Is the selection of sex-typical parental roles based on an assessment process? A test in the monogamous convict cichlid fish

In the biparental convict cichlid fish, Archocentrus nigrofasciatun, males and females both spend time defending their territory and their offspring, but the typically larger male parent spends more time defending the territory and the female spends more time with the offspring. Because size correlates with a convict cichlid's ability to win a fight, the larger male parent has a clear advantage in repelling intruders compared with his smaller female mate. We tested the hypothesis that male and female convict cichlids accept their parental roles as a result of their relative sizes, rather than inherent sex differences (e.g. females are more nurturing). We allowed pairs to form in which one member was smaller or larger than the other member, or of the same size (both small = 50-55 mm; both large = 70-75 mm), thus producing four pairing types. During the S-day stationary larval stage, we subjected each breeding pair each day to a conspecific intruder that was either larger or smaller than one of the parents, or of the same size. Male and female parents adjusted their parental roles based on the size of their mates and/or the size of the intruder. Large parents displayed more defensive behaviour than small parents, regardless of sex. Male parents responded to increased threat (i.e. increasing intruder size) by increasing their defensive behaviour; but only until intruder size matched their own size, after which defensive effort decreased. Large female parents similarly responded to increased threat by increasing their defensive behaviour, but only to support their smaller mates (i.e. they did not independently attack the intruder). Larger females also showed a corresponding reduction in time spent near the offspring. Small males, in contrast, showed only a marginal increase in their time with the offspring. We conclude that the female has a more flexible parental role and, when her relative abilities change, she is more likely to expand her parental roles. (C) 2004 The Association for the Study orAnimal Behaviour. Published by Elsevier Ltd. All rights reserved.