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 par ental roles. However, these parental sex differences often disappear when o nly one parent is present. For example, under natural conditions, the femal e convict cichlid fish, Archocentrus nigrofasciatus, typically remains with the offspring while the male spends most of his time patrolling the territ ory and chasing intruders. With the removal of the mate, either parent is c apable 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 specia lization in A. nigrofasciatus. When presented with an intruder, widowed mal es left the offspring unattended more often and spent more time attacking t he intruder compared with widowed females. For intact pairs, males showed a tendency to leave the offspring more than their mates but this sex differe nce was not significant. However, these paired individuals rarely left the offspring unattended. With an intruder present, paired males and females sp ent the least amount of time with the offspring (compared with widows and p aired individuals without an intruder present), with males spending signifi cantly more time with the intruder than females. Unlike pairs without an in truder, parents with an intruder changed roles only in support of the other parent. Thus, females rarely approached the intruder unless the male was a lso 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 t he male returned to the offspring and joined the female during those period s when the intruder was least threatening. (C) 2001 The Association for the Study of Animal Behaviour.