Context-dependent behavioural plasticity compromises disruptive selection of sperm traits in squid

PLoS One. 2021 Aug 30;16(8):e0256745. doi: 10.1371/journal.pone.0256745. eCollection 2021.


Sperm morphology is generally uniform within a species due to selective pressures that act to achieve better fertilization outcomes under postcopulatory competitive circumstances. Therefore, polyandry that intensifies post-mating sperm competition should constrain intraspecific sperm polymorphism. Contrary to this paradigm, we previously found that a polyandrous squid, Heterololigo bleekeri, produces dimorphic eusperm (flagellum length dimorphism; FLD), which is closely associated with alternative reproductive tactics (ARTs); large males (consorts) transfer their spermatophores inside the female's mantle cavity, while small males (sneakers) do so outside the mantle. Thus, FLD was considered as the consequence of different insemination strategies that arise from different modes of sperm competition, sperm storage and the fertilization environment. However, in other squid species showing ARTs, the choice of mating behaviour is rather conditional (i.e., switching mating tactic between consorts and sneakers), which poses the question of whether sperm FLD could have evolved. Here, we investigated five species in the family Loliginidae that exhibit ARTs and found that all species showed sneaker-biased FLD. However, in a species with conditional ARTs, we found FLD rather ambiguous and the testicular somatic index to be nearly continuous among individuals at transitional state, suggesting that plasticity in mating behaviour compromises the disruptive selection on a sperm morphological trait.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Behavior, Animal / physiology*
  • Decapodiformes / physiology*
  • Female
  • Male
  • Reproduction / physiology
  • Sperm Tail / physiology
  • Spermatozoa / physiology*

Associated data

  • figshare/10.6084/m9.figshare.14803266
  • Dryad/10.5061/dryad.cvdncjt4g

Grant support

This study was funded by Kakenhi (#21K06333 to N.H.), the faculty of Life and Environmental Sciences in Shimane Univ. (to N.H.), AUCANI (grant 967/2018 to JEARM and LHA), FAPESP (grant 2017/16182-1 to JEARM and LHA), CAPES (Financial Code 001 to JEARM and LHA) and CNPq (grants 477233/2013-9 and 142170/2017-8 to JEARM and LHA).The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.