User:Kmbio/Idiosepius paradoxus

I am going to write about cryptic female choice in Japanese pygmy squids. Idiosepius paradoxus is a species that is underrepresented on Wikipedia, with only a few lines of information provided. In addition, many articles on cryptic female choice in regard to this species can be found on google scholar. Females of this species have the ability to displace sperm from their bodies after copulation, and I am interested in researching this process and its consequences for both male and female Japanese pygmy squids.

Outline

Lead

• The article already has a few sentences introducing the species and its geographical locations. I may add more details to this overview if the content presents itself while I am exploring the articles I have gathered.

Article body

Appearance

• This section is started but is very brief. I will expand upon the appearance of the species, and possibly include information on the anatomical structures that are important for mating.

Distribution and Habitat

• This section is also started but brief, so I will include details mainly on habitat, with inclusion of habitat requirements for females to spawn. I may also include information on sexual dimorphism in relation to seasonal changes like water temperature in this section.

Diet

• I may add this section if I have enough information on diet that is important to my main focus on cryptic female choice or reproduction/mating behaviors.

Reproduction and Sexual Selection

• Anatomy (incorporate into next two subsections)
  • Since there are quite a few specialized structures on the male and female for reproduction, I will cover any anatomy in regards to reproduction specifically. I will include details on the anatomy of the egg mass.
• Copulation and Spawning
  • In order to discuss cryptic female choice, it is important to understand the mating, spawning, and insemination process. In addition, I will explain how external fertilization is made more successful by the anatomy of structures and methods involved.
• Cryptic Female Choice
  • This will be the largest section as it is the focus of my research. I will include information on cryptic female choice and sexual selection, as well as the consequences of such methods/processes for the species. It seems as though there are differing results in regard to female preference of male traits, so I will describe all sides without favoring one in particular. I may touch on how this post-copulatory mechanism could have evolved in this particular species as well.

2nd Draft

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

Appearance

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

Distribution and Habitat

I. paradoxus is found farthest North of all the species in genus Idiosepius. 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. 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.

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. 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. With small prey, the beak is not needed for biting or severing any body parts. 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.

Reproduction and Sexual Selection

Copulation and Spawning

I. paradoxus mates through a polyandrous system, in which females copulate with numerous males. 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. 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. 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. 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. In this species, sperm form swarms when swimming from spermatangia to the seminal receptacle. The receptacle does not become full until about 8 copulations, after which no more sperm can be held until spawning has occurred.

The female can mate with multiple males and retain sperm from each before adhering to a substrate such as seagrass to spawn. 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. 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. This process is repeated for multiple rows of eggs. Each egg is wrapped in 8-10 gelatinous layers, and these may function in protection against small microorganisms. Females may spawn several times in this fashion from a full seminal receptacle.

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. 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. 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.

There is evidence from multiple studies that smaller males are preferred by females, meaning females remove more spermatangia from larger males. 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. 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. 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. 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.

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. 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.

References

1. Kasugai, T., Sato, N., and Yoshida, M. 2017. 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.
2. Fujiwara, E., Hirohashi, N., Iwata, Y., Kasugai, T., Sato, N., and Watanabe, Y. 2019. How female squid inseminate their eggs with stored sperm. Current Biology. 29(2):R48-R49.
3. Kasugai, T., Munehara, H., and Sato, N. 2013. Female Pygmy Squid Cryptically Favour Small Males and Fast Copulation as Observed by Removal of Spermatangia. Evolutionary Biology. 41:221-228.
4. Sato, N. 2017. Seasonal changes in reproductive traits and paternity in the Japanese pygmy squid Idiosepius paradoxus. Marine Ecology Progress Series. 582:121-131.
5. Sato, N., Takegaki, T., and Uchida, Y. 2018. The effect of predation risk on post-copulatory sexual selection in the Japanese pygmy squid. Behavioral Ecology and Sociobiology. 72(129).
6. Hirohashi, N., Iida, T., Iwata, Y., Sato, N., and Warwick, S.H.H. 2016. Complex adaptive traits between mating behaviour and post-copulatory sperm behaviour in squids. Reviews in Fish Biology and Fisheries. 26:601-607.
7. Kasugai, T., Munehara, H., and Sato, N. 2012. Sperm transfer or spermatangia removal: postcopulatory behaviour of picking up spermatangium by female Japanese pygmy squid. Marine Biology. 160:553-561.
8. Awata, S., Munehara, H., and Sato, N. 2009. 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.
9. Fujiwara, E., Kasugai, T., Sato, N., and Yoshida, M. 2013. High-speed camera observations of copulatory behaviour in Idiosepius paradoxus: function of the dimorphic hectocotyli. Journal of Molluscan Studies. 79(2):183-186.
10. Kasugai, T., and Segawa, S. 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.
11. Ikeda, Y., Kasugai, T., and Shigeno, S. 2004. Feeding and external digestion in the Japanese pygmy squid Idiosepius paradoxus (Cephalopoda: Idiosepiidae). Journal of Molluscan Studies. 70(3):231-236.
12. Ikeda, Y., and Kasugai, T. 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.
13. Kasugai, T., Munehara, H., and Sato, N. 2014. Spermatangium formation and sperm discharge in the Japanese pygmy squid Idiosepius paradoxus. Zoology. 117(3):192-199.
14. Ikeda, Y., Kasugai, T., Munehara, H., and Sato, N. 2010. Structure of the seminal receptacle and sperm storage in the Japanese pygmy squid. Journal of Zoology. 282(3):151-156.
15. Sato, N., and Takeshita, F. 2016. Adaptive Sex-Specific Cognitive Bias in Predation Behaviours of Japanese Pygmy Squid. Ethology. 122(3):236-244.