29
males. In captivity, males may initiate copulation without obvious courtship (which
females may avoid through escape responses), and male–male aggression occurs.
The extent to which these behaviours are artefacts of spatial constraint in captivity
is not known (Adamo et al. 2000) and may pose challenges for cultivation. Hanlon
et al. (1999a) observed that males initiate mating in the head-to-head posture, and
then direct jets of water on at the female’s buccal membrane, likely to flush spermatangia placed there by previous mating, and then transfer their own spermatangia
to the buccal membrane using the hectocotylus. The male then manipulates the
spermatangium on the female to break it open so that sperm are released. Females
appear to terminate mating and are then guarded briefly by the male.
Some squid species (e.g. Loligo vulgaris: Arnold 1990; I� illecebrosus:
Hendrickson 2004) but not others (e.g. D� gigas: Nigmatullin et al. 2001) aggregate
for spawning. Spawning grounds, e.g. for L� reynaudii, may be used repeatedly,
spawning may not be synchronized within an entire population, and squid move
between grounds over an extended period (Sauer et al. 2000). Nonetheless, spawning aggregations are harvested and support managed fisheries (Rodhouse 2001). In
captivity, L� vulgaris mating behaviour and male–male aggression may be induced
by the presence of a recently laid egg mass (or visually similar object) in the tank
or even in the visual field (Arnold 1990), as well as by pheromones present in the
egg mass (King et al. 2003; Cummins et al. 2011). Arnold (1990) observed that on
detecting such an object, individual sexually mature squid investigate the object
tactilely and may jet water at it (possibly an effort to flush away sperm from other
males, see ‘Cuttlefish’ above). Males begin to dart about, display to other males,
and place themselves between females and rival males. Females and males display
to each other, accentuating oviducal gland and testes, respectively ( L� reynaudii,
Hanlon et al. 2002). A male will swim alongside a female and raise one or two medial arm in an S-shaped curved display posture. Dark bands or patches also feature
in this display, especially in competition with rival males, who may also be chased
(Byrne et al. 2003; Mather 2004). Male–male contests may also include physical
contact such as fin beating (Hanlon et al. 2002). Social hierarchies determined via
dominance in agnostic displays develop in captivity (Arnold 1990), while paired
males have an advantage over intruder males in the wild (Hanlon et al. 2002), an
effect due to female choice, as females jet to avoid unwanted male mating attempts.
Copulation of paired L� vulgaris, described by Arnold (1990) and of L� reynaudii described by Hanlon et al. (2002), is preceded by the male positioning himself
alongside but slightly below the female, flashing chromatophores. The male then
grabs the female and positions his arms close to her mantle opening. He reaches into
his mantle with his hectocotylus and picks up spermatophores, which are quickly
ejaculated and cemented to the inside of the female mantle near the opening of the
oviduct. The male then releases the female. Copulatory behaviour may be interspersed with egg laying, and newly released sperm may be observed on just-laid
egg masses. Female choice may operate on several levels, including female manipulation of sex ratios, avoidance of mating attempts, and selection of stored sperm
to fertilize eggs (Hanlon et al. 2002), leading to multiple paternity within egg strings
(Shaw and Sauer 2004). Copulation alternated with egg laying will continue until
2 Behaviour
males. In captivity, males may initiate copulation without obvious courtship (which
females may avoid through escape responses), and male–male aggression occurs.
The extent to which these behaviours are artefacts of spatial constraint in captivity
is not known (Adamo et al. 2000) and may pose challenges for cultivation. Hanlon
et al. (1999a) observed that males initiate mating in the head-to-head posture, and
then direct jets of water on at the female’s buccal membrane, likely to flush spermatangia placed there by previous mating, and then transfer their own spermatangia
to the buccal membrane using the hectocotylus. The male then manipulates the
spermatangium on the female to break it open so that sperm are released. Females
appear to terminate mating and are then guarded briefly by the male.
Some squid species (e.g. Loligo vulgaris: Arnold 1990; I� illecebrosus:
Hendrickson 2004) but not others (e.g. D� gigas: Nigmatullin et al. 2001) aggregate
for spawning. Spawning grounds, e.g. for L� reynaudii, may be used repeatedly,
spawning may not be synchronized within an entire population, and squid move
between grounds over an extended period (Sauer et al. 2000). Nonetheless, spawning aggregations are harvested and support managed fisheries (Rodhouse 2001). In
captivity, L� vulgaris mating behaviour and male–male aggression may be induced
by the presence of a recently laid egg mass (or visually similar object) in the tank
or even in the visual field (Arnold 1990), as well as by pheromones present in the
egg mass (King et al. 2003; Cummins et al. 2011). Arnold (1990) observed that on
detecting such an object, individual sexually mature squid investigate the object
tactilely and may jet water at it (possibly an effort to flush away sperm from other
males, see ‘Cuttlefish’ above). Males begin to dart about, display to other males,
and place themselves between females and rival males. Females and males display
to each other, accentuating oviducal gland and testes, respectively ( L� reynaudii,
Hanlon et al. 2002). A male will swim alongside a female and raise one or two medial arm in an S-shaped curved display posture. Dark bands or patches also feature
in this display, especially in competition with rival males, who may also be chased
(Byrne et al. 2003; Mather 2004). Male–male contests may also include physical
contact such as fin beating (Hanlon et al. 2002). Social hierarchies determined via
dominance in agnostic displays develop in captivity (Arnold 1990), while paired
males have an advantage over intruder males in the wild (Hanlon et al. 2002), an
effect due to female choice, as females jet to avoid unwanted male mating attempts.
Copulation of paired L� vulgaris, described by Arnold (1990) and of L� reynaudii described by Hanlon et al. (2002), is preceded by the male positioning himself
alongside but slightly below the female, flashing chromatophores. The male then
grabs the female and positions his arms close to her mantle opening. He reaches into
his mantle with his hectocotylus and picks up spermatophores, which are quickly
ejaculated and cemented to the inside of the female mantle near the opening of the
oviduct. The male then releases the female. Copulatory behaviour may be interspersed with egg laying, and newly released sperm may be observed on just-laid
egg masses. Female choice may operate on several levels, including female manipulation of sex ratios, avoidance of mating attempts, and selection of stored sperm
to fertilize eggs (Hanlon et al. 2002), leading to multiple paternity within egg strings
(Shaw and Sauer 2004). Copulation alternated with egg laying will continue until
2 Behaviour