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.
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 female's 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 female's 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.
Graduate School of Fisheries Science and Environmental Studies, Nagasaki University, Nagasaki, Nagasaki, Japan.|Current Address: Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, Penglais, Aberystwyth, United Kingdom.
Noriyosi
N
Sato
Center for Information Biology, National Institute of Genetics, Mishima, Shizuoka, Japan.|Current Address: Marine Biological Science Section, Education and Research Center for Biological Resources, Faculty of Life and Environmental Science, Shimane University, Kamo 194, Okinoshima-cho, Oki, Shimane, Japan.
Masa-Aki
MA
Yoshida
Port of Nagoya Public Aquarium, 1-3 Minato-machi, Minato-ku, Nagoya, Aichi, Japan.
Takashi
T
Kasugai
D000818:Animals; D003307:Copulation; D049832:Decapodiformes / Q000235:genetics / Q000502:physiology*; D005260:Female; D005306:Fertilization; D007314:Insemination; D008297:Male; D052586:Mating Preference, Animal
Cephalopod; cryptic female choice; disruptive selection; paternity analysis; postcopulatory sexual selection