Male Alternative Reproductive Tactics and Associated Evolution of Anatomical Characteristics in Loliginid Squid

Abstract

Loliginid squids provide a unique model system to explore male alternative reproductive tactics (ARTs) and their linkage to size, behavioral decision making, and possibly age. Large individuals fight one another and the winners form temporary consortships with females, while smaller individuals do not engage in male-male agonistic bouts but use various sneaker tactics to obtain matings, each with varying mating and fertilization success. There is substantial behavioral flexibility in most species, as smaller males can facultatively switch to the alternative consort behaviors as the behavioral context changes. These forms of ARTs can involve different: mating posture; site of spermatophore deposition; fertilization success; and sperm traits. Most of the traits of male dimorphism (both anatomical and behavioral) are consistent with traditional sexual selection theory, while others have unique features that may have evolved in response to the fertilization environment faced by each temporary or permanent male morph.

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

“…pleii , such ML-based discontinuities in sperm FL and TSI are absent ( Fig 3B and 3D ), which is consistent with previous observations that adult males with intermediate body size (132–178 mm ML) could change their mating tactics flexibly in response to female spawning behaviours [ 12 ]. Thus, an ontogenetic transition from sneaker to consort might occur within the same individuals [ 10 , 12 , 16 ]. Such flexibility in male mating behaviour was also observed in S .…”

“…This phenomenon is also observed in Loligo forbesi [ 15 ]. Hence, squid ARTs display a broad spectrum of adaptive traits including a variable intensity of phenotypic plasticity with a complex repertoire of behaviour, morphology and physiology [ 16 ]. In light of these interspecific variables, here we address the evolutionary consequences of sperm flagellum length dimorphism (FLD) in closely related species with different levels of tactical plasticity.…”

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

“…The most distinctive feature in cephalopod reproduction is that females of loliginid squids possess two physically separate sperm storage sites linked to discrete male alternative reproductive tactics (ARTs). The males exclusively or conditionally adopt different mating positions and deposit their sperm packages in a specific sperm storage site on females (see Marian et al., 2019). Females have a seminal receptacle on their buccal membrane and store sperm transferred by head‐to‐head copulation with males before they reach the spawning grounds, possibly before they become sexually mature, and for considerable durations (Drew, 1911).…”

Dynamic Courtship Signals and Mate Preferences in Sepia plangon

“…For instance, the hectocotylus, ligula, and calamus in males are morphological adaptations to transfer the sperm to the females (Voight, 1991 , 2002 ; Thompson and Voight, 2003 ). Alternative mating tactics in squids and cuttlefish enhance the mating opportunities of small males by avoiding male competitions (Hanlon et al, 2002 ; Wada et al, 2005 ; Zeidberg, 2009 ; Brown et al, 2012 ; Lin and Chiao, 2018 ; Marian et al, 2019 ). Male octopus mate “at a distance” to escape and avoid sexual cannibalism (Hanlon and Forsythe, 2008 ; Huffard and Bartick, 2015 ).…”