25
been a selective force for cuttlefish intelligence (Brown et al. 2012). A size-based
dominance hierarchy is true for older, though not newly hatched cuttlefish (Warnke
1994). Boal (1996) tackled the problem of social recognition through laboratory observations. She found that cuttlefish kept together in tanks did not react differently
to familiar vs unfamiliar conspecifics and were not closer to familiar than unfamiliar ones. Given visual stimuli, they were more aroused (with a higher ventilation
rate) by the sight of prey items than that of conspecifics (Boal and Ni 1996). When
they were maintained in a small or a large tank, cuttlefish spaced themselves more
widely in the large one and seldom approached to within two body lengths. In a
small tank, there were more male agonistic zebra displays and more displacement
of one animal by another (Boal et al. 1999). More importantly, cuttlefish in the large
tank consumed 25 % more shrimp prey, suggesting that the crowding in the small
(1.5 m diameter for three animals) tank was stressful and that this stress was reducing food intake. This is not good news for anyone who wishes to cultivate cuttlefish
in captivity; a more complex habitat may provide visual separation and reduce this
stress.
Squid are different, in that they prefer to swim with conspecifics (Hurley 1978),
in approximately parallel orientation and within a body length or two in captivity,
even in a very large tank, 15 m in diameter (Mather and O’Dor 1984). Because the
adults do not live after egg laying and the young are planktonic, again there is little
likelihood of kin recognition. Most squid gather with conspecifics, though Moynihan and Rodaniche (1982) noted S� sepioidea swimming with Doryteuthis (Loligo)
plei. Groups sort by size; although S� sepioidea are attracted to conspecifics whatever the size, smaller animals are at risk for cannibalism from larger ones and so
maintain several body lengths distance. It has been suggested that squid on the end
of a line are sentinels, watching for predators and escaping first from them (Hanlon
and Messenger 1996). The presence of sentinels would suggest cooperative behaviour, where individuals would assume periods of excess risk and trade off this risk
for better protection outside of their sentinel time (Drickamer et al. 1996). However,
Adamo and Weichelt (1999) found that such sentinel behaviour was not true for S�
lessoniana. With predator threat (Mather 2010) or when schools are larger (Mather
and O’Dor 1984), squid more closely to one another, possibly monitoring spacing
through water deformation received through their lateral line analogue (Budelmann
and Bleckmann 1988). Like cuttlefish, many squid have visual displays, including
mostly male agonistic ones (Di Marco and Hanlon 1997). In captivity, males set up
a dominance hierarchy, with larger ones dominating smaller and winning agonistic
interactions. But, as for cuttlefish (Warnke 1994) and octopuses (Mather 1980), the
presence of a dominance hierarchy in a crowded situation does not prove any social
recognition in the wider spaces of the natural environment.
Octopuses are perhaps the most solitary of cephalopods, with their density likely
dictated by a lack of predator pressure rather than any mutual attraction. Such a lack
can be direct, as when predators are excluded from a specific area (Aronson 1986
for Octopus briareus), or indirect, when shelter is limiting (for E� dofleini, Hartwick
et al. 1978). Octopuses observed in the wild do not defend territories (Aronson
1986; Mather et al. 1985), although they may defend their immediate surroundings,
2 Behaviour
been a selective force for cuttlefish intelligence (Brown et al. 2012). A size-based
dominance hierarchy is true for older, though not newly hatched cuttlefish (Warnke
1994). Boal (1996) tackled the problem of social recognition through laboratory observations. She found that cuttlefish kept together in tanks did not react differently
to familiar vs unfamiliar conspecifics and were not closer to familiar than unfamiliar ones. Given visual stimuli, they were more aroused (with a higher ventilation
rate) by the sight of prey items than that of conspecifics (Boal and Ni 1996). When
they were maintained in a small or a large tank, cuttlefish spaced themselves more
widely in the large one and seldom approached to within two body lengths. In a
small tank, there were more male agonistic zebra displays and more displacement
of one animal by another (Boal et al. 1999). More importantly, cuttlefish in the large
tank consumed 25 % more shrimp prey, suggesting that the crowding in the small
(1.5 m diameter for three animals) tank was stressful and that this stress was reducing food intake. This is not good news for anyone who wishes to cultivate cuttlefish
in captivity; a more complex habitat may provide visual separation and reduce this
stress.
Squid are different, in that they prefer to swim with conspecifics (Hurley 1978),
in approximately parallel orientation and within a body length or two in captivity,
even in a very large tank, 15 m in diameter (Mather and O’Dor 1984). Because the
adults do not live after egg laying and the young are planktonic, again there is little
likelihood of kin recognition. Most squid gather with conspecifics, though Moynihan and Rodaniche (1982) noted S� sepioidea swimming with Doryteuthis (Loligo)
plei. Groups sort by size; although S� sepioidea are attracted to conspecifics whatever the size, smaller animals are at risk for cannibalism from larger ones and so
maintain several body lengths distance. It has been suggested that squid on the end
of a line are sentinels, watching for predators and escaping first from them (Hanlon
and Messenger 1996). The presence of sentinels would suggest cooperative behaviour, where individuals would assume periods of excess risk and trade off this risk
for better protection outside of their sentinel time (Drickamer et al. 1996). However,
Adamo and Weichelt (1999) found that such sentinel behaviour was not true for S�
lessoniana. With predator threat (Mather 2010) or when schools are larger (Mather
and O’Dor 1984), squid more closely to one another, possibly monitoring spacing
through water deformation received through their lateral line analogue (Budelmann
and Bleckmann 1988). Like cuttlefish, many squid have visual displays, including
mostly male agonistic ones (Di Marco and Hanlon 1997). In captivity, males set up
a dominance hierarchy, with larger ones dominating smaller and winning agonistic
interactions. But, as for cuttlefish (Warnke 1994) and octopuses (Mather 1980), the
presence of a dominance hierarchy in a crowded situation does not prove any social
recognition in the wider spaces of the natural environment.
Octopuses are perhaps the most solitary of cephalopods, with their density likely
dictated by a lack of predator pressure rather than any mutual attraction. Such a lack
can be direct, as when predators are excluded from a specific area (Aronson 1986
for Octopus briareus), or indirect, when shelter is limiting (for E� dofleini, Hartwick
et al. 1978). Octopuses observed in the wild do not defend territories (Aronson
1986; Mather et al. 1985), although they may defend their immediate surroundings,
2 Behaviour