males, and has led to the development of adaptations to increase male's chance of reproductive success. Sperm competition results in a sexual conflict between males and females. Males have evolved several defensive tactics including: mate-guarding, mating plugs, and releasing toxic seminal substances to reduce female re-mating tendencies to cope with sperm competition. Offensive tactics of sperm competition involve direct interference by one male on the reproductive success of another male, for instance by mate guarding or by physically removing another male's sperm prior to mating with a female. For an example, see Gryllus bimaculatus.

<span class="mw-page-title-main">Hectocotylus</span> Cephalopod sex organ

A hectocotylus is one of the arms of male cephalopods that is specialized to store and transfer spermatophores to the female. Structurally, hectocotyli are muscular hydrostats. Depending on the species, the male may use it merely as a conduit to the female, analogously to a penis in other animals, or he may wrench it off and present it to the female.

<span class="mw-page-title-main">Southern blue-ringed octopus</span> Species of mollusc

The southern blue-ringed octopus is one of three highly venomous species of blue-ringed octopuses. It is most commonly found in tidal rock pools along the south coast of Australia. As an adult, it can grow up to 20 centimetres (8 in) long and on average weighs 26 grams (0.9 oz). They are normally a docile species, but they are highly venomous, possessing venom capable of killing humans. Their blue rings appear with greater intensity when they become aggravated or threatened.

<span class="mw-page-title-main">Firefly squid</span> Species of cephalopod also known as the sparkling enope squid

The firefly squid, also commonly known as the sparkling enope squid or hotaru-ika in Japan, is a species of squid in the family Enoploteuthidae. W. scintillans is the sole species in the monotypic genus Watasenia.

<i>Metasepia tullbergi</i> Species of cuttlefish

The paintpot cuttlefish is a small, poorly researched species of cuttlefish found in the Indo-Pacific, between Japan and Hong Kong. It is one of the two species classified in the genus Metasepia. Metasepia cuttlefish are characterized by their small, thick, diamond-shaped cuttlebone, and distinctive body coloration.

<i>Metasepia pfefferi</i> Species of cuttlefish

Metasepia pfefferi, also known as the flamboyant cuttlefish, is a species of cuttlefish occurring in tropical Indo-Pacific waters off northern Australia, southern New Guinea, as well as numerous islands of the Philippines, Indonesia and Malaysia.

<span class="mw-page-title-main">Idiosepiidae</span> Family of molluscs

Idiosepiidae, also known as the pygmy squids, is a family of squids in the superorder Decapodiformes. They are the smallest known squids.

Idiosepius minimus is a species of bobtail squid native to the "coast of Africa" where it occurs in shallow, inshore waters. Specimens collected under the junior synonyms I. biserialis and I. macrocheir were described from Mozambique. Since then, the further collecting effort off Mozambique has seen additional specimens gained. As a result it has been inferred that this species has a relatively restricted distribution since Idiosepius has not been recorded elsewhere in Africa.

Idiosepius thailandicus, also known as the thai pygmy squid, is a species of bobtail squid native to the Indo-Pacific waters off Thailand. The extent of this species' distribution is still to be determined and records of Idiosepius dwarf squid away from Thailand, south to Indonesia and north to Japan, may be attributable to this species.

<i>Idiosepius pygmaeus</i> Species of mollusc

Idiosepius pygmaeus, also known as the two-toned pygmy squid, Tropical Pygmy squid, is a species of bobtail squid native to the Indo-Pacific. It occurs in waters of the South China Sea, Japan, Philippines, Palau, Indonesia, Northern Mariana Islands, as well as northern and northeastern Australia. It inhabits shallow, inshore waters.

<i>Thysanoteuthis rhombus</i> Species of cephalopod known as the diamond squid or diamondback squid

Thysanoteuthis rhombus, also known as the diamond squid,diamondback squid, or rhomboid squid, is a large species of squid from the family Thysanoteuthidae which is found worldwide, throughout tropical and subtropical waters. T. rhombus is given its name for the appearance of the fins that run the length of the mantle. They are a fast growing species with a lifespan of approximately 1 year. The diamond squid is the only cephalopod species known to be monogamous. T. rhombus often preys on fish and other small cephalopods at varying water depths. This species is commercially fished in Japan, specifically in the Sea of Japan and Okinawa.

<span class="mw-page-title-main">Female sperm storage</span>

Female sperm storage is a biological process and often a type of sexual selection in which sperm cells transferred to a female during mating are temporarily retained within a specific part of the reproductive tract before the oocyte, or egg, is fertilized. This process takes place in some species of animals, but not in humans. The site of storage is variable among different animal taxa and ranges from structures that appear to function solely for sperm retention, such as insect spermatheca and bird sperm storage tubules, to more general regions of the reproductive tract enriched with receptors to which sperm associate before fertilization, such as the caudal portion of the cow oviduct containing sperm-associating annexins. Female sperm storage is an integral stage in the reproductive process for many animals with internal fertilization. It has several documented biological functions including:

Sexual antagonistic co-evolution is the relationship between males and females where sexual morphology changes over time to counteract the opposite's sex traits to achieve the maximum reproductive success. This has been compared to an arms race between sexes. In many cases, male mating behavior is detrimental to the female's fitness. For example, when insects reproduce by means of traumatic insemination, it is very disadvantageous to the female's health. During mating, males will try to inseminate as many females as possible, however, the more times a female's abdomen is punctured, the less likely she is to survive. Females that possess traits to avoid multiple matings will be more likely to survive, resulting in a change in morphology. In males, genitalia is relatively simple and more likely to vary among generations compared to female genitalia. This results in a new trait that females have to avoid in order to survive.

<span class="mw-page-title-main">Bigfin reef squid</span> Species of squid

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Cryptic female choice is a form of mate choice which occurs both in pre and post copulatory circumstances when females in certain species use physical or chemical mechanisms to control a male's success of fertilizing their ova or ovum; i.e. by selecting whether sperm are successful in fertilizing their eggs or not. It occurs in internally-fertilizing species and involves differential use of sperm by females when sperm are available in the reproductive tract.

<i>Sepia esculenta</i>

Sepia esculenta, the golden cuttlefish, is a cuttlefish ranging from the Russian seas to the Philippines and throughout the western Pacific. This species of cuttlefish is a nektobenthic organism living with a range of depths between 10m-150m(33 ft-492 ft) but is primarily found within the shallow, coastal waters from japan to the Philippines at a depth between 10m-100m. Members of this species are roughly 18 cm in length.

<i>Sepiadarium austrinum</i> Species of cuttlefish

Sepiadarium austrinum, the southern bottletail squid, is a species of cuttlefish in the genus Sepiadarium. It was first described by S. Stillman Berry in 1921 based on a specimen found in St. Vincent Bay in South Australia.

References

  1. ↑ Barratt, I.; Allcock, L. (2012). "Idiosepius paradoxus". IUCN Red List of Threatened Species . 2012: e.T162657A937941. doi: 10.2305/IUCN.UK.2012-1.RLTS.T162657A937941.en . Retrieved 19 November 2021.
  2. 1 2 Kasugai, Takashi; Segawa, Susumu (2005). "Life cycle of the Japanese pygmy squid Idiosepius paradoxus (Cephalopoda: Idiosepiidae) in the Zostera beds of the temperate coast of central Honshu, Japan". Phuket Marine Biological Center Research Bulletin. 66: 249–258.
  3. 1 2 3 Reid, A. 2005. Family Idiosepiidae. In: P. Jereb & C.F.E. Roper, eds. Cephalopods of the world. An annotated and illustrated catalogue of species known to date. Volume 1. Chambered nautiluses and sepioids (Nautilidae, Sepiidae, Sepiolidae, Sepiadariidae, Idiosepiidae and Spirulidae). FAO Species Catalogue for Fishery Purposes. No. 4, Vol. 1. Rome, FAO. pp. 208–210.
  4. 1 2 3 4 5 6 Sato, Noriyosi; Yoshida, Masa-Aki; Fujiwara, Eiji; Kasugai, Takashi (2013). "High-speed camera observations of copulatory behaviour in Idiosepius paradoxus: function of the dimorphic hectocotyli". Journal of Molluscan Studies. 79 (2): 183–186. doi:10.1093/mollus/eyt005. hdl: 10069/32938 . Retrieved 2023-02-17.
  5. 1 2 3 4 5 Iwata, Yoko; Sato, Noriyosi; Hirohashi, Noritaka; Kasugai, Takashi; Watanabe, Yoshiro; Fujiwara, Eiji (2019-01-21). "How female squid inseminate their eggs with stored sperm". Current Biology. 29 (2): R48–R49. doi: 10.1016/j.cub.2018.12.010 . ISSN   0960-9822. PMID   30668945. S2CID   58949271.
  6. 1 2 3 4 5 6 7 Sato, Noriyosi; Yoshida, Masa-aki; Kasugai, Takashi (2016-11-17). "Impact of cryptic female choice on insemination success: Larger sized and longer copulating male squid ejaculate more, but females influence insemination success by removing spermatangia". Evolution. 71 (1): 111–120. doi:10.1111/evo.13108. ISSN   0014-3820. PMID   27805265. S2CID   8866473.
  7. ↑ Current Classification of Recent Cephalopoda
  8. ↑ Sato, Noriyosi; Awata, Satoshi; Munehara, Hiroyuki (2009-06-01). "Seasonal occurrence and sexual maturation of Japanese pygmy squid (Idiosepius paradoxus) at the northern limits of their distribution". ICES Journal of Marine Science. 66 (5): 811–815. doi:10.1093/icesjms/fsp145. hdl: 2115/43087 . ISSN   1095-9289.
  9. ↑ Sato, Noriyosi (2017-11-06). "Seasonal changes in reproductive traits and paternity in the Japanese pygmy squid Idiosepius paradoxus". Marine Ecology Progress Series. 582: 121–131. doi:10.3354/meps12338. ISSN   0171-8630.
  10. 1 2 3 KASUGAI, T. (2004-08-01). "Feeding and External Digestion in the Japanese Pygmy Squid Idiosepius Paradoxus (Cephalopoda: Idiosepiidae)". Journal of Molluscan Studies. 70 (3): 231–236. doi: 10.1093/mollus/70.3.231 . ISSN   1464-3766.
  11. ↑ Takeshita, Fumio; Sato, Noriyosi (2016). Herberstein, M. (ed.). "Adaptive Sex-Specific Cognitive Bias in Predation Behaviours of Japanese Pygmy Squid". Ethology. 122 (3): 236–244. doi:10.1111/eth.12464.
  12. 1 2 Sato, Noriyosi; Kasugai, Takashi; Munehara, Hiroyuki (2014-06-01). "Spermatangium formation and sperm discharge in the Japanese pygmy squid Idiosepius paradoxus". Zoology. 117 (3): 192–199. doi:10.1016/j.zool.2014.02.001. hdl: 10069/34531 . ISSN   0944-2006. PMID   24813852.
  13. 1 2 3 Sato, N.; Kasugai, T.; Ikeda, Y.; Munehara, H. (2010). "Structure of the seminal receptacle and sperm storage in the Japanese pygmy squid". Journal of Zoology. 282 (3): 151–156. doi:10.1111/j.1469-7998.2010.00733.x. ISSN   0952-8369.
  14. ↑ Hirohashi, Noritaka; Iida, Tomohiro; Sato, Noriyosi; Warwick, Sauer H. H.; Iwata, Yoko (2016-09-01). "Complex adaptive traits between mating behaviour and post-copulatory sperm behaviour in squids". Reviews in Fish Biology and Fisheries. 26 (3): 601–607. doi:10.1007/s11160-016-9434-1. ISSN   1573-5184. S2CID   254988171.
  15. ↑ Kasugai, Takashi; Ikeda, Yuzuru (2003). "Description of the Egg Mass of Pygmy Cuttlefish, Idiosepius paradoxus (Cephalopoda: Idiosepiidae), with Special Reference to its Multiple Gelatinous Layers". The Veliger. 46 (2): 105–110.
  16. ↑ Sato, Noriyosi; Kasugai, Takashi; Munehara, Hiroyuki (2013-03-01). "Sperm transfer or spermatangia removal: postcopulatory behaviour of picking up spermatangium by female Japanese pygmy squid". Marine Biology. 160 (3): 553–561. doi:10.1007/s00227-012-2112-5. hdl: 10069/31698 . ISSN   1432-1793. S2CID   253740276.
  17. 1 2 3 Sato, Noriyosi; Kasugai, Takashi; Munehara, Hiroyuki (2014-06-01). "Female Pygmy Squid Cryptically Favour Small Males and Fast Copulation as Observed by Removal of Spermatangia". Evolutionary Biology. 41 (2): 221–228. doi:10.1007/s11692-013-9261-4. hdl: 10069/34511 . ISSN   1934-2845. S2CID   255343132.
  18. ↑ Noriyosi Sato, Takashi Kasugai, Hiroyuki Munehara, Spermatangium formation and sperm discharge in the Japanese pygmy squid Idiosepius paradoxus, Zoology,Volume 117, Issue 3,2014, Pages 192-199,https://doi.org/10.1016/j.zool.2014.02.001.
  19. 1 2 Sato, Noriyosi; Uchida, Yu; Takegaki, Takeshi (2018-07-12). "The effect of predation risk on post-copulatory sexual selection in the Japanese pygmy squid". Behavioral Ecology and Sociobiology. 72 (8): 129. doi:10.1007/s00265-018-2540-4. hdl: 10069/38504 . ISSN   1432-0762. S2CID   253806315.

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