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Sperm competition risk affects ejaculate strategy in terms of sperm number but not sperm size in squid

Citation

Iwata, Yoko et al. (2021), Sperm competition risk affects ejaculate strategy in terms of sperm number but not sperm size in squid, Dryad, Dataset, https://doi.org/10.5061/dryad.cvdncjt4g

Abstract

In polygamous species, the mode of sperm storage in females influences evolution of sperm quantitative and qualitative traits because it provides the arena for sperm competition, cryptic female choice and fertilization processes. In this study, we compared ejaculate traits of two squid species, Heterololigo bleekeri and Loligo reynaudii. Both species show dimorphic sperm traits associated with alternative reproductive tactics where consort and sneaker males transfer sperm to different storage sites within a female (on the oviduct and near the mouth, respectively). Due to differences in reproductive behaviours and sperm placement, sperm competition risk is expected to be higher in sneakers than in consorts of both species, and higher overall in L. reynaudii. Our results demonstrate that the instantaneous number of released sperm is adjusted to the expected sperm competition risk via an elaborate sperm package. Consort sperm are similar in size, however, sneaker sperm have a significantly longer flagellum in H. bleekeri than in L. reynaudii, most likely due to intra-tactic conflicts associated with sperm storage conditions. From consideration of the different mating tactics, we suggest that while levels of sperm competition determine quantitative traits, sperm quality traits are determined more by the mode of sperm storage and fertilization.

Methods

See Materials & Methods of the paper below; 
Yoko Iwata, Noriyosi Sato, Noritaka Hirohashi, Yoshiro Watanabe, Warwick H. H. Sauer, Paul W. Shaw. (2021) Sperm competition risk affects ejaculate strategy in terms of sperm number but not sperm size in squid. Journal of Evolutionary Biology
https://onlinelibrary.wiley.com/doi/10.1111/jeb.13894

Funding

EU Marie Curie Incoming Fellowship

Japan Society for the Promotion of Science, Award: 10J07243

Japan Society for the Promotion of Science, Award: 14J40174

Japan Society for the Promotion of Science, Award: 15H06150

the National Research Foundation, South Africa

the South African Squid Management Industrial Association

EU Marie Curie Incoming Fellowship

the National Research Foundation, South Africa

the South African Squid Management Industrial Association