Parental division of labour and the shift from minimal to maximal role specializations: an examination using a biparental fish

In biparental species, parents often cooperate by emphasizing different parental roles. However, these parental sex differences often disappear when only one parent is present. For example, under natural conditions, the female convict cichlid fish, Archocentrus nigrofasciatus, typically remains with the offspring while the male spends most of his time patrolling the territory and chasing intruders. With the removal of the mate, either parent is capable of raising the offspring alone, and when doing so, they each perform all parental roles. We tested how the presence and absence of the mate and the presence and absence of an intruder influence parental sex-role specialization in A. nigrofasciatus. When presented with an intruder, widowed males left the offspring unattended more often and spent more time attacking the intruder compared with widowed females. For intact pairs, males showed a tendency to leave the offspring more than their mates but this sex difference was not significant. However, these paired individuals rarely left the offspring unattended. With an intruder present, paired males and females spent the least amount of time with the offspring (compared with widows and paired individuals without an intruder present), with males spending significantly more time with the intruder than females. Unlike pairs without an intruder, parents with an intruder changed roles only in support of the other parent. Thus, females rarely approached the intruder unless the male was also present and the male rarely approached the offspring without the female also being present. We speculated that the male's inability to remove the intruder caused females to support the male in attacking the intruder and the male returned to the offspring and joined the female during those periods when the intruder was least threatening. (C) 2001 The Association for the Study of Animal Behaviour.